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The alarm mode can be activated by pressing the ALARM button. An audible beep
will continuously sound if the measurement result is below the value defined in
SET-UP (see page 20).
Press the START/STOP button again to stop the test.
The last result remains displayed until the next measurement is made or the switch
is turned.
When the insulation measurement has stopped, the device under test will be auto-
matically discharged by the Model 5070.
The DISPLAY button can be used to view the test results available after the test.
This information depends on the measurement mode selected (see § 4.2.1).
If the measurement mode was either "Timed Run" or "Timed Run + DD", pressing
the GRAPH button displays the insulation measurement versus time curve (see
§ 4.3.2).
Press the TEMP button to correct the measurement result to the reference tem-
perature defined in SET-UP (see § 4.10).
6.2 Step Function Mode
This function is based upon the principle that ideal insulation produces the same
resistance no matter what the test voltage applied.
Any negative variation of this resistance means that the insulation may be defective.
The resistance of defective insulation will decrease as the test voltage increases.
This phenomenon is rarely observed with "low" test voltages, therefore at least
2500V must be applied.
The usual test condition is a voltage increasing in 5 steps, each lasting for 1 minute
minimum.
Assessment of the result:
• A deviation of the resistance = f(test voltage) curve that exceeds 500ppm/V
generally indicates the presence of mold or other deterioration.
• A larger deviation or a sudden drop indicates the presence of localized physical
damage such as arcing or perforation of the insulation, etc.
60
Megohmmeter Model 5070
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