Analog multimeter is a kind of multi-functional, multi-range measuring instrument, general multimeter to measure dc current and dc voltage, ac current, voltage, resistance and audio power equality, some still can measure ac current, capacitance and inductance and the parameters of the semiconductor.
The working principle of multimeter test
The basic working principle of multimeter is to use a sensitive magnetoelectric dc ammeter (microammeter) as the head.when a small current passes through the head of the meter, there is a current indication.however, the head cannot pass the high current, so the current, voltage and resistance in the circuit must be measured by shunting or lowering the voltage in parallel with series resistance on the head.here are some of them.
1. Principle of dc current measurement.
By shunting the meter in parallel with an appropriate resistance (called a shunt resistance), the current range can be extended.changing the resistance of the shunt resistance changes the range of current measurements.
2. Principle of dc voltage measurement.
The range of voltages can be extended by a suitable resistor (called a multiplier resistor) connected in series to the meter head for voltage reduction.changing the resistance of the multiplier can change the measurement range of the voltage.
3. Principle of ac voltage measurement.
Because header is dc list, so measurement, need to add a and half-wave rectifier circuit, string type, will be to communicate into a dc and then through the meter, so you can according to the size of the dc to ac voltage measurement.the method of extending ac voltage range is similar to that of dc voltage range.
4. Resistance measurement principle.
The appropriate resistance is connected in parallel and in series on the head of the meter, and a battery is connected in series at the same time to allow the current to pass through the measured resistance, which can be measured according to the magnitude of the current.changing the resistance of the shunt resistance changes the range of the resistance
Attention to analog electrical tester
Multimeter is a more precise instrument, if used improperly, it will not only cause inaccurate measurement but also damage easily.however, as long as we master the usage methods and precautions of the multimeter and proceed cautiously, the multimeter can be durable.when using multimeter, the following matters should be noted:
(1) the measuring current and voltage shall not be misaligned.the meter will burn out easily if the voltage is measured by means of a wrong electrical barrier or current block.when the multimeter is not in use, it is best to turn the baffle to the highest ac voltage gear to avoid damage due to improper use.
(2) when measuring dc voltage and dc current, pay attention to the polarity of "+" And "-", and do not connect wrong.if the pointer is found to be open and reversed, the watch rod should be replaced immediately so as not to damage the pointer and the watch head.
(3) if the voltage or current under test is not known, the highest gear should be used first, and then the proper gear should be selected to test, so as to avoid the damage of the head caused by excessive needle deflection.the closer the chosen baffle is to the measured value, the more accurate the measured value will be.
(4) when measuring the resistance, do not touch the bare ends of the element (or the metal parts of two watch rods) by hand, so as to avoid the parallel connection between the human resistance and the measured resistance, making the measurement result inaccurate.
(5) when measuring the resistance, such as the two table bar sub, "Zero ohm" Knob to maximum, pointer still amounted to less than zero, this kind of phenomenon is usually caused by the battery voltage is insufficient in the table, should change new battery can be measured accurately.
(6) when the multimeter is not in use, do not rotate it in the resistance file, because there are batteries in it. If you are not careful, it is easy to make two rods touch and short-circuit each other.