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In electronics design and testing, you sometimes want to have two synchronized clock signals that are related by a frequency ratio; One clock needs to maintain a certain frequency ratio with the other clock.

 

Or perhaps you want to simulate an amplifier with an offset; The amplifier output needs to maintain a defined offset from the input amplitude.

 

These requirements may sound basic, but building you own clock reference device or a frequency/amplitude coupling circuit takes time and resources. It’s much easier to use a dual-channel function generator that has built-in signal coupling.

 

Let’s look at how to generate frequency-coupled and amplitude-coupled signals using a dual-channel function generator.

 

How to Generate Two Frequency-coupled Signals with a Function Generator

 

Frequency coupling allows you to specify the frequency relationship of two signals using either a ratio (multiplying) or an offset (adding). Figure 1 shows an example of a frequency coupling ratio of “3.” When the frequency of Channel 1 is set to 3 kHz, the frequency of Channel 2 automatically sets to 9 kHz (Figure 2).

 

Dual-channel frequency coupling setting on ratio on a Keysight 33612A Trueform function generator.

Figure 1. Dual-channel frequency coupling setting on ratio on a Keysight 33612A Trueform function generator.

 

Frequency ratio of 3 as observed on the oscilloscope (see box marked in red).

Figure 2. Frequency ratio of 3, as observed on the oscilloscope (see box marked in red).

 

Here is an example of frequency coupling by offset where the offset difference between Channel 2 and Channel 1 is 2 kHz (Figure 3). When the frequency of Channel 1 is set to 3 kHz, Channel 2 automatically tracks Channel 1 and outputs a 5 kHz signal (see Figure 4).

 

Dual-channel frequency coupling setting on offset.

Figure 3. Dual-channel frequency coupling setting on offset.

 

Frequency offset of 2 kHz as observed on the oscilloscope (see box marked in red).

Figure 4. Frequency offset of 2 kHz as observed on the oscilloscope (see box marked in red).

 

How to Generate two Amplitude-coupled Signals from a Function Generator

 

You can also couple the amplitude and offset of two signals (Figures 5 and 6). Enabling this dual-channel feature and setting the amplitude and offset saves you configuration time. Rather than setting the amplitude and offset of both channels independently, the function generator will keep track of your settings for you. You can even couple signals of different waveform shapes! Figure 6 shows how you can control the amplitude of a square wave and sine wave using only one amplitude setting.

 

Dual-channel amplitude and offset coupling setting on a Keysight 33612A Trueform function generator.

Figure 5. Dual-channel amplitude and offset coupling setting on a Keysight 33612A Trueform function generator.

 

Amplitude and offset coupling of two signals as observed on an oscilloscope.

Figure 6. Amplitude and offset coupling of two signals as observed on an oscilloscope.

 

Benefits of Dual-channel Frequency Coupling and Amplitude Coupling

 

Here are some situations where coupling the amplitude and/or frequency of your test signals is useful.

 

Creating multiple reference pulse clocks to test circuitry

Some electronic devices operate with multiple frequency reference clocks. Dual-channel frequency coupling comes in handy for quick design verifications.

 

Creating two very different arbitrary waveform signals that track each other in frequency

Consider this example of simulating a pacemaker pulse and an ECG arbitrary pulse wave that has the same frequency. When combining these two signals together, pacemaker manufacturers can test a pacemaker’s pulse rejection capability using the resulting signal, shown in Figure 7.

 

Two frequency-coupled signals combined into a single signal output.

Figure 7. Two frequency-coupled signals combined into a single signal output.

 

Testing the differential gain of an amplifier

Testing the differential gain of an amplifier requires synchronized input signals. A function generator and oscilloscope are the ideal test setup for this (Figure 8). If you have perfectly identical input signals for the amplifier, you should see a zero-difference output (straight line), as shown by the oscilloscope’s output in Figure 9. If the output is not flat, you know there’s something wrong with your amplifier.

 

Function generator and oscilloscope set up to test an instrumentation amplifier.

Figure 8. Function generator and oscilloscope set up to test an instrumentation amplifier.

 

Green and blue lines are identical input signals into the Op Amp, and the yellow line is the resultant output from the Op Amp.

Figure 9. Green and blue lines are identical input signals into the Op Amp, and the yellow line is the resultant output from the Op Amp.

 

Using the dual-frequency coupling with ratio of 2, the output of the amplifier will show the differential gain output (yellow line), as shown in Figure 10.

 

Green and blue lines are frequency-coupled signals (with a ratio of 2) generated by a function generator for the input of Op Amp, and the yellow line is the resultant output from the Op Amp.

Figure 10. Green and blue lines are frequency-coupled signals (with a ratio of 2) generated by a function generator for the input of Op Amp, and the yellow line is the resultant output from the Op Amp.

 

Benefits of Frequency Coupling and Amplitude Coupling

 

Clearly, dual-channel tracking simplifies your configuration settings. You don’t have to configure channels separately, which is often tedious and repetitive. As a result, your testing will be less error prone and more efficient. If you are using a programming interface, automatic frequency coupling and amplitude coupling simplifies your code.

 

Now that you know how to couple two signals together, you should be able to perform fast simulation on your products or processes. Thanks to this coupling capability, the signal generation process has never been simpler, quicker, or less frustrating.

 

To learn more about frequency coupling and amplitude coupling your signals using a Keysight function/waveform generator, read this app brief “Effortlessly Couple or Synchronize Two Signals on a Waveform Generator.”

A typical part of an engineer’s job is to perform measurements with a multimeter. For example, if you are working as a building maintenance engineer or electrician, your daily routine may require you to measure power from AC mains or other high voltages. Before you start performing a measurement, what is the first thing that comes to your mind? Should you just grab the nearest handheld multimeter available? No!


Imagine you need to select a helmet. You need to select one with high quality to protect your head. But a helmet’s structure, design, and protective ability vary for different kinds of activities. A helmet designed for rock climbing needs to protect you against small rocks, falling objects, and sharp faces. A bicycle helmet needs to protect your head during impact to reduce the likelihood of injury in the event of an accident. A motorcycle helmet needs to protect you against high-speed impacts with the road and other vehicles. It’s important to choose the right helmet for your activity.


Likewise, different multimeters are designed with different levels of protection against common electrical hazards.

 

For your own safety and the safety of those near you, you must choose a multimeter that is designed and tested to protect you against electrical hazards you might encounter. Remember you only have one life, and there are no second chances. Here are some safety considerations that you need to take note of before you start making measurements with a multimeter.

 

1. Understand your multimeter’s safety indicators

Safety certification is important to ensure the multimeter is compliant with the relevant safety standards. Usually, the manufacturer of the multimeter will obtain safety certifications from third-party independent testing agencies, such as the Canadian Standard Association (CSA), to ensure the product has been tested and complied to the relevant safety standard.

 

Products that successfully pass the independent testing are labeled with the logo of the independent testing agency on the back of the multimeter.

 

The accessories used with a multimeter ─ like probes ─ should also be tested and marked with a third-party safety agency logo. Before you start measuring, be sure to select a multimeter and accessories that have passed these tests.

