D. N. Yadav (Copyright Protected)
Basics of Process Instrumentation DI03005011 SEM: III
Unit No.
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Unit – I
Introduction to
Process
Instrumentatio
n
1.1 Importance of instrumentation in chemical plant
1.2 Classification of instruments
1.3 Basic elements of instruments
1.4 Static and dynamic characteristics
1.5 Selection criteria for various measuring devices
in chemical industry for:
1.5.1 Temperature
1.5.2 Pressure
1.5.3 Level
1.5.4 Flow
1.6 Calibration of Instrumentation
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1.1 Instrumentation in Chemical Plant
In the context of the chemical industry, instrumentation refers to the art and science of
measuring and controlling process variables. These variables include, but are not limited to,
temperature, pressure, flow rate, level, pH, and composition. It comprises designing,
selection, installation, operation, and maintenance of devices and systems used to gather
information about a process and manipulate it to achieve desired outcomes. Think of it as
the "eyes and hands" of a chemical plant, providing vital information to operators and
automatically adjusting conditions to ensure safe and efficient operation.
Figure 1 Simple Instrument Model
Measurement
Prepared by: Dhaval N. Yadav
Lecturer in Chemical Engg. Dept. SKJP, Bharuch
D. N. Yadav (Copyright Protected)
Basics of Process Instrumentation DI03005011 SEM: III
Measurement is an essential activity in every branch of science and technology. It basically
means quantification of a parameter. A measuring instrument is a device that determines
the value of a quantity or a condition. It basically converts a physical or a chemical condition
(e.g. heat, pressure, light etc.) to a signal (generally electrical) which can be measured or
interpreted. Lord Kelvin famously stated, "To measure is to know," and "If you cannot
measure it, you cannot improve it". Thus, the fundamental purpose of measurement in
industrial manufacturing and processing is to obtain a numerical value corresponding to the
variable which is being measured so that we can determine and improve the quality of the
product or the efficiency of production.
Why is Instrumentation Needed?
The need for instrumentation in chemical plants stems from several critical factors:
● Safety: Chemical processes often involve hazardous materials, high temperatures,
and extreme pressures. Instrumentation allows for continuous monitoring of these
conditions, enabling early detection of deviations that could lead to accidents,
explosions, or environmental releases. Safety interlocks, triggered by instrument
readings, can automatically shut down equipment or activate emergency procedures.
● Quality Control: Maintaining product quality and consistency is paramount in the
chemical industry. Instrumentation ensures that raw materials are fed at precise
rates, reaction temperatures are held within narrow limits, and final products meet
specifications. This leads to reduced waste, improved product yield, and customer
satisfaction.
● Process Optimization and Efficiency: By accurately measuring process variables,
engineers can analyse plant performance, identify and optimize operating conditions
for maximum efficiency. This leads to lower energy consumption, reduced raw
material usage, and increased production rates, which ultimately increases the
profitability of a plant.
● Environmental Protection: Many chemical processes generate waste products or
emissions that need to be carefully controlled. Instrumentation plays a crucial role in
monitoring and regulating these outputs to comply with environmental rules and
regulations to minimize ecological impact.
Prepared by: Dhaval N. Yadav
Lecturer in Chemical Engg. Dept. SKJP, Bharuch
D. N. Yadav (Copyright Protected)
Basics of Process Instrumentation DI03005011 SEM: III
● Economic Viability: Ultimately, effective instrumentation contributes directly to the
economic viability of a chemical plant. By enhancing safety, improving quality,
optimizing efficiency, and ensuring environmental compliance, instrumentation helps
plants operate profitably and sustainably.
● Troubleshooting and Diagnostics: When something goes wrong in a chemical plant,
instrumentation provides the data necessary to diagnose the problem quickly and
accurately. Historical trends and real-time readings help operators and engineers
pinpoint the root cause of issues, minimizing downtime and production losses.
1.2 Classification of Instruments
Instruments used in process industries can be categorized in several ways, helping us
understand their fundamental operation and application. The primary classification bases
often include their energy requirements, the nature of their output signal, and their
interaction with the measured medium.
1.2.1 Classification by Energy Consideration: Passive vs. Active Instruments
This classification is based on whether the instrument requires an auxiliary power source to
generate its output signal.
Passive Instruments:
These instruments do not require an external power supply. Their output energy is derived
solely, or almost entirely, from the energy of the input signal or the process itself.
They are often referred to as "self-operated" instruments. The input signal might be directly
converted into a readable output, or there might be an energy conversion within the
instrument without external aid.
Prepared by: Dhaval N. Yadav
Lecturer in Chemical Engg. Dept. SKJP, Bharuch
End of Document
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