List of field instruments & Their working principles

 List of field instruments & Their working principles

TABLE OF CONTENTS

☞ Most used field instruments list

☞ Working Principle of listed. Instruments ( Instruments works on)

☞Use of listed Instrument

☞Working of listed instrument

LIST OF MOSTLY USED FIELD INSTRUMENTS 👇🏻

_________

1. Pressure Gauge

2. Manometer

3. Pressure Transmitter

4. Differential Pressure Transmitter

5. Pressure Switch

6. Differential Pressure Switch

7. RTD (Resistance Temp. Detector)

8. TC (Thermocouple)

9. Temperature Gauge

10. Pyrometer

11. Temperature Transmitter

12. DPT FT (DP type Flow Transmitter)

13. Electro Magnetic FT

14. Vortex FT

15. Coriolis Mass FT

16. Thermal Mass FT

17. Turbine FT

18. Rota Meter/Variable area FT

19. Flow Switch (Solid state FS/Thermal dispersion)

20. Paddle Wheel Flow switch

21. Ultrasonic Flowmeter

22. DPT LT (Differential Pres. Type LT)

23. Float based Level Gauge

 24. Ultrasonic LT

 25. Radar LT

26. Level Troll (Displacer Type LT)

27. Capacitance Level Switch

28. pH Meter (Potential of Hydrogen)

29. ORP/redox Meter (Oxidation-reduction potential)

 30. Conductivity Meter 

31. Positioner

 32. Promixy Sensor

 33. Load Cell

34. IR Gas Detector

35. IR Flame Detector

 36. Solenoid Valve

 37. Dew Point meter

Example :

1. Pressure Gauge

- Working Principle : 

Hook's Law

- Use to measure :

 Pressure

- Working :

The force is proportional to the extension.

2. DP type flowmeter

Working Principle : 

Bernouli's Theorem

Flow of fluid passing in a pipe line through any obstruction is proportional to square root of DP measured through the tapping given across the obstruction

Q = √DP

- Straight Run = 10D - 5D

- Use to measure Volumetric flow

- Most gases & Viscous flow

- Highly repeatable

- Wet steam, Dry steam

- Slurry flow.

3. Vortex Flow meter

Working Principle :

Von Karman Effect

When there is a column-shaped obstruction in flowing fluid, it will generate alternating vortices downstream. The flow velocity of fluid and vortex generation frequency are proportional to eachother. Therefore detecting the number of vortices makes it possible to measure flow

- Straight Run = 50D - 5D

- Use to measure volumetric flow

- No moving parts

- Liquid, Gas, Steam

- Low pressure drop

- Not affected by fluid density changes

- Mostly used in steam applications

- Low viscosity fluids

- Not used in low flow ranges

4. Mass Flow meter

Working Principle :

Corioliss effect

When there is no flow through oscillating tube the tube will not twist. But there is flow through oscillating tube the tube will twist thais called corioliss effect.

At each side of flow tube, there are magnetic/coil pickoff called inlet pickoff and outlet pickoff. Because of the vibration the coil moves into the magnetic field and generates a sine wave that is propostional to that motion.

Because coils and magnets are reference to eachother, the sine wave represents the relative velocity and position of the tubes.

By detecting the sine signal from the two pickoff, we can determine the status of the flow rate.

PHASE SHIFT INDICATES MASSFLOW

•m ~ ∆t

FREQUENCY INDICATES DENSITY

- Straight Run = 0 - 0

- Mostly use to measure mass flow.

- Extremely accurate

- Direct measures mass

- low maintenance

- Can measure density, temperature, Mass & Volumetric flow.

5. Ultra-Sonic Flowmeter

It is a flow meter that measures the velocity of a fluid with ultrasound to calculate volumetric flow.

Working Principle : 

Transit time Differential

The ultrasonic flow meter operates by alternately transmitting and receiving a burst of ultrasound between the two transducers by measuring the transit time that it takes for sound to travel between the two transducers in both directions. The difference in the transit time (∆ time) measured is directly proportional to the velocity of the liquid in the pipe.

- No pressure loss

- No contact with the fluid necessary

- small to large nominal diameter

6. Rotameter

Working Principle : 

Variable area

The flow of a liquid raises the float inside a tapered tube, increasing the area through which the liquid can pass. The larger the flow, the higher the float will be raised.

