1. Meter size. That is, the size of the meter, this is a very basic problem. The digital display meter should be installed on the cabinet, so it is necessary to consider the overall coordination. If it is too large, it may not be installed. If it is too small, the display number will not be seen clearly . In addition, the large-sized instrument generally has strong functional extensibility, and the same function price may be expensive,and the small-sized instrument may have poor functional extensibility.At present, the international standard sizes of digital display meter plates are mainly as follows: 48*24mm; 48*48mm; 48*96mm; 72*72mm; 96*96mm; 96*48mm; 160*80mm.
2. Display digits.This is directly related to the measurement accuracy of the digital display meter.Generally speaking, the higher the display digits, the more accurate the measurement,and the more expensive the price, mainly the following:two digits (99, special); three digits (999, very few); three and a half digits (1999, the general digital display meter is the mainstream); four digits (9999, intelligent digital display is the mainstream); four and a half digits (19999); four and three-quarters digits(39999);five digits and more than five digits (common in counters, accumulative meters and high-end instruments),users can select several digits digital display meters according to measurement accuracy requirements.
3. Input signal. Refers to the measurement signal directly input into the instrument.Some industrial signals are directly connected to the instrument to measure. Some signals are connected to the instrument after being converted,and the nature of the measurement signal must be clarified.Otherwise,the instrument can not be used, or even damage the instrument and the original equipment. To find out the type of signal: current or voltage, AC or DC, pulse signal or linear signal, etc., but also to understand the size of the signal. The name of the meter is not the same concept as the input signal. For example, the input signal is a 0-75mVdc ammeter (the name is an ammeter, but the input signal is a voltage signal because the current is passed through the shunt to obtain the voltage signal); the input signal is 0- 10Vdc tachometer (name is tachometer, input signal is voltmeter, because the inverter converts the speed signal into voltage signal).
4. Working power. All digital display meters require working power. The working power of the digital display meter mainly includes: 220Vac; 110/220Vac; 85-265VAC/DC switching power supply, 24Vdc (generally customized), 5Vdc (small panel meter).
5. Instrument function.Instrument functions are generally modular,optional, the price of the instrument will vary with the function, The digital display meter mainly has the following optional functions:alarm function and the number of groups of alarm output(i.e. relay action output), feed power output and output voltage size and power, transmitting output and transmitting output type(4-20mA) Or 0-10V, etc.), communication output and communication methods and protocols (RS485 or RS232, Modbus or other protocols), for the regulating control Instruments, optional functions are more,specifically, refer to the manufacturer's selection spectrum to select a standard model, and communicate with the manufacturer and confirm that it is correct before ordering.
6. Several important parameters should be paid attention to: measurement accuracy (the smaller the value is more accurate),response speed (the smaller the value，the faster the response),the working environment, temperature coefficient (the smaller the value is less affected by temperature),overload capacity.
7. Special requirements. If the user has special requirements, it should be proposed to let the manufacturer confirm whether it can meet the requirements. Do not take it for granted. For example, IP protection level, high temperature working place, strong interference occasion, special signal occasion, special working mode, etc.
In fact, the selection of digital display meter is not complicated.For simple digital display meter,you can buy it to use.For those users who use it for the first time or choose a digital display meter with complex function, as long as you grasp the above points, you can also purchase the right product.