Automatic voltage calibration

It is assumed that you have connected a configured HVPS to the calibration setup described on the automatic calibration and characterisation page.

  • On the HVPS option dialogue box, press the Voltage Calibration button (yellow rectangle)
  • Check that the probe indicated in (1) corresponds to the probe you are using for the calibration. If this is not the case, you need to press cancel (3), and edit line 2 of the config.ini file to point to the probe you are using (refer to section 2.2 of the automatic calibration and characterisation page).
  • Be sure that the high voltage enable switch (s2) of the HVPS is in the on position
  • Start the calibration process by pressing start (2). Alternatively you can can cancel the process (3), which will close the window.
  • The true (measured) output voltage of the HVPS is plotted as a function of the voltage the HVPS reads on (5). This takes about 1 minute. Once the process has finished, correction factors will be calculated, and indicator (6) shows the error between the voltage read by the HVPS and the measured voltage after calibration (so this should ideally be 0, but nothing is perfect in this world).
  • Indicator (7) shows the current calibration factor stored in the board. If you have just reset the board to default settings, the second and 0 order terms should be 0, and the first order term should be the default value as described in column c1 of the resistor ratio table.
  • Indicator (8) shows the new calibration factors obtained by linear regression on the acquired data (5). It is a second order polynomial of the form c2 x^2 + c1 x + c0. The three indicators corresponds to the parameters c2, c1, and c0 stored in the HVPS
  • Button (9) allows you to toggle between quadratic and linear correction (in the latter case, c2 is forced to be 0). You can see the effect on the error (6) when you change from linear to quadratic.
  • Check box (10) allows you to turn on or off the offset of the correction. If unchecked, c0 is forced to 0. The impact can be seen on the error on (6). Usually, you have much better accuracy with a quadratic fitting with offset enabled (default settings).
  • To keep the new calibration values you just obtained, click on (11). This option is greyed out until the calibration process is over.
  • Click on (12) to discard the new calibration values and keep the previous values shown on (7). This option is greyed out until the calibration process is over.
  • The program waits until you press either (11) or (12). You must choose one of these two options for the program to continue

  • A new calibration is performed, this time in closed-loop mode, using the selected calibration values. For a range of voltage set points between 5% and 95% of the board rated voltage, the voltage read by the HVPS and the true (measured) voltage are plotted on graph (13). Ideally, this graph should show two superposed straight lines with equation y=x.
  • The graph (14) displays the error between the HVPS read voltage (white) and the measured voltage (red) as a function of the desired set point. The white curve should be close to 0 (within +/- 0.2 percent of the board rating). The red curve shows the real error between the voltage the user sets and the true output voltage of the HVPS. It should be within +/- 0.5% of the board voltage rating).
  • Once the measurement is finished, the button (15) is enabled. Pressing on it allows to close the window and go back to the main interface. The calibration value you selected is saved in the HVPS memory, and a file with the calibration data is saved in the support directory.