How to use digital multimeter and precautions
(1) When measuring resistance, the measured resistance cannot have a parallel branch. It is best to remove the measured resistance from the circuit (at least one end is disconnected from the line) before measuring. Polar elements such as transistors and electrolytic capacitors under test
When checking the equivalent resistance of the device, attention must be paid to the polarity of the two test leads. The digital multimeter has two test leads, red and black. The red test lead is the positive pole of the internal battery, and the black test lead is the negative pole of the internal battery.
(2) When measuring voltage, connect the digital multimeter in parallel to both ends of the circuit under test; when measuring current, connect the multimeter in series with the circuit under test.
(3) When using a digital multimeter to measure a DC circuit, the polarity can be automatically displayed.
(4) When measuring an AC circuit, only the voltage and current of the sinusoidal AC can be measured, and the two test leads of the digital multimeter have no distinction between positive and negative.
(5) Before the digital multimeter measures the resistance, the two test leads should be short-circuited, and the initial error value should be recorded. After the measurement, the actual measurement value is obtained by subtracting the initial error value from the measured value.
(6) Before the digital multimeter measures the capacitance, the two ends of the capacitor must be short-circuited first, and the capacitor should be discharged to ensure personal safety and the digital multimeter will not be damaged. After the measurement is completed, the capacitance should also be
Discharge, to avoid burying potential safety hazards.
(7) When the digital multimeter displays "BATT" or "LOWBAT", it means that the internal battery voltage is lower than the working voltage, and the battery should be replaced at this time. If the measurement is still carried out, the measured value will be higher than the actual value
On the high side.
(8) When the gear position of the digital multimeter is misused, the internal protection circuit will take effect, and the display will display "000", or the number on the low position will flash.
(9) It is forbidden to change the range when measuring high voltage (above 220V) or high voltage (above 0.5A), so as to prevent arcing and burning of switch contacts.
(10) The digital multimeter can directly read the measured voltage, current, and resistance values from the LCD screen, but you need to pay attention to the measurement unit on the right side of the screen. If the switch of the digital multimeter
There are not only the selection of test items, but also the conversion of the range. The measured parameter value is small, but the unit is large, indicating that the range selection is too large, and it needs to be changed to a small range for measurement. If the measured value exceeds the maximum value of the selected range, the multimeter will only display the number "1" in the highest digit, and it needs to be changed to a larger range for measurement. In some digital multimeters, only the test items can be selected on the transfer switch, but there is no range change. When measuring, the multimeter automatically changes to the appropriate range according to the size of the test parameters, and the reading is more convenient.
(11) During the test of the multimeter, do not touch the metal part of the test lead with your hands. On the one hand, it can ensure the accuracy of the measurement, and on the other hand, it can also ensure personal safety. When measuring high voltages above 100V, use one hand whenever possible.
(12) Some digital multimeters have an automatic shutdown function, but some digital multimeters do not have this function. After use, be sure to turn the power switch to the off position to save battery power.
(13) The output voltage of the digital multimeter is low, and it is inconvenient to test some components with special voltage characteristics (such as thyristors, light-emitting diodes, etc.).
(14) Since the digital multimeter uses an operational amplifier circuit inside, the internal resistance of the voltage range is very large, at least in the megohm level, which has little influence on the circuit under test and has high measurement accuracy, but the extremely high output impedance makes it easy to Affected by the induced voltage, the measured data may deviate in some occasions where the electromagnetic interference is relatively strong.
