Proportional Valve — Level Error

Briefing

This scenario introduces the concept behind PID control without requiring you to configure a PID block. A fill valve feeds a tank that is continuously drained by a downstream process. Your goal is to hold the tank level near the **50% setpoint** using a simple proportional strategy: **Valve output % = Kp × (Setpoint − Level %)** where Kp = 1.5. When the level is 30% (20% below setpoint), the valve opens to 30%. When the level reaches 47% (3% below setpoint), the valve is at only 4.5% — barely open. When the level exceeds 53% the valve output goes negative — meaning it should close. The physics engine computes this and publishes: - **VALVE_OPEN_ZONE** — proportional output > 10%: open the fill valve - **VALVE_CLOSE_ZONE** — proportional output < 5%: close the fill valve - **SENSOR_FAULT** — level sensor out of valid 4–20 mA range You are implementing a *bang-bang on a proportional zone*: FILL_VALVE open when proportional demand is high, closed when demand is low. This is the conceptual building block for understanding why a PID controller exists and why you need integral action to eliminate steady-state error.

Objectives

• Latch RUN_BIT on START, reset on STOP
• FILL_VALVE latches ON (S=) when RUN_BIT AND VALVE_OPEN_ZONE
• FILL_VALVE latches OFF (R=) when VALVE_CLOSE_ZONE or SENSOR_FAULT or STOP
• FAULT_LAMP mirrors SENSOR_FAULT

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1Level below setpoint (30%) → FILL_VALVE opens on START

   LT_RAW = 3000 (30%) → error = 20%, valve_pct = 30% → VALVE_OPEN_ZONE true → FILL_VALVE latches on

2. #2Level near setpoint (50%) → FILL_VALVE closes (VALVE_CLOSE_ZONE)

   LT_RAW = 5000 (50%) → error = 0%, valve_pct = 0% → VALVE_CLOSE_ZONE true → FILL_VALVE resets

3. #3Sensor fault (LT_RAW < 500) → FILL_VALVE closes, FAULT_LAMP on

   Out-of-range sensor reading trips SENSOR_FAULT, which resets the valve and lights the fault lamp

4. #4STOP immediately closes FILL_VALVE

   Valve is open; pressing STOP resets it within one scan