When measuring insulation resistance with a multimeter, what factors may cause inaccurate measurement data? Why?
A) The battery voltage is insufficient.
The battery voltage is too low, causing the circuit to not work properly, so the measured readings are inaccurate.
B) The test wire connection method is incorrect.
By mistake, the "L", "G", and "E" terminals are connected incorrectly, or the "G", "L" terminals, and the "G" and "E" terminals are connected to both ends of the product under test.
C) The "G" terminal is not connected.
The product under test may suffer from errors caused by current leakage due to factors such as contamination and moisture, resulting in inaccurate testing. At this time, the "G" terminal must be connected to prevent errors caused by leakage current.
D) The interference is too large.
If the product under test is subject to excessive electromagnetic interference from the environment, the meter reading will jump. Or the pointer moves. causing inaccurate readings.
E) Human reading error.
When measuring with a pointer megohmmeter, the indication value is inaccurate due to artificial viewing angle error or scale error. Electrician world
F) Instrument error.
The instrument itself has too large an error and needs to be recalibrated. Number 9. When measuring a capacitive load in the field of a high-resistance insulation meter (such as a main transformer), the pointer shows that the resistance value suddenly drops in a certain range (not a slow and small swing within the maximum value range during normal testing), and swings back and forth quickly. This is what reason?
This phenomenon is mainly caused by discharge and sparking in a certain part of the test system.
The insulation meter is charging to the capacitive test object. When the capacitive test object is charged to a certain voltage, if there is breakdown discharge and ignition in any part of the test line inside the meter or the test object, the above phenomenon will occur.
Judgment method:
(1) Do not connect the instrument test socket to the test line, turn on the power and high voltage, and check whether there is sparking in the instrument (if there is sparking, you can hear the sound of discharge and sparking).
(2) Connect the L, G, and E test wires without connecting the product under test. Leave the end clamp of the L test wire floating in the air and turn on the high voltage to see if there is sparking in the test wire.
If there is sparking, check:
a) L and G test whether the core wire (L end) and the exposed wire (G end) are too close, causing arcing and ignition.
b) Poor contact between the L-end core wire plug and the shielding ring of the test socket or the test clip and the product under test causes sparking.
c) There is an open circuit between the test lead, the plug and the clip, causing gap discharge.
(3) Connect the product under test and check whether there is discharge or spark near the contact point between the terminal clamp and the test product.
(4) Eliminate the above reasons, connect the product under test, and turn on the high voltage. If the instrument still has the above phenomenon, it means that the insulation breakdown of the product under test causes partial discharge or arcing.
