EMC Basics: What are EMC & EMI Measurements and Why We Care

Blog Post created by nickben Employee on Jul 16, 2018


Conceptualizing your next product, designing it, and then releasing it to market are more or less the main phases encountered during a product development cycle. But what if you had gotten as far as finishing your product design only to discover late that you cannot push the product to market, because it didn’t meet some standards set by local regulators. Therefore, testing your product early in the cycle to make sure it works appropriately is just as important as designing it. In this blog we’ll discuss the basics of EMC and EMI pre-compliance – something all electronic products will eventually have to get certified compliance for in a test house. However, compliance testing certification occurs very late in the development process and if you instead did pre-compliance testing earlier on, fixing these problems are easier and less costly (Figure 1).


Product Development Cycle including EMI Testing

Figure 1: Pre-compliance testing can uncover problems during earlier stages of development, where solutions are easier and less costly. It can also reduce the risk of design rework and associated schedule delays.


What is It

Let’s first figure out the difference between EMC and EMI. EMC and EMI stand for electromagnetic compatibility and electromagnetic interference respectively. EMC, you can say, is the umbrella term whereas EMI is the actual phenomena you will be testing for.


All electronic products, whether it be your smartphone or your smart refrigerator, must eventually pass compliance tests in a recognized test house and be certified before they can be brought to market. This certification is required as it demonstrates that your product won’t electromagnetically interfere or be interfered with by any other electronic products in close proximity. To get your device certified, test houses are mainly concerned with making sure your device can pass 4 EMC tests in particular – radiated emissions and immunity tests and conducted emissions and immunity tests.


In short, the difference between radiated tests (emissions and immunity) and conducted tests (emissions and immunity) is that the first refers to unintentional release of electromagnetic energy from an electronic device. The latter refers to internal electromagnetic emissions propagated along a power or signal cable, creating noise. Looking at Figure 2 below we see a snapshot of the 4 different tests.


EMC Testing, Conducted & Radiated Emissions

Figure 2: Four types of EMC Measurements.


The difference between emissions and immunity tests are that the emissions is concerned with the amount of electromagnetic energy emitted from your device while immunity is concerned with how susceptible your device is to electromagnetic energy being emitted from surrounding devices.


Why Testing For It Matters

Regulatory bodies, like the FCC in the US, set up standards (CISPR) that devices are tested against. As you would expect, standards vary from one device to another – meaning you would measure the amount of EMI on your smartphone differently than you would military-grade avionic equipment. If you have a good signal analyzer with an EMI application, then you’ll have pre-loaded and configured limits for CISPR and MIL-STD tests that allow you test against these standards quickly. EMI measurements are made to ensure that there is no interference between devices when in operation. When you’ve designed your product, and have it sent off to a test house, the test house will traditionally put your device in an anechoic chamber. An anechoic chamber is used to completely block out signals exiting from within the chamber to outside of it and other signals outside the chamber from entering in it. Within the chamber an antenna is used to test a number of different points on your device. This anechoic chamber setup is similar to the one you see below in Figure 3


 EMC Test in an Anechoic Chamber

Figure 3: EMC Test in an Anechoic Chamber. An antenna is directionally pointed at the device under test (DUT).


However, simply sending off your product for EMC testing at a certified test house is not the answer. This is because these tests are very expensive to do, and you don’t want to risk having to do design revisions and throwing off your entire schedule. That’s why it’s important to do some due diligence on your end.


What’s The Solution

The solution is simple – make sure you conduct your own EMC tests in house (pre-compliance testing) for your device prior to sending it off to a test house for certification (compliance testing). In the off chance that your device doesn’t pass at the test house, it will not only throw off your design cycle and time to market, but also cost you a lot of money.


This is where signal analyzers come in handy. Using a signal analyzer, EMI close-field probes and an EMI application, you can conduct your own EMI measurements in house to ensure your device is on track to fulfilling the EMC requirements of the standard that it will be tested against at a test house. You can take a look at Figure 4 below to see some example tools you can equip yourself with to conduct EMC pre-compliance measurements.


EMC Testing Tools

Figure 4: A set of tools you can use to conduct your own EMC testing.



So, in summary, if you are working towards getting your device to market you definitely need to make sure your device is EMC pre-compliant prior to sending it off to a test house for certification. A signal analyzer with an EMI application and EMI close-field probes are the right tools you need for making sure you can test for EMI accurately. Your design cycle will not only stay on track, but you will also make your manager one happy, and less broke, person.


Thanks for taking the time to read this blog, if you enjoyed it feel free to give it a like, comment, and share. Stay tuned for more blogs to come that discusses more about EMC testing. For more in-depth information on EMI conducted and radiated measurements check out the following application note: Making Conducted and Radiated Emissions Measurements.