Stanmax Electronics - Residual Voltage Tester 

foto MSOM 4.jpg


This Residual Voltage Tester what we called Mains Switch Off Measurement unit (MSOM) is specifically designed to automate the recently introduced Plug Discharge Tests. Users are experiencing much longer testing times than anticipated, which leads to higher costs for both the customer and the test site.

The Plug Discharge Test is found to be hard to reproduce when using the conventional way of testing, which is to unplug the DUT and trying to find the worst-case situation by trial and error. This proved to be a time-consuming and not well-defined process and, depending on the standard, can take up to a full day or more of testing where the test engineer must be present at all times, as also the expensive equipement requirement for this test (100MOhm impedance probes, digital storage oscilloscope with protective earth disconnected, etc.)

The MSOM device offers a safe, all-in-one solution, which automates the complete test procedure according to the various standards. No isolation transformer is required between mains and the EUT.


- Fully automated and integrated Plug Discharge Tester

- Including LabView based control software

- Front panel control buttons and status display

- Suitable for 50/60Hz, 90..230VAC

- Reliable RS-232 communication interface

- Fully customizable on request to suit your needs

- Automatic positive-peak detection, including options to disconnect the DUT at any point of the 50 or 60Hz wave signal, with single-degree resolution.

- 100MOhm +/- 5MOhm input impedance as required by the standard

- Automatic test report generation (contact Stanmax for all options)

- DUT can be switched on/off in software

- Internal calibration-RC network

- Various test setups; Line to Neutral, Line to Earth, Neutral to Earth

- Automatic calculation of time constant (37% of initial voltage) for IEC 60950.

- Automatic data export to plot time vs voltage graphs


IEC 61010

IEC 60065

IEC 60335

IEC 60950 (both Pluggable Equipment Type A and Type B)

IEC 60601 (Medical Equipment) 


Calibration generator to calibrate the MSOM device


Optimized for Windows 7, 64-bit machines (32-bit or other Windows version available upon request)

Flexible GUI, suitable for both low and high resolution monitors

Direct visualization of the discharge waveform at the DUT

Calibration RC.png

Figure 1 MSOM2 Screenshot (Calibration RC)

Extra information on standards

For IEC 61010, 6.1.2: 10 sec after interruption of the supply, no hazardous live parts. (33V RMS, 46.7V peak or 70VDC (normal conditions) (5 sec?)

For IEC60065: 9.1.6: 2 seconds after withdrawal of the mains plug: no hazardous live parts (A part is not hazardous live if the open circuit voltage does not exceed 35V peak (ac) or 60VDC. Test MAY be repeated 10 times to determine the most unfavorable situation.

For IEC 60950: 1 at disconnection of ac mains supply, the risk of electric shock from stored charge on capacitors is reduced.: time constant not exceeding 1s for pluggable type equipment. (1 time constant = 37% of its original value)

For IEC60335-1: 22.5: After 1 second, the voltage between the pins of the plug is measured. The voltage shall not exceed 34V. The test is performed 10 times.

Examples of conventional Plug Discharge Test


Figure 2 MSOM2 Screenshot (Boormachine 1sec) 


Figure 3 MSOM2 Screenshot (Boormachine 50msec)


Figure 4 MSOM2 Screenshot (Boormachine 50msec Autoscale)


Figure 5 MSOM2 Screenshot (Stofzuiger)