There seems to be lots of confusion around the DSO Quad calibration process, and no documentation, so I’ve put the following guide together based on what the firmware actually does. This is all based on the v2.33 app source, but the calibration function in v2.32 is identical.
First, the bugs:
- Don’t bother trying to calibrate channel B, positive adjustment to the zero calibration for any range also modifies the drift/offset calibration (which affects all ranges).
- Exit option selection is broken in two ways. Calibration changes to the 10V range also change the exit option (without changing the displayed text), so don’t try to calibrate 10V range if you want to save changes. And navigation through the cyclic buffer of exit options is not handled correctly anyway - pay attention to calibration step 5 below.
- (Not a calibration bug, but related) Signal levels reported by the Quad when in use will only match calibrated values when ypos is 25 (1 div up from the bottom of the screen).
I have modified the app firmware to fix the first two of these, which I can post if anyone is interested, but until the ypos-dependent amplitude issue is fixed, calibration is a bit pointless anyway.
The - and + controls:
In the Zero column, change zero calibration. One value per range per channel
In the Diff column, change gain calibration. One value per range per channel.
In the Votage column, change drift/offset calibration. One value per channel, for all ranges.
The value displayed in a cell only updates when the cell is selected, so to get valid readings in a cell, you need to navigate through it to see the effect of calibration changes in other cells.
Navigating through a cell may change the displayed value, but does not overwrite/lose calibration settings. (E.g. If you navigate through a calibrated Zero cell with the probe not grounded, you will get a non-zero reading, but you don’t lose your zero calibration.)
- Ground the probe.
- Adjust the zero column value to 0. (You can confirm the zero voltage by navigating through the Votage cell, you should see 0.00uV.)
- Connect the probe to a suitable reference voltage for the range being calibrated.
- Adjust the gain calibration in the Diff column until the value in the Votage column matches the reference voltage. (Yes, this requires making a change in the Diff column, then navigating through the Votage cell to update the voltage reading.) Note that the values displayed in the Diff column are in thousandths. You should expect to have a value fairly close to 1000 (1.00), but only 2 decimal places are displayed for values above 999, so don’t expect a visible change for every adjustment above 1.00.
- Navigate down to the bottom row, select “+” once to change to “Exit with save”. (This is important; reaching “Exit with save” any other way will not save your changes.) Press button 2 (square) to save and exit. If it doesn’t say “Save the calibration data” at the top of the screen for a second, you have just lost all your changes