Some independent testing agency logos are as follows:

VDE certification markTuV technical inspection association certification mark CSA Group certification mark ETL SEMKO certification mark

Be cautious of the CE marking:

CE certification markThe “CE” marking is an abbreviation for "European Conformity" (from the French phrase “Conformité Européene”). The CE marking indicates the product's conformity to the applicable European Union safety, health, and environmental requirements, a mandatory conformity mark on all products sold in the European Union.

 

Manufacturers are permitted to self-certify. They must meet the standards, issue their own Declaration of Conformity, and mark the product “CE.” Therefore, the CE marking is not a guarantee of independent testing.

 

For safety purposes, you should not accept a multimeter that has only a CE mark unless you know the manufacturer to be trustworthy and you have reviewed the manufacturer’s Declaration of Conformity.

 

2. Pay attention to voltage rating of the measurement circuit and measurement limit of your multimeter

Before you start to perform a measurement, you need to understand the maximum voltage rating of your circuit. Use a multimeter that will be able to withstand the maximum voltage of the circuit. In general, manufacturers label the multimeter’s measurement limits on the front panel. A multimeter provides protection circuitry to prevent damage to the instrument and protect against the danger of electric shock, provided the measurement limits are not exceeded.

 

To ensure safe operations of the instrument, do not exceed the measurement limits shown on the front panel of the multimeter.


3. Take precautions when performing live measurements

Here are a few safety precautions you should take when making live measurements with a multimeter:

  • When measuring a live circuit, use insulated tools like safety glasses, insulated mats, and insulated gloves.

insulated gloves with handheld DMM

Figure 1. Wear insulated gloves when using a multimeter.

 

  • Inspect the test leads for damaged insulation or exposed metal. Check the test leads for continuity. If the test leads are damaged, replace them before you use the multimeter.
  • It is recommended that you disconnect circuit power and discharge all high-voltage capacitors before testing resistance, continuity, diodes, or capacitance.
  • When making measurements, always connect the common test lead before you connect the live test lead. When you disconnect the leads, disconnect the live test lead first. Avoid holding the test lead in your hands to minimize personal exposure if transients occur. Before use, verify the multimeter’s operation by measuring a known voltage.


Conclusion – Safety First!

Safety is always the top priority no matter what you are measuring, so there are a few precautions you should take. Always choose a multimeter with a voltage rating higher than the circuit you are measuring. Remember to check that the multimeters and probes you are going to use are marked with third-party safety agency logos such as CSA, ETL, TÜV, or VDE. Do not overlook the safety of the probes! With safety in mind, you will be assured that the high voltage goes into your measurement instrument instead of you!

 

To learn more, download the Think SAFETY when Selecting a Handheld Multimeter application note.

For more info about Keysight’s DMMs, visit www.keysight.com/find/dmm

How can you determine which digital multimeter (DMM) is best for your application?

There are five key specs you need to consider before purchasing a digital multimeter to make sure you’re picking the right DMM for your testing needs: number of display digits, counts, range, resolution, and accuracy. Let’s look at each of these in more detail.

 

1. Display Digits

In general, most manufacturers specify a DMM display by digits of resolution. For example, the digits of resolution for Keysight digital multimeters goes from 3 ½ digits to 8 ½ digits.

 

A 5 ½ digit DMM, for example, has five full digits that display values from 0 to 9, and a fractional digit. Fractional digit is the most significant digit in the display. It is the ratio of the maximum value the digit can attain over the number of possible states. For example, a ½ digit has a maximum value of one and has two possible states (0 or 1). A ¾ digit has a maximum value of 3 with four possible states (0, 1, 2, or 3). The higher the digits of resolution, the more precise and accurate your measurements will be. It also means that a multimeter with higher digits of resolution will be more expensive.


2. Counts

Nowadays, manufacturers have started to specify the display in terms of “count” because “digits of resolution” often creates confusion. The count of a DMM refers to how large a number the multimeter can display before it changes the measurement ranges and how many digits it can show in total. This affects how precise a measurement the DMM can display. For example, a 4½ DMM can also be specified as a 19,999-display count or 20,000 display count multimeter.


3. Resolution

Resolution is defined as the smallest change in an input signal that produces a change in the output signal. Resolution will be improved when the DMM’s measurement range is reduced. Ultimately, you want the multimeter to display the best resolution of your measurement reading. You can play around with the multimeter and select the measurement range that gives you the reading with optimum resolution.

 

4. Range

Range is correlated to resolution, the resolution display on the multimeter will depend on the measurement range that you select.

To choose a digital multimeter, you need to know the minimum and maximum measurement range, and the resolution you require. This information is usually available in the DMM’s data sheet.

 

4.1 Autorange vs. Manual Range Multimeters

Most of the digital multimeters today offer both auto ranging measurements and manual ranging measurements.

 

4.1.1 Auto Ranging Measurements

For auto ranging measurements, all you have to do is select your desired measurement functions and let the multimeter automatically choose the best range. Normally, you should select auto ranging when you do not know the potential measurement reading range.


4.1.2 Manual Ranging Measurements

Manual ranging measurements are normally selected when the desired measurement value is known. Based on your measurement value, you can choose the desired measurement range. If the measurement value is unknown and you would like to use the manual range, it is recommended that you use the “step down” method. Start with the highest range and then step down to lower ranges to achieve the optimum resolution on the display.

 

5. Accuracy

The accuracy of a DMM is different from its display resolution. The accuracy is the maximum allowable limit of error in the readings. Normally, manufacturers display DC voltage (DCV) accuracy as a benchmark when comparing with other manufacturer specifications, as DCV has better accuracy compared to other functions. The accuracy specification is expressed as ±((% of reading + % of range).

 

Summary

There is a range of digital multimeters available on the market. To select the right multimeter, you need to know the target application, the measurement range, and required resolution. If you require a higher measurement accuracy, make sure to select a DMM with a higher resolution.

 

To learn more, download the How to Select a Handheld DMM That is Right for You application note.

For more information about Keysight’s DMMs, visit www.keysight.com/find/dmm.

A two-quadrant power supply is traditionally one that outputs unipolar voltage but is able to both source as well as sink current. For a positive polarity power source, when sourcing current it is operating in quadrant 1 as a conventional power source. When sinking current it is operating in quadrant 2 as an electronic load. Conversely, a negative polarity two-quadrant  power source operates in quadrants three and four. Often a number of questions come up when explaining two-quadrant power supply operation, including:

  • What does it take to get the power supply operating as a voltage source to cross over from sourcing to sinking current?
  • What effect does crossing over from sourcing to sinking current have on the power supply’s output?

 

 

For a two-quadrant voltage source to be able to operate in the second quadrant as an electronic load, the device it is normally powering must also be able to source current and power as well as normally draw current and power. Such an arrangement is depicted in Figure 1, where the device is normally a load, represented by a resistance, but also has a charging circuit, represented by a switch and a voltage source with current-limiting series resistance.

 

 

 

Figure 1: Voltage source and example load device arrangement for two-quadrant operation.

