AEMC’s Megohmmeter Model 1060 is a portable instrument housed in a rugged casing.
This instrument is designed to check the safety of electrical installations and equipment.
With the Model 1060, you can:
Quickly measure insulation resistance, using a wide range of test voltages
Perform timed tests, with the instrument automatically calculating the Polarization Index, commonly
referred to as PI, and Dielectric Absorption Ratio, commonly called DAR
Check continuity and capacitance
Store test results in the instrument for later display and analysis
Connect to a computer and display timed test results in real-time
And download test data to a computer and generate reports for further analysis
These are just a few of the Model 1060’s capabilities.
For details on all its features and functionality, consult the documentation that comes with
the instrument.
In Part 1 of this two-part video series, we explain some of the basic functions of the
Model 1060.
We begin by describing how to set up the instrument for testing.
We then demonstrate two commonly used methods for testing insulation resistance: the manual
“spot reading” test, and the timed resistance test.
Along the way, we describe how to store results in the instrument.
We also show how to display Polarization Index and Dielectric Absorption Ratio values, both
of which are automatically calculated by the instrument.
In Part 2 of this series, we will discuss using the Model 1060 with DataView, AEMC’s
data analysis software.
This will include instructions for using DataView to connect your computer to the Model 1060,
configuring the instrument from the DataView Megohmmeter Control Panel, running a test
and viewing results in real time, downloading tests stored in the instrument, and generating
reports from this data.
Before we begin, let’s pause a moment to talk about safety.
Before performing any insulation resistance test, be sure to observe all safety instructions
specified in the documentation that comes with your test instrument.
Insulation resistance testing involves the application of high DC voltages.
Therefore carefully preparing the system under test, and the instrument used to conduct the
test, is crucial to your safety and helps prevent damage to your wiring and machinery,
and personal injury to you and others.
For more information on this topic, as well as insulation testing basics in general, please
see our video “Understanding Insulation Resistance Testing,” available on the AEMC
YouTube channel.
Our first task is to ensure the instrument’s time and date information is correctly configured.
An accurate clock is essential for analyzing test results to identify trends over time.
Turn the instrument’s dial to SET-UP.
After a few moments the message PUSH btn appears on the LCD, indicating the instrument is in
configuration mode.
Press the V/TIME button to display the current time.
The hours setting blinks, indicating it is in edit mode.
Use the Up and Down buttons to change the time if necessary.
To activate the Down button, press the yellow 2nd key to display the 2nd symbol on the LCD.
While this symbol is displayed, buttons perform the functions shown in yellow.
For example, in 2nd mode the Up button becomes the Down button; pressing it decreases the
displayed value.
To leave 2nd mode, press the yellow 2nd button.
When finished setting the hours, press the Right button to edit the minutes setting.
Press V/TIME to display the current date, and use the Up, Down, and Right buttons to
select settings and make changes.
When finished setting the date, press V/TIME to select the format in which the time and
date are displayed.
Options are USA and European formats.
Use the Up button to make the selection, and press V/TIME to return to the PUSH btn screen.
The first type of test we’ll look at is often called the Spot Reading measurement.
This is relatively straightforward: simply connect the megohmmeter leads across the insulation
to be tested, apply test voltage for a fixed period of time (typically a few seconds or
so), then take a resistance reading.
Spot testing is suitable for a system with small or negligible capacitance effect, for
example a short wiring run like the one we are using for our demonstration.
With the instrument OFF, connect the leads
to the terminals and the insulation to be tested.
Then turn the instrument dial to a test voltage setting.
In general, the higher the resistance to be measured, the higher the test voltage.
In cases where the resistance is unknown, it’s good practice to start with the lowest
voltage, and gradually increase until the measurement results are consistent.
As another rule of thumb, we recommend testing at twice the system voltage, as long as the
system voltage does not exceed 1000 volts.
In our example, we will start with the 250 volt setting.
After a few moments a voltage reading appears on the screen.
This is the external voltage present in the test specimen.
As a safety feature, if during testing external voltage exceeds 25 volts, a warning symbol
appears and the instrument immediately stops the test.
To measure resistance, press the START/STOP button.
The voltage reading changes to the test voltage.
At the top of the screen an analog meter displays the measurement visually.
After a few seconds, the resistance reading appears in the main display.
Also note the flashing symbol, alerting you that the test voltage is higher than 120 volts.
The reading will continue until you press START/STOP a second time.
The analog meter disappears, and the final resistance measurement and test voltage are
displayed.
You can now save the test results in the instrument’s memory.
With the test displayed, press the MEM button.
At the top of the display is a meter indicating how much instrument memory is free for storing
tests.
In our example, all memory is free.
In the middle of the display is the Object and Test numbers, with the Test number blinking.
