Wednesday, January 26, 2011

【 Weak current College 】 on digital multimeter selection 】

Digital multimeter meters with the accuracy is high, the measure of the wide, measurement speed, small size, strong anti-interference ability, easy to use, etc and are widely used in national defense, scientific research, factories, schools, and other areas of metrology and measurement technology, but its specifications, performance indicators, use of environmental and working conditions also vary, depending on the circumstances, therefore you should choose the appropriate digital multimeter.

Select digital multimeter General from several areas to consider:

1. function

Now the digital multimeter in addition to measuring AC, DC voltage, AC, DC current, resistance, and so on five features, there are figures, keep posting, reading, error detection, read the diode IEE488 interface or RS232 interface and other functions, use the selection according to the specific requirements.

Second, the scope and range

Digital multimeter many range, but the basic range, the highest accuracy. Many digital multimeter with automatic range feature, no need to manually adjust the range, allows measurements convenient, secure and fast. There are many digital multimeter has had the ability, in measurement range values exceed the quantum but haven't reached the maximum display time can not change the range, thereby increasing the accuracy and resolution.

3. accuracy

Digital multimeter maximum error of not only its variable error, but also to see it fixed the error. Select time depends on the stability of the error and the linearity error is the number of requests, the resolution meets the requirements. General digital multimeter if 0.0005 ~ 0.002 level, at least 61 digits display; 0.005 ~ 0.01 level, at least 51 digits display; 0.02 ~ 0.05 level, at least 41 digits display; 0.1 following, at least 31 bits of the digital display.

4. input resistance and zero-current

Digital multimeter input resistance is too low and zero current too high will cause measurement error, key measurement device allows extreme is the number that you want to see the signal source resistance. Signal source impedance should choose a high input impedance, low zero current instrument, so that its impact can be ignored.

Fifth, string mode suppression ratio and common-mode rejection ratio

In the presence of various interference such as electric and magnetic fields and a variety of high-frequency noise or for distance measurement, easily into the interference signal, resulting in inaccurate readings should therefore be based on the usage environment select series and high common-mode rejection ratio, particularly for equipment for high precision measurement, you should choose the belt protection-G digital multimeter, can inhibit the common mode interference.

6. display and power supply

Digital multimeter display form is not limited to digital, you can also display the graphics, text and symbol for on-site observations, operation and management. According to it's display of dimensions can be divided into small, medium, large and very large four categories.

Digital multimeter with power General 220V, and some new digital multimeter power range is very wide, 110-240. Some small digital multimeter with battery to use, there are also some digital multimeter available AC, internal nickel-cadmium batteries or an external battery.

7. response time, measurement speed, frequency range

Response time as short as possible, but there are some tables of response time longer, take some time to stabilize after reading. Measurement of the speed shall be based on whether or not combined with the system test, such as coupling, the speed is important, but the sooner the better. Frequency range, the appropriate choice according to your needs.

VIII. the AC voltage conversion form

AC voltage measurement points average conversion, peak and RMS conversion. When the waveform distortion is large, the average conversion and peak transfer not accurate, valid values are converted to wave, brings the measured result more accurate.

9 resistor connection modes

Resistance measurement connection modes have four line, two-wire system. With low resistance and high-precision measurement, you should choose four wire connection mode of resistance measurement.

With LSI and display technologies, digital multimeter to miniaturization, low power, low-cost, digital multimeter is also clearly divided into two types of portable and desktop. Portable General 31 bits or 41 bit, small size, light weight, low power consumption, suitable for the production plant or field use; desktop up to 61 61 or, accuracy and resolution is getting higher and higher, the use of microprocessor and GPIB interface equipment, measurement, scientific research and production departments as a standard table and precise measurements.

In short, the choice is not necessarily need to have all of the above conditions, should be based on the use of specific requirements to choose the most appropriate digital multimeter.

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