1, instrument size
That is the size of the meter, which is a very basic problem. Digital display meter should be installed in the cabinet body. So, it is necessary to consider the overall coordination, big may not fit, too small not clear digital display. In addition, the large volume of instruments function expansion is strong, the same function price may will be more expensive, the small size of the instrument may expand the function of the poor. At present, the international standard size of digital display panels are mainly the following: 48 * 24mm; 48 * 48mm; 48 * 96mm; 72 * 72mm; 96 * 96mm; 96 * 48mm.
2, the display number
Which is directly related to the digital display meter measuring accuracy, generally speaking, display number is high, accurate measurement, prices are also more expensive, mainly the following: two (99, special); three (999, rarely); three semi (1999, ordinary digital display meter majority); four (9999, intelligent digital display table mainstream); four and a half (19999); three out of four (3999); five or more than five (common on the counter, the cumulative table and high-end instruments), the user can according to the requirements of the measurement accuracy to select several digital display table.
3, input signal
Refers to the direct input instrument of measuring signal, some industrial signal is directly connected to the measuring instrument, some signal is transformed after access instrument, must make clear the nature of signal measurement, or to buy the instrument can not be used, even damage 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 clarify the size of the signal. Instrument and the name of the input signal is not the same concept, cite a few examples: the input signal is table (name of the current table 0-75mVdc current, input signal is a voltage signal, because the current through the shunt voltage signal). The input signal is 0-10Vdc tachometer (the name was a tachometer, input signal is the voltage meter, because the inverter will speed signal is converted into a voltage signal).
4, working power
All digital display tables are required to work, the main power supply of the digital display table: 220Vac; 110/220Vac; 85-265VAC/DC switching power supply, 24Vdc (general to order), 5Vdc (small panel table).
5, instrument function
Spectral selection of RS232 or RS485 output or price of instrument function is modular and can be selected, the instrument will function with different and somewhat difference, digital display meter mainly has the following optional function: alarm function and alarm output group number (i.e., relay output), feed the power output and the output voltage and power transmission output and transmission output type (4-20mA 0-10V), communication and communication mode and protocol is MODBUS or other protocol), for regulating and controlling instrument, optional features more specific to according to the manufacturer to choose a standard models, and manufacturers to communicate and confirm the correct to order.
6, a few important parameters should be concerned about: measurement accuracy values (smaller more accurate), response rate (value smaller faster response), working environment, temperature coefficient (value more small temperature influence smaller), overload capacity
7, special requirements
If users have special requirements should be put forward, to allow manufacturers to confirm whether meet the requirements, do not take it for granted, such as: IP rating, high temperature working conditions, the situation of strong interference, signal of special occasions, special operating mode, and so on.
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