A client has asked for additional sensor outputs to be measured meaning we're tight on channels on a CR1000. The additional outputs are from the same sensor, which has 2 analogue outputs with a shared reference analogue ground channel. The cable is long, so I want to use differential measurements, but I thought this may be possible using 3 SE channels rather than 2 Diff channels, given that the reference is from the same connection. Am I right in thinking that, and could someone share some example code please?
It would have to be two differential channels. The measurement hardware reads the channels as an H and L pair. That is the way things are physically wired.
With the one you are stuck reading single ended, I would recommend using the measurement option to read the ground offset every time. That will take out some of the potential error.
Thank you for the reply. I was thinking I could measure the 3 SE channels and code subtraction of the AG reading from the other 2 readings?
I was thinking I could measure the 3 SE channels and code subtraction of the AG reading from the other 2 readings?
Tha'ts not how this works.
How long is the cable?
Maybe increase its conductor diameter (less resistance) and increase the settling time/integration interval to compensate for dodgy environments.
Also, the two signals already come with a shared reference.. what is the problem you encountered connecting it to anaolog ground on the logger and measuring the two signals as single ended vs that common reference?
Are the signals weak (say less than 1 mV) and or is the source of high resistance?
Maybe you should look into an op-amp circuit to convert this voltage signal at the source into a low resistance source for the logger to have no problems with long/thin wiring to get the analog signals across?
Thank you for the reply. The supplier of the instrument has clarified that we should just ground the AG connection, not measure relative to it, so the issue is resolved. The manufacturer supplys loggers which can only make single ended measurements, meaning we often have to 'translate' their instructions to improve measurements on more capable loggers.
Could you explain my misunderstanding of subtracting the AG reading from other SE channel measurements though?