PLCI/O module choice PLC choose three steps and principles

Generally the price of the I/O module of PLC controller more than half the price. PLC I/O module has switch I/O module, analog I/O module and various special function module, etc. Different I/O module, the circuit and function also is different, a direct impact on the application of PLC and price, and shall, according to the actual need to choose them. ( A) The choice of switch I/O module 1. Switch input module and the choice of switch input module is used to receive the switch signal input device, converts the signal to PLC internal accept low voltage signal, and implement of PLC internal and external signal electrical isolation. When the choice basically should consider the following aspects: 1) The type of input signal and the voltage level switch input module and a dc input, ac input and three types of ac/dc input. When the choice is mainly according to the input signal and the surrounding environmental factors, etc. Dc input module of the delay time is shorter, can also directly with close to switches, photoelectric switches and other electronic input device connected; Ac input module reliability is good, suitable for oil mist, dust under the conditions of use. Switch input module of the input signal and the voltage grade are: dc 5 v, 12 v, 24 v, 48 v, 60 v, etc. ; Ac, 110 v, 220 v, etc. When the choice is mainly based on input devices in the field and the distance between the input module to consider. General 5 v, 12 v, 24 v at close range for transmission occasions, such as 5 v input module farthest shall not exceed 10 metres. Far away higher module should be chosen as the input voltage level. 2) Input connection mode switch input module mainly has remit point and grouping type two kinds of connection mode, as shown in figure 6 - 2. Figure 6 - 2 switch input module and the connection mode of a) Hui point input b) Grouping type input link point switch input module and all share a common end point ( COM） ; And grouping type switch input module is the input points into several groups, each group ( Several input point) Has a public side, between the groups are separated. Grouping of switch input module and a junction point higher price, if you don't need to separate between the input signal, generally choose link point. 3) Pay attention to at the same time, through to the number of input points to is made of high input module ( Such as 32 points, 48 points, etc. ) , the module should be considered at the same time, through to the points of general not more than 60% of the input points. 4) Enter the threshold level in order to improve the reliability of the system, the size of the input threshold level must be considered. The higher the threshold level, the stronger anti-interference ability, transmission distance is more far, specific see PLC instructions. 2. The switch output module selection switch output module is PLC internal low voltage signal is converted to drive the external output device switch signal, and implement electrical isolation of PLC controller signals inside and outside. When the choice basically should consider the following aspects: 1) Output mode switch output module has relay output, thyristor output and transistor output three ways. Relay output price cheaper and can be used to drive ac load, and can be used in the dc load, and wide applicable voltage size, conduction voltage drop is small, at the same time to have a better ability to withstand transient overvoltage and overcurrent, but it belongs to the contact element, the movement speed is slow, Drive the perceptual load, contact action frequency shall not exceed 1 hz) , short service life, low reliability, can apply to not frequent on and off. For frequent on and off load, should choose thyristor output or output transistor, they belong to the non-contact components. But thyristor output can only be used for ac load, and the transistor output can only be used for dc load. 2) Output connection mode switch output modules are grouped and separated two kinds of connection mode, as shown in figure 6 3. Figure 6 - The connection mode of 3 switch output module a) Packet output of type b) Dividing output packet type output is several dots as a group, a group has a public side, between groups are separated, can be used to drive different power supply of the external output device; Is dividing the output each output point has a public side, the isolation between the dots. When the choice is mainly depending on the type of PLC output devices of power supply and voltage grade of how much. General integral PLC both packet type output, and dividing the output. 3) Ability to drive the output of the switch output module current ( The drive ability) Must be greater than the PLC controller rated current of the external output device. Users should according to the current actual output device the size to choose the output current output module. If the actual output device is larger, the current output module can't direct drive, can increase the amplification in the middle. 4) Notice at the same time, choose the number of dots to switch output module, can through to the number of dots at the same time should also be considered. At the same time, through to the output device of the total current value must be smaller than is allowed by the current value of the public end, such as a 220 v / 2 a output module, at 8 o 'clock each output point can withstand current of 2 a, but is not allowed by the current output common 16 a ( 8×2A) , usually much smaller than this value. Generally speaking, at the same time, through to the points of not more than 60% of the same output public points. 5) Output the maximum current is related to such factors as the type of load, environmental temperature, specifications of the switch output module it is closely related to the different load types, especially the maximum output current. In addition, the maximum output of thyristor current temperature decreases with the environment, should also pay attention to in the practical use.
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