 

There is no particular control on a two-quadrant power supply that one has to change to get it to transition from sourcing current and power to sinking current and power from the device it is normally powering. It is simply when the source voltage is greater than the device’s voltage then the voltage source will be operating in quadrant one sourcing power and when the source voltage is less than the device’s voltage the voltage source will be operating in quadrant two as an electronic load. In figure 1, during charging the load device can source current back out of its input power terminals as long as the charger’s current-limited voltage is greater than the source voltage.

 

It is assumed that load device’s load and charge currents are lower than the positive and negative current limits of the voltage source so that the voltage source always remains in constant voltage (CV) operation. A step change in current is the most demanding from a transient standpoint, but as the voltage source is always in its constant voltage mode it handle the transition well as its voltage control amplifier is always in control. This is in stark contrast to a mode cross over between voltage and current where different control amplifiers need to exchange control of the power supply’s output. In this later case there can be a large transient while changing modes. There is a specification given on voltage sources which quantifies the impact one should expect to see from a step change in current going from sourcing current to sinking current, which is its transient voltage response.  A transient voltage response measurement was taken on an N6781A two-quadrant DC source, stepping the load from 0.1 amps to 1.5 amps, roughly 50% of its rated output current.

 

 

Figure 2: Keysight N6781A transient voltage response measurement for 0.1A to 1.5A load step

 

However, the transient voltage response shown in Figure 2 was just for sourcing current. With a well-designed two-quadrant voltage source the transient voltage response should be virtually unchanged for any step change in current load, as long as it falls within the voltage source’s current range.  The transient voltage response for an N6781A was again capture in Figure 3, but now for stepping the load between -0.7A and +0.7A.

 

 

 

Figure 3: Keysight N6781A transient voltage response measurement for -0.7A to +0.7A load step

 

As can be seen in Figures 2 and 3 the voltage transient response for the N6781A remained unchanged regardless of whether the stepped load current was all positive or swung between positive and negative (sourcing and sinking).

 

While the transient voltage response addresses the dynamic current loading on the voltage source there is another specification that addresses the static current loading characteristic, which is the DC load regulation or load effect.  This is a very small effect on the order of 0.01% output change for many voltage sources. For example, for the N6781A the load effect in its 6 volt range is 400 microvolts for any load change. In the case of the N6781A being tested here the DC change was the same for both the 0.1 to 1.5 amp step and the -0.7 to +0.7 amp step change.

There are two more scenarios which will cause a two-quadrant power supply transition between current sourcing and sinking.  The first is very similar to above with the two-quadrant power supply operating in constant voltage (CV) mode, but instead of the DUT changing, the power supply changes its voltage level instead.  The final scenario is having the two-quadrant power supply operating in constant current with the DUT being a suitable voltage source that is able to source and sink power as well, like a battery for example. Here the two-quadrant power supply can be programmed to change from a positive current setting to a negative current setting, thus transitioning between sourcing and sinking current again, and its current regulating performance is now a consideration.  Both good topics for future postings!

Don’t you hate it when your power supply can’t provide enough current, even though you are pulling power well within the power supply’s maximum power output? You have to disconnect all your cables from your power supply, which you have meticulously connected, find another supply with enough current output, and reconnect everything again. It’s very frustrating, especially when you have a deadline looming. I share your pain. I have been through it. That’s why I’m sharing a trick I learned to overcome this frustration.

 

We’re going to look at how an autoranging power supply helps alleviate the pain and gives you more capability. An autoranging power supply is also fondly called an autoranger.

 

Single-range and Multi-range Power Supplies

Often a basic power supply is a single-range power supply. I’ve plotted a single-range power supply’s output characteristic in Figure 1 below. Pmax is the power supply’s maximum output power. This power supply only outputs Pmax at maximum rated voltage, Vmax, and current, Imax. This single-range power supply has a single range for both output voltage and current.


Single-range DC power supply output characteristic.

Figure 1. Single-range DC power supply output characteristic.

 

In a multi-range power supply, we have wider output voltage and current ranges, as shown in Figure 2 below. This multi-range power supply is also called a dual-range power supply since it has only two ranges for voltage and current output.

 

Multi-range DC power supply output characteristic.

Figure 2. Multi-range DC power supply output characteristic.

 

This dual-range power supply is able to output a much higher Vmax or Imax within the same maximum-rated power output as our single-range power supply. However, the dual-range power supply can only supply Vmax when the output current range is limited to I1. Imax can only be reached if voltage range is limited to V1. Both voltage and current outputs have two operating ranges within the same Pmax power envelope. For most power supplies, you will need to manually select the correct range. 

 

The Wonderful Autoranger

A multi-range power supply has an infinite number of ranges. Even better, it automatically selects the correct range. This type of multi-range power supply is known as an autoranging power supply. The output characteristic of an autoranging power supply is shown in Figure 3.

 

Autoranging DC power supply output characteristic.

Figure 3. Autoranging DC power supply output characteristic.

 

With an autoranger, the voltage and current output is automatically limited to ensure the power output does not exceed its rated maximum power output. 

 

Let’s use the N6755A as an example. The N6755A is a 500W autoranging DC power supply with Vmax = 20V and Imax = 50A. If you set the output voltage to 15V, the output current is automatically limited to 33A, and if you reduce the output voltage to 10V, the current output is limited to 50A. 

 

The same happens for current. The 500W N6755A has a voltage and current range that equals a 1000W single-range power supply. An autoranger has significantly more output voltage and current range combinations compared to a multi-range power supply. 

The high-performance N6700 family autoranging DC power supply.

Figure 4. The high-performance N6700 family autoranging DC power supply.

 

Why Do I Need an Autoranger?

 

  • You Need High Voltage and High Current, But Not High Power

Autoranger is not for everyone. But if you need high voltage and current, but not high power, an autoranger is perfect for you. DC/DC converter testing is a perfect example of this need. A DC/DC converter accepts a wide range of input voltage and is able to output a constant amount of power. During testing, an autoranger is able to supply a wide range of voltages to the DC/DC converter while still providing enough power. Figure 4 below illustrates this point. As input voltage decreases, the DC/DC converter pulls more current to maintain its output power. The autoranger is able to decrease its output voltage and increase available current to the DC/DC converter.

 

 

DC/DC converter voltage and current draw from an autoranging DC power supply.

Figure 5. DC/DC converter voltage and current draw from an autoranging DC power supply.

 

  • You Need Flexibility in Your Testers

An autoranger gives you flexibility. Your test station is often set up to test a wide range of product families. Your test station has a wide range of voltage and current needs. Imagine stuffing your test rack with multiple power supplies and the complexity of connecting them together. An autoranging power supply saves you space and keeps your setup simple.

 

  • You are Protecting Mother Nature

An autoranger is more efficient. To cover wide voltage and current demands, you can simply get a high-power single-range power supply that covers the entire voltage and current range you need. While this solution can work, it is not energy efficient. Generally, a power supply’s efficiency reduces as its output power reduces. Therefore, using a high-power single-range power supply at half its rated maximum power output is not only a waste of money, it is also a waste of precious energy resources. Always get an autoranging power supply with just enough power for your application and you will save money and help the environment.

 

Using a high-power single-range power supply to provide low power is not only a waste of money, it is a waste of precious energy resources.

