Because measuring instruments even with similar functions often have very different working principles and structures in different frequency bands.For different purposes, instruments often use with different accuracy. For example, metering instruments used as the standard of metering work often have the highest accuracy. In the laboratory, more precise measuring instruments are generally used for quantitative measurement, while in production and maintenance, simple measuring instruments are often used for measurement. In fact, when choosing an electronic instrument, we need to consider far more than these. Usually, the items we need to consider when choosing an instrument include:
(1) range. In other words, what is the maximum and minimum value measured? What kind of instrument is more appropriate?
(2) Accuracy. What is the maximum error allowed to be measured? Does the error and resolution of the instrument meet the requirements?
(3) Frequency response characteristics. What is the frequency range that is being measured? Is the instrument frequency response flat in this range?
(4) Does the input impedance of the instrument meet the requirements in all measuring ranges? If the input impedance is not constant, is the value varying within the allowable range?
(5) Stability. What is the maximum allowable time range between two calibrations? Can work without supervision for long periods of time?
(6) environment. Does the operating environment of the instrument meet the technical requirements? Is the power supply suitable?
(7) isolation and shielding. Is the instrument grounded properly? Does the electromagnetic field in the working environment affect the normal operation of the instrument?
(8) Reliability. What is the specified service life of the instrument? Is it easy to maintain?
Of course, it is not necessary to consider all of the above items when actually choosing an instrument. For example, when measuring the amplitude-frequency characteristics of an audio amplifier, the main consideration is whether the frequency range and range of the measuring instrument are appropriate. Is the measurement error within the allowable range? We can choose electronic voltmeter (millivoltmeter) or oscilloscope as the measuring instrument according to the existing instruments in the laboratory. When using, pay attention to preheat, zero and calibrate the instrument. In order to ensure equal precision measurement, the same group of instruments should be used as far as possible in the experiment.
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