22
Megohmmeter Models 6528/6529
3.8.2.3 Conducting a Dielectric Absorption Ratio (DAR) Test
The dielectric absorption ratio test is typically accomplished by
measuring the insulation resistance taken at the 30 second time
interval and comparing it to the insulation resistance measurement
at the 60 second time interval. The instrument allows user
programming of both time points if necessary.
As with the PI ratio, these two time points are labeled T1 and T2.
The DAR ratio is then calculated by dividing the T2 measurement
(e.g., 60 seconds) by the T1 measurement (e.g., 30 seconds).
Generally, ratios of 1.25 or less are considered questionable.
Ratios between 1.25 and 1.6 are considered acceptable and ratios
higher than 1.6 are considered good.
1. Turn the rotary switch to an insulation voltage setting. Choices
are
250V, 500V, 1000V
(available on both the Models 6528
and 6529) and
50V
and
100V
(available on the Model 6529
only). The test voltage to select depends on the voltage of the
installation to be tested.
2. Press the
SET-UP
key four times until you see
DAR
in the
secondary display along with the test run time.
3. Press and hold the
TEST
button until the test begins.
The top line of the secondary display will indicate a countdown
timer showing the remaining time to complete the test. The bottom
primary display will show a real time value of the insulation
resistance measurement in progress.
At the conclusion of the test the secondary display will show
DAR
and the elapsed test time.
The bottom primary display will show the
DAR
ratio.
3.8.2.4 Programming DAR the T1 and T2 test time points
The instrument allows for user programming both time points if
necessary. Acceptable values can be programmed between
1 second and 30 minutes for each test point. The time for T2
must at least 1 second longer than T1.
1. Select the desired insulation resistance test voltage using the
rotary switch.
2. Press the
SET-UP
key four times until you see DAR on
the top line of display along with the test run time.
3. Press and hold the
SET-UP
key >2s until the Alarm threshold
is shown. Press
SET-UP
key again until
T1
appears and the
leading time digit begins to blink. You can adjust the time for
T1
by using the
▲
arrow to increment the blinking digit and the
►
arrow to advance to the next digit.
4. Once completed press the
SET-UP
key again.
5. The time T2 will now appear in the secondary display with the
first digit blinking; repeat the
▲
and
►
arrow sequence to
adjust the desired time for T2.
6. Press the
TEST
button to lock-in the new times for T1 and T2.
DAR
T1
DAR
T2
DAR
DAR
