PLC control system with its own has a clear positioning - input/output circuit

Of PLC control system, although the wiring work accounted for the proportion of small, but it is the foundation of programming design, only the correct wiring, programming can smooth work. And make sure the correctness of the connection, must be within the input/output circuit of PLC has a clear positioning.

dc input circuit

as shown in the above, as a form of dc input circuit ( Only draw all the input circuit) 。 When an external circuit when the switch is closed, the PLC internal light coupling leds light up, light activated triode saturated conductivity, the guide communication, then transmitted to the processor, to think that we should have a signal input CPU: the outside world, the switch is off, the optical coupling light-emitting diodes, light activated triode cut-off, CPU think we should have no signal.

as shown in the above, you can see the difference between dc and ac input circuit input circuit, mainly added a rectifier link. Ac input of the input voltage is commonly AC120V or 230 v, alternating current through a resistor R current limiting and capacitance C isolation, repass bridge rectifier for direct current, then the working principle and the dc input circuit.

see from above, as a result of swine flu in the input circuit to increase the current limit, isolation and rectifying the three links. As a result, the input signal of the delay time longer than the dc input circuit, which is its disadvantages. But due to its input is high voltage, therefore the reliability of the input signal is higher than the dc input circuit.

type leakage input circuit

as shown in the above, the current public side (from the PLC COM side or M side) Flow into, thus the input flow, which is the external positive electrode of DC power supply capacity of the PLC in public.

as shown in the above, this figure is just picture out of the situation all the way, if there is a multichannel input, all input diode connected to the anode, constitutes a total of anode circuit.

mitsubishi A series PLC AX40/41/42/50/60 and Q series QX40/41/42 input module type all belong to leakage input module.

as shown in figure 3 type circuit is also the source of the form of input circuit, at this point, the flow of electric current and leakage circuit instead. Prototype from PLC input circuit input circuit flow into, and carry out from public, namely public termination external power of the cathode.

if all input circuit diode cathode is linked together, make up for the cathode circuit, as shown in the figure below

mitsubishi A series PLC AX80/81/82 and Q series QX80/81 all belong to this kind of input circuit input module.

hybrid input circuit for this type of PLC public port can connect the anode of an external power supply can also connect the cathode, simultaneously has the characteristics of the source input circuit input circuit and the drain, so we can let the be mixed input circuit input circuit, as shown in the figure below:

as a source input, public termination power of the cathode; As input, the leakage public termination the anode of power supply. So we can according to the needs of the scene to wiring, great flexibility.

AX50 - mitsubishi A series PLC S1/60 - S1/70/71/81 - S1 and Q series QX70/71/72.

it is important to note here, mitsubishi and SIEMENS about 'source input' and 'input' leakage circuit division on the contrary, the above is according to the division of mitsubishi method to introduce.

external switch signal input circuit connection and PLC and PLC controller

external input signal, in addition to like button some dry node signal, now some sensors provide NPN and PNP open collector output signal. Stem nodes and PLC input module connection is simpler. For the different PLC input circuit, what is the use of input NPN and PNP input sometimes feel nothing laid a hand on him.

here mainly introduce the two input and PLC input circuit connection. As shown in the figure below, respectively is a form of NPN and PNP output circuit

it can be seen that NPN open collector output circuit output OUT side through the switch tube and OV connection, when the motion sensor, switch tube in saturated conductivity, the OUT side and OV, same output OV low level signal; PNP open collector output circuit output OUT side by high level signal switch tube and + V.

NPN and PNP output circuit and PLC input module connected NPN open collector output

analysis by above knowable, NPN open collector output for OV, when output OUT side and connected to the PLC input, current flowing from the input end of the PLC, the PLC into public end, this is the PLC type leakage circuit form, namely: type NPN open collector output can only pick up leak or hybrid input circuit forms of PLC, connection diagram as shown in the figure below

PNP open collector output

for + V high level, when the output OUT side and connected to the PLC input current flow from the input end of the PLC, carry OUT from PLC of the public, this is the PLC type leakage circuit form, i. e. , the PNP type open collector output can only meet the source or hybrid input circuit forms of PLC, connection diagram as shown in the figure below

it is because the PLC input module circuit and external sensor output signal is diversity in form, we in the PLC input module before wiring to fully understand the type of PLC input circuit and sensor output signal of the form, only in this way, can ensure that the PLC input module connection is correct, to prepare for the back of the PLC programming and debugging.

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