An object can be thought of as a “box” of test results.
Up to 99 objects can be stored in memory, and each object can store up to 99 tests.
The displayed numbers are derived by incrementing the Object and Test combination of the most
recent test stored in memory.
In our example no tests are in memory, so by default the test will be stored as Test
1 in Object 1.
To change this setting, use the Up, Down, and Right buttons to select and change the
Object and Test fields.
Then press MEM to store the measurement.
You can also print the measurement by connecting the instrument to a serial printer, as explained
in the instrument’s user documentation.
Note that a single Spot Reading test is of limited value.
But the results become meaningful when a series of tests, all featuring the same test voltage
and duration, are performed over time and the results compared.
This comparison can help predict a potential insulation failure in time to take preventive
action.
Now we’ll demonstrate a more complex insulation resistance measurement method known as the
timed resistance test.
This involves configuring the test to run for a defined period of time.
Timed resistance tests on large rotating electrical machinery, especially systems with high operating
voltage, require high insulation resistance ranges and a very constant test voltage.
This test is also useful for measuring resistance in transformer windings and cable insulation.
Since this test provides meaningful results within a single 10-minute duration, it is
relatively independent of temperature.
It is also independent of the size of the system under test.
By recording measurements at certain intervals during the timed test, the Model 1060 can
automatically calculate and display values such as the Polarization Index and the Dielectric
Absorption Ratio.
To configure and run a timed test, turn the dial to SET-UP.
Press the yellow 2nd button, then press the Clock button.
This displays how long the test will run, in minutes and seconds.
Use the Up, Down, and Right buttons to change these settings.
In our example, we will set the test duration to 10 minutes.
In a real-world test, you can configure additional parameters such as data storage rate, alarms,
and variables that determine how Dielectric Absorption Ratio is calculated.
These are described in the Model 1060 user manual.
For the sake of simplicity we will leave these at their default settings.
Connect the instrument to the test specimen, as instructed by the Model 1060 user manual.
In our demonstration, we will again connect to a short wiring run.
Turn the dial to the desired voltage setting.
As with our manual test, we will run our first test at 250 volts.
Press the yellow 2nd button, then press the clock button.
The clock symbol now appears on the LCD.
Press the START/STOP button.
After a few seconds the resistance reading appears on the screen.
The test will run for the duration of the time configured through SET-UP.
As the test runs, the LCD displays how much time remains before test completion.
When the test is finished, the last instantaneous resistance measurement appears on the screen.
You can cycle through all measurements taken during this test by pressing the yellow 2nd
button and then pressing the R(t) button.
This displays the first measurement recorded during the test, along with the time it was
taken.
Use the Up and Down buttons to scroll through test results.
The interval between each saved sample is programmed in the SET-UP menu.
In our demonstration, we are using the default interval of 5 seconds.
Note the blinking clock symbol, indicating you are viewing incremental test results.
To leave this mode, press the 2nd button and then press R(t).
We can now view the Polarization Index and Dielectric Absorption Ratio values.
These are commonly called PI and DAR respectively.
The R-DAR-PI button lets you cycle though the resistance, PI, DAR, and capacitance values.
For instance, to display the Dielectric Absorption Ratio, press R-DAR-PI after the test measurement
is complete.
The instrument automatically calculates DAR by dividing the 1 minute measurement by the
30 second measurement.
Although DAR is no longer commonly used with newer insulation systems that require longer
than one minute of stress before breakdown, it still may have applicability when testing
older insulation materials.
With the Dielectric Absorption Ratio displayed, press R-DAR-PI to display the Polarization
Index.
This value is derived by dividing the 10 minute resistance measurement by the 1 minute measurement.
Polarization Index and Dielectric Absorption Ratio are useful on long cables, or when monitoring
the aging of insulation on electrical machines.
Measurements of this type can be initially affected by interfering currents from capacitive
charges and dielectric absorption.
After test voltages have been applied for several minutes, these influences eventually
cancel out each other.
So to ensure accuracy, measurements should be performed over an extended period, typically
10 minutes or more.
An important feature of the Model 1060 is its ability to be configured and operated
from a computer running DataView software.
Once connected, you can set up and start a test, and view measurement results graphically
in real time.
This provides an easy-to-understand view of your test results, to help determine whether
or not they indicate a possible problem.
DataView also enables you to download tests stored in the instrument, generate reports
from this data, and perform numerous other tasks including instrument configuration.
This concludes Part 1 of our quick introduction to the Megohmmeter Model 1060.
In Part 2 of this two-part video series, we explain in detail how to use DataView with
the Model 1060.
For more information about this and all other AEMC products, please visit our web site.
And be sure to check our YouTube channel for instructional videos about other topics in
electronics.