Undergraduate Technology Lab Course • ELET 285
ELET 285: Process Control & Instrumentation
An applied laboratory curriculum exploring industrial relay logic, electromechanical actuators, timers, level and flow dynamics, and the critical engineering transition from open-loop timed sequence control to closed-loop sensor-regulated feedback systems.
Interactive Simulation Laboratories
Select a laboratory below to launch the drag-and-drop relay logic matrix, animate tank hydraulics, and test industrial control strategies:
Laboratory 1
Open-Loop Tank Level Control via Relay Timer
Investigate timed sequence process control without feedback. Construct a 3-wire Start/Stop seal-in latch and an On-Delay Timer (TON) circuit to meter fluid into a 10-gallon tank. Test the system under nominal conditions, unmetered downstream leaks, and residual starting volumes.
- Control Strategy: Timed fill sequence ($t = \text{Target Volume} / Q$)
- Relay Instructions: N.O. Pushbuttons, N.C. Pushbuttons, Relays (CR1), On-Delay Timers (T1:TON)
- Lab Experiments: Calibration run, load disturbance underfill, and pre-fill overflow hazard
Laboratory 2
Closed-Loop Level Control via High-Level Switch (LSH-1)
Transition to true closed-loop negative feedback. Replace the blind timer with a discrete float switch (LSH-1) mounted at the 75% cutoff mark (7.5 Gallons). Verify how sensor feedback completely overcomes supply pressure surges and leaky drain valves.
- Control Strategy: Sensor feedback cutoff & Tank Full panel indication
- Field Devices: Float switch (LSH-1 at 75%), Pilot Lamp (PL-1), Solenoid Valve (SOL-1)
- Lab Experiments: Nominal closed-loop cutoff, supply pressure disturbance, and leak rejection
Comparative Analysis: Open-Loop vs. Closed-Loop Level Control
Compare key operational and safety metrics between the two control schemes investigated across Lab 1 and Lab 2:
| Metric / Parameter | Lab 1: Open-Loop (Relay Timer) | Lab 2: Closed-Loop (LSH-1 Switch) |
|---|---|---|
| Feedback Mechanism | None (Operates blindly on time $t$) | Direct process sensor (Float switch LSH-1 at 75%) |
| Fill Cutoff Trigger | Timer reaches Preset value (T1_DN = 1) |
Liquid contacts sensor float (LSH1 = 1) |
| Supply Pressure Variation | Fails: results in underfill or overflow | Compensated: fill time adjusts; level is exact |
| Discharge Leak Disturbance | Fails: level falls short proportional to leak | Compensated: continues fill until level hits 7.5 Gal |
| Residual Starting Level ($V_0 > 0$) | Hazardous: tank overflows and spills liquid | Safe: shuts off immediately upon reaching 7.5 Gal |
| Instrumentation Cost | Lower initial cost (No vessel penetrations) | Requires level sensor mount, wiring, calibration |
| Typical Industrial Role | Batch metering when fluid source is tightly regulated | Critical level regulation, high-level spill prevention |
Relay Ladder Logic Implementation Details
Compare the schematic structure of the open-loop timer circuit with the closed-loop level switch circuit:
Rung 000: 3-Wire Seal-In Control (Both Labs)
The momentary green Start button (PB1_START, N.O.) is wired in parallel with an auxiliary contact from control relay CR1. When Start is pressed, CR1 energizes and latches itself ON through the seal-in branch.
Fail-Safe Stop Button: Physical stop pushbuttons use Normally Closed (N.C.) contacts. In software ladder logic, a Normally Closed instruction (--[/]--) evaluates to True when unpressed, and opens when the button is hit, breaking the rung and dropping the latch.
Lab 1 vs. Lab 2 Output Interlocks
Lab 1 (Timer Cutoff): The solenoid valve SOL1_VALVE is energized through CR1 and a Normally Closed contact addressed to T1_DN. When the preset timer elapses, the contact opens, terminating flow regardless of liquid position.
Lab 2 (Sensor Cutoff): SOL1_VALVE is energized through CR1 and a Normally Closed contact addressed to LSH1. Power is cut only when fluid physically tilts the float. A parallel Normally Open contact triggers the PL1_FULL indicator lamp.