Module 15 – Instrumentation & Control

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

1. Understand the purpose of instrumentation in a petrochemical plant.

2. Identify common types of process instruments.

3. Understand basic control loop concepts.

4. Recognize alarm systems and their importance.

5. Understand operator interface with DCS/PLC and panel systems.

15.1 – Introduction to Instrumentation & Control

Definition:

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

• Control = maintaining process variables at desired values to ensure safe and efficient operation.

Importance:

• Ensures product quality, safety, and energy efficiency.

• Helps operators monitor and respond to abnormal conditions.

Operator Role:

• Monitor instruments and alarms.

• Make adjustments according to SOPs.

• Report faulty instruments or abnormal readings.

Analogy:

• Instruments = “sensors in a smart home”

• Control = “thermostat maintaining room temperature”

15.2 – Common Process Instruments

• Pressure Transmitter (PT)

Measures pressure in vessel/pipeline

Check readings, report drift or abnormal pressure

• Temperature Transmitter (TT)

Measures temperature

Monitor trends, alarm responses

• Flow Transmitter (FT)

Measures flow rate of feed/product

Detect low/high flow conditions

• Level Transmitter (LT)

Measures liquid level in tank/column

Prevent overfill or dry running

• Analytical Instruments

Measures composition, moisture, impurities

Supports product quality monitoring

• Control Valves

Regulates flow, pressure, temperature

Adjust as per controller or manual SOP

• Safety Interlocks

Triggers shutdown or alarms

Do not bypass; monitor status

Operator Tips:

• Regularly check readings and trends.

• Report any abnormal drift or sensor malfunction.

• Understand the connection between measurement and process effect.

15.3 – Control Loops (Conceptual)

Definition:

• Control loop = measurement → controller → final control element → process variable

Types of Control:

1. On/Off Control – Simple, switches equipment fully on or off.

   • Example: Tank level switch activating pump.

2. PID Control – Proportional-Integral-Derivative control, maintains variable at setpoint smoothly.

   • Example: Reactor temperature control using heater or cooling water.

3. Feedforward / Cascade Control – Uses upstream measurements to predict and adjust downstream variables.

Operator Role:

• Monitor loop performance and trends.

• Adjust setpoints when authorized.

• Notify control room of abnormal behavior.

Analogy:

• Control loop = “thermostat controlling home temperature using heater and temperature sensor feedback.”

15.4 – Alarm Systems

Purpose:

• Alert operators to abnormal conditions before they become unsafe or cause off-spec product.

Alarm Categories (Conceptual):

1. High / Low – Simple threshold alarms (e.g., high pressure).

2. Deviation / Rate-of-Change – Detect rapid changes in process variable.

3. Critical / Safety – Triggers ESD or emergency action.

Operator Tips:

• Respond promptly to alarms.

• Follow SOP for acknowledgment and corrective action.

• Do not silence alarms without investigation.

Analogy:

• Alarms = “smoke detector or car dashboard warning lights”

15.5 – DCS & PLC Concepts

DCS (Distributed Control System):

• Centralized monitoring and control for large, continuous processes.

• Allows operators to view trends, alarms, loops, and setpoints.

PLC (Programmable Logic Controller):

• Often used for discrete operations, sequences, and interlocks.

• Integrates with DCS or standalone panel control.

Operator Role:

• Monitor DCS/PLC screens.

• Adjust setpoints within authorized range.

• Follow control sequences for startup/shutdown.

• Escalate alarms or abnormal conditions.

Analogy:

• DCS = “central dashboard of a smart home controlling temperature, lights, and security”

• PLC = “smart switches for specific equipment like pumps or motors”

15.6 – Operator Interface & Panel Interaction

Key Operator Tasks:

1. Read instruments and check trends.

2. Respond to alarms with SOP guidance.

3. Adjust manual valves or setpoints as required.

4. Record observations in logbooks or digital records.

5. Communicate with control room, maintenance, and lab teams.

Analogy:

• Operator panel = “cockpit of an airplane”

15.7 – Conceptual Troubleshooting of Control Loops

Common Issues:

1. Sensor drift → incorrect measurement → wrong control action

2. Control valve stuck → flow or temperature deviation

3. Setpoint misalignment → off-spec product

4. Alarm flood → operator confusion

Operator Approach:

• Verify instrument reading vs field reality

• Check loop status and trends

• Adjust manually if safe and authorized

• Notify maintenance for corrective action

15.8 – Quiz / Knowledge Check

1. Name three types of process instruments and their function.

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

3. Why are alarms critical for operators?

4. What is the difference between DCS and PLC?

5. Give an analogy for instrumentation and control.

6. What should an operator do if a control valve is not responding?

15.9 – Media Sites Integration

• Videos:

  • PID loop concept animation

  • DCS and PLC panel walkthrough

  • Alarm response demonstration

• Diagrams / Infographics:

  • Control loop schematic

  • Instrument locations on process units

  • Alarm hierarchy diagram

• PDF Downloads:

  • Instrumentation checklist

  • Control loop monitoring template

  • Alarm response guide

• Interactive:

  • Embedded quizzes

  • Scenario exercises: respond to abnormal readings

15.10 – Summary & Key Takeaways

1. Instrumentation measures process variables; control maintains them at setpoints.

2. Operators monitor instruments, trends, and alarms to maintain safe and efficient operation.

3. PID, feedforward, and cascade loops are common in petrochemical plants.

4. DCS provides centralized control; PLC handles discrete or interlock functions.

5. Proper panel interaction, troubleshooting, and communication are essential for operator effectiveness.