Multimeter measures the relationship between resistance pointer deflection angle and resistance
When measuring resistance, please note:
1. The resistance being measured should be removed from the circuit before measurement.
2. Do not touch the two test leads together for a long time.
3． Do not touch the metal rods of the two test leads or the two pins of the resistance being measured with both hands at the same time. It is best to hold the two test leads at the same time with your right hand.
4. If the ohm setting is not used for a long time, the battery in the meter should be removed.
When a multimeter measures resistance, the measured value reflected on the meter is actually the corresponding current passing through the resistance being measured. The greater the resistance being measured, the smaller the current, that is, the smaller the deflection angle. The relationship between the pointer deflection angle and the measured resistance is:
α=(RZθ)/(RX+RZ)
In the formula: α---pointer deflection angle;
RZ--center resistance of multimeter;
RX---The measured resistance;
θ---The angle when the pointer is fully deflected, this angle is mostly 90°
It can be seen from the ohm scale of the multimeter that its scale is an uneven reverse scale. The smaller the deflection angle, the greater the indicated resistance. The resistance value between each scale line at the high-resistance end is very different. If you look at the pointer at an angle on this section of the scale line during measurement, it will cause a large error. Especially when measuring small resistance, the error is more obvious. Therefore, in order to ensure accurate measurement, when measuring small resistance, you should try to keep the pointer as close to the center position by shifting gears.
Precautions for measuring accuracy of multimeter
(1) Keep your eyes perpendicular to the pointer when reading;
(2) Before measurement, place the multimeter horizontally and perform mechanical zero adjustment;
(3) When measuring resistance, zero adjustment must be performed every time you change gears. If it cannot reach zero, replace the battery with a new one;
(4) When measuring the resistance in an RC circuit, cut off the power supply in the circuit and discharge all the electricity stored in the capacitor before measuring again. After excluding human reading errors, we conduct some analysis on other errors;
(5) When measuring resistance or high voltage, do not hold the metal part of the test lead with your hands to avoid shunting of human body resistance, increasing measurement errors or causing electric shock.
Digital multimeters, also known as digital multimeters (DMM), come in many types and models. Every electronic worker hopes to have an ideal digital multimeter. There are many principles for choosing a digital multimeter, and sometimes they even vary from person to person. But for a handheld (pocket) digital multimeter, it should generally have the following characteristics: clear display, high accuracy, strong resolution, wide test range, complete test functions, strong anti-interference ability, relatively complete protection circuit, and beautiful appearance , generous, easy to operate, flexible, good reliability, low power consumption, easy to carry, affordable and so on.
