Principle of resistance measurement by multimeter
The principle of measuring resistance in a multimeter is actually based on Ohm's law.
In a multimeter, its voltage is the voltage of the battery; it has several resistance values, including the resistance we want to test, its adjustable resistance (the internal resistance of the multimeter is different at different stops), and its constant resistance. And the current is calculated when our test resistance is equal to zero.
Measured with a multimeter on the resistance reading is actually the current reading, just R measured = 0 when the current: I = U/ (Rg + R fixed + R adjustable) marked as R = 0, there is no current, the resistance is marked in the non-resistive large, I and is a function of the relationship between them, they are not simple proportional relationship. Select a different resistance gear, R fixed different, R = 0, I is different, so before each measurement should be zeroed.
This gives us a formula: I = U / (Rg + R fixed + R tuning + R measured) U is the voltage of its internal battery, Rg is the resistance of the meter head, R fixed, and the meter head in series with a constant value resistance, R tuning, zeroing variable resistance, R measured, the resistance to be measured. As the size range of the resistance to be measured varies, different constant value resistors are used, which makes it possible to divide the multimeter into several grades.
Operating procedures
1, before using the multimeter should be familiar with the functions, according to the object being measured, the correct choice of gear, range and pen jack.
2, in the size of the measured data is not clear, should be the first range switch, placed in the maximum value, and then by a large range to switch to the small range file, so that the instrument pointer in the full scale of 1/2 above the place can be.
3, the measurement of resistance, after selecting the appropriate multiplier file, the two pens touch so that the pointer points to zero, such as the pointer deviates from zero, you should adjust the "zero" knob, so that the pointer to zero to ensure that the measurement results are accurate. If you can not zero or digital display meter issued a low-voltage alarm, should be checked in time.
4, in measuring the resistance of a circuit, you must cut off the power supply of the circuit under test, and do not measure with electricity.
5,When using the multimeter for measurement, pay attention to the safety of the person and instrumentation equipment, the test shall not touch the metal part of the meter pen with hands, and do not allow switching the gear switch with electricity to ensure accurate measurement and avoid accidents such as electrocution and burnt instrumentation.