 

Conclusion

Autoranging power supplies provide flexibility with the right amount of power, voltage, and current. Getting an autoranging power supply with just enough power saves you money and protects our environment. Let’s do our bit to help mother nature. Our autoranging power supplies can help you. Check them out at www.keysight.com/find/power

 

I’d love to hear your questions and comments in the comments section below!

 

Download the 10 Practical Tips to Help Your Power Testing and Analysis application note for more ways to improve your power supply’s operation and measurement capabilities.

Whether you use your frequency counter on the bench or in an automated test system, you want your measurements to be as accurate as possible. There’s a key component in your frequency counter that dictates its accuracy: the timebase oscillator.

 

Measurement accuracy in frequency counters begins with the timebase because it establishes the reference against which your input signal is measured. The better the timebase, the better your measurements can be. I said ‘can be’ because you need to do scheduled maintenance of your frequency counter. To maximize your counter’s accuracy, you need to calibrate it. Here’s why:

 

The frequency at which quartz crystals vibrate is heavily influenced by ambient temperature.

 

There are three main categories of timebase technologies, divided up based on how they address thermal behavior: room temperature crystal oscillators (RTCO), oven controlled crystal oscillators (OCXO) and temperature compensated crystal oscillators (TCXO).

 

Standard Timebase – A Room Temperature Crystal Oscillator

 

The first category is the standard timebase, also known as room temperature crystal oscillator (RTCO). A standard timebase doesn’t employ any kind of temperature compensation or control. While this has the advantage of being inexpensive, it also gives the largest frequency errors. The curve in Figure 1 shows the thermal behavior of a typical crystal. As the ambient temperature varies, the frequency output can change by 5 parts per million (ppm) or more. This works out to ± 5 Hz on a 1 MHz signal, so it can be a significant factor in your measurements.

 

Frequency Counter: The frequency output of an unprotected crystal can vary widely in response to ambient temperature. Putting the crystal in a controlled thermal environment (an oven) helps maintain a stable output frequency.

Figure 1. The frequency output of an unprotected crystal can vary widely in response to ambient temperature. Putting the crystal in a controlled thermal environment (an oven) helps maintain a stable output frequency.

 

The obvious solution to this temperature-induced variance is to control the temperature, which leads us to our next type of oscillator.

 

Oven-controlled Crystal Oscillators (OCXO)

 

For an OCXO, the crystal oscillator is housed in an oven that holds its temperature at a specific point in the thermal response curve. Surrounding the crystal with temperature-control circuitry gives it better timebase stability. Typical errors are as small as 0.0025 ppm (±0.0025 Hz on a 1 MHz signal). Additionally, oven-controlled timebases also help minimize the effects of crystal aging. This means you don’t have to calibrate your frequency counter as often.

 

OCXOs are very accurate but more expensive and have a bigger footprint than other timebase options. So, many engineers opt for temperature-compensation circuitry instead of temperature-controlled circuitry.

 

Temperature Compensated Crystal Oscillators (TCXO)

 

Temperature compensated crystal oscillators (TCXOs) are designed to account for temperature changes instead of trying to hold a fixed temperature. One method of compensating for frequency changes due to temperature variation is to add external components with complementary thermal responses.

 

This approach can stabilize the thermal behavior enough to reduce timebase errors by an order of magnitude relative to RTXO (approximately 1 ppm, ±1 Hz on a 1 MHz signal).

 

Choose a Timebase That’s Right for You

 

Now you have learned that different types of timebases bring a different response to a counter.

 

The quality of your frequency counter’s timebase will affect your measurement accuracy. Depending on the accuracy that you need, you can choose the right one.

 

It’s also worth pointing out that the timebase does not need to be housed within the frequency counter. You can connect a precision source or house-standard external source to the counter to improve measurement accuracy. You should also note that, no matter what timebase you select, leaving your timebase powered up will provide the most accurate results.

 

To learn more about frequency counter measurements, download the 10 Hints for Getting the Most from Your Frequency Counter application note.

Frequency counters are widely used to accurately measure the frequency of repetitive signals. There are two basic types of frequency counters:

  • Direct counting frequency counters
  • Reciprocal counting frequency counters

 

Understanding the effects of these two different counters will help you choose the best counter for your needs and use it correctly. Today, we’ll look at the basics of direct counters and reciprocal counters.

 

How a Direct Counting Frequency Counter Works

 

Direct counters simply count cycles of a signal over a known period of time. This period is known as the gate time. The resulting count is sent directly to the counter’s readout for display. This method is simple and inexpensive. But it means that a direct counter’s resolution is fixed in Hertz and the count accuracy is lower than a reciprocal frequency counter.

 

For example, with a 1 second gate time, the lowest frequency the counter can detect is 1 Hz (since 1 cycle of the signal in 1 second is 1 Hz).

 

Thus, if you are measuring a 10 Hz signal, the best resolution you can expect for a 1 second gate time is 1 Hz (or 2 display digits). For a 1 kHz signal and 1 second gate, you get 4 digits. For a 100-kHz signal, 6 digits, and so on, as shown in Figure 1 below:

 

Frequency Counter: The number of digits displayed by a direct counter versus frequency (for a 1 second gate time).

Figure 1. The number of digits displayed by a direct counter versus frequency (for a 1 second gate time).

 

How a Reciprocal Counting Frequency Counter Works

 

Reciprocal counters measure the input signal’s period and then reciprocate it to get frequency. Because of this architecture, the counter’s resolution is always the full number of display digits.

 

In other words, a reciprocal frequency counter will always have same number of digits of resolution regardless of the input frequency. You’ll see the resolution of a reciprocal counter specified in terms of the number of digits for a specific gate time, such as “10 digits per second.”

 

By looking at the frequency resolution specification, you can determine whether a counter is a direct counter or reciprocal counter. If it specifies resolution in Hertz, it’s a direct counter. If it specifies resolution in digits-per-second, it’s a reciprocal counter.

 

Figure 2 compares the resolution of direct and reciprocal counters. In the lower frequency spectrum, reciprocal counters have a substantial advantage over direct counters. We can see that the reciprocal counter has a constant resolution, whereas the direct counter has less resolution for lower frequencies.

 

Frequency Counter: Comparing resolution for direct and reciprocal counters (for a 1 second gate time).

Figure 2. Comparing resolution for direct and reciprocal counters (for a 1 second gate time).

 

As an example, at 1 kHz, a direct counter gives a resolution of 1 Hz (4 digits). A 10 digit/second reciprocal counter gives a resolution of 1 μHz (10 digits).

 

If precision resolution is not a priority, a reciprocal counter still offers a significant speed advantage. The reciprocal counter will give 1 mHz resolution in 1 ms, while a direct counter needs a full second to give you just 1 Hz resolution (Figure 3).

 

Frequency Counter: The gate times needed to yield various resolutions with a 10 digits/second reciprocal counter.

Figure 3. The gate times needed to yield various resolutions with a 10 digits/second reciprocal counter.

 

Should You Use a Direct or Reciprocal Frequency Counter?

