How can I pick the right multimeter for my needs?
1,Functions
In addition to measuring AC and DC voltage, AC and DC current, resistance and other five functions, there are digital calculations, self-test, readings to maintain, error readout, diode detection, word length selection, IEEE-488 interface or RS-232 interface and other functions, the use of the use of specific requirements according to the selection.
2,Range and range
Digital multimeter has many ranges, but its basic range accuracy * high. Many digital multi-meter has automatic range function, do not have to manually adjust the range, making the measurement convenient, **, rapid. There are many digital multi-meter over-range capability, in the measurement of the value over the range but not yet reached the * large display can not be changed when the range, thus improving the accuracy and discriminating power.
3, accuracy
Digital multi-meter allows the * error should not only look at its variable term error, but also look at its fixed term error. When choosing, we also need to look at the stability error and linearity error to find out how much, whether the discriminatory power to meet the requirements. General digital multi-meter such as the requirements of 0.0005 level to 0.002 level, at least 61 digital display; 0.005 level to 0.01 level, at least 51 digital display; 0.02 level to 0.05 level, at least 41 digital display; 0.1 level below, at least 31 digital display.
4, input resistance and zero current
Digital multi-meter input resistance is too low and zero current is too high will cause measurement errors, the key is to look at the measurement device allowed by the limit value is how much, that is, to see the size of the signal source of the internal resistance. When the signal source impedance is high, the instrument with high input impedance and low zero current should be selected so that its effect can be ignored.
5,Series-mode rejection ratio and common mode rejection ratio
In the presence of a variety of interference such as electric field, magnetic field and various high-frequency noise or long-distance measurement, it is easy to mix into the interference signal, resulting in inaccurate readings, so it should be used in accordance with the environment to select the series, common mode rejection ratio of the instrument is high, especially for high-precision measurements, it should be selected with a protective end of the G digital multi-meter, which can be very good suppression of common-mode interference.
6,Display form and power supply
The display form of the digital multi-meter is not only in digital, but also can display charts, text and symbols, in order to facilitate on-site observation, operation and management. According to the external dimensions of its display device can be divided into small, medium, large and large four categories.
Digital multi-meter power supply is generally 220V, and some new digital multi-meter power supply range is very wide, can be between 1100V ~ 240V. Some small digital multi-meter with a battery can be used, there are some digital multi-meter available in the form of alternating current, internal nickel-cadmium batteries or external batteries.
7, response time, measurement speed, frequency range
The shorter the response time, the better, but there are some table response time is relatively long, to wait for a period of time before the reading can be stabilised. Measurement speed should be based on whether or not the system test with the joint, such as the joint, the speed is very important, and the faster the better. Frequency range, the appropriate choice according to need.
8, AC voltage conversion form
AC voltage measurement is divided into average conversion, peak conversion and RMS conversion. When the waveform distortion is large, the average conversion and peak conversion is inaccurate, while the RMS conversion can not be affected by the waveform, so that the measurement results are more accurate.
9, resistance wiring
There are four-wire and two-wire wiring systems for resistance measurement. For small resistance and high-precision measurement, you should choose the resistance measurement wiring with four-wire system.
With the development of large-scale integrated circuits and display technology, digital multi-meter gradually to miniaturisation, low-power, low-cost direction, digital multi-meter is also clearly divided into portable and desktop two. Portable generally 31 or 41 bits, small size, light weight, low power consumption, suitable for production workshops or field use; desktop up to 61 or 71 bits, accuracy and resolution is getting higher and higher, the use of microprocessors and GP-IB interface devices, in the metrology, scientific research and production departments as a standard table and precision measurement.
