Tips for picking up your multimeter

What are the techniques for selecting a multimeter? Choosing a multimeter depends on the specific requirements you use to select the most appropriate digital multimeter. The general is to consider from the following aspects.

1. In addition to measuring AC and DC voltage, AC and DC current, resistance and other five functions, the function DMM has digital calculation, self-check, reading hold, error readout, diode detection, word length selection, IEEE- 488 interface or RS-232 interface and other functions, when used according to specific requirements.

2. Range and Range The DMM has many ranges, but its basic range accuracy is the highest. Many digital multimeters have auto-range function, do not need to manually adjust the range, making the measurement convenient, safe and rapid. There are many DMMs that have over-range capabilities that do not require a range change when the measured value exceeds this range but have not reached the maximum display, thereby improving accuracy and resolution.

3. Accuracy The maximum allowable error of a digital multimeter depends not only on its variable term error but also on its fixed term error. The choice depends on the stability and linear error requirements, whether the resolution meets the requirements. General digital multimeters require 0.0005 level to 0.002 level, at least 61 digits, 0.005 level to 0.01 level, at least 51 digits, 0.02 level to 0.05 level, at least 41 digits, 0.1 level. Below, there should be at least 31 digits displayed.

4, input resistance and zero current Digital multimeter's input resistance is too low and zero current will cause measurement error, the key depends on the measurement device allows the limit value is how much, that depends on the size of the signal source resistance. When the source impedance is high, the instrument with high input impedance and low zero current should be selected so that the influence can be ignored.

5, string mode rejection ratio and common mode rejection ratio in the presence of a variety of interference such as electric fields, magnetic fields and various high frequency noise or long-distance measurement, easy to interfere with the signal, resulting in inaccurate readings, it should be based on the use of the environment to choose For instruments with high string and common-mode rejection ratios, especially for high-precision measurements, a digital multimeter with a protected terminal G should be selected to suppress common-mode interference.

6. Display forms and power supply The display form of the digital multimeter is not limited to numbers, but can also display graphs, words and symbols for on-site observation, operation and management. According to the size of its display device can be divided into small, medium, large and super large four categories.

The power supply of the digital multimeter is generally 220V, and some new digital multimeters have a wide range of power supply, which can be between 1100V and 240V. Some small digital multimeters can be used with batteries, and some digital multimeters can use AC power, internal nickel-cadmium batteries, or external batteries.

7. The shorter the response time, measurement speed, and frequency range response time, the better. However, there are some forms that have a relatively long response time. It will take some time for the reading to stabilize. The speed of measurement should be based on whether it is used in conjunction with system testing. When used in conjunction, speed is important, and the speed is as fast as possible. The frequency range is appropriately selected as needed.

8, AC voltage conversion form AC voltage measurement points mean conversion, peak conversion and rms conversion. When the waveform distortion is large, the average value conversion and the peak conversion are inaccurate, and the RMS conversion may not be affected by the waveform, so that the measurement result is more accurate.

9、Resistance connection mode The resistance measurement connection has four-wire system and two-wire system. For small resistance and high-precision measurements, select the four-wire resistance measurement connection.

With the development of large-scale integrated circuits and display technologies, digital multimeters have gradually developed toward miniaturization, low power consumption, and low cost. Digital multimeters are also clearly classified into portable and desktop. Portable is generally 31 or 41 bits, small size, light weight, low power consumption, suitable for production workshop or field use; desktop up to 61 or 71 bits, with higher accuracy and resolution, microprocessor and The GP-IB interface device is used as a standard meter and precision measurement in the measurement, scientific research and production departments.