How to choose the appropriate digital display instrument correctly
　　
First, select the number of digits to display
　　
This is directly related to the measurement accuracy of digital displays. Generally speaking, the higher the number of display digits, the more accurate the measurement and the more expensive the price. There are mainly the following types: two digits (99, special); Three digits (999, very rare); Three and a half digits (1999, ordinary digital displays dominate); Four digits (9999, with intelligent digital displays being the mainstream); Four and a half (1999); Four and three-quarters (3999); Five digit and above (commonly found in counters, accumulative meters, and instruments), users can choose the number of digits for the digital display according to their measurement accuracy requirements.
　　
Choose the appropriate instrument size for yourself. The volume size of the instrument is a very basic issue. The digital display meter needs to be installed on the cabinet, so overall coordination should be considered. If it is too large, it may not fit properly, and if it is too small, the displayed numbers may not be clear,
　　
In addition, larger instruments generally have stronger functional expandability, and the same functionality may be more expensive, while smaller instruments may have poorer functional expandability.
　　
At present, there are several standard sizes for digital display panel: 48 * 24mm; 48 * 48mm; 48＊96mm；72＊72mm； 96＊96mm；96＊48mm； 160＊80mm。
　　
Select the correct input signal. It refers to the measurement signal directly input into the instrument. Some industrial signals are directly connected to the instrument for measurement, while others are converted and connected to the instrument. It is necessary to understand the nature of the measurement signal, otherwise the purchased instrument cannot be used and may even damage the instrument and existing equipment.
　　
To determine the type of signal: current or voltage, AC or DC, pulse signal or linear signal, etc., it is also necessary to determine the magnitude of the signal. The name of an instrument is not the same concept as the input signal. For example, an ammeter with an input signal of 0-75mVdc (named an ammeter, but the input signal is a voltage signal because the current passes through a shunt to obtain the voltage signal); The input signal is a 0-10VDC tachometer (named tachometer, but the input signal is a voltmeter because the frequency converter converts the speed signal into a voltage signal).
　　
Pay attention to instrument functions. The functions of the instrument are generally modular and selectable, and the price of the instrument may vary depending on the different functions.
　　
The digital display meter mainly has the following optional functions: alarm function and the number of alarm output groups (i.e. relay action output), the size and power of the power supply output and output voltage, the type of transmission output and transmission output (4-20mA or 0-10V, etc.), communication output and communication mode and protocol (RS485 or RS232, Modbus or other protocol). For regulating and controlling instruments, there are more optional functions, and a standardized model should be selected according to the manufacturer's selection spectrum. After confirming with the manufacturer, the order can be placed.
　　
Choose a suitable working power source. All digital displays require a working power supply, which mainly includes 220Vac; 110/220Vac； 85-265VAC/DC switching power supply, 24Vdc (usually customized), 5VDC (small panel meter).