Select PLC reference conditions

The functions produced by each manufacturer or agent PLC are similar, and the difference is not obvious. Therefore, the size of the controlled system, future expansion, and budget are taken into consideration. In terms of selection, preliminary decisions on the manufacturer's PLC directory can be made. Possible considerations are as follows:

 

1 Provides basic capacity features

 

(1) The voltage range of the input signal.

 

(2) The provided instruction functions: basic operation instructions, extendable application instructions, data processing instructions, arithmetic instructions, PID instructions, and so on.

 

(3) The instruction processing speed (ie execution speed) of the PLC is usually calculated in usec.

 

(4) The included memory capacity is usually measured in K bytes.

 

(5) Timer and counter functions.

 

(6) The capacity of the data buffer.

 

(7) The amount of expansion of I/O points.

 

(8) Other special functions: such as floating-point arithmetic, perpetual calendar and system clock, high-speed computing capability, and so on.

 

2 peripheral expansion capabilities

 

(l) Convenience of connecting to a personal computer.

 

(2) Ease of using personal computers to compile software.

 

(3) Supply of D/A or A/D conversion modules.

 

(4) PLC network function.

 

(5) Control motion device functions, such as stepper motors, servo motors, and positioning controllers.

 

3 PLC power specifications

 

The vast majority are AC power supplies. The following should be noted:

 

(1) The range of voltage.

 

(2) How long is the allowable transient time of the power off and the PLC remains unaffected and continues to operate.

 

(3) Power protection measures, and the maximum voltage and current that can be tolerated.

 

(4) How much V, A, or W is the power consumption of the entire machine.

 

4 PLC input specification matters needing attention

 

(l) Maximum input voltage.

 

(2) Enter the maximum allowable current.

 

(3) The minimum current when the input is 0N.

 

(4) The maximum current when the input is OFF.

 

(5) Insulation type of circuit.

 

5 PLC output specification notes

 

(l) The type and value of the external voltage.

 

(2) is a resistive load or an inductive load.

 

(3) The maximum leakage current value when the output is open.

 

(4) The response time of the output at 0N and 0FF.

 

(5) Circuit insulation adopted by the output circuit.

 

6 Environmental conditions

 

(1) The temperature range used by the PLC.

 

(2) Shock resistance.

 

(3) Impact resistance.

 

(4) Noise resistance.

 

(5) The ability to withstand electric shock.

 

(6) The entire insulation resistance of the system.

 

(7) Grounding settings.

 

(8) The limitation of the work environment is mainly the IP protection level.