One of the formulas used in the rotameters is:

Q=kA√GH

Where,

Q = volumetric flow rate

k = a constant

A = annular area contained between the float and the wall of the tube

g = the force of gravity

h = the pressure drop of the float

- Cheap and easily available.

- Can measure fluids with a small or medium velocity, e.g., a velocity of 1 LPM to 10 LPM.

- Metal and glass rotameter covers are highly inert, allowing them to resist chemical reactions. Due to this inertness, the equipment is good to use with corrosive fluids.

- Taking readings with a rotameter is simple as it provides a linear measurement scale, providing higher precision and accuracy.

- Rotameters do not require any external force outside the measuring substance, reducing inaccurate readings.

- Because of their small design, they can be used in a wide range of systems.

S.N.	Name of Instrument	Working Principle	Use of Instrument	Working
1	Pressure Gauge	Hooke's Law	To Measure Pressure	The force is proportional to the extension.
2	Manometer	Hydrostatic Balance	To Measure Pressure	A pressure is measured by the height of the liquid it will support.
3	Pressure Transmitter	Change of Capacitance	To Measure Pressure	Capacitive pressure sensors measure changes in electrical capacitance caused by the movement of a diaphragm.
4	Differential Pressure Transmitter	Differential Capacitance	To Measure Differential Pressure	As the pressure difference across the diaphragms changes, the diaphragms move, altering the distance between them and thus changing the capacitance. The capacitance change is then converted into an electrical signal by a sensing circuit within the transmitter.
5	Pressure Switch	Electromechanical	To Actuate Turn On or Off on Pre-set Pressure	Triggered by pressure to turn an electrical circuit on or off.
6	Differential Pressure Switch	Electromechanical	To Actuate Turn On or Off on Pre-set DP Pressure	DP Switches work off the basis of a difference in pressure between two low and high points. The difference is converted to axial movement that is used to actuate the contacts of a micro switch depending on setpoints.
7	RTD (Resistance Temp. Detector)	Change in Resistance	To Measure Temperature	When the temperature of a metal increases, the resistance to the flow of electricity increases as well.
8	TC (Thermocouple)	Seebeck Effect	To Measure Temperature	A phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances which can be measured, and this corresponds to temperature.
9	Temperature Gauge	Gas-actuation, Bimetal or Expansion Principle	To Measure Temperature	When two metals with different coefficients of expansions are joined to form a bimetal. The expansion of bimetal is proportional to changes in temperature.
10	Pyrometer	Planck's Law	To Measure Temperature	Planck's Law states that the energy content in each quantum of electromagnetic radiation is proportional to the frequency. Pyrometers work by detecting infrared (IR) radiation.
11	Temperature Transmitter	Electronic	To Transmit Temperature Signal	A temperature transmitter receives input from sensors like RTD or thermocouple installed in the field, and converts the received input to a signal which is understandable by the systems like PLC or DCS or ESD. The converted signal is sent to PLC or DCS or ESD for further processing.
12	DPT FT (DP type Flow Transmitter)	Bernoulli's Theorem	To Measure Flow	Flow of fluid passing in a pipe line through any obstruction is proportional to the square root of the pressure difference measured through the tapping given across the obstruction.
13	Electro Magnetic FT	Faraday's Law	To Measure Flow	When a conductive medium passes through a magnetic field B, a voltage E is generated which is proportional to the velocity v of the medium, the density of the magnetic field, and the length of the conductor.
14	Vortex FT	Von Kármán Effect	To Measure Flow	When fluid passes in a pipe with the bluff body, generates vortices alternately on either side of the body. The frequency of vortices generated is proportional to the flow rate of the fluid.
15	Coriolis Mass FT	Coriolis Effect	To Measure Flow	A Coriolis meter is based on the principles of motion mechanics. When the process fluid enters the sensor, it is split. During operation, a drive coil stimulates the tubes to oscillate in opposition at the natural resonant frequency. As the tubes oscillate, the voltage generated from each pickoff creates a sine wave. This indicates the motion of one tube relative to the other. The time delay between the two sine waves is called Delta-T, which is directly proportional to the mass flow rate.
16	Thermal Mass FT	Thermal Dispersion	To Measure Flow	The rate of heat absorbed by a fluid flowing in a pipe or duct is directly proportional to its mass flow.
17	Turbine FT	Mechanical	To Measure Flow	As the media moves through the pipe, the turbine begins to spin, and the motion is detected electronically by a magnetic pick-up, an inductive pick-up, or optical detection. The rotational speed of the turbine within the flow is a direct function of the volumetric flow rate.
18	Rota Meter/Variable area FT	Variable Area	To Measure Flow	The flow of a liquid raises the float inside a tapered tube, increasing the area through which the liquid can pass.
19	Flow Switch (Solid state FS)	Thermal Dispersion	To Actuate Turn On or Off on Pre-set Flow	During the measurement, heat is generated by the heating module. If there is no medium flowing in the pipe, the heat received by the thermal sensing module is a fixed value.
20	Paddle Wheel Flow Switch	Paddle Mechanism	To Actuate Turn On or Off on Pre-set Flow	The paddle design flow switch is built with a hinged or spring-mounted paddle to make direct contact with the media flowing through the pipe.
21	DPT LT (Differential Pres. Type LT)	Hydrostatic Pressure	To Measure Level	The pressure at the base of the vessel containing liquid is directly proportional to the height of the liquid in the vessel.
22	Float based Level Gauge	Buoyancy Principle	To Measure Level	A float moves up and down due to buoyancy.
23	Ultrasonic LT	Ultrasonic	To Measure Level
24	Radar LT	Radar	To Measure Level
25	Level Troll (Displacer Type LT)	Archimedes	To Measure Level	The buoyancy force on an object is equal to the weight of the fluid displaced by the object.
26	Capacitance Level Switch	Capacitance	To Actuate Turn On or Off on Pre-set Level	Detects and measures material by capturing the change of capacitance value.
27	pH Meter	Nernst's Law	To Measure

