Module 23 – Instrumentation & Control Systems

Objective:
By the end of this module, a trainee will be able to:

1. Understand basic instrumentation types used in petrochemical plants.

2. Recognize common control loops and their purposes.

3. Understand operator interaction with DCS (Distributed Control System) or PLC (Programmable Logic Controller).

4. Monitor alarms, trends, and process variables effectively.

5. Apply basic troubleshooting for instrumentation and control issues.

23.1 – Introduction to Instrumentation & Control Systems

Definition:

• Instrumentation = devices that measure, monitor, and transmit process variables such as temperature, pressure, flow, and level.

• Control Systems = automated systems that regulate process variables to maintain desired operating conditions.

Importance:

• Ensures process stability, safety, and product quality.

• Allows operators to monitor processes remotely.

• Provides alarms and interlocks to prevent abnormal conditions.

Operator Role:

• Monitor readings, trends, and alarms on control panels.

• Respond to abnormal signals or equipment status.

• Communicate with maintenance if instruments show abnormal behavior.

Analogy:

• Instrumentation = “sensors on a car (speedometer, fuel gauge, temperature gauge).”

• Control system = “cruise control maintaining speed automatically.”

23.2 – Common Types of Instrumentation

• Temperature Transmitter (TT)

Measures process temperature

Monitor trends, check calibration if readings abnormal

• Pressure Transmitter (PT)

Measures pressure

Verify against gauges, alarm on deviation

• Flow Meter (FT)

Measures liquid or gas flow

Ensure flow within process limits

• Level Transmitter (LT)

Measures liquid level in tanks/columns

Monitor high/low alarms, maintain level control

• Valve Positioner (PV)

Shows valve opening

Ensure valve responds to control signal

• Gas Detector

Detects toxic/flammable gases

Respond to alarm, ensure safety

• pH/Conductivity Sensor

Measures chemical properties

Monitor trends, prevent off-spec product

Operator Tips:

• Regularly check sensor readings vs expected values.

• Report abnormal trends, faulty instruments, or alarms.

• Never adjust calibration unless trained and authorized.

23.3 – Control Loops & Process Regulation

Definition:

• Control Loop = a system that measures a process variable and adjusts output to maintain setpoint.

Types of Loops:

1. ON/OFF Control – simplest, turns equipment fully on or off based on setpoint.

2. PID Control (Proportional-Integral-Derivative) – continuously adjusts output to maintain setpoint.

3. Cascade Control – one loop controls another loop for more precise control.

4. Feedforward Control – anticipates changes based on measured disturbances.

Operator Role:

• Monitor setpoints, control response, and loop performance.

• Detect loop oscillations, slow response, or saturation.

• Notify maintenance if control issues persist.

Analogy:

• PID control = “thermostat adjusting heater output to maintain room temperature.”

23.4 – DCS / PLC Overview

DCS (Distributed Control System):

• Centralized monitoring with operator stations, controllers, and field devices.

• Ideal for continuous processes like butadiene plants.

PLC (Programmable Logic Controller):

• Focused on discrete control of equipment like pumps, compressors, and valves.

Operator Role:

• Observe process variables and alarms on screens.

• Execute manual actions if automated systems cannot resolve abnormal conditions.

• Follow SOPs for start/stop, interlock override, or ESD activation.

Analogy:

• DCS = “central dashboard of a city traffic control system.”

• PLC = “traffic light controller at a single intersection.”

23.5 – Alarm Management

Definition:

• Alarm = alert indicating process variable is outside normal range.

Types of Alarms:

1. High/Low Process Variable – e.g., temperature, pressure, level.

2. Equipment Status – pump failure, compressor trip.

3. Safety/ESD Alarm – fire, gas, or critical overpressure.

Operator Role:

• Acknowledge alarms according to SOP.

• Investigate cause promptly.

• Take corrective action or notify maintenance.

• Avoid ignoring recurring alarms (“alarm fatigue”).

23.6 – Basic Instrumentation Troubleshooting

• Sensor reading stuck

Faulty transmitter, broken wiring

Verify with backup instrument, notify maintenance

• Alarm triggered but process normal

Sensor calibration drift, false alarm

Confirm with secondary measurement, report

• Valve not responding

Actuator issue, control signal lost

Check manual operation, verify control signal, notify maintenance

• Flow reading zero

Blocked line, sensor fault

Inspect line, compare with other measurements, notify maintenance

Operator Tips:

• Always cross-check with secondary instruments or visual inspection.

• Never bypass alarms without proper authorization.

• Document all troubleshooting actions.

23.7 – Quiz / Knowledge Check

1. Name four common types of process instrumentation.

2. What is a PID control loop and why is it important?

3. How does an operator respond to a high-pressure alarm?

4. What is the difference between DCS and PLC?

5. Why is alarm management important?

6. Give an analogy for instrumentation and control systems.

23.8 – Media Sites Integration

• Videos:

  • Operator interaction with DCS/PLC

  • Control loop demonstration (ON/OFF, PID)

  • Alarm response simulation

• Diagrams / Infographics:

  • Process instrumentation layout

  • Control loop schematic

  • Alarm priority flowchart

• PDF Downloads:

  • Instrumentation checklist

  • Control loop monitoring guide

  • Alarm response guide

• Interactive:

  • Embedded quizzes

  • Scenario exercises: detect abnormal variable and take action

23.9 – Summary & Key Takeaways

1. Instrumentation measures key process variables; control systems maintain setpoints.

2. Operators monitor DCS/PLC, alarms, and trends continuously.

3. Control loops (ON/OFF, PID, cascade, feedforward) regulate process performance.

4. Alarm management ensures timely response to abnormal conditions.

5. Troubleshooting instrumentation requires cross-checking readings, following SOPs, and communication with maintenance.