Uni-T UT512D Insulation Resistance Tester (Review)

The Uni-T UT512D insulation resistance tester (a.k.a. IR tester or Megohmmeter) is a specialized instrument for measuring the insulation resistance of electrical equipment and systems like cables, motors and generators, transformers, lightning arresters, etc.
 
The UT512D comes in a hard-plastic protective carrying case together with three test leads (red, green, and black), a USB cable, eight (!) LR14 batteries and a user manual in eight languages. There is also a short carrying strap that attaches to the top of the meter.
 

Handheld?

The Uni-T UT512D is a rather large device (230 mm by 161 mm by 80 mm) weighing almost two kilograms (1,800 g, including batteries). It is portable, but I am not sure if you can consider it a handheld device as you need your two hands to hold it.

The UT512D User Interface

The 5.3″ monochrome display (protected by a film that is rather difficult to peel off) is clear, and even better readable with the backlight switched on. Below the display is a keypad with power and mode buttons on the left, and parameter adjustment buttons in the middle. On the right are some function buttons and on the bottom buttons to save data and read it back. A clearly identified TEST button is in the right bottom corner, accessible with your right thumb.
 

Above the display are the connections for the three test leads. There are four sockets because the red test lead needs two. Internally, the red socket next to the green socket is connected to the green socket. This is shown on the red connector. It is not possible to stick the red connector in the wrong way around.

PC Tool

On the right side of the UT512D, protected by a large lid, is a USB-B port for connecting the instrument to a computer. This allows you to record samples and display graphs, a utility for that is available on the Uni-T website. The recorded data can be exported as a CSV (comma-separated values) file for further processing in e.g. a spreadsheet.

What Can You Do With the UT512D?

As its name implies, an insulation resistance tester is for testing insulation. This is useful for e.g. troubleshooting and preventive maintenance, safety compliance testing and quality control.

The tester applies a high voltage to the insulation under test. By measuring the resulting current flowing through the insulation, the tester calculates the insulation resistance. High resistance indicates good insulation, while low resistance suggests insulation breakdown or degradation.

 

Programmable Output Voltage

The UT512D has a programmable output voltage from 250 V up to 2,500 V. Setting the output voltage is a bit curious. With the Up & Down buttons you first select a kind of range (250 V, 500 V, 1,000 V or 2,500 V) and then with the Left & Right buttons you can fine adjust the output value in steps of 10% of the range, 2 steps up (to 120% of the range except for 2,500 V, which is the maximum value) and 5 steps down (to 50% of the range except for 250 V, which is the minimum value). Example: after selecting the 1,000 V range you can step down in steps of 100 V to 500 V (5 steps, 50%) or step up to 1,200 V (two steps, 120%).

Continuous Testing

By default, when the UT512D is switched on, it is in continuous insulation resistance testing mode, but it doesn’t do anything. To make it test, you must press the Test button for two seconds (this is printed below the button in case you didn’t read the manual). It then starts to test and beep (I haven’t found a way to switch off the beeper) and shows the actual output voltage, the measured current and, in large digits, the measured resistance. This value is also shown on a bar graph.

 

Timer-Controlled Tests

A timer runs during a measurement. This is useful for duration testing to see for instance if an insulation breaks down after some time. The timer can also run in reverse, so to say, meaning that you can program a measurement duration, 5 minutes for instance. When the timer expires, the instrument switches to Hold mode, showing the last measured values.

The timer also serves for polarization index (PI) and dielectric absorption ratio (DAR) measurements. In these modes, the insulation resistance is measured twice, spaced a (programmable) interval apart. When the timer expires, the calculated PI or DAR value is displayed and stored. The manual has tables explaining how to interpret these values.

Pass/Fail Testing

A compare function is available to quickly compare a measured resistance to a programmable reference. The display shows Pass when the measured resistance is higher than the reference value. The PC utility shows it too, in green, but small.
 

Finally, the UT512D has DC and AC voltage test modes. In these modes, the instrument becomes an AC or DC voltmeter but starting at 30 V. In DC mode it goes up to 1,000 V, in AC mode it is limited to 750 V.

Save and Recall

You can press the Save button at any moment, during a test or when idle (except when in Read mode). This will store everything that’s on the screen, like a screenshot. Pressing the Read button, you can recall the saved screens (called data groups). A counter shows the number of stored data groups, there is room for 999 groups. Holding down the USB button for two seconds will transfer the data groups to a computer over USB.
 

 

Conclusion

As I don’t have anything to compare the Uni-T UT512D to, I can’t say much about its precision and accuracy or if it is larger or heavier than similar instruments from competitors. But what I can say is that it is an easy-to-use and well-built instrument. The multi-language manual is very readable and shows some examples of how to use the device properly. The PC utility works fine and is easy to use as well. The tough carrying case makes it easy to transport everything and has room for an extra set of batteries. All in all, a nice product.