Brief Review of the Megger MTR105 Rotating Machine Tester

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This is my brief look at the MTR105 Rotating Machine Tester, although from Megger, this is from their Baker Instruments Division that have a long history of manufacturing motor testing devices.

https://megger.com/rotating-machine-tester-mtr105

This is a bit more upmarket than the standard insulation testers available, the closest to it is probably the Gossen Metrawatt MetraHit Coil that offers an inter-turn test function alongside an insulation tester and multimeter functions.

The MTR105 offers Insulation testing up to 1000V and 200 GigaOhm resistance level, built into the insulation testing function is DAR, PI, Temperature Compensated and 3 Phase insulation testing. DC and AC voltage measurement up to 1000V with a true RMS function for AC and frequency up to 400Hz. AS part of the voltage measurement it offers 3 phase voltage measurement including phase rotation indication of the supply. To go with this a separate function offers 3 phase rotation indication of a motor, so that it can be matched to the supply.

A continuity function with an adjustable threshold and 2 wire bi-directional resistance test up to 1 MegOhm with a 200mA test current for resistance values below 4 Ohms. It also has a 4 wire resistance mode included for testing larger motor windings from 1 milliOhm to 10 Ohms with a 0.01 milliOhm resolution. An LCR meter is included using either 120Hz or 1kHz test frequencies, capacitance from 0.1nF to 1.0mF and inductance from 2mH to 1H. It has a temperature function with a T-Type thermocouple that works in conjunction with the temperature compensated insulation test mode.

Test data is saved on board the instrument to memory slots that you have to provide a name for, al individual tests are then saved under the slot selected. There is no direct connection to a computer, the data is downloaded to a USB stick as csv files for each individual test. This can be read by the Megger PowerDB Software and pulled into a certificate or pulled into a spreadsheet program such as Excel to create your own certificates.

Couple of pictures of what arrives with the meter, set of 3-phase leads, 3 test probes, 3 grippers, t-type thermocouple, 4 wire kelvin leads with crocodile clips a hanging strap, all to go in a soft case. A USB stick to download data to, calibration certificate and quick-start guide are also included but not shown in the pictures. A charger with a set of 6 NiMh AA cells and 4-wire duplex pin leads are available as extras that I have purchased alongside the meter.

I have been asked for my test data from it, so I will also add that in as a pdf.

Next post will show some picture of the instrument tests.

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These are some measurements from the MTR105, note the colour screen, but be warned it seriously affects battery life, investment in the rechargeable cells is strongly advised. The colour of the screen changes to match the colour of the test function on the rotary selector switch, the screen has 4 levels of backlight so you save some battery life.

The three phase insulation test is automatic. This is just a phase to phase test for 1 minute and does not include a test to earth, this has to be done individually for each phase as per a normal insulation tester. The result is displayed for all three phases at the end of the test.

Temperature compensated insulation test requires either manual entry of a temperature value or a value captured from the temperature function of the meter. The motor class and desired temperature compensation value are selected in the settings screen. This is just a spot test, no temperature compensation is available for the timed test functions. A the end, the temperature compensated insulation value and the settings are displayed along with the raw insulation resistance value.

The instrument also includes a guard terminal for 3-wire insulation testing to provide further diagnostics - quite useful for testing bushings.

I did have problems using the 3-phase voltage function on the output of an inverter, the readings were quite erratic. If you have an inverter with a sinusoidal output filter installed then it should work fine. I did make up my own filter unit as an add on, and it did improve the stability with the inverter on full output, but was still a little erratic at lower outputs.

Overall the accuracy of the meter compares well to the U1461A from Keysight and the MetraHit Coil from Gossen Metrawatt. It doesn't quite have the accuracy of the U1461A, nor its resolution for some of the tests, but for motor testing I think it is fine. Sadly for me the MTR105 does not record a polarisation index curve plot, which the U1461A does do.

Next will be the teardown.

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A little look inside the MTR105 then.

Case is a standard two part design with separate compartments for the battery cells and the 500mA HRC fuses. The meter is rated to CAT III 600V. Both compartments have seals around them and the two halves have a lip seal protecting against any dirt ingress.

The PCBs are a multi-stack arrangment, with two main boards the full size of the meter and two smaller boards at the top of the meter that hold the input jacks for the instruments, some selection relays and the input protection.

Removal of these smaller boards reveals the main MPU of the meter, an ARM STM32F7676. It also reveals an internal SD Micro card, not sure if this is for the Firmware or data storage.

The HV transformer is the rather unique design I have seen in other Megger instruments that seems to incorporate the windings into the PCB and has the transformer core clipped through the PCB.

I will try an add some higher resolution pictures next.

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Some high resolution pics of the main board and the two MPUs.

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The MTR105 packs quite punch, you need quite a few instruments to match its test capabilities. It comes at a price - in the UK recommended retail price is £1,760 not including VAT. The alternative test setup in the picture is around £400 cheaper.

If you want to see the MTR105 in operation then there is a video I have uploaded to YouTube;

https://youtu.be/yIhKgnDcTi0

There is a host more videos on there going through the individual test functions.

That is is for this review, thanks for reading.