 

The choice comes down to cost versus performance. If your resolution requirements are flexible and you aren’t too concerned with speed, a direct counter is the economical choice. However, many cases require a reciprocal counter for faster, higher resolution measurements. Reciprocal counters also offer continuously adjustable gate times (not just decade steps), so you can get the resolution you need within the minimum amount of time.

 

To learn more, download the 10 Hints for Getting the Most from Your Frequency Counter application note.

A resistance meter normally works by sending a small, precise current through the resistance to be measured. Then it measures the voltage drop. Once the meter knows the current and voltage, it applies Ohm’s law to derive resistance. Ohm’s law says that resistance is voltage divided by current, or R = V/I.

 

For example, if there is a 10 mA (0.01 A) current going through a resistor and there is a voltage drop of 1 V over the resistor, then the resistor is R=V/I = 1 V / 0.01 A = 100 ohms.

 

Different test conditions may have different impacts on resistance measurements. In this article, we will discuss some common mistakes that result in resistance measurement error and ways to counter them.

 

Trap 1. Impact of Temperature on Resistance

From the R=V/I equation, you might think that making an accurate resistance measurement on a material sample is trivial, but in reality, this may not be true. The reason for this is that the resistivity of all materials varies with temperature. When you attempt to measure a sample’s resistance, you inevitably heat it up to some extent. This is referred to as the Joule self-heating effect.

 

Joule self-heating makes resistance measurements a tricky balance between two factors:

    1. To keep the resistor from heating up and the resistance value from changing, you need to keep the current (= power) low.
    2. Small currents mean that we need to measure smaller voltages, which in-turn requires a higher voltage measurement resolution.

V = I x R(T)    Resistance depends on temperature!

How Much Power Can I Apply to a Structure?

After understanding the effect of temperature on the resistance measurement, how do you establish the relationship between temperature and resistance? We just learned that temperature change is directly proportional to the power applied to the DUT. We also know that Power = Voltage x Current. The expression of the voltage across a resistor in terms of applied power and resistance is shown in the equation below.

 

 

To determine the maximum power we can apply to a structure without changing its resistance, we need to know something about its thermal characteristics. Let’s look at an example of copper. We know that the resistance of copper changes by about 0.35% for every degree Celsius change in temperature. For a 10 mm by 10 mm sample and resistance tolerance of 0.1%, we can see that maximum allowable power is about 0.04 mW:

 

 

Plugging this back into the top equation, we see that this amount of power creates a voltage change of approximately one microvolt, which tells us roughly how much voltage measurement resolution the instrumentation needs to have.

 

 Need 1 mV of voltage measurement resolution!

  

Trap 2. Thermo EMF in Resistance Measurement

Another factor to consider when making any type of measurement (not just resistance measurements) is thermo electromotive force (or EMF). Thermo EMF is a transient voltage pulse that is generated when a reed relay switch opens or closes. Since virtually all SMUs employ reed relays, thermo EMF effects are something that you need to consider when making sensitive low-level measurements.

 

The picture shown in Figure 1 is of a commercial grade relay chart. It is NOT characteristic of the relays used in SMUs, which are specially designed to minimize EMF. We can see thermo-EMF is generated over the time period when a relay is operating. This EMF can have a significant impact on low resistance measurements; it will distort the resistance value measured.

 

 Figure 1. Thermo-EMF example of general reed relay.

 

Now let’s take a look at how to perform a modified Kelvin measurement that can eliminate the effects of thermo EMF, as well as the effects of any offset voltages in your circuitry. Figure 2 shows a picture of a standard Kelvin measurement on a resistor R with the EMF and offset voltages modeled as voltage sources. 

 

 

Figure 2. Modified Kelvin resistance measurement.

 

First, set up one SMU as a current source and source current through the resistor you want to measure. Then use another measurement resource (either a voltmeter or an additional SMU) to measure the voltage across the resistor. After calculating the resistance, reverse the current flow and repeat the measurement. Then take the two resistance values that you have measured and average them.

 

If you check this by going through the KVL and KCL equations for this circuit, you will see that by measuring twice with both positive and negative current, the EMF and offset voltages cancel out. Of course, when making this measurement, you also need to make sure that you do not apply too much power to the resistor so that thermal effects do not alter its resistance value.

 

 

 

Trap 3. Floating vs. Grounded Measurements

In electrical circuits, voltage is always measured between two points: a point of high potential and a point of low or zero potential.

 

The term “reference point” denotes the point of low potential because it is the point to which the voltage is referenced. A floating measurement is a differential measurement that is not referenced to ground (zero potential). It can be a concern if anyone is mistakenly making a floating measurement while expecting a ground measurement.

 

Let’s examine the counter measures to address this concern. As you can see from Figure 3 below, the configuration using a Keysight B2980A electrometer for these two cases is quite different.

 

If you are floating your DUT with respect to earth ground (such as in the top left of Figure 3), you can measure the resistance between the high terminal and the low terminal. Parasitic resistances and capacitances may provide a “sneak path” to ground on the low side. You can mitigate measurement errors by connecting the negative terminal of Vs source to the low terminal. In this way, the ammeter and the DUT low terminal have a “common” reference point.

 

The bottom left shows the circuit diagram that corresponds to a floating device measurement. The test device is connected between the VS positive output and the Ammeter input. Since the Ammeter measures very low currents and is very noise-sensitive, it should be measured close to ground potential in order to shield the test device for better measurement results.

 

On the top right, you can see the case where the DUT is grounded. Since the low side is grounded, the applied test voltage and the current measurement must both occur at the DUT's high side terminal. The bottom right shows the circuit diagram that corresponds to a grounded device measurement. In this configuration, the Ammeter is connected to the VS positive output because the device is grounded on one side.

 

Neither one of these configurations is necessarily “better” than the other, and you can obtain good high resistance measurement results using either setup.

 

 Figure 3. Floating vs. grounded measurement.

 

Conclusion

Temperature, thermo EMF and floating measurement affect your resistance measurements. Learning more about these impacts will help you get more accurate measurements in your work. For more tips related to resistance measurement, download the Resistance Measurements application note.

Why Perform Current-Voltage (IV) Measurements?

IV measurements obtain the current vs. voltage or resistance characteristics by providing a voltage/current stimulus and measuring current/voltage reaction. This is a basic electrical measurement and a fundamental way to understand the characteristics of various materials and devices under test (DUT).

 

Figure 1 shows the IV curves of some common electrical components. In the first graph, we see a linear relationship between voltage and current, so we immediately know that we are looking at a resistor. The graph in the center shows an exponential relationship between voltage and current. This probably means we are looking at a diode (or something that exhibits diode-like behavior). Finally, the graph on the far-right indicates that we are looking at some transistor curve. The characteristic of IV curves are able to provide us with immediate insight into a component, making them crucial in science and engineering. 

 

Resistor, diode and transistor IV curves

Figure 1. IV curves of common electrical components

 

So, how do you make quick and accurate IV measurements? The most common tool for measuring IV curves is a source measure unit (SMU).

 

What is a Source Measure Unit (SMU)?

