How to use MF47 pointer multimeter

Next, we will use the MF47 multimeter to introduce the structure of the pointer multimeter.

The MF47 multimeter is a highly sensitive, multi-range portable rectifier meter that can measure basic items such as AC and DC voltage, DC current, resistance, etc. It can also estimate the function of capacitors, etc. The appearance of the MF47 multimeter is shown in Figure 1, without a battery box.

① Meter head: The meter head is the main component of the multimeter and determines the sensitivity of the multimeter. The meter head consists of a needle, a magnetic circuit system and a deflection system. In order to improve the measurement sensitivity and facilitate the expansion of the current range, the meter head usually uses a magnetoelectric DC ammeter with a large internal resistance and high sensitivity. In addition, there is a mechanical zero adjustment knob on the meter head to calibrate the zero position of the needle at the left end.

The meter head of the multimeter is a flexible ammeter, and the current can only flow in from the positive pole and out from the negative pole. When measuring DC current, the current can only flow in from the red test pen connected to the "+" jack and out from the black test pen connected to the "-" jack; when measuring DC voltage, the red test pen is connected to a high potential and the black test pen is connected to a low potential, otherwise, on the one hand, the value cannot be measured, and on the other hand, it is easy to damage the needle.

Figure 1 Appearance of MF47 multimeter
② Dial: The dial consists of a variety of scales and various symbols with explanatory functions. Only by accurately understanding the reading methods of various scales and the meanings of various symbols can we use the multimeter skillfully and accurately. The symbol A-V-Ω on the dial indicates that this meter is a multimeter that can measure current, voltage and resistance. There are many scales printed on the dial, among which the one marked with "Ω" on the right end is the resistance scale, the right end is marked with zero, and the left end is marked with ∞, and the scale value distribution is uneven. The symbol "-" indicates DC, "~" indicates AC, "≈" indicates the scale line shared by AC and DC, hFE indicates the transistor expansion multiple scale line, and dB indicates the decibel level scale line.

③Switch: The switch is used to select the type and range (or magnification) of the measured quantity. It is a multi-position rotary switch. The measurement items of the MF47 multimeter include: current, DC voltage, AC voltage and resistance. Each position is divided into several different ranges (or magnifications) for selection.

When the converter switch is in the current gear, it can be connected to the five touch points respectively for current measurement in the range of 500mA, 50mA, 5mA, 0mA and 50μA. Similarly, when the converter switch is in the resistance gear, the resistance can be measured with ×1, ×+, ×+0, ×1k and ×+k magnifications respectively. When the converter switch is in the DC voltage gear, it can be used for DC voltage measurement in the range of 0.25V, 1V, 2.5V, 10V, 50V, 250V, 500V and 1000V. When the converter switch is in the AC voltage gear, it can be used for AC voltage measurement in the range of 10V, 50V, 250V, 500V and 1000V.

④ Mechanical zero adjustment knob and resistance zero adjustment knob: The function of the mechanical zero adjustment knob is to adjust the position of the needle when it stops. When the multimeter is making any measurement, the needle should point to the "0" position on the left end of the dial scale. If it is not in this position, adjust the knob to make it in place.

The function of the resistance zero adjustment knob is that when the red and black test leads are short-circuited, the needle should point to the "0" position on the right end of the resistance (ohm) scale. If it is not at the "0" position, adjust the knob to make it in place. It should be noted that every time the resistance range is changed, the knob should be adjusted to make the needle point to the "0" position to reduce the measurement error.

⑤ Test pen jack: The test pen is divided into red and black. When using, the red test pen should be inserted into the jack marked with "10", and the black test pen should be inserted into the jack marked with "-". In addition, the MF47 multimeter also provides 2500V AC and DC voltage expansion jacks and 5A DC current expansion jacks. When using, move the red test pen to the corresponding jacks respectively. Before use,
check whether the pointer is pointing to the mechanical zero position. If it is not pointing to the zero position, the zero adjuster on the cover can be rotated to make the pointer indicate the zero position. Insert the red and black plugs of the test stick into the "+" and "-" sockets respectively. When measuring AC and DC 2500V or DC 5A, the red plug should be inserted into the socket marked with 2500 or "5A" respectively.

