Hello, I have a T7 with CB37 expansion. I am mostly running some LJT-Resistance but I also have a few LJT-relay drivers and LJT-DAC. I am programming in LabVIEW. I am getting a weird issue where my Ain channels are reading half of the voltage applied: If I connect Vs to any Ain I get 2.6-2.7V and if I connect the 2.5V from the LJT-Resistance I get 1.26-1.27V. The multimeter is confirming the expected voltages. Likewise connecting DACA to Ain0 as-in the LJT-DAC example I am glso getting just above half the expected voltage. This is also happening in Kipling, two attached pictures show setting 7V to TDAC0 and then reading 3.6V on Ain0.
Side note: I don't think I am writing to TDAC0 correctly in LabVIEW, I will start another thread for this problem.
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I'm having trouble with your screenshots. The following might help in the future.
https://labjack.com/support/app-notes/screenshots
Nonetheless, what you describe is very strange. Lets start with the "T7 Ground Offset Check" here:
https://labjack.com/support/software/applications/t-series/kipling/device-information/hardware-issues-detected
If that goes well, add the register "AIN0" to the Register Matrix active list and see if you read about 5V with AIN0 jumpered to VS.
The ground offset hovers between 0.000217V and 0.000138V. Certainly at ResIndex=11 and I thought it was the same at 7. I'll check again tomorrow.
It appears to happen only when the CB37 is connected. I'm reading 5.27V,ich.
Oh, and let me know if you want any screenshots. I duplicated it in Kipling today too.
So the ground offset test worked fine?
And then the extra step I added was fine also and read 5.27 volts?
"If that goes well, add the register "AIN0" to the Register Matrix active list and see if you read about 5V with AIN0 jumpered to VS."
5.27 volts is actually slightly out of spec. Should be fine, but it is slightly over the 5.25V upper limit for supply voltage:
https://labjack.com/support/datasheets/t-series/appendix-a-5
How are you powering the T7? If you measure AIN0 versus GND with a DMM does it agree with that 5.27 volt reading?
So you still see some problem but only when the CB37 is connected? Can you describe the minimum connections to see a problem and what problem you see?
In your screen picture it appears that AIN0 is reading 3.60 volts. Is this wrong and what is connected to AIN0? Make sure you are only connecting 1 signal to AIN0 (don't connect to AIN0 on both the T7 and CB37 at the same time).
It looks like all your other channels are reading very close to 0.0. Do you have all these channels jumpered to GND? For initial troubleshooting use minimum connections. USB, 1 jumper wire, and with/without CB37.
I'm reading grounds offset today with nothing connected at 0.000374V and drifting some. I'm reading 5.00Vwith the DMM for Vs.
AIn0 was connected to DACA which was set to 7V.
Maybe I should be doing an RMA for the LJ and maybe the CB37.
I did not jumper any channels to GND either.
The ground offset test is not with nothing connected. Readings are meaningless with nothing connected:
https://labjack.com/support/app-notes/floatingunconnected-inputs
The ground test is a specific test detailed here in "T7 Ground Offset Check":
https://labjack.com/support/software/applications/t-series/kipling/device-information/hardware-issues-detected
So you will just have just USB. No other connections to the T7 (except for the single small jumper wire used during steps 4-6.
If that goes well, install a single small jumper wire securely from AIN0 to VS. Add the register "AIN0" to the Register Matrix active list and see if you read about 5V.
Another good basic test is in the quickstart. Again you just have USB, and then add a single small jumper wire securely clamped from AIN0 to DAC0 in steps 7 & 8:
https://labjack.com/support/quickstart/t7
Sorry, I guess I am not communicating clearly. When I run the ground offset test with nothing but USB and those where the values I stated. I also mentioned that I read AIN15 while reading other sensors and this increased the offset slightly.
I also jumpered Vss to AIN and read 5.25V on the LJ, 5.01V on the DMM.
Let me know if there are any other tests or if I'm not making sense. Thanks for your help.
Hmmm ... how about the quickstart steps 7 & 8?
I am trying all combinations of CB37 connections and the only one that is giving me half voltage is when I plug a LJTick into the channel I am measuring Vss. Looks like that's what I've done.
Connecting a DAC channel to AIN works as expected. Thanks!
So it sounds like your problem here was having 2 different signals connected to the same analog input at the same time. AIN0-3 appear on screw terminals on the T7 itself and also on the DB37/CB37, so this mistake usually happens on these 4 channels. The duplicate terminals have resistors between them, so if you connect 2 different signals you wind up with a voltage in between them.