Process of change from the traditional electrical diagram for the ladder diagram, introduction to programming -

PLC program design, generally adopt the intuitive method, that is to say, it based on the learning experience of circuit designers itself, a more subjective and directly. Must experience a touch like the blind trial and error, tryanderror) Period, after debugging the software to conform to the requirements of the required function or action; Therefore designed programs vary from person to person, in addition to the original programmer, user or maintenance personnel is not easy to understand its action process, i. e. the readability of the program is low. There are some rich vein, but programming books rarely mentioned that this part of the only anecdotal. Here let's just holding the savage light mood, to 'three phase induction motor fault warning control circuit as an example, the process of change from the traditional electrical diagram for the ladder diagram, introduction to programming, believe that later for the relevant circuit transformation or programming, you or licensed instance.

1, the traditional electrical figure

known three-phase induction motor fault alarm control circuit, the traditional electrical diagram, as shown in figure 1. Figure 1

three-phase induction motor fault warning control circuit diagram 2,

action

1. When the power supply is normal, only green light gl, motor action.

2。 Press the start button pb1, electromagnetic contactor MC movement, the motor running, immediately indicator rl on, green light gl quenched.

3。 Press the stop button pb2, electromagnetic contactor MC blackouts, motor to stop operation, light rl, green light gl.

4。 Motor in operation, due to overload or other failure reason, the thermoelectric yi th - deposition Ry action, motor to stop operation, the alarm buzzer bz, indicator light rl, green light gl.

5。 Press the button switch pb3, buzzer bz stop alarm, white light wl on, green light gl, red light rl quenched.

6。 After troubleshooting, press the thermoelectric yi th - Ry reset lever, the white light wl, green light gl, rl extinguish a red light, can again starting motor.

using PLC, is to software instead of hardware wiring. Traditional electrical diagram, main circuit is PLC cannot be replaced; PLC can replace part of the control circuit. From the traditional electrical diagram transformation for the first steps of the ladder diagram, is I/o coding, also is the traditional electrical diagram of the input/output component, first determine its proposed in PLC corresponding external input/output terminal number, as well as the external input component connection mode is to use a/b contact, as shown in table 1.

( a) : external pick a contact way connection

b) : external mining contact output connection

4 b, outer wiring diagram of PLC

input/output component by the I/o coding, and external input component is adopted after a/b contact connection mode, external wiring diagram of PLC is shown in figure 2. As shown in figure vigor vigor - Vb series PLC model, USES the NPN wiring, 24 v terminals and s/s terminals and pick up.

external figure 2 PLC wiring diagram 5, PLC ladder diagram

from the traditional electrical diagram into the program design step of ladder diagram is as follows:

1) The control circuit in the electrical diagram directly into the corresponding ladder diagram. Because the PLC controller ladder diagram, contact before, and the output coil must be located at the end of the loop. Therefore, first of all should be drawn to electrical diagram, will figure in contact with the output coil position moderate changes, to meet the requirements of the PLC ladder diagram, redrawn after electrical diagram, as shown in figure 3.

redraw figure 3 after the electrical diagram (

2) In the I/o code after the number of components, instead of the electrical diagram of the input/output component, is here to take care of that, th - C - ry A contact and c - B contact to independence, each became a control loop, as shown in figure 4.

figure 4 I/o code after electrical diagram (

3) The electrical diagram shown in figure 4, rotate 90 ° to the left, then flip vertical ( 颠倒) , can become a PLC ladder diagram, but due to:

1) Y1, x0 contact,

2) Y1 and y2, output coil is not in conformity with the general programming software format, so must be moderate correction, as shown in figure 5 to the right.

the revised figure 5 moderately flip and ladder diagram of

does if you use visio to map the electrician, turn 90 ° to the left, then flip vertical, becomes very easy.

( 4) Used to draw the ladder diagram programming software, as shown in figure 6, with moderate revised flip and ladder diagram, is exactly the same.

figure 6 programming software to draw the ladder diagram of

6, instructions converts ladder diagram to instruction, are as follows:

7, PLC controller transformation and ladder diagram

traditional electrical wiring diagram of PLC after complete conversion external input/output wiring and ladder diagram. After using software program to replace the hardware wiring of PLC external input/output wiring and ladder diagram, as shown in figure 7 below.

figure 7 to replace hardware wiring of PLC software program

8, conclusion

PLC the research purpose is to replace the order is given priority to with relay control, i. e. using software program to replace the hardware wiring, so as to change the software can change the control sequence, and easily the different requirements of control can be achieved. General PLC is developed on the basis of the traditional relay control circuit, and the relay contact and coil to be symbolic, when converted into general ladder diagram or instructions, the control can be realized. Control loop, but this has done is based on the learning experience of circuit designers itself, a more subjective and directly, and ordinary users is often difficult to understand its action process, i. e. the readability of the program is low.

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