Hi, whether you call it insulation resistance testing, PAT or portable appliance testing
or mega-Ohm measurements, you're sending a voltage to test for leakage current
due to damage, moisture, contamination wear out or aging.
Basically, you're testing to see if something is unsafe.
So it's a good idea when making these types of measurements to pay attention to your own safety.
Remember, always follow manufacturer instructions and warnings.
A best practice is if you can make the measurement with just one hand, it's really hard to get hurt.
Our first step is to get the instrument and probes set up. I personally like to use clamps for a hand-free measurement.
It connects really well to the device and makes it simpler to get that one-handed measurement.
So I'm going to take my common, get that connected, hook this up to my device under test
and for my positive side, I like to select a remote switch probe and adapter.
This switch allows you to control your readings at your test point
rather than going back and forth to your instrument.
So the first thing that we want to do is go ahead and test to see if there's any voltages
on our device under test. If there are any voltages, then you would want to
remove those before continuing on with your insulation measurements.
One of the advantages of using products like the
Agilent U1450A or U1460A series insulation meters is that they have the ability to test
to see if there is a live circuit and will not make the measurement in those cases.
It's also really helpful to have an instrument that not only has the insulation measurement
side of the instrument, but also a full-fledged DMM function instrument. It allows you to
test for your live voltages. It has an ambient temperature reading since insulation measurements
are greatly affected by temperature. It also has the ability for you to use a direct temperature
measurement to get a more accurate reading of your device under test.
The next thing that we want to do is make sure that our probes are working correctly.
So we're going to go ahead and make a short measurement using the Ohms function
and we know that we have some good connections going on with our cables here.
The next thing that we are going to want to do is move over to the insulation measurements.
Now we're ready to connect to our device under test and make the insulation measurement.
First thing that I'm going to do is connect to the low side of our device under test.
Another feature to look for in some insulation meters is whether or not
it has an earth bond connection test to make sure that you've got a good ground.
Now we're going to switch over to the insulation measurement side.
Selecting a meter that provides you with a wide variety of voltage ranges helps
you to select the right voltage for testing your device under test. You don't want to
get too large of a voltage. For this test we're going to use the 500-volt range.
Before we connect at the positive side, we want to make sure that we've got a good open connection,
so I'm going to use the remote switch probe to take a measurement and I see that I've
got over 260 G Ohms of impedance. That's good for an open resistance test. I should be getting
the maximum. Now I'm going to connect to my positive side and make the actual insulation
measurement test. Again, this is where the one-handed rule comes in very helpful.
Make the measurement, and I'm getting about 4 G Ohms of resistance, which is good for this type of test.
Then just to double-check and make sure that nothing changed while I was making the reading,
a best practice is to reverse the whole process, making the open test,
checking your ground connection and possibly even doing another short test.
So whether you're making spot measurements, timed dielectric absorption ratio measurements,
polarization index measurements or an insulation resistance test or just measuring the earth bond
resistance, following these steps will help you make good measurements while staying safe.
Thanks for watching.