When building the script to create calibration/interpolation tables. I need a programmable voltage source which can give stable voltages (It does not need to be very precise, but high precision does have benefits)
For that I used a schematic which was proposed by Performa01.
https://www.eevblog.com/forum/testgear/sag1021-vs-sdg1032-what-to-expect/msg2445294/#msg2445294On the PCB I used a gnd spring / turned pin to have a good probe connection. The wires that hold the banana plugs are doubled and soldered on the backside as well. This makes this sturdy enough to connect it to the DMM with ease. I also added a 10 uF capacitor for noise control.
With this and the script I can produce voltages from -3 V to 3 V. The graphs show how stable those voltages are over a longer period targetting 2.5V. The voltage is "PID" controlled about every second using the fine channel.
To get to this point the script goes trough the following fases:
- Create coarse output-input mapping (for each coarse output we need to know the channel 1 input)
- Create close to zero voltage
- Create fine output-input mapping (for each fine adjustment correction we need to know the channel 2 input)
After that the mappings can be used to quickly set a precise output. (But even then the output keeps being error corrected using real measurements.)
The following project step is to generate a scala of voltages and determine which offset on the scope negates those. But also measure the ADC response of the 500uV/Div range.
For this I would like to have the scope measure less noise then now is the case. Somehow the capacitor does not dampens the noise (about 1mV) as much as I would like to.
Maybe I have to "can" the circuit to see whether that makes a difference? (The used coax cables might also be of non optimal quality.)
The planned scope measurements are actually quite robuust against noise regarding to accuracy, the largest problem it gives is that this signal goes out of screen much earlier when using the 500uV range, but I don't know how robuust the DMM measurements are on a noisy signal.
So suggestions are welcome!