What might be the cause of a bad resistance reading on a mechanical multimeter?
If the mechanical multimeter, i.e. pointer multimeter resistance file is damaged, while other files can be tested normally, indicating that the meter head should not be affected. According to the testing principle of the multimeter resistance file, it is very likely that the shunt and voltage shunt precision resistor of the resistance file is burnt out or caused by the resistance value. The most likely cause of damage to the mechanical multimeter resistance file is that the resistance file is treated as a voltage file to test the voltage. Therefore, every time before the test, the first habit to look at the gear selection is not correct, to develop good testing habits.
Pointer multimeter resistance block is bad, the other gears can be used, indicating that the multimeter head is good. This is caused by incorrect use. There are two reasons for this, one is pulled in the DC current block when measuring the AC220V voltage burning current block of several small resistance value of the wire-wound resistor (regardless of what model pointer multimeter, they are wire-wound resistors, are wound with copper resistance wire, and the resistance value is very small, for example, the MF-47 type in four resistors, respectively, for 0.54Ω 5.4Ω 54Ω 540Ω). But mention the Lord that the multimeter is only resistance block has a problem, then there is no is a problem in this block.
The second reason is that; for beginners electronics, electricians, in the use of multimeter resistive block measurement components or check the circuit, not the multimeter gear dial to AC 500V block, and then in the 220V AC line or jack to test the AC power caused by. There are many models and manufacturers of commonly used pointer multimeters. The most common and used more than the old 500-type and Nanjing production of MF-47 type multimeter. The following MF-47 to analyze and solve the problem.
① MF-47 type multimeter has a DC current block (DCA), a total of five commonly used block plus a 5A high-current expansion jack, 0 ~ 0.05mA ~ 0.5mA ~ 5mA - 50mA ~ 500mA.
② It has direct current voltage (DCV) eight commonly used stops plus an extension jack that can measure DC2500V. 0 ~ 0.25V ~ 1V ~ 2.5V ~ 10V ~ 50V ~ 250V ~ 500V ~ 1000V ~ 2500V.
③ It has six stops for alternating current voltage (ACV), 0~10V~50V~250V~500V~2500.
④ It has DC resistance block (Ω) five stops.R×1Ω R×10Ω R×100Ω Rx1KΩ R×10KΩ There is also a road buzzer for measurement (when the line resistance value is 3~10Ω, the buzzer will sound). Due to space limitations, omitted transistor DC amplification hFE, infrared remote control transmit signal detection, audio level DB and other functions.
First resistance block measurement, the black pen inserted in a hole → head negative → 20.2Ω resistor, 220.4Ω resistor, 2430Ω resistor, they are all in parallel with the head for the state. And at this time, the red pen inserted in the multimeter ten jack through a 1A fuse → 1.5V dry cell in series with the resistor and then through a 20k resistor → 1...7k resistor block zero variable potentiometer → a 500Ω resistor → another head calibration R + → head positive + number. Understand the closed loop is good, according to personal experience, you can find along the way.
With another multimeter to find the measurement of these resistors, the general situation of this failure will only burn the resistance of the resistance level pulled at the time of the resistance. And these resistors for non-standard value of the resistance, you can find close to the damaged resistance in series or another piece of copper resistance wire to wind a resistance instead of copper wire can be intercepted from the wire-wound variable potentiometer.