An SMU combines the capabilities of a current source, voltage source, current meter and voltage meter into a single unit. This gives it the ability to evaluate the IV characteristics of devices across all four measurement quadrants without the need for any additional equipment. You get substantial cost and space savings compared to having multiple instruments.

 

Besides being able to output and measure voltage or current very accurately, SMUs also possess a compliance feature that allows a limit to be placed on the voltage or current output to prevent device damage.

 

As Figure 2 shows, a source measure unit packs an amazing amount of measurement capability into a very small package. SMUs can act as ideal 4-quadrant sources, meaning they will always try to maintain their programmed current or voltage until they reach the limit of their output power or a user-defined limit.

 

Circuit diagram of a simplified equivalent circuit (2-wire measurements) in an SMU

 

Figure 2. Simplified equivalent circuit (2-wire measurements) in an SMU


In addition, while sourcing current or voltage, SMUs can simultaneously measure both current and voltage. Figure 2 represents a single SMU channel, and this channel can exist as a standalone product or as one SMU channel within a mainframe that supports multiple SMU channels.

 

Notice that the “Low Force” side of the SMU can be connected to chassis ground via a relay. In fact, the default boot-up state of most SMUs has them configured with their low side grounded. However, it is sometimes convenient to float the “Low Force” side connection (for example when making differential measurements). In those cases, keep in mind that disconnecting the low side from ground is possible.

 

Why Use an SMU for IV Measurements?

Without an SMU, here are some common test challenges that you may face when performing IV measurements:

  • Difficulty in controlling and synchronizing multiple instruments
  • Complex cabling and setup
  • Difficulty in obtaining accurate, reliable measurements


When using multiple instruments simultaneously for an IV measurement, it is not easy to obtain good performance and accuracy due to the cabling and grounding with various instruments. In contrast, an SMU typically provides superior measurement performance that goes down to sub pA and sub µV resolutions.

 

SMUs integrate many capabilities into a single channel. It is possible to source voltage and measure both the sourced voltage and current (or source current and measure both the sourced current and voltage). But usually, either only voltage is sourced while current is measured, or only current is sourced while voltage is measured. Hence, the most common SMU use models are shown here (also in Figure 3):

  • VSIM – Source voltage and measure current
  • ISVM – Source current and measure voltage

 

Two of the most common modes of SMU operation

Figure 3. Two of the most common modes of operation for an SMU

 

For why would you need to measure a source if the SMU will always hold its sourced value? When you specify a sourced value, you also must specify some limit on the measure unit value. And if for some reason the measured unit hits its limit, the value you expect to source may not actually be what you set. Below is a simple example to explain this (Figure 4).

 

IV curve of a sweep voltageFigure 4. IV curve of a sweep voltage

 

Suppose we are sweeping the voltage applied to a DUT (sourced value) and measuring the current flowing through the DUT. If the IV curve of the DUT hits the set current limit before the applied voltage reaches its stop value, then the applied voltage will remain at the voltage level for the rest of the sweep. In fact, all voltage and current data points beyond the limit value will be the same. However, unless you tell the SMU to measure its applied voltage, you will not be able to see it happening. If you are only measuring current, then all you will see is that the current does not change for the last part of the sweep.

 

All SMUs have some sort of indicator to tell you that a measurement has hit the limit. However, if you do not see this indicator, then reviewing the measured data is the only other way to catch this.

 

Source Measure Units Make IV Measurements Easier

So, what are reasons that make an SMU the preferred choice for IV measurements – as opposed to using multiple discrete instruments?

 

It ultimately boils down to two things:

  • Convenience, and
  • Form factor.

 

A good example of this is shown in Figure 5, which shows measurement of current and voltage at the inputs and outputs of a four-terminal DUT. Performing these operations with discrete sources and meters is complicated and time-consuming, and requires many manual connection changes to modify a measurement setup.

 

In contrast, the same measurements can be performed using a 2-channel SMU with a very 'clean' setup. One channel can be connected to the device input, and the other channel can be connected to the device output. All the necessary connections to measure different current and voltage parameters can be performed without the need to modify any physical connections.

 

IV measurement with multiple instruments versus IV measurement with a 2 channel SMU

Figure 5. IV measurement setup comparison: using multiple instruments (left) vs. using a 2-channel SMU (right)

 

Summary

IV measurements are an important part of testing as they provide unique insights into your device under tests. Source measure units (SMUs) are recommended instruments for IV measurements as they are able to provide better measurements, easy to set-up and operate, and take up minimal bench space – which makes them a cost effective investment.

 

If you'd like to know more about how to make accurate resistance measurements – which is one of the more challenging areas of measurement science – download this Application Note: Resistance Measurements Using the B2900A Series of SMUs. You will learn how you can overcome measurement issues such as residual test lead resistance, thermal electromotive force and leakage currents in the measurement path.

Do you have issues where the voltage at your load is lower than what you’ve set at your power supply? Do you always need to guess the amount of voltage to increase (to compensate for lead losses) just to get the right amount of voltage to appear at your load? If you have these issues, remote sensing can help! Remote sensing is a life saver, especially when you are setting test stations on your manufacturing floor or performing part qualifications.

 

Download the free "4 Ways to Build Your Power Supply Skill Set" eBook.

 

Remote sensing allows you to have your desired voltage appear at your load. It works by sensing the voltage that appears at your load instead of the voltage that appears at the output terminals of your power supply. This is accomplished by connecting the load directly to your power supply’s sense terminals using two separate wires. By measuring voltage across the load, the power supply will adjust the output voltage until the voltage across the load reaches the desired voltage. No need to manually compensate for voltage drop across your load leads.

 

How Does Remote Sensing Work?

You’ve probably seen that sometimes the voltage at your load is different than the voltage at your supply. What’s causing this accuracy issue, and why does remote sensing help? To answer this, let’s use an example. In Figure 1, we have a power supply set for 5 V output. If your load is located at the output of the power supply, you’ll get almost 5 V at your load. Now, imagine that the load is 6 feet away from your power supply. You’re now transferring power to your load using a pair of 6-foot wires. If you’re using 14WAG wire for your connection, each wire will have a resistance of about 0.015 Ω.

The resistance of your copper wire doubles for every 3-gauge increase in wire size

Now, when you have 10 A flowing to your load, each wire will cause a voltage drop of 0.15 V (10 A x 0.015 Ω). You now have a total drop of 0.3 V on the wires. Instead of 5 V, you now have only 4.7 V (5 V – 0.3 V) across your load.

 

Figure 1 shows sense lead tied to output terminals

Figure 1. Sense lead tied to output terminals

 

The thinner the wire, the less voltage you have across your load. In the table below, you can see that wire resistance increases as wire size decreases. As a general rule, the resistance of your copper wire doubles for every 3-gauge increase in wire size.

 

AWG wire sizeResistance in mΩ/ft (at 20°C)
2216.1
2010.2
186.39
164.02
142.53
121.59
100.999

Table 1. Wire size vs. wire resistance

 

Let’s use the same setup, but now with remote sensing. To set up remote sensing, connect the sense terminals directly to the load. Wire size doesn’t matter for remote sensing ─ more on that shortly. When using remote sensing, the power supply will regulate the voltage across the load so that 5 V appears across the load. In this case, the power supply will increase the voltage at the output of the power supply to 5.3 V to offset the 0.3 V drop across the load wires. This will give you 5 V across your load. This is all done automatically by the power supply. No need for manual adjustments and calculations.