S.N.	Name of Instrument	Working Principle	Use of Instrument	Working
28	ORP/Redox Meter	Oxidation-Reduction Potential	To Measure the Potency and Purity of Drug Solutions	The ORP meter consists of an electrode that is used as a probe or sensor to measure the redox potential of water. The working is similar to pH measurement, where the ORP measurement is a result of electrons’ movement inside the water.
29	Conductivity Meter	Ohm's Law	To Measure the Electrical Conductivity in a Solution	Conductivity is the ability of a material to conduct electric current. Instruments measure conductivity by applying a potential across two plates in the sample and measuring the current passing through the solution.
30	Positioner	Force Balance	To Accurately Position the Control Valve According to Commanded Control Signal	Positioning is based on a balance of two forces: one proportional to the instrument signal and the other proportional to the stem position.
31	Proximity Sensor	Faraday's Law of Induction	To Measure the Physical Distance Between Individuals and Their Interactions	Capacitive proximity sensors work by detecting changes in capacitance between the sensor and an object.
32	Load Cell	Wheatstone Bridge	To Measure Unknown Weight or Resistance	When a load, force, or stress is applied to the sensor, it changes its resistance, leading to a change in output voltage when an input voltage is applied.
33	IR Gas Detector	Absorption of Energy by Hydrocarbons	To Detect Combustible, Flammable, and Toxic Gases, and Oxygen Depletion	The photo-diode's resistance and output voltage change in proportion to the IR light received. When the IR transmitter emits radiation, it reaches the object and some of the radiation reflects back to the IR receiver.
34	IR Flame Detector	Detecting UV Radiation Emitted by the Flame	To Detect and Respond to the Presence of a Flame	IR flame detectors observe IR radiation emitted by fires, which produce unique patterns in IR wavelengths. These patterns can be detected by thermal imaging cameras within the detector.
35	Ultrasonic Flowmeter	Transit-Time Differential	To Measure Flow	The ultrasonic flow meter operates by alternately transmitting and receiving a burst of ultrasound between the two transducers, measuring the transit time for sound to travel between them in both directions. The difference in transit time is directly proportional to the velocity of the liquid in the pipe.
36	Solenoid Valve	Electromagnetism	To Control On/Off Action	A solenoid converts electrical energy into mechanical work through electromagnetic forces. When an electric current passes through the coil, a magnetic field is generated, causing a metal core to move and actuate the valve.
37	Dew Point Meter	Chilled Mirror Technology	To Measure Dryness in Applications	This principle works when a sample of process gas flows across a special polished coated mirror. The mirror temperature is lowered until water vapor of the gas condenses out on the mirror. An optical circuit constantly monitors the mirror surface for equilibrium between optical LED detectors. The mirror's temperature is measured by a Platinum Resistance Thermometer embedded in the mirror block. The resistance measurement determines the dew point.