The most popular beginners must see the connection

2022-07-30
  • Detail

Beginners must see the connection mode between PLC and these 7 devices

Abstract: the common input devices of PLC include buttons, travel switches, proximity switches, transfer switches, code dialers, various sensors, etc., and the output devices include relays, contactors, solenoid valves, etc. Correctly connecting input and output circuits is the premise to ensure the safe and reliable operation of PLC

plc common input devices include buttons, travel switches, proximity switches, transfer switches, code dialers, various sensors, etc., and output devices include relays, contactors, solenoid valves, etc. Correctly connecting input and output circuits is the premise to ensure the safe and reliable operation of PLC

1. The project has obtained 12 authorized invention patents. The connection between PLC and master electrical equipment

Figure 1 is the wiring diagram of master electrical input equipment such as buttons, travel switches and transfer switches. The PLC in the figure is a DC sink input, that is, all input points share a common terminal com, and the com terminal has a DC24V power supply. For grouping input, you can also refer to the method of more than 90million tons in the figure below for grouping connection

as shown in Figure 1 below, the connection between PLC and master electrical input equipment

2, the connection between PLC and rotary encoder

rotary encoder is a photoelectric rotary measuring device, which directly converts the measured angular displacement into digital signal (high-speed pulse signal). Because the output pulse signal of rotary encoder can be directly input to PLC, the high-speed counter of PLC is used to count the pulse signal to obtain the measurement result. Different types of rotary encoders have different phase numbers of output pulses. Some rotary encoders output three-phase pulses of a, B and Z, some only have two phases of a and B, and the simplest is only phase a

see Figure 2 below for the connection between rotary encoder and PLC

see Figure 2 for the connection diagram between rotary encoder outputting two-phase pulse and FX series PLC. The encoder has 4 leads, including 2 pulse output lines, 1 com terminal line and 1 power line. The power supply of encoder can be external power supply or DC24V power supply of PLC. The "-" end of the power supply shall be connected with the com end of the encoder, and the "+" end shall be connected with the power end of the encoder. The com end of the coder is connected with the PLC input com end, and the A and B two-phase pulse output lines are directly connected with the PLC input end. Pay attention to the response time of the PLC input when connecting. Some rotary encoders also have a shield wire, which should be grounded when used

3. Connection between PLC and sensor

there are many kinds of sensors, and their output modes are also different. When two-wire sensors such as proximity switches and photoelectric switches are used, due to the large leakage current of the sensor, wrong input signals may occur, resulting in the misoperation of the PLC. At this time, the bypass resistance R can be connected in parallel at the PLC input end, as shown in Figure 3. When the leakage current is less than LMA, its influence may not be considered

as shown in Figure 3 below, the connection between PLC and two-wire sensor

where: I is the leakage current (MA) of the sensor, uoff is the upper limit value (V) of PLC input voltage low level, RC is the input impedance (K Ω) of PLC, and the value of RC varies according to different input points

4. Connection between PLC and multi position dial switch

if some data in PLC control system needs to be modified frequently, multi position dial switch can be used to connect with PLC and set data outside PLC. As shown in Figure 4, it is the schematic diagram of a one digit dial switch, which can input 0-9 of a decimal number or 0-F of a hexadecimal number

as shown in Figure 4, the schematic diagram of one position dial switch

as shown in Figure 5, the four position dial switches are assembled together to connect the com terminals of each dial switch to the com terminal on the PLC input side. The four data lines of each dial switch are connected to the four input points of PLC in a certain order. It can be seen from the figure that the use of dial switches takes up many PLC input points, so this method is generally not used for occasions that are not very necessary

as shown in the following figure 5, the connection between the 4-bit dial switch and the PLC

5, the connection between the PLC and the output device switch

. Group connection is determined according to the type and level of output equipment voltage. As shown in Figure 6, take FX2N as an example to illustrate the connection method between PLC and output equipment. The connection method in the figure refers to the case that the output equipment has the same power supply, so the common terminals of each group are connected together, otherwise, they should be connected in groups. Only the connection between y0-y7 output points and output equipment is shown in the figure, and the connection methods of other output points are similar

as shown in Figure 6 below, the connection between PLC and output equipment

6, the connection between PLC and inductive load

the output end of PLC is often connected with inductive output equipment (inductive load). In order to suppress the voltage generated when the inductive circuit is disconnected, the internal output components of PLC are damaged. Therefore, when PLC is connected with inductive output equipment, if it is a DC inductive load, freewheeling diodes shall be connected in parallel at both ends; In case of AC inductive load, the resistance capacitance absorption circuit shall be connected in parallel at both ends. As shown in the figure

as shown in Figure 7 below, the connection between PLC and inductive output equipment

in the figure, the freewheeling diode can be selected with a rated current of 1a and a rated voltage greater than 3 times the power supply voltage; The resistance value can be taken as 50-120 Ω, and the capacitance value can be taken as 0.1-0.47 μ F. The rated voltage of the capacitor shall be greater than the peak voltage of the power supply. Pay attention to the polarity of freewheeling diode when wiring

7. Connection between PLC and Seven Segment LED display

plc can directly use switching value output to connect with Seven Segment LED display, but if PLC controls multi bit led seven segment display, there are many output points required

as shown in Figure 8 below, the error between PLC and two digit manual measurement is very large: the connection of its Seven Segment LED light display is shown in Figure 8. In the circuit, the chip cd4513 with locking, decoding and driving functions is used to drive the common cathode led seven segment display. The data input terminals A-D of the two cd4513 share the four outputs of PLC, of which a is the lowest and D is the highest. Le is the latch enable input. On the rising edge of the Le signal, the BCD number input from the data input is locked in the on-chip register, and the number is decoded and displayed. If a decimal number is not entered, the display turns off. Le is high level, and the displayed number is not affected by the data input signal. Obviously, the number of output points occupied by N displays is p=4 + n

if the PLC uses relay output module, a pull-down resistor shall be connected to each output terminal of the PLC connected to cd4513 to prevent the input terminal of cd4513 from hanging when the contact of the output relay is disconnected. When the status of PLC output relay changes, its contact may shake, so it is necessary to send data output signal first, and then lock the data into cd4513 with the rising edge of Le signal after the signal is stable

Copyright © 2011 JIN SHI