Calibration

Your VM module was calibrated at the factory using a fancy voltmeter and should be fairly accurate (within +/- 0.1V) right out of the bag.

Warm-Up Time

Much of VM’s circuitry is analog, and it is somewhat temperature-dependent. The meter is most accurate when it’s had a chance to warm up for a few minutes after being powered up and reach operating temperature.

The module may think it has something connected to the front input for several seconds when it is first powered up. This is normal and is caused by the unit’s calibration being out of whack because it is cold.

Auto Calibration

Your module was calibrated using our system and our power supply, so it is conceivable that it might be off a bit when installed in your system. If the voltage readings seem off, you might want to try running the module’s auto calibration routine:

• Make sure your system has been powered up for at least 15 minutes, so it has had a chance to reach operating temperature
• Unplug everything from the module’s input and output jacks
• Press and hold the button for about 10 seconds. The top two LEDs on the meter will flash magenta indicating that auto-calibration is complete

During auto-calibration, VM sends a test signal back to itself through the input jack and uses it to set all the voltage thresholds based on the actual response of the circuitry in your particular module.

Manual Calibration & Fine Tuning

If the meter still seems off, or it just doesn’t match another meter you want it to match, then you can manually calibrate it.

There is a voltage threshold point for each volt from -16 to +16 stored in the meter. These threshold points can be edited individually (tenths of a volt are calculated on the fly based on the whole-volt points and cannot be modified).

To modify a calibration point, perform the following procedure:

• Make sure your system has been powered up for at least 15 minutes, so it has had a chance to reach operating temperature
• Connect a stable DC voltage to the front input
• Set that voltage to match the threshold you want to edit. For example, if you want to edit the +5V threshold point, set the voltage going into the input to exactly 5V. It probably won’t display exactly right on the meter, but that’s okay (and probably also why you’re recalibrating it in the first place).
• Press and hold the button for about 10 seconds. The top LED will blink magenta indicating that the threshold point has been updated. The meter should then display exactly the voltage you are supplying to the input.

How does the module know which threshold to update? It always assumes you are trying to change the one closest to whatever voltage it sees on the input. If you’re trying to edit the +5V point, as long as the meter thinks it sees somewhere between 4.5V – 5.4V, it will update the +5V point. If it sees 5.7V, then it will update the 6V threshold since that is closest. If the current calibration is more than 1/2 volt off from where you want it to be, you may have to perform the procedure a couple of times per point to walk it into range.

When setting your input voltage, make sure you meter it in such a way that your meter sees exactly the same voltage as the VM module does.

You can use this manual calibration procedure to change one inaccurate threshold point or all of them if you want.