Common faults and precautions of multimeter
The easy-to-fault parts and causes of the multimeter
1. The meter head is usually a high-sensitivity magnetoelectric microammeter or milliampere meter. The performance of its failure is usually: shaking the meter head; the hands of the watch swing abnormally: no movement or no damping. The reasons for such failures are as follows:
(1) The support part of the watch needle is stuck,
(2), the hairspring is twisted.
(3), the mechanical balance is not good;
(4) The meter head coil is disconnected or the shunt resistor is disconnected.
2. The performance of the failure of the DC current gear is: the needle does not move, that is, there is no indication; the errors of each range are inconsistent, there are positive and negative t. When using a small range range, the pointer deflects quickly and the damping is small. When using a large range range, there is no indication. instruct. The reasons for such failures are as follows:
(1) The meter head is faulty or the resistor connected in series with the meter head is disconnected or the range switch is blocked
(2) A certain gear of the shunt resistor is poorly welded, the resistance value increases or partly burns out;
(3) The shunt resistor is disconnected or the connection of the shunt branch is broken.
3. The performance of the failure of the DC voltage range is: the needle has no indication, the error of a certain range is large, and the error becomes smaller with the increase of the range; the small range range is normal, and there is no indication when it exceeds a certain range. Possible reasons for these failures are:
(1) The range switch is in poor contact or burned out;
(2), voltage divider resistor output
faults, such as value change, open circuit, etc.
(3) The voltage divider resistor is damaged or its connection is disconnected.
4. The performance of the failure of the AC voltage gear is: the pointer swings slightly or the indication is extremely small. The error is very large. Sometimes it is lower than 50~1o; the indicated value of each file is lower than the same error. These failures occur due to:
(1), breakdown of rectifier components
(2), a certain element in the rectification assembly is broken down and broken circuit; full-wave rectification becomes half-wave rectification; (3), the performance of the rectification assembly is not good, and the reverse resistance decreases.
5. There is a failure of the resistance gear: when the short-circuit is zeroed, the hands have no indication; when the test pen is short-circuited, the hands cannot be adjusted to zero; when the zero is adjusted, the hands jump; some ranges do not indicate or the error is too large. These failures occur because:
(1) A test lead is disconnected or the common point of the range switch is disconnected, the zero-adjusting rheostat has a breakpoint, the battery is used up or the lead wire is broken;
(2) The voltage of the battery is insufficient, the range switch is in poor contact, or the resistance of the gauge head is increased; (3) The zeroing rheostat is in poor contact;
(4) The shunt resistance of this file is open or the range switch is in poor contact;
(5) The shunt resistance of this gear changes value or burns out.
