9 PLC programming program debugging and result analysis

8. Sequential start-up control of blowers and induced draft fans

I/O Allocation Table

Ladder Diagram Programming

PLC Wiring Diagram

▲Program monitoring diagram when PLC is powered on, blue indicates connection

Program debugging and result analysis

The characteristic of Sm0.1 is that it is connected in the first cycle of the scan and not connected afterwards. When i0.0f on the online control panel is pressed, i0.0 is connected, and at this time Q0.0 is connected to output (i.e. indicator light Q0.0 is on), the induced draft fan starts, and at the same time timer T37 is connected and starts timing. When the timer counts to 50 (i.e. indicator light Q0.1 is on), the blower starts. At this time, both fans are running. When I0.1f on the online control panel is pressed, I0.1 is connected, and the blower stops running (i.e. indicator light Q0.1 is off). At the same time, timer T38 is connected and starts timing. After 5s of timing, the induced draft fan stops running. (i.e. indicator light Q0.0 is off).

9. Liquid Mixing

Use S7-200 to realize automatic control of liquid mixing. When the start button is pressed, liquid valve A opens and liquid A flows into the mixer. When the liquid level reaches the middle limit, valve A closes and liquid valve B opens at the same time, and liquid B flows into the mixer. When the liquid level reaches the upper limit, valve B closes and the motor is started for stirring. After stirring for one minute, the motor stops and valve C opens, and the mixed liquid flows out. When the liquid level reaches the lower limit, the container is emptied after another 5S, and valve C is closed. At the same time, valve A is opened and liquid A is injected. This cycle repeats periodically. If the stop button is pressed, it must wait for a cycle to complete before stopping.

I/O Allocation Table

Ladder Diagram Programming

PLC Wiring Diagram

Program debugging and result analysis

When I0.03f on the online control panel is pressed (I0.3 is closed), valve A opens (Q0.0 is on), when I0.0f on the online control panel is pressed (I0.0 is closed in the middle limit), valve A closes, valve B opens (Q0.0 is off, Q0.1 is on), when I0.1f on the online control panel is pressed (I0.1 is closed in the upper limit), valve B closes, the motor starts to stir (Q0.1 is off, Q0.2 is on), and timer T37 starts timing for one minute. After one minute, the mixer stops stirring, valve C opens (Q0.2 is off, Q0.3 is on), and when the liquid level reaches the lower limit, valve C continues to open (Q0.3 is on), and timer T38 starts timing. After 5s, valve C closes. Valve A opens (Q0.3 is off, Q0.0 is on), and enters the next cycle. Press I0.4f on the online control panel (that is, I0.4 is closed, which means stop). The system will not stop immediately, but will stop after running a cycle.