 

Figure 2 shows sense lead being connected directly to load.

Figure 2. Sense lead connected directly to load

 

The sense terminals on the power supply function like a voltmeter and have high input impedance. This means current flowing into the sense terminals is negligible and wire size does not significantly affect accuracy. You can use thinner wires for sense, but make sure these wires are properly shielded to reduce noise.


As you can see, remote sensing works pretty much like 4-wire resistance measurements. Instead of a small source current used in resistance measurement, we now have large current following through the leads and load. Remote sensing is especially useful if you have to connect to your load through long wires, complex relay topologies, or connectors.

 

Best Practices for Connecting Sense Leads

We just learned that remote sensing can significantly improve the accuracy of your output voltage at load. However, connecting your sense leads incorrectly can do more harm than good. To avoid this, let’s talk about best practices for connecting your sense leads to get the best results.

 

1. Use Two-Wire Twisted, Shielded Cables

Whenever possible, use two-wire twisted and shielded cables for your sense leads. A twisted pair, shielded cable protects your sense leads from noisy environments. You want to make sure the sense terminals are getting the cleanest possible measurements from your load. Noisy sense measurements will lead to fluctuations of your output voltage.

 

2. Make the Right Ground Connections to Avoid Ground Loops

If you are using a shielded cable for your sense leads, make sure to connect the shield to ground at only one point. Connecting your shield to ground at multiple points may look like a good idea because you are making more solid connections to ground, but it creates ground loops.

Ground loop current can cause noise to appear on your sense leads

How is that possible? Well, not all grounds are at the same potential to each other, especially grounds located far apart. When you connect these grounds together through your cable’s shield, current will flow between these points. This is called ground loop current. Ground loop current can cause noise to appear on your sense leads.

 

Figure 3 shows ground loop current flowing between to ground points.

Figure 3. Ground loop current flowing between to ground points

 

Figure 4 shows how in a correct ground connection, the shield is only connected to ground at a single point.

Figure 4. In a correct ground connection, the shield is only connected to ground at a single point

 

Figure 5 shows the physical connection on a typical DC power supply using a 2-core twisted and shielded cable

Figure 5. Physical connection on a typical DC power supply using a 2-core twisted and shielded cable

 

3. Keep the Sense Leads and Load Leads Separate

Do not twist or bundle your sense leads together with the load leads. Crosstalk will occur between the sense leads and load leads, causing inaccurate measurements on the sense leads.

 

4. Connect Your Sense Leads Properly

It may seem obvious, but you should have a solid connection between your sense terminals and load. An open connection at the sense terminal may cause the power supply to quickly increase output voltage because the sense terminal detects no voltage. This can be disastrous for your load!

 

Fortunately, Keysight power supplies use internal sense protect resistors. These resistors prevent the output voltage from rising too high if there’s an open connection at the sense leads.


Conclusion

Using remote sensing significantly improves your power supply’s accuracy with little investment. I encourage you to take advantage of this feature. Most modern power supplies come equipped with remote sensing. Use the best practices we discussed above to get better accuracy from your power supply.

 

I’d love to hear your questions and feedback in the comments section below!

 

Download the 10 Practical Tips You Need to Know About Your Power Products application note for more ways to improve your power supply operation and measurement capabilities.

 

Typically, power supply users require only positive voltage for their testing as opposed to negative voltage. However, there are instances where you may need negative voltage from a power supply. Driving devices such as operational amplifier and transistors will sometimes require negative voltage biases. It is important to keep in mind that when we use terms like positive voltage and negative voltage, they are relative to a reference point. Voltage cannot be defined in absolute terms but instead is measured relative to a voltage reference.

 

Download the free "4 Ways to Build Your Power Supply Skill Set" eBook.

 

Most power supplies will not let you program a negative voltage value. This means that if you need a negative voltage, you would have to program a positive value and reverse the output to achieve the voltage that you need. This could be a bit troublesome especially if you are using a power supply to frequently power devices require both positive and negative voltage values. Keysights new E36300 quickly and easily solves this problem.

 

You can create up to +25 volt and -25 volt DC outputs using Channels 2 and 3 of Keysights new E36312A or E36313A bench power supplies. They can also be configured to track each other.

 

All three outputs of the E36312A and E36313A bench power supplies are electrically isolated from earth ground.  By connecting the output terminals as shown in the diagram below, you will use Channel 2 as your positive voltage source and Channel 3 as the negative voltage source. In the figure below, we provided an example of +18V and - 18V DC supplies.

 

 

You can use the front panel voltage knob or numeric keypad to adjust the output voltage of Channels 2 and 3.

 

If you need symmetrical output voltages, you can use the track mode feature, so that both DC outputs track each other.  Then, you will only need to program Channel 2 to 18V and Channel 3 will automatically be set to 18V.  Enable tracking mode by pressing Output Settings > Operation Mode >  Mode Tracking.     

 

Note that the front panel meter will always read positive voltage and current values for Channels 2 and 3. 

 

For other tips, read our application note Speed up Your Test with an Upgraded Bench Power Supply.

 

Our "Power Up Your Bench Contest" Week #6 winner is Jon Snowman.

 

Here is Jon's story:

 

Background

I’m an engineer who was inspired at high school to learn electronics, and I have continued it as a hobby ever since. I am therefore immensely passionate about helping schoolchildren become as engaged and excited about science, technology, engineering and maths (STEM) subjects as I am, and to encourage them to take them up at university and in their future careers.

 

Introduction

Engaging schoolchildren with STEM subjects is considered difficult, since they can appear too academic with too few practical elements and demonstrations. To address this, I began designing and building VertigoIMU - a compact inertial and GPS datalogger which gives physics students previously impossible insight into physical systems. From the ground up, I have captured the schematic, designed the PCB and fabricated prototypes to be tested by the school.

 

VertigoIMU comprises a 9 degree of freedom IMU (3 axes of each of acceleration, gyroscope and compass), a high precision 10Hz GPS unit, barometric pressure, humidity and temperature. Data is logged to a microSD card for analysis.

 

 

Some examples of where we have successfully deployed VertigoIMU:

• On a rotating bicycle wheel to demonstrate the equations of circular motion such as centripetal acceleration (a = w^2 x r).

• On the GreenPower competition vehicle – an electric vehicle built by the students – to examine the lateral forces on the wheels to inform decisions about tyres. A plot of acceleration whilst being driven in a circle is shown below.

 

 

 

Next Steps

VertigoIMU prototypes are being tested at the school with great success. However, the principal complaint is that battery life is not long enough. Since the GPS must maintain a lock before datalogging commences, and between datalogging runs, an optimised ‘standby’ mode is required, in which the GPS retains lock and all sensors are initialised and ready.

