Comparison of Calibration Methods of Analog Multimeter and Digital Multimeter
working principle
From the input terminal of the signal to be tested to the output terminal of the rectifier, the structure and function of the digital multimeter and the analog multimeter are the same, and the path of the measurement circuit is changed through the switch to form a multi-range DC voltmeter, DC ammeter, AC voltmeter, AC ammeter and ohmmeter, etc., to complete the measurement of various signals. The main difference between the two lies in the display form of the result. The analog multimeter uses an ammeter head to display the magnitude of the measured signal through the pointer deflection angle, while the digital multimeter converts the measurement result into a digital signal through the A/D converter. After counting and The display drive circuit displays the measurement results on the liquid crystal display.
Test method comparison
1 Verification items
The functions and ranges of multimeters used in various railway units are different, and most units are used as working measuring instruments, such as multimeters equipped in power supply depots and depot workshops to measure voltage, current and resistance; in maintenance workshops of locomotive depots, multimeters Most of them are used to measure voltage and resistance values; in the measurement standard of "Train Tail Safety Protection Device Host Test Station Verification Device" in the train depot, digital multimeters are only used as supporting equipment for 0~50 V DC voltage
Measurement. The multimeter can only check the required parts according to the needs of users. Therefore, when verifying the multimeter, you can choose the verification items according to the actual usage, and the corresponding qualified items should also be indicated when issuing the certificate.
2. Appearance and power-on inspection Both analog and digital multimeters should be inspected visually. The difference is that before verifying the voltage and current function of the analog multimeter, first observe whether the pointer is at the mechanical zero position, if not, adjust the pointer to zero through the mechanical zero adjustment screw; before verifying the resistance, first make sure that the multimeter is Install the battery, then short-circuit the measuring stick, turn the zero potentiometer to make the pointer coincide with the zero position of the resistance, if the zero position of the resistance cannot be reached, it means that the battery voltage is too low, and the battery needs to be replaced. The digital multimeter does not need to perform mechanical zero adjustment, but it needs to be checked with power on to ensure that the battery can supply power normally.
basic error check
When verifying the basic error of the analog multimeter, the full inspection range must be determined first, and the rest of the functions and ranges only need to verify the upper limit of the range and the graduation line that can determine the maximum error. In railway measurement, generally only the voltage, current and resistance files of the multimeter are verified, so there are several scales indicating voltage, current and resistance on the dial, corresponding to several full inspection ranges.
Test results and cycle
Analog multimeters are generally marked with a meter rating below the dial. For instruments whose accuracy level is lower than 0.5, if the verification is qualified, a verification certificate will be issued; if the verification is not qualified, a verification result notification will be issued
book, and it is not allowed to issue a downgraded test certificate. However, digital multimeters generally do not mark the instrument grade. If the inspection unit does not require grading, it can be judged whether the verification data is qualified according to the technical indicators in the manual.
The verification period of analog multimeters and digital multimeters is also different. The verification period of analog multimeters with an accuracy level lower than 0.5 is generally not more than 2 years, while the verification period of digital multimeters is generally 2 years.
Not more than 1 year.
When the multimeter is used as a special measuring instrument for railways, if the user unit has special requirements for its technical indicators, it must confirm its technical indicators after passing the verification according to the general verification regulations. If it does not meet the requirements for use, it cannot be used.
