Hi all!
I am using 3458A with option 001 in DCV sampling mode to measure properties of sinus signals from hundereds up to 8000 samples. I have observed, that DMM makes sometimes delay 100 ns in sampling.
The question is: What can be the reason for the 100 ns delay and how to prevent from it?
During exploring this problem, I simplified measurement setup up to the following combination, to ommit possible interferences from other sources. (In original setup, DMM has added home made small circuit to provide optical clock signal for synchornization of other devices). So he is simple test setup:
1) DMM input is connected to the 33220A output.
2) DMM is programmed via HPIB-USB adaptor for TRIG SGL
3) HPIB is disconnected.
4) DMM is triggered via ext.trigger
5) ext.trigger cable is disconnected
6) when sampling is finished, HPIB is connected and samples read out from the DMM to the computer.
I repeated this experiment outside of measurement laboratory in the other room, on the other floor, with different DMM. The problem still exists.
The problem with 100 ns delay occurs sometimes less, sometimes very often. Up to now, I have tried and found following things:
- the problem is not due to some delays in generated signal. (I have sampled with DMM signals from different generators , moreover I have sampled same signal in parallel with PXI high speed digitizer. Generated signal is really clear)
- it is ussual, that the problem occurs one day at some combinations of aperture time, other day or week on other combinations
- this problem was observed by other users too, but only after hundreds or thousands of samples. The idea for this problem was, that DMM has problem with timing during saving data to memory. Now, I see the problem sometimes during first hundred of samples too.
- sometimes it seems, that 100ns delay occurs at same sample nummer, sometimes this delay "floats" along samples and change position in sampled signal.
- when I place some EMI filter before the 3458A power plug, the problem dissapears for some DCV mode aperture time configurations, but newly appears at different configurations. Same happens sometimes, when I change the capacitance (e.g. I use longer cable for trigger input) on the trigger input of the DMM.
- this problem occurs not only with one DMM, I have seen this problem on 3 DMM, two of the quite new, one was older.
- details mentioned above says me, that there is some problem in the power net but I am not sure, because I have access to more power nets in the laboratory and changing them has no effect.
Sorry for long text and thanks in advance for response
I am using 3458A with option 001 in DCV sampling mode to measure properties of sinus signals from hundereds up to 8000 samples. I have observed, that DMM makes sometimes delay 100 ns in sampling.
The question is: What can be the reason for the 100 ns delay and how to prevent from it?
During exploring this problem, I simplified measurement setup up to the following combination, to ommit possible interferences from other sources. (In original setup, DMM has added home made small circuit to provide optical clock signal for synchornization of other devices). So he is simple test setup:
1) DMM input is connected to the 33220A output.
2) DMM is programmed via HPIB-USB adaptor for TRIG SGL
3) HPIB is disconnected.
4) DMM is triggered via ext.trigger
5) ext.trigger cable is disconnected
6) when sampling is finished, HPIB is connected and samples read out from the DMM to the computer.
I repeated this experiment outside of measurement laboratory in the other room, on the other floor, with different DMM. The problem still exists.
The problem with 100 ns delay occurs sometimes less, sometimes very often. Up to now, I have tried and found following things:
- the problem is not due to some delays in generated signal. (I have sampled with DMM signals from different generators , moreover I have sampled same signal in parallel with PXI high speed digitizer. Generated signal is really clear)
- it is ussual, that the problem occurs one day at some combinations of aperture time, other day or week on other combinations
- this problem was observed by other users too, but only after hundreds or thousands of samples. The idea for this problem was, that DMM has problem with timing during saving data to memory. Now, I see the problem sometimes during first hundred of samples too.
- sometimes it seems, that 100ns delay occurs at same sample nummer, sometimes this delay "floats" along samples and change position in sampled signal.
- when I place some EMI filter before the 3458A power plug, the problem dissapears for some DCV mode aperture time configurations, but newly appears at different configurations. Same happens sometimes, when I change the capacitance (e.g. I use longer cable for trigger input) on the trigger input of the DMM.
- this problem occurs not only with one DMM, I have seen this problem on 3 DMM, two of the quite new, one was older.
- details mentioned above says me, that there is some problem in the power net but I am not sure, because I have access to more power nets in the laboratory and changing them has no effect.
Sorry for long text and thanks in advance for response
Hi lhornburg, here is list of all commands, which goes repeatedly for each measurement after last reset. It is last state after trying if I see some effect of changing position of some commands:
X_Tint - integration time, X_Taper - aperture time , X_Samples - number of samples
X_Taper is everytime at least 25us longer than X_Tint, X_Samples is up to 8000.
PRESET DIG
TARM HOLD; DISP 0
APER X_Tint
MFORMAT DINT
OFORMAT DINT
DCV 10
DELAY 0
NRDGS 1
AZERO OFF
TRIG EXT
MEM LIFO
TARM SGL
ISCALE?
//here goes hardware trigger signal//
//here goes HPIB read command to read out ISCALE//
DISP 0,"SAMPLE 1..."
SWEEP X_Taper,X_Samples
MEM LIFO
TARM SGL
RMEM 1, X_Samples
//here goes HPIB read command to read out 4 * X_Samples bytes//
Now, I have observed, that with command TRIG AUTO occurs timing error 100 ns at some devices at stable time. E.g. with one DMM occurs error every time after 3.7 s and only one times per measurement, i.e. not after 3.7 s multiples(e.g. 7.4 s). With second DMM, this error occures after 9s, with third DMM two times - after 0.06 s and 0.21 s....
This time of error occurrence becomes longer, when DMM is turned off before measurement. During warm up, time of error occurrence becomes shorter and then stabilizes. Reset command has no effect.