Teach you how to choose electronic measuring instruments

　　Since measuring instruments are in different frequency bands, even instruments with similar functions often have very different working principles and structures. Instruments with different accuracy are often used for different purposes. For example, measuring instruments used as measurement standards often have the highest accuracy. Laboratories generally use more precise measuring instruments for quantitative measurements, while simple test instruments are often used for production and maintenance. In fact, when choosing an electronic instrument, there are far more things to consider. The issues that usually need to be considered when choosing an instrument generally include:

　　(1) Range. That is, what are the maximum and minimum values ​​of the measured value? Which instrument is more suitable?

　　(2) Accuracy. That is, what is the maximum error allowed for the measured value? Do the error and resolution of the instrument meet the requirements?

　　(3) Frequency response characteristics. That is, what is the frequency range of the measurement? Is the frequency response of the instrument flat within this range?

　　(4) Does the input impedance of the instrument meet the requirements in all ranges? If the input impedance is not constant, is its value change within the allowable range?

　　(5) Stability. What is the maximum time allowed between two calibrations? Can it operate without supervision for a long time?

　　(6) Environment. Does the instrument use environment meet the technical requirements? Is the power supply appropriate?

　　(7) Isolation and shielding. Is the grounding method of the instrument appropriate? 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, when choosing an instrument, you don't have to consider all of the above items. 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 select an electronic voltmeter (millivoltmeter) or an oscilloscope as a measuring instrument based on the existing instruments in the laboratory. When using it, pay attention to preheating, zeroing and calibrating the instrument. To ensure equal precision measurement, the same set of instruments should be used as much as possible during the experiment.