Pressure and Temperature Instruments API

Pressure and Temperature Instruments API

Pressure and temperature instruments will familiarize you with many of the more common measuring instruments-how they work, when they are used, and how they are protected from damage. You will learn different pressure and temperature measuring instruments.

Pressure Measurement Instruments

Following are the common types of the pressure measuring instruments.


A barometer consists of a glass tube inverted in a bath of mercury. The change in atmospheric pressure will change the mercury level in the tube. The increase in air pressure will increase the mercury level in the tube and vice versa.


Manometer consists of a U-shaped tube containing a liquid. One side is open to the atmosphere, and the other side is attached to the measuring side. Manometers tell the difference between two pressures.

Bourdon Tube Gage

Bourdon tube gage consists of a radial rube with an oval cross-section. One end of the radial tube is free. The pressure is exerted on the inside of the tube which moves the free part of the tube. The motion in the tube indicates the pressure and is indicated on the dial.

Diaphragm Gage

Diaphragm gage is used for measuring small pressure changes. It consists of a diaphragm membrane that deflects when pressure is applied to it. The change in deflection is transferred mechanically via a transmission mechanism. This mechanism will amplify the small difference in strength, and the pressure will be indicated on the dial.

Temperature Measurement Instruments

Following are the common types of temperature measuring instruments.

Expandable Elements Thermometer

These thermometers have expandable elements that expand with temperature change. The change in temperature is indicate on the scale.

Bimetallic Thermometer

Bimetallic thermometers consist of two metals. Each metal has different rate of thermal expansion. General construction includes a spiral bimetallic strip which rotates the mechanism. This rotation is indicated by the pin on the dial.

Electrical Thermometer

Electrical thermometers convert heat energy into electrical signals. These electrical signals are converted to digital values to indicate the temperature value.

API Manuals

API manuals are developed by the American Petroleum Institute. The purpose of developing API manuals is to provide a learning resource about different types of equipment and important concepts used in industries.

The content is provided in the form of fill in the blanks so that learners can test knowledge. The answer to each fill in the blank is also given on the right side. Review questions are provided at the end of each section to judge the understanding of the learner about the topic.

What You Will Learn in Pressure and Temperature Instruments API

In section 1, you will learn about pressure as an operating variable and how instruments are used to measure pressure. Instruments covered include the barometer, manometer, bourdon tube, diaphragm, and bellows gage.

In section 2, you will learn about temperature as an operating variable and temperature-measuring instruments. You will learn the principles of the expandable-elements thermometer, bimetallic thermometer, and electrical thermometer.

Pressure and Temperature Instruments API Contents

Section 1

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  • Introduction to Instrumentation
  • Pressure Measurement
  • Barometer
  • Manometer
  • Bourdon Tube Gage
  • Diaphragm Gage
  • Bellows Gage

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Section 2

  • Temperature Measurement
  • Expandable Elements Thermometer
  • Bimetallic Thermometer
  • Electrical Thermometer

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