What Is Instrument Calibration. Instrument Calibrator.

Calibration Of an Instrument Is a Process of Determining Its Accuracy. Accuracy Of an Instrument Tends to Decrease Over Time Due to Hard Operating Conditions Mechanical Shocks or Exposure to Extreme Temperature or Pressure.

In Order to Be Confident in The Accuracy of The Measurement That the Instruments Produce the Calibration of Instruments Need to Be Carried Out on a Regular Basis.

Calibration Is Done by Comparing the Measurements of Two Instruments in Which the Measured Value from an Instrument Under Calibration Is Compared with the Measurement of Instrument Having Known and High Accuracy.

Why Do We Need to Calibrate Instruments

In A Process Plant the Control System Controls the Plant. The Control System Obtains the Measurement Data from the Various Instruments in the Plant and Controls the Plant Based on this Measurement Data.

So, If the Measurement Data Is Incorrect the Controlling of The Plant Will Also Be Incorrect.

So, From This We Can Say That in A Process Plant Everything Is Based on Measurements and Therefore the Measurements Done by The Instruments in The Plant Should Be Accurate to Be Able to Control the Plant Properly.

So, To Maintain the Accuracy of The Measurement’s Calibration Should Be Done Regularly.

How Calibration is Done.

The Only Way to Check that If an Instruments Output Accurately Corresponds to Its Input Is to Give that Instrument a Known Input Value While Measuring the Corresponding Output Signal Values. For This a Process Calibrator Is Used.

Calibrator Should Be More Accurate Than the Instrument You Calibrate with Its Calibrators Are Calibrated Regularly by More Accurate Reference Standard Maintained by National Metrology Institute and

After Calibrating by More Accurate Standard These Institute Issue a One-Year Valid Certificate for Calibrators.

Before Starting Any Calibration, The Validity of The Calibration Certificate of a Calibrator Must Be Assured.

Different Types of Calibrators.

There Are Different Types of Calibrators available in The Market. The Type of Calibrator Selected for a Particular Calibration Task Depends on

1. The Type of Sensor to Be Calibrated,

2.The Environment in Which It Is to Be Calibrated

3.The Required Accuracy of The Calibration.

Some Of the Commonly Used Calibrators are Dry Block Calibrator, Pneumatic Calibrator, Signal Reference Calibrator Etc.

During Calibration of An Instrument the Readings or Output of The Instrument to Be Calibrated Is Checked at Several Points Throughout the Calibration Range of The Instrument.

Calibration Range Is the Range of Values Over Which the Instrument Has Been Tested. The Calibration Range Is Different from Instrument Range.

Instrument Range Refers to The Range Within Which the Instrument Has Capability to Measure.

Consider That the Name Plate of a Pressure Transmitter Shows an Input Pressure Range from 0 To 750 PSIG and an Output Of 4 To 20 Milli Amps.

This Means That the Instrument Has Capability to Handle and Input of 0 To 750 PSIG and Produce Corresponding Output.
This Range Is Known as Instrument Range.

Now Consider That We Need to Use This Transmitter for An Application Where We Need to Give an Input Of 0 To 300PSIG And Get an Output Of 4 To 20 Milli Amps. Here Calibration Is Done Only for 0 To 300 PSIG This Range Is Known as Calibration Range.

Calibration Range Is Defined by The Zero and Span Values. The Zero Value Is the Lower End of The Range and The Span Value Is Algebraic Difference Between the Upper and Lower Range Values.

Now Let’s Check What Is the Zero Value and The Span Value of The Transmitter Having a Calibration Range Of 0 To 300 PSIG.

Here The Lower Range 0 Is a Zero Value and The Span Value is the Algebraic Difference Between the Upper and Lower Range Values.
That Is Here It Is the Difference Between 300 And 0, Which Is 300 PSIG.

Read more: How RTD is Calibrated

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