The RK2672AM is a Chinese high voltage test set. This article describes a process for calibration of the device.
This process should not be attempted unless you have the requisite competencies, experience, tools and test equipment. There are dangerous voltages involved, so assess the hazards, plan your work, don’t attempt it if fatigued or alcohol enhanced.
Above is the front panel of the RK2672AM.
Above is the main control board of the RK2672AM.
This article applies to that exact controller board.
It contains 5 multi turn trimpots used for calibrating the display. The PCB overlay has designations for each of the trimpots. In at least one case, the setting of one trimpot depends on another, so the calibration needs to be performed in the order given here.
The following steps will be described:
- AC voltmeter calibration;
- DC voltmeter calibration;
- AC current calibration – 2mA range;
- AC current check – 20mA range;
- DC current calibration – 2mA range;
- DC current check – 20mA range; and
- Test current calibration.
AC voltmeter calibration
Set switches for 2mA AC, test lead connected from AC output jack to AC HV meter to ground terminal on front panel.
In my case, I used a 40kV probe on a DMM. An ordinary DMM is not suited to this measurement, and DIY probes are a risk.
Wind V-adj knob to minimum, power on and start test. Adjust V-adj knob until HV meter indicates 3kV and allow to stabilise for a few seconds. Now adjust RP2 so that the RK2672AM voltage display agrees with the HV meter.
Adjust V-adj down to minimum and power off.
DC voltmeter calibration
Set switches for 2mA DC, test lead connected from DC output jack to DC HV meter to ground terminal on front panel.
In my case, I used a 40kV probe on a DMM. An ordinary DMM is not suited to this measurement, and DIY probes are a risk.
Wind V-adj knob to minimum, power on and start test. Adjust V-adj knob until HV meter indicates 3kV and allow to stabilise for a few seconds. Now adjust RP2 so that the RK2672AM voltage display agrees with the HV meter.
Adjust V-adj down to minimum and power off.
AC current calibration – 2mA range
Set switches for 2mA AC, test lead connected from AC output jack via 50K 5W resistor to AC mA meter to ground terminal on front panel.
Depress the TEST/PRE-SET switch and adjust the PRE-SET current being displayed using the screwdriver adjusted pot on the front panel to 1.5mA to prevent tripping during this test. Restore the switch to TEST position.
Wind V-adj knob to minimum, power on and start test. Adjust V-adj knob until mA meter indicates 1mA and allow to stabilise for a few seconds. Now adjust RP3 so that the RK2672AM current display agrees with the mA meter.
Adjust V-adj down to minimum and power off.
AC current check – 20mA range
Set switches for 20mA AC, test lead connected from AC output jack via 50K 5W resistor to AC mA meter to ground terminal on front panel.
Wind V-adj knob to minimum, power on and start test. Adjust V-adj knob until mA meter indicates 5mA and allow to stabilise for a few seconds. Now check that the RK2672AM current display agrees with the mA meter.
Adjust V-adj down to minimum and power off.
DC current calibration – 2mA range
Set switches for 2mA DC, test lead connected from DC output jack via 50K 5W resistor to DC mA meter to ground terminal on front panel.
Depress the TEST/PRE-SET switch and adjust the PRE-SET current being displayed using the screwdriver adjusted pot on the front panel to 1.5mA to prevent tripping during this test. Restore the switch to TEST position.
Wind V-adj knob to minimum, power on and start test. Adjust V-adj knob until mA meter indicates 1mA and allow to stabilise for a few seconds. Now adjust RP9 so that the RK2672AM current display agrees with the mA meter.
Adjust V-adj down to minimum and power off.
DC current check – 20mA range
Set switches for 20mA DC, test lead connected from DC output jack via 50K 5W resistor to DC mA meter to ground terminal on front panel.
Wind V-adj knob to minimum, power on and start test. Adjust V-adj knob until mA meter indicates 5mA and allow to stabilise for a few seconds. Now check that the RK2672AM current display agrees with the mA meter.
Adjust V-adj down to minimum and power off.
Test current calibration
Set switches for 2mA DC, test lead connected from DC output jack via 50K 5W resistor to DC mA meter to ground terminal on front panel.
Wind V-adj knob to minimum, power on and start test. Adjust V-adj knob until mA meter indicates approximately 1mA and allow to stabilise for a few seconds. Note the current. Now, adjust the PRE-SET pot slowly downwards until the tester just trips off.
Depress the TEST/PRE-SET switch and adjust RP4 so that the displayed current matches the current noted in the previous step.
Adjust V-adj down to minimum and power off.
Tools
The 10 turn pot adjustment screws are not easily accessible with an ordinary screwdriver whilst powered up without risk of touching live parts.
I used a 3×0.5mm screwdriver bit, right angle drive and insulated driver handle to adjust the pots. I could hold the insulated part of the right angle drive and the insulated driver handle to reduce risk of inadvertent electric shock.