MF-52 pointer multimeter circuit

A multimeter is a multi-purpose portable measuring instrument that has the advantages of wide measurement range, easy use, small size, and easy portability.
The multimeter uses a magnetoelectric measuring mechanism (meter head) and a measuring circuit to achieve various measurements through a conversion switch. The meter head of a multimeter is
the core of the multimeter. It is a highly sensitive magnetoelectric ammeter
. Generally, it can only pass a few microamps to hundreds of microamps
to achieve full-scale deflection. The smaller the full-scale current,
the higher the meter sensitivity. Multimeters use transfer switches to implement
a variety of measurement functions to achieve voltage reduction, shunting, rectification,
etc., to measure different electrical physical quantities.
    A multimeter is a commonly used measuring instrument tool for electricians. Its internal
structure consists of a DC ammeter, capacitor, resistor, diode
, switch, battery, etc. Figure 5-4 shows a
typical pocket multimeter circuit . It has DC current
measurement settings, AC and DC voltage measurement settings, DC resistance measurement
settings, and transistor hFE measurement. The hFE measurement method is as follows:
Turn the switch to the RXlk position, short-circuit the measuring rod to the
ohm zero position, then turn the switch to the hFE position, and insert the three poles
of the transistors e, b, and c into the corresponding e and b of the multimeter. ,
c jack,
the value of hFE can be read on the hFE scale line. You should pay attention to the following points when using a multimeter.
    1) When using the DC resistance mode, first adjust the "fr" knob so that when the two test leads are short-circuited, the pointer points to zero, then separate the test rods to
measure both ends of the resistance being measured, and then the resistance of the resistance being measured can be measured. Resistance, the resistance reading is read on the first scale line, and must be multiplied by the times of the gear.
    z) When testing the transistor hFE, turn the switch to the RXlk gear of the multimeter, short-circuit the test rod, and adjust Ohm zero position, and then
turn the switch to the hFE position. Insert the three poles of the transistor e, b, and c into the corresponding e, b, and c sockets of the multimeter. You can read the
size of hFE on the hFE scale line. Look at the PNP tube. There are three scale lines. Look at the fourth scale line for NPN tubes (hFE is only measured for small power tubes).
    3) The reverse leakage current of the PN junction can be estimated by measuring the resistance with an MF-52 multimeter. The method of use is as follows: First Turn the switch
to the ohm range and adjust the "center" knob so that the pointer points to zero when the test leads are short-circuited. Then touch the black test lead to the N area and the red test lead to the P area.
Estimate the leakage current on the current scale line according to the following range: RXlk gear, full scale is about 200pA. Rxl00 gear, full scale is 2mA. R×
10 gear, full scale is about 20mA. 't
    4) Use a multimeter to estimate the audio power level on the amplifier speaker, first turn the switch On the 10V level, when the radio is working,
use a test rod to touch both ends of the speaker (80 impedance). The power "fifth" scale line will indicate
the power . If the speaker impedance is 411. The reading should be multiplied by 2. 'If the impedance is 1610. The reading should be divided by 2.