TOS8870A
WARNINGS AND CAUTIONS FOR OPERATING THE TESTER
9
2.3.2 Cautions in electric charging in insulation resistance test
1) Electric charging
•
Do not touch charged high-voltage areas such as the DUT, test lead-wire, probe and
output terminal, etc. to prevent electric shock for a while after the power has been
turned off.
In insulation resistance tests, the test lead-wire, test probe, and DUT are charged with high voltage.
Although the Tester is provided with a discharge circuit, it takes some time to discharge after the
power has been turned off. Do not touch the DUT, test lead-wire, test probe, output terminal, or
other charged high-voltage areas for a while after turning off the power. Before touching any of
them, be sure to check the following points:
Check the following two points before touching high-voltage areas:
1.
The DANGER lamp is turned off.
Check point 1 above before checking point 2.
2.
When the LOW terminal and HIGH VOLTAGE terminal are short-circuited using
the LOW side test lead-wire, a high voltage is not output.
When the power is turned off, the discharge circuit inside the Tester is activated to discharge forc-
ibly. Therefore, do not disconnect the DUT from the Tester during testing.
If it is disconnected, check the two points above before touching high-voltage areas.
2) Consideration of discharge time
The time required to discharge electric charge depends on the characteristic of the DUT and the test
voltage.
The built-in discharge circuit operates for about 70 ms after an insulation resistance test is com-
pleted. Since the discharge resistance is about 150 k
Ω
, the charge voltage may remain if the time
constant by the capacitance of the DUT exceeds 70 ms.
If the DUT is disconnected from the Tester during a test, use the following discharge time as a
rough standard.
Suppose that the high-voltage area such as the DUT and the test lead-wire are an equivalent circuit
and that it can be expressed as a capacity of 0.01 µF and a parallel resistance of 100 M
Ω
, then the
time required to attenuate the voltage of the DUT down to 30 V will be about 3.5 seconds. at the test
voltage of 1000 V, and about 2.8 seconds at 500 V. If the time constant of the DUT is known, the
attenuation time down to 30 V, after the power has been cut off, of the DUT can be determined by
multiplying the attenuation time given above with such a time constant.
Fig.2-5
Example of discharge of equivalent circuit
WARNING
DUT
TOS8870A
100
M
Ω
0.01
µ
F
HIGH VOLTAGE
output terminal
LOW terminal
About 150 k
Ω
Operates for about 70 ms