1. DC current measurement: When measuring 0.05~500mA, turn the switch to the required current range. When measuring 5A, the switch can be placed on the 500mA DC current limit and then the test rod is connected in series to the circuit under test. 　　
2. AC and DC voltage measurement: When measuring AC +10~100V or DC 0.25~100V, turn the switch to the required voltage range. When measuring AC and DC 2500V, the switch should be rotated to AC +100V or DC +100V respectively, and then the test rod is connected across the circuit under test. 　　
3. DC resistance measurement: Install batteries (one each of R14 type 2#1.5V and 6F22 type 9V). Turn the switch to the resistance range to be measured, short-circuit the two ends of the test rod, adjust the zero ohm adjustment knob so that the pointer is on the ohm "0" position (if it cannot indicate the ohm zero position, it means that the battery voltage is insufficient and the battery should be replaced), and then connect the test rod across the two ends of the measured circuit for measurement. 　　
Note:
1. When accurately measuring resistance, you should choose a suitable resistance range so that the pointer can point to the base one-third area of ​​the dial as much as possible. 　　
2. When measuring the resistance in the circuit, you should first cut off the circuit power supply. If there is a capacitor in the circuit, it should be discharged first. 　　
3. When checking the leakage resistance of the electrolytic capacitor, you can turn the switch to the R×1K range. The red rod of the test rod must be connected to the negative pole of the capacitor, and the black rod to the positive pole of the capacitor.

　　Precautions for using a multimeter
　　(1) Before using the multimeter, you should first perform "mechanical zeroing", that is, when there is no electricity to be measured, make the multimeter pointer point to the position of zero voltage or zero current.
　　(2) When using the multimeter, do not touch the metal part of the test lead with your hands. This can ensure the accuracy of the measurement on the one hand, and personal safety on the other hand.
　　(3) When measuring a certain amount of electricity, you cannot change gears while measuring, especially when measuring high voltage or high current. Otherwise, the multimeter will be damaged. If you need to change gears, you should disconnect the test leads first, and then measure after changing gears.
　　(4) When using the multimeter, it must be placed horizontally to avoid errors. At the same time, you must also pay attention to prevent the influence of external magnetic fields on the multimeter.
　(5) After using the multimeter, the conversion switch should be set to the maximum AC voltage. If it is not used for a long time, the battery inside the multimeter should also be removed to prevent the battery from corroding other devices in the meter.

How to use the ohmmeter:
　　1. Choose the appropriate magnification. When measuring resistance with an ohmmeter, choose the appropriate magnification so that the pointer indicates near the midpoint. It is best not to use the left third of the scale, as the scale is poorly distributed.
　　2. Adjust to zero before use.
　　3. Do not measure with power on.
　　4. The measured resistor cannot have parallel branches.
　　5. When measuring the equivalent resistance of polar components such as transistors and electrolytic capacitors, it is necessary to pay attention to the polarity of the two pens.
　　6. When measuring the equivalent resistance of nonlinear components with different magnifications of the ohmmeter, the measured resistance value is different. This is because the midpoint resistance and full-scale current of each gear are different. In mechanical meters, the smaller the magnification, the smaller the measured resistance value.

　　When the multimeter measures DC:
　　1. Perform mechanical zeroing.
　　2. Select the appropriate range.
　　3. When using the current range of the multimeter to measure current, the multimeter should be connected in series in the quilt circuit, because only by connecting in series can the current flowing through the ammeter be the same as the current of the branch being measured. When measuring, the branch being measured should be disconnected, and the red and black test pens of the multimeter should be connected in series between the two disconnected points. In particular, it should be noted that the ammeter cannot be connected in parallel in the quilt circuit. Doing so is very dangerous and can easily burn the multimeter.
　　4. Pay attention to the polarity of the measured electricity.
　　5. Use the scale and reading accurately.
　　6. When choosing the 2.5A range of DC current, the red test pen of the multimeter should be inserted into the 2.5A measurement jack, and the range switch can be set to any range of the DC current range.

　　7. If the DC current measured by the quilt is greater than 2.5A, the 2.5A range can be expanded to 5A range. The method is very simple. The user can connect a 0.24 ohm resistor between the "2.5A" jack and the black test lead jack, so that the gear becomes a 5A current range. The connected 0.24A resistor should be a wire wound resistor of more than 2W. If the power is too small, it will burn out.