How to characterise for use with the fmc adc 100m PTS
Each USB relay box contains a precision 4.096V voltage reference (VREF) chip, which is used in all three supported input ranges (100mV, 1V and 10V) by means of voltage dividers.
Proper characterisation of each USB relay box involves measuring the VREF with a 6 digit (or better) digital multimeter (DMM) and storing the measured values in the EEPROM of the box. These values will be later retrieved by the FMC-ADC-100M PTS software when using the box, to take into account any imperfections in the VREF output.
The actual characterisation procedure involves the following steps:
- Power up the DMM. For optimal results, you might want to have the instrument running for some time to warm it up (if in doubt, check the instrument's user manual).
- Connect the USB relay box to the FMC-ADC-100M PTS and power-up the PC.
- When prompted for the FMC-ADC bar code, close the terminal window.
- Start a new terminal and run test24 of the PTS to retrieve the existing characterisation values (if any):
$ cd fmc-adc-tst
$ sudo su
$ export PYTHONPATH="/home/user/fmc-adc-tst/pts/:/home/user/fmc-adc-tst/pts/common/:/home/user/fmc-adc-tst/pts/gnurabbit/python/"
$ python tests/test24.py
- In a similar way, without closing the terminal (so that you don't loose root access and the exported PYTHONPATH environment variable) run test18 (
$python tests/test18.py
). The test will start outputing whatever is present in the AWG IN input to each one of the outputs, one by one, while leaving all three other outputs at VREF, waiting for your input before moving to the next one and going through each voltage range, giving you the opportunity to measure the VREF (and write it down on a piece of paper, text file, or similar!). - If you notice significant drift and you wish to reprogram the EEPROM with the newly-measured values, then, again without closing the above terminal, run test21 (
$python tests/test21.py
) and follow on-screen instructions.
Prerequisites
The above requires that the ADC PTS (Production Test System) is installed. Please see
13 June 2022