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How to repair mechanical multimeter magnetoelectric meter head and resistance blocking fault?

Last Update Time: 2019-01-28 13:37:51

1. The magnetoelectric meter is faulty.

1) The head pointer swings large and has no damping effect.

The fault is that the movable coil is broken and the hairspring is desoldered.

 

2) The indication is unstable.

This fault is the loosening of the terminal of the meter head or the de-welding or poor contact of the moving coil lead wire, the hairspring, the shunt resistor, and the like.

 

3) The zero point changes greatly, and the power-on inspection error is large.

This failure may be caused by improper matching of the bearing and the bearing, the shaft tip wear is serious, the friction error is increased, the balance spring is severely deformed, the hairspring is too dirty and the loop is elastic, the hairspring is elastically fatigued, and the magnetic gap has foreign matter.

 

2. Resistance blocking failure.

1) The common fault of electric blocking is the damage of each gear resistance (the reason is mostly improper use, using electric blocking to detect the voltage. Before use, pinch the two test leads by hand. Generally, the pointer will swing if the meter has broken, such as corresponding resistance block was burnt out ,it should be replaced.

 

2) After the R × 1 block and the two test leads are shorted, adjusting the zero potentiometer cannot deflect the pointer to the zero position.

This fault is mostly caused by insufficient voltage in the built-in battery of the multimeter, or the electrode contact spring is rusted by the leakage of the battery, resulting in poor contact. Such failures often occur when the meter is not replaced for a long time. If the battery voltage is normal, the contact is good: adjust the zero adjustment potentiometer pointer deflection is unstable, can not be adjusted to the ohmic zero position, then the zero adjustment potentiometer is damaged. Replace the zero potentiometer and the fault can be eliminated.

 

3) In R × 1 block can be zero, other range shifts can not be adjusted to zero, or just R × 10k, R × 100k block can not adjust to zero.

The cause of the fault is due to the reduced shunt resistance or insufficient internal voltage of the high-resistance range. Replace the resistor or laminate battery and the fault can be eliminated.

 

4) The measurement error is large in R×1, R×10, and R×100.

In R × 100, the zero adjustment is not smooth, even if it is adjusted to zero, after several measurements, the zero adjustment becomes abnormal. This fault occurs because there is black dirt on the contact of the range switch. The resistance increases and is unstable. It is ensured that the contact is good and the fault can be eliminated by the contact of each of the switch contacts until the silver is exposed.

 

5) The test leads are short-circuited and the head indicates instability.

The cause of the fault is mostly due to the presence of false solder joints in the line, poor battery contact or internal disconnection of the lead of the test leads. The repair should be done from the most easily troubled fault, that is, first ensure that the battery is in good contact, the test leads are normal, if the indicator is still unstable It is necessary to find fake solder joints in the line to repair.

 

6) Seriously misaligned when measuring resistance in a certain range, while the remaining gears are normal.

This type of failure is often caused by the fact that the corresponding resistance in the meter box indicated by the range switch has been burned or broken. The resistor needs to be replaced and the fault can be eliminated.

 

7) The pointer is not deflected, and the resistance value is always infinite.

The cause of the failure is mostly due to the disconnection of the test leads, the poor contact of the transfer switch, the poor contact between the battery electrode and the lead reed, the absence of voltage for the battery to fail for a long time, and the zeroing of the potentiometer. After finding the specific cause, make a targeted repair, or replace the built-in battery, and the fault can be eliminated.

This article is from Allicdata Electronics Limited.

 

 

The mechanical multimeter structure can refer to the following article:

What is the structure of a common mechanical multimeter?