DT9816 arbitrarily stops reacting to trigger

[Wolfram.T]

Hello everyone,

I've got a problem with the triggered analog readout of the DT9816. I'm using the C# DotNET API and usually it's working fine, but sometimes the device stops reacting to the trigger and doesn't aqcuire any more data. This behaviour happens arbitrarily, sometimes after a few 100 trigger pulses, sometimes after a few thousand, and sometimes I can capture tens of thousands of measurements without any issue. The delay between triggers is usually about 40 mS.

When the device is in the non-working state, I need to either unplug and replug the USB cable or restart the entire PC. Just a restart of our software doesn't solve the issue. Our software doesn't report any runtime errors either, there are just no more data packets arriving. We've already tested this on another PC running a different operating system (Win10 / Win11) with the same results.

Any ideas as to why this could be happening?

Thank you very much for your time,
Wolfram

[DAQman]

Hello,

You could have a ground loop that, for the most part, is not affecting operation. However, the severity of a ground loop can ebb and flow with ground currents and cause problems at strange times. A valid trigger signal drops below 0.8 volts and goes above 2.4. However, in the presents of a ground loop, the trigger signal may drop only to 0.9 or greater, or its high level may fall short of 2.4 volts. One way to test this condition is to remove the signal connections and use a function generator to trigger it repeatedly. Because you write your own code, you could wire a digital signal to the trigger input and do the same test without a function generator by toggling the digital line.

Best regards,
John

[Wolfram.T]

Hello John,

thank you for your input. I'll check the wiring and try a different trigger source. Maybe having a look with an oscilloscope won't hurt either.

Best regards,
Wolfram
 

[Wolfram.T]

Hello again,

we're currently checking our wiring.
Is there any preference as to how the 4 ground pins on the device should be used or are they all the same?
I'm talking about the left side pins 15 and 19 as well as the right side pins 29 and 38 - not the analog ground on pin 9.
On our device the ground pin 15 is labeled in a greyish color instead of white like all the other pins, but the manual doesn't mention it as being special.

Best regards,
Wolfram

[DAQman]

Hello,

The four ground terminals are connected internally and should be used for digital signals. The analog ground is used for analog signals. The analog ground is routed so that noise from digital signals is kept separate. There is no electrical isolation, so the two grounds are connected internally. The DT9816 establishes its ground via the USB connector. If you have a sensor that requires a power supply, it could be a second ground point, and if the two are different, a ground loop is born.

I'm not aware that pin 15 ground is different from the others.

Best regards,
John

[Wolfram.T]

Hello John,

thank you very much for the information. I think that explains the issues we're having.

Best regards,
Wolfram