Zero Setting Method and Principle of Pointer Multimeter
1. Mechanical zero adjustment: The pointer is not pointing to the 0 position. Use a screwdriver to turn the mechanical zero adjustment knob to reset the pointer to 0. Mechanical zero adjustment principle: There is a mechanical zero adjustment screw inside the mechanical zero adjustment knob. By turning the mechanical zero adjustment knob, it is equivalent to turning the mechanical zero adjustment screw, thereby resetting the pointer to 0.
2. Ohm zero adjustment: turn the multimeter to the resistance gear, because only the resistance gear in the multimeter can work with the internal battery. Short circuiting the probe is equivalent to short circuiting the internal battery to have current flowing through the meter head. The probe deflects and does not point to 0. Turn the resistance zero adjustment Potentiometer to return the pointer to 0. Ohm zero adjustment principle: the resistance zero adjustment Potentiometer controls an adjustable resistance, Turning the resistance zero adjustment Potentiometer is equivalent to changing the resistance value of the adjustable resistance so as to change the current flowing through the meter head for zero adjustment.
Measurement principle: DC: DC AC: AC
The measurement principle of DCV DC voltage range: The measurement range of the voltage range is expanded by connecting a resistor in series with the meter head to divide the voltage. Since the measurement is a DC signal, the meter head can be used to measure it directly without traveling half a wave. By changing the resistance value of the series dividing resistor in the DC voltage range, the measurement range can be changed.
DCmA DC current measurement principle: By shunting a resistor in parallel with the meter head, the measurement range of the current range can be expanded. By changing the resistance value of the shunt resistor in the DC current range, the measurement range can be changed.
Measuring principle of ACV AC voltage range: the measuring range of AC voltage range is expanded by means of resistance voltage division in series with the meter head, and the AC signal is rectified into DC signal through the meter head in the half wave rectification circuit for measurement, because the head of the pointer meter is a DC Ammeter, The meter head cannot flow through the AC signal, so a half wave rectifier circuit must be added to the AC voltage range to make a rectifier. The measured AC signal is converted into a DC signal through the rectifier and flows through the meter head for measurement. Therefore, when measuring AC power, it needs to be rectified once through the rectifier diode. When measuring AC voltage, the rectifier must be used to convert the measured AC signal into a DC signal and flow through the meter head for measurement. It is equivalent to installing a rectifier on the basis of expanding the voltage range by serially dividing the resistance in the DC voltage range, forming the AC voltage range.
During the positive and negative half cycle of AC power, D1 rectification is used to convert the AC signal into a DC signal and flow it through the meter for measurement. During the negative half cycle of AC power, D2 rectification is used to protect the D1 rectifier diode. To prevent both positive and negative half cycles of AC power from going through D1 rectification, a D2 rectifier diode is added due to the high AC voltage signal, which can easily breakdown D1, In this case, during the positive half cycle, D1 rectification is used to convert the AC signal into a DC signal and flow through the meter for measurement. During the negative half cycle, D2 rectification is used to convert the AC signal into a DC signal and flow through the meter for measurement.
Measurement principle of Ω resistance range: The resistance range is the only range in the multimeter that uses batteries for operation. The pointer meter has two internal batteries, one is 1.5V and the other is 9V. The resistance range is divided into five ranges. Among them, RX10K uses internal 9V RX1K RX100 RX10 RX1, and the four ranges share internal 1.5V. If the measured resistance value is large, the current flowing through the measured resistance is very small. At this time, the deviation of the meter needle is very small, indicating that the measured resistance value is large, If the resistance value of the measured resistance is very small, the current flowing through the measured resistance is large, and at this time, the deviation of the meter needle is also large, indicating that the resistance value of the measured resistance is very small.
