UT512 Review

[ocw]

The UT512 is an insulation resistance tester with a test voltage between the range offered by the UT511 and UT513.  The UT512 tests at 500, 1,000, 1,500 and 2,500 volts.  While the 5,000 volts offered in the UT513 would have been nice at times, I wanted to have a minimum test voltage available no higher than 500 volts.  So, the UT512 was my choice.

You need to be careful about making measurements on something rated at near the UT512's test voltage.  Its specifications say that the test voltage is the stated value -0%, +20%.   That means that the actual no-load voltage for a 2,500 volt test could be as high as 3,000 volts.  I measured 2,803 volts on my unit while on that range.

The resistance accuracy easily met its 3% accuracy specification for all readings except for some 2 digit "low" resistance readings.  It worked fine for high voltage resistance readings and reasonable for insulation tests.  As others have reported for the 511 and 513 models, it would occasionally lockup after arcing during an insulation test.  The presented a hazardous situation when I extended the meter's use.

UT512                           500V          Specs        1,000V       Specs         1,500V      Specs        2,500V         Specs                                      549V        Measured    1,112V     Measured     1,561V   Measured    2,803V       Measured Resistor   Accuracy   Measured   Accuracy   Measured   Accuracy   Measured   Accuracy   Measured   Accuracy 1M             0.05%         1.0M             0.0%    3M             0.05%         3.1M           +3.33%       3.1M         +3.33%        3.1M        +3.33%       10M           0.1%          10.2M          +2.0%         10.2M       +2.0%         10.1M        +1.0%        10.1M         +1.0% 30M           1.0%          29.6M          -1.33%        29.9M       -0.33%        29.9M        -0.33%        29.3M         -2.33% 60M           1.0%          60.2M          +0.33%       60.7M       +1.17%       60.6M        +1.0%         60.2M         +0.33% 100M         1.0%          99.4M          -0.6%          100M          0.0%          100M          0.0%          100M            0.0% 300M         1.0%          298M           -0.67%        301M         +0.33%       301M         +0.33%       296M           -1.33% 1G             1.0%          1.00G           0.0%          1.00G          0.0%          0.999G       -0.1%         0.986G        -1.4% 5G             1.0%          4.90G          -2.0%          4.97G         -0.6%          4.97G        -0.6%         4.97G          -0.6% 10G           1.0%                                                9.92G         -0.8%          9.88G         -1.2%        9.88G          -1.2% 40G           5.0%                                                                                                                       39.5G          -1.25%

I thought that the UT512 might be a good way of testing some old high voltage capacitors on my shelf.  I started with a 0.03 uF, 15 kV capacitor.  Not surprisingly, it handled a wimpy 2,800 volts without any problem. 

I then jumped to a 10 uF, 3 kV oil filled capacitor.  If it would have been a 2.5 kV capacitor, using the UT512 set for 2,500 volts would have been above the capacitor's limits due to its actual 2,803 test voltage.  With the UT512's 2 mA limit, it took some time to charge the 10 uF capacitor due to the RC time constant.  Then the meter locked up during the charging process.  I was worried about the voltage on the capacitor with the locked up meter still attached.  I safely shorted out the capacitor--BAMMMMM!  That sure wasn't a 2 mA "spritz" arc-over!  Obviously that size of a capacitor can hold a deadly charge.

I added a 10M ohm resistor in series to slow charging to the capacitor.  It took forever to make it to 2,000 volts before I finally gave up.  0.1 to 1 uF capacitors may be its useful limit.  When taken out of the test mode it will discharge a capacitor.  But, that process can be slow for capacitors above 0.1 uF.  And, watch out when connecting polarized capacitors.  The red clip has negative voltage on it as compared to the green clip!

A picture of the UT512's circuit board is attached.  Significant IC's on the board include a C8051F352 microcontroller, ADG658 multiplexer, TL494C power controller and SP34063AE regulator.  The microcontroller and regulator had pads (which were easy to remove) covering them.

A picture of the meter measuring a 40G ohm is attached.  Also attached is a picture of its computer interface display while measuring a 5G ohm resistor.  I show the measurement as it just completed the initial ramp up in voltage.  The computer display can obviously keep track of a changing resistance.

While the meter is interesting for experiments, I don't see it being used frequently.