 

Longer battery life is essential so that students can capture exciting data with VertigoIMU, especially applications in which the unit must be powered up and achieve GPS lock for a long period before datalogging commences. Some examples include:

• Roller coasters – the students are planning a visit to a local theme park

• Flight analysis – capturing the angle of attack of a BASE jumper

 

 

How the E36312A would help

This power optimisation would benefit hugely from an E36312A power supply, as I am currently using lithium polymer batteries only. The main reasons are:

 

1. High precision (<20mA) current readback mode. This would allow me to quantify and optimise the standby power consumption. This is not possible with standard bench power supplies as they typically have current precisions of around 10mA.

 

2. Overvoltage protection (OVP) and overcurrent protection (OCP). Short circuiting or over-charging/discharging of lithium batteries can be dangerous. The safe OCP/OVP modes of the E36312A would enable safer working in my home lab.

 

3. Programmable. This would permit me to simulate the discharge curve of a battery to understand details such as the total run time of the device and calibrate the battery gauge.

 

4. Multiple channels. This would accelerate develop

 

 

Congratulations Jon.  We are sending you our branding new E36312A!

 

Don't miss out.  Submit your entries now to win our brand new E36312A Triple Output DC Power Supply!

 

Go to www.keysight.com/find/PowerUpYourBench for more details. #PowerUpYourBench

Our "Power Up Your Bench Contest" Week #5 winner is Rafael Souza. See a video of his story here

Congratulations Rafael.  We are sending you our branding new E36312A!

 

Don't miss out.  Submit your entries now to win our brand new E36312A Triple Output DC Power Supply!

 

Go to www.keysight.com/find/PowerUpYourBench for more details. #PowerUpYourBench

Our "Power Up Your Bench Contest" Week #4 winner is Martin Glunz from Germany

 

Here is Martin's story...

 

1. Purpose of this document Entry to Keysight

"Power Up Your Bench” contest

 

2. Who am I

My name is Martin Glunz, a professional electronics engineer living in Germany. Not only I’m working for a company that is making industrial electronics as a R&D engineer, I’m doing some engineering at home. One of my goals is to reduce my home’s standby power consumption. I’ve done some research within this topic in the past, one of my projects was a “zero standby power” supply for the doorbell installation, done in a quite unusal way using the standard off-the-shelf doorbell transformer.

 

3. What do I want to achieve with this power supply

That’s quite easy to say: Testing the power consumption and efficiency of my circuits to save more energy. This power supply has a quite accurate voltage and current readback according to the data sheet, so this saves me the usage of two multimeters in the first place. Using a standard bench supply, there’s always the necessity to use external precision meters if one needs accurate results. My main strategy to save power is to use a intermediate DC bus (running at 19V DC) to provide power to the lot of standby boxes (like internet router, NAS box, ...). Those require various supply voltages from 5V DC to 15V DC. I’m currently using a variety of home made DC/DC converters to convert the 19V DC bus to the required voltages. Since the 19V DC bus must be supplied from the mains power, there’s a centralized power supply unit using redundant sources. To achieve my main goal, the efficiency of the involved power supplies (mains power to 19V DC, 19V DC to whatever is required) is very important to know and to be able to optimize. Your typical wall wart or power brick supply (from mains to 5V / 12V DC) in the low watts range (2W ... 20W) has still a not so good efficiency, even regarding the latest energy star regulations. So it is possible to achieve better total efficiency using the 19V DC bus approach. I’m using comercially available 19V DC supplies with good effiency here, but I’m building my own DC/DC converters to provide the local lower voltages. To achieve better total efficiency than the standard off-line power supply, these must have efficiency better than 95%. Evaluating the efficiency of such a DC/DC converter isn’t a simple task if one needs accurate results. Moreover, variation of input voltage and output load have influence on the efficiency, and the DC/DC circuit must be optimized for the typical load.

 

4. Where does this supply help me here

 

4.1. Power consumption of devices All of the devices I plan to optimize fall into the available output power range of the E36312A supply. Typically the range is from 1W at 5V DC to 20W at 12V DC. The accurate voltage and current readback together with the logging and exporting capabilities will be a great help to find out the typical power supply requirements of my devices. The supply promises to provide an easy way to make measurement of consumed DC power over time.

 

4.2. Efficiency of my converters Second, after knowing the power requirement of a device, I can go for the optimization of the DC/DC converter circuit. Doing so requires a precise measurement of input and output power of the converter, and taking measurements at varying input voltage and load conditions.

 

4.2.1. Input power measurement done by the supply The E36312A supply eases the task of measuring the input power to the DC/DC by using the precise readback, remote sensing and logging. 

 

4.2.2. Input voltage variation done by the supply An additional useful feature is the sequencing / ramping capability: This will be used to semiautomatically measure input power over input voltage at constant load.

 

4.2.3. Save a voltmeter In case one output channel provides enough power for the DC/DC converter, a second channel would be used to read back the output voltage of the DC/DC, with current limit set to zero (or a near zero voltage). Now one can read back the output voltage of the DC/DC using one channel of the power supply, only one additional amp meter will be required to read the DC/DC output current and finally calculate the efficiency.

 

4.2.4. Output load variation done by the supply Imagine now, three of four measurements are done by the bench power supply unit at constant DC/DC output load, and only one measurement left: efficiency over load variation. If one uses a constant current sink or a simple power resistor as the load to the DC/DC converter, and has the DC/DC converters output connected to the bench power supply to read back the output voltage, one could also supply some current (in CC mode) from the bench power supply into the load. This reduces the current drawn from the DC/DC output by the amount supplied from the bench supply. Now it is possible to evaluate (and semi-automate by using the remote control capabilities) the efficiency of my (or anyone elses) DC/DC converters by using just three components: The E36312A bench power suppy, a precise ampmeter and a suitable load resistor / current sink.

 

Congratulations Martin.  We are sending you our branding new E36312A!

 

Don't miss out.  Submit your entries now to win our brand new E36312A Triple Output DC Power Supply!

 

Go to www.keysight.com/find/PowerUpYourBench for more details. #PowerUpYourBench

Our "Power Up Your Bench Contest" Week #3 winner is John Hubert.

 

Here is John's story:

I work for a RF transmitter company called Nautel Ltd., my time is spent doing customer service testing and repairing of circuit boards. I personally feel the image included says a lot but I can say that this power supply would go a long way to improving my bench space. Since I work with RF many of our systems require multiple power supplies of different voltage levels. Most of these boards are very sensitive to voltage noise as they create reference voltages which cause me untold grief with some of these poorly regulated noisy supplies. The data logging features would greatly increase the information available to help me troubleshoot some issues. I also find myself having to simulate fault conditions and inputs; the sequencing and list features would greatly improve my ability to quickly test boards with complex inputs, as manually adjusting voltages usually cause timing problems. I have been trying to get my department head to purchase some of these units and I feel if I could show the company the quality of life and performance improvements built into your device we might be able to justify purchasing new equipment. A while ago we acquired an EXA spectrum analyzer 9010B and it has been a rock solid piece of equipment and a joy to use, it has become the favorite to use by many my fellow co-workers. I thank you for your time and consideration. 

 

Congratulations John.  We are sending you our branding new E36312A!

 

Don't miss out.  Submit your entries now to win our brand new E36312A Triple Output DC Power Supply!