ammeter on Power supply gives incorrect reading when using LabVIEW drivers

[vaguy]

When automating power supply stepping on the +25 volt channel, the "actual" current read by the VI's in the VB API do not always give the correct result - frequently off by a factor of 2 or so.I have tried inserting time delays up to 300mS between changing the supply settings and reading the outputs. The voltage output is always correct, bit the current reading is erratic. I have tried running the VB in the standalone mode and notice that when I enable the power supply using the front panel on-off button that the ammeter on the front panel also reads incorrectly for about a second.

There is an example LabVIEW program that shows using the API to set an output and then read the actual outputs and it seems to work ok, but it is in a loop, and I expect that the ammeter does not read correctly on the first few loops either.

If I connect the DMM to the power supply terminals, I get the correct currents leading me to believe that my voltage setting VI's are ok. I have also double checked that the circuit is not going into current limit. I am running the latest versio

[gdrag]

Hello VA guy,

When you are in the VB standalone application, by "ammeter on the front panel", do you mean the one that shows that the current is on the output?

That one there?

That should update much quicker than 1 second.

How are you communicating with your VB?  Are you using a USB cable?  If you are, could you try using a different USB port?  Also, do you have another device that you can try controlling through USB on the same computer and check the response time? Can you check controlling the VB with another computer?

[vaguy]

Yes, the current on the output.

I am communicating using USB on my fastest port, which is the faster USB. I will be at conferences next week, and will demoing a VB with some TI parts. I will check then.

It is really odd, because it only happens sporadically.

[JoeFriedchicken]

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vaguy wrote:

When automating power supply stepping on the +25 volt channel, the "actual" current read by the VI's in the VB API do not always give the correct result - frequently off by a factor of 2 or so.I have tried inserting time delays up to 300mS between changing the supply settings and reading the outputs. The voltage output is always correct, bit the current reading is erratic.

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Would you use the standalone application at the same time as LabVIEW and use the scope to capture the voltage ouput from the power supply when you enable its outputs?

[vaguy]

Sure, I will be at a conference next week, but can do that when I get back. Note though that the voltage reading is always correct. It is the current that is off.

[JoeFriedchicken]

Thanks.

Would you also share your setup information? What voltage do you set, what current limit do you set, what is the channel's load?