VIPSolutionsGive step-by-step solution with explanation and final answer: f) Start (NO) and stop (NC) push button switches are used to control a process. Show the M340 PLC program using sequential function chart that will indicate whether the system should remain ON or should shut down (turn OFF). When start switch is pressed, variable started should become true and when stop switch is pressed the variable stopped should become true. Clearly show the transition conditions and the action commands for each of the steps. [5 marks]
Question:
Give step-by-step solution with explanation and final answer: f) Start (NO) and stop (NC) push button switches are used to control a process. Show the M340 PLC program using sequential function chart that will indicate whether the system should remain ON or should shut down (turn OFF). When start switch is pressed, variable started should become true and when stop switch is pressed the variable stopped should become true. Clearly show the transition conditions and the action commands for each of the steps. [5 marks]
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Asked by: aj
Created at: 2025-05-28 07:55:36
Asked by: aj
Created at: 2025-05-28 07:55:36
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Let's break down the problem and provide a step-by-step solution with an annotated Sequential Function Chart (SFC) for a Schneider M340 PLC.
### **Problem Recap**
- **Start** (NO) and **Stop** (NC) pushbuttons control a process.
- **Variables:**
- `started`: TRUE when process started
- `stopped`: TRUE when process stopped
- Requirement:
- When **Start** is pressed, `started := TRUE`
- When **Stop** is pressed, `stopped := TRUE`
- Show:
- SFC steps, transitions, actions, and transition conditions.
---
## **1. Define Inputs and Variables**
- **Inputs:**
- `Start_PB` (Start PushButton, Normally Open, active when pressed)
- `Stop_PB` (Stop PushButton, Normally Closed, active when NOT pressed)
- *Note: NC means, input is TRUE when button is NOT pressed. Pressing it makes input FALSE.*
- **Memory Variables:**
- `started` (BOOL)
- `stopped` (BOOL)
---
## **2. SFC Steps and Overview**
We need **two main steps**:
1. **Stopped (Idle) Step**
2. **Started (Running) Step**
### **Transitions:**
- From **Stopped** to **Started**: When Start_PB is pressed (TRUE)
- From **Started** to **Stopped**: When Stop_PB is pressed (FALSE, since NC)
---
## **3. SFC Diagram**
```
+-------------------+ Start_PB +-------------------+
| |---------------------> | |
| Stopped | | Started |
| | <---------------------| |
+-------------------+ Stop_PB = FALSE +-------------------+
```
---
## **4. SFC Steps, Transitions, and Actions**
### **Step 1: Stopped**
- **Actions:**
- `started := FALSE`
- `stopped := TRUE`
- **Transition to Started:**
- Condition: `Start_PB = TRUE`
---
### **Step 2: Started**
- **Actions:**
- `started := TRUE`
- `stopped := FALSE`
- **Transition to Stopped:**
- Condition: `Stop_PB = FALSE` (*Pressed, since it's NC*)
---
## **5. SFC Table Summary**
| Step | Actions | Transition Condition | Next Step |
|-----------|------------------------------------------------|----------------------------|------------|
| Stopped | started := FALSE; stopped := TRUE; | Start_PB = TRUE | Started |
| Started | started := TRUE; stopped := FALSE; | Stop_PB = FALSE (pressed) | Stopped |
---
## **6. Step-by-Step SFC Solution**
### **Initial Step: Stopped**
- `started := FALSE`
- `stopped := TRUE`
- **Wait for**: `Start_PB = TRUE`
### **When Start_PB is pressed:**
- Transition to **Started** step.
### **Started Step:**
- `started := TRUE`
- `stopped := FALSE`
- **Wait for**: `Stop_PB = FALSE` (button pressed)
### **When Stop_PB is pressed:**
- Transition back to **Stopped** step.
---
## **7. SFC Code Example (Pseudo-code for M340)**
```sfc
// Step 1: Stopped
Step Stopped:
started := FALSE;
stopped := TRUE;
IF Start_PB = TRUE THEN
TRANSITION TO Started;
END_IF
// Step 2: Started
Step Started:
started := TRUE;
stopped := FALSE;
IF Stop_PB = FALSE THEN
TRANSITION TO Stopped;
END_IF
```
---
## **8. Final Answer Summary**
**In summary:**
- The M340 PLC SFC has two steps: **Stopped** and **Started**.
- **Transition from Stopped to Started** when Start_PB is pressed (TRUE).
- **Transition from Started to Stopped** when Stop_PB is pressed (input becomes FALSE due to NC).
- In each step, set the variables `started` and `stopped` accordingly.
---
### **Drawn SFC (Text Representation)**
```
[Stopped]--------------------(Start_PB=TRUE)-------------------->[Started]
| |
|<-------------------(Stop_PB=FALSE)----------------------------|
```
**Actions in Stopped:**
- started := FALSE
- stopped := TRUE
**Actions in Started:**
- started := TRUE
- stopped := FALSE
---
**This SFC program fulfills the requirements and will correctly indicate the system's ON/OFF state based on the pushbuttons.**
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