Wednesday, May 22, 2024

Instrumentation In Control System

Instrumentation System:

Instrumentation is an essential part of control and automation systems. It is considered a tool used to measure, monitor, and manage all the devices, sensors, actuators, and transducers that measure the process variables like temperature, flow, pressure, and levels. It helps in increasing productivity and improving product quality. in this article, we will discuss and explore all about the instrumentation.
 
Instrumentation System
Instrumentation System


What is the instrumentation system?


An instrumentation system is an accurate measuring system used in the control system engineering field for displaying, monitoring, and controlling the processes application and physical systems. You can find it at home, work, and office reaching to the space and space crafts. The instrumentation system configuration is shown in the next figure.

Sensors function
Sensors function


History of instrumentation:


For decays in order to measure a process parameter, they used the changing of the object volume or shape and displayed it on an attached scale like temperature or pressure. However, this type of measurement had many disadvantages like accuracy and reliability. 

By discovering and developing the measuring systems, the complete instrumentation systems are used and give a more easy and accurate system for monitoring and controlling any process value in both open and closed control systems.


What are the main components of the Instrumentation System?


Instrumentation System Component
Instrumentation system components

The main components of the Instrumentation system are:

Transducers.

 Transducers or sensors: as shown in the figure, the transducer or sensor has two stages of devices the first stage deals with the physical or process parameter while the second stage is the wires connected to the transmitter and carry the output signal of the transducer. Normally the output signal of the transducer is DC millivolts or DC volts.

Efficiency is an important consideration in any transducer. Sensor efficiency is defined as the ratio of the power output in the desired form to the total power input. Mathematically, if P represents the total power input and Q represents the power output in the desired form, then the efficiency E, as a ratio between 0 and 1, is given by:

E = Q/P and E% = 100Q/P

Where: E% represents the efficiency as a percentage.

Transmitters.

 that convert the output signal from the transducer to a standard electrical signal. It includes the electronic circuits and components. Normally the output standard signals for the transmitters are 0-20 mA or 4-20 mA. Some special transmitters output are 0-5 and 0-10 volts. 

The mA transmitters are used to avoid the voltage drop of the output signals. Also, the 4-20 mA is preferable to confirm the health of the transmitter at the 0 value of its input signal.

There are two types of transmitters, based on the number of wires at the transmitter output. One is 4 wires transmitters where 2 wires for power supply and another 2 wires for output signals. The other type is the 2-wire transmitter which has only 2 wires holding the supply for the loop and the measured current at the same time.

The conditioning stage.

The signal conditioning stage is the stage that formalizes and prepares the standard output signals from the transmitters to be suitable for the next phase of the process or to be synchronized with the used application based on the process. 

As the output signal of the transmitter is an analog signal, the signal conditioning stage included A/D (analog to digital converter) used with the DAQ (Data acquisition system). When the data is digitalized, it can be used easily through software and computers for logging, storing, and analyzing.

The signal conditioning module can also include isolation circuits, filtering circuits, amplification circuits, and converting circuits as well as range minimum and maximum range adjustment.

What are the examples of the Instrumentation systems?

The Instrumentation System is represented and used with most household or industrial application processes or mechanical. We can find it in the following controlling and monitoring applications:


How is the instrumentation system used in the control system?

In the control system, the transducer or sensor is attached to the output of the process and converts the process output parameter (temperature, pressure, level …) to an electrical signal proportional to that process value.

The type of the transducer and the type of the output signal are determined based on the type of the process. As the output signal of the transducer depends on the process type, its output signal is converted to a standard milliamps value representing the process output signal.
 
The output signal from the transmitters is processed depending on the uses of these signals sometimes used as it is in the analog input modules for the PLC (Programmable Logic Control) or connected to signal conditioning modules when the data will be used further than control.

In the modern control system, the data has many options like logged, stored, analyzed, and used in many reports which is why the signal conditioning modules that include DAC converters are used.

Why do we test and calibrate the instrumentation system?


As explained the instrumentation system deals with physical quantities like temperature and pressure, these physical and the device's surrounding parameters can affect and damage the components of the system over time or cause deviation in reading from the exact value.

The wrong readings of the instrumentation system led to the wrong action from the controller and as a result failure or risky operation of the process. The test is normally applied by injecting a well-known physical parameter or its equivalent electrical signal to the input of the device measuring the output of it and comparing it with the standard table for conversion.

If the deviation from the reference value is more than the predefined acceptance range, the device should be calibrated. The test of the devices may protect the devices from sudden failure by predicting the device's healthy condition.

What is the calibration and how is the calibration done for the instrumentation system?


The calibration is the resetting or adjusting of the device to ensure its accuracy and the measurement reliability of the system. The very simple calibration is the zero and span calibration which is done by applying the value equivalent to the minimum value representing the zero input and maximum value representing the span value then checking the output of the system by using a multimeter to measure the output mA value.

Depending on the type of the device, it could have a potentiometer that can be rotated to adjust the output until it reaches the 4 and 20 mA at the output of the transmitter for example. Some types of transmitters use a magnetic switch for adjusting while some of them use the calibrator or softwire for calibration. After the calibration was done, the system was checked at values of 0%, 25%, 50%, 75%, and 100% to confirm its healthy operation

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