Precautions for using digital voltmeter

Digital voltmeter is a precision measuring instrument and must be operated strictly according to technical conditions. Otherwise, not only will the measurement be inaccurate, but the instrument may also be damaged in serious cases. Therefore, pay attention to the following matters:

(1) Before use, the instrument must be adjusted and calibrated. Otherwise, it will not work properly. After the instrument is powered on and preheated for the prescribed preheating time, it can be pre-adjusted. The pre-adjustment method varies depending on the instrument model. The following are some common situations:

① For voltmeters that need to be adjusted for "positive and negative balance" before calibration, the calibration switch should be set to the "positive and negative balance" position first, and the "balance" potentiometer should be adjusted to make the positive and negative indications of the meter equal or within the allowable error range. Then the calibration switch should be set to the correction position, and the positive and negative should also be balanced. If unbalanced, it should be adjusted repeatedly to balance and reach the specified calibration voltage value.

② For voltmeters that need to be adjusted to "zero balance" before calibration, the calibration switch should be set to the "zero balance" position first, and the "zero balance" potentiometer should be adjusted to make the displayed value change around "o". Then, the calibration switch should be set to the "correction" position, and the "correction" potentiometer should be adjusted to make it display the specified correction voltage value. At this time, the opposite polarity should also display this voltage value. If they do not coincide, the "zero balance" potentiometer should be adjusted repeatedly until both the positive and negative sides display the same specified correction voltage value.

③ For the voltmeter that performs "zero adjustment" and "positive and negative calibration" separately, the selection switch should be placed in the positions of "zero calibration", "positive calibration" and "negative calibration" in turn, and the corresponding adjustment potentiometer should be adjusted so that the corresponding indications "0", +un and -un are displayed in each position.

④ If the ideal indication is still not achieved after the above zeroing and calibration, it should be sent to the measurement and inspection department, where a professional will open the cover and adjust the internal "zeroing", "calibration" and "range" potentiometers to achieve the ideal state.

⑤ In order to reduce the impact of zero current, some instruments have "zero current" adjustment. A zero current potentiometer should be adjusted according to regulations to make it display zero. However, the adjustment of zero current and zero voltage should be taken care of each other and should not be out of adjustment.

After preliminary adjustment, when all items meet the specified requirements, formal measurement work can be carried out.

(2) Pay attention to the ambient temperature and humidity during use. Violating the regulations will increase the error or even cause the instrument to fail to work at all.

(3) Instruments with built-in standard batteries are strictly prohibited from being tilted at a large angle or inverted. It is best to remove the batteries during transportation to prevent damage.

(4) The measurement dimension of the digital voltmeter should correspond to the type of input signal. It is strictly forbidden to exceed the maximum input voltage specified by the meter, otherwise the meter will be damaged.

(5) Pay attention to shielding and grounding during use to reduce interference.

(6) Since the digital voltmeter has zero current and the input impedance is not infinite, when using it, pay attention to the error caused by the internal resistance of the signal source being measured.

(7) If a digital voltmeter needs to be used in conjunction with a printer, attention should be paid to the coding of the two, the level value of the logic state, and the consistency of the pulse width, polarity and waveform. Otherwise, the printer will not work or will malfunction.