Pressure Transmitter Working Principle

Pressure transmitters are used to measure the pressure or level of industrial liquids and gases. The output is transmitted to a control system. Accurate and stable process measurements ensure the safe, reliable, and profitable operation of your plant.

A pressure transducer, often called a pressure transmitter, is a transducer that converts pressure into an analog electrical signal. Although there are various types of pressure transducers, one of the most common is the strain gage base transducer. The conversion of pressure into an electrical signal is achieved by the physical deformation of strain gages which are bonded into the diaphragm of the pressure transducer and wired into a wheat stone bridge configuration. Pressure applied to the pressure transducer produces a deflection of the diaphragm which introduces strain to the gages. The strain will produce an electrical resistance change proportional to the pressure.

pressure transmitter
100% output 4 to 20 ma

4-20 mA Output Pressure Transducers

These types of transducers are also known as pressure transmitters. Since a 4-20mA signal is least affected by electrical noise and resistance in the signal wires, these transducers are best used when the signal must be transmitted long distances. It is not uncommon to use these transducers in applications where the lead wire must be 1000 feet or more.

Applications of Pressure Transmitter

Pressure transmitters are used in a wide variety of applications. They are used in machinery to warn machine operators of high pressure levels before a disaster takes place. Pressure transmitters also ensure that machines do not apply too much or too little pressure during production. Pressure transmitters can be used in conjunction with other devices to measure depth, altitude, water flow, and even pressure loss in order to prevent leaks in a system.

Advantages of Pressure Transmitter

Pressure transmitters have several important advantages that other types of gauges do not. For example, pressure transmitters directly measure pressure levels as well as differences in pressure. Pressure transmitters can withstand virtually any environment and can even be completely submerged. They are made of piezoelectric materials, which are immune to both radiation and electromagnetic fields. Pressure transmitters can also be connected to other systems, such as electrical circuits, and can be calibrated to measure pressure relative to atmospheric pressure.

Disadvantages of Pressure Transmitter

Although pressure transmitters can be advantageous, they also have several disadvantages. For example, pressure transmitters are often expensive, although this differs for each version, and are usually difficult to find.

Pressure trasmitter

Pressure Transmitter technical specification

Sr. NoParameterMinimum Requirements
2TypeVariable capacitance /Piezo resistance/ Resonant silicon sensor
3LocationPump house manifold, product header line/ hydrant line/ foam line / blue dye line etc.
4Accuracy0.065 % of span
5Over range protection150% of range
6Field IndicatorInbuilt, Digital in Engineering Unit (Kg/cm2) with smart protocol.
7Output Signal4 –20mA along with HART/ Modbus
8Power24 V DC, 2 Wire
9ProtectionCircuit protected against Lightening & surges (Minimum up to 1 KVA of surges), Reverse Polarity
10Enclosure classEx-proof, IP 65 /NEMA 4 or better, PESO / CCOE approved and Intrinsically Safe
11I.S. BarrierRequired (If applicable)
12Area ClassificationZone I & II, Gr. IIA/IIB, T3 as per IS2148
13ExecutionIntrinsic safe with active barrier in control room / Ex-Proof
14MountingOn 2” Pipe / ½” pipe as per site requirement
15Wetted Parts (M.O.C)SS 316
16Case MaterialPolyurethane coated Die cast Aluminium/ polyester powder coated Aluminium (suitable for use in corrosive environment)
17Range0- 15 Kg/cm2 or as per BOQ or site requirement.
18Process Connection½” NPT(F)
19Electrical Connection½” NPT(F)
20ManifoldSS316 – 2 way suitable to process connection.
Sr. NoParameterMinimum Requirements
21Mounting Kit

Necessary accessories suitable for 2” NB/ ½” NB pipe

mounting. Tapping from pipeline shall be vertical.

22Tag PlateMetal tag plate to be provided

Pressure Transmitter Inspection and Test Plan

This content provides you with sample transmitter inspection and test plan. This is draft ITP and you need to modify it to meet your PO requirements.

Transmitter Inspection and Test Plan TaskVendorTPI InspectionClient
Pressure Transmitter mill test reportHRR
Pressure Transmitter Performance/Function testHWR
Pressure Transmitter Visual / Dimension InspectionHWR
Pressure Transmitter Insulation resistance testHWR
Pressure Transmitter  Documentation review prior to release(Final activity of Technical Inspection)HHR
Pressure Transmitter Pre-shipment InspectionHHR

H: Hold Point implies that relevant production activities shall not proceed until the continuation of work is permitted by Purchaser. (Notification req’d)

W: Witness point implies that Purchaser intends to witness the designated inspection feature. If Purchaser decides not to witness the relevant feature, production can proceed without permission of Purchaser. (Notification req’d)

S: Witness, but spot check basis. Initial operation will be witness point and subsequent operation will be witnessed at discretion of Purchaser considering the results of previous inspection. (Notification not req’d : Randam Inspection)

R: Review inspection & test records (Notification not req’d)

General Note for Transmitter ITP:

1) Pressure Transmitter Witness/hold point by Code Inspector, when applied by Code /Local Regulation, is to comply with its requirements and to specify in Vendor’s ITP.

2) Type of Inspection by Pressure Transmitter Purchaser may be changed according to equipment criticality and vendor QC evaluation at job stage.

3) When requested in the requisition, detailed Pressure Transmitter ITP shall be submitted by Vendor.

4) Monitoring/Observation of Pressure Transmitter Vendor shop daily routine works (i.e. Storage of materials, Adherence to approved procedures, Testing tool calibration check, workmanship, cleanliness and etc.) shall be done by Purchaser during inspection visit.

5)100% Transmitter inspection which is covered by the combination of witness / spot check / record review inspection & tests listed above and vendor’s original

QC activity shall be confirmed by Purchaser’s inspector prior to shipment.

6)Unless otherwise specified in Pressure Transmitter  REQ., the sampling Q’ty of ” S (Spot Witness Check) ” shall be as follows:

3 to 20→3Pcs(all if total 2 and less) , 21 to 50→5Pcs, 51 to 100→10Pcs,101 to 200→20Pcs, 201 to 300→30Pcs, 301 to 500→50Pcs

Minimum 25 pcs or more of the commodity shall be arranged for H/W/S inspection and test at one time inspector’s visit as much as practical.

7) Final Pressure Transmitter Visual Inspection/Documentation Review/Pre-Shipment Inspection may be combined within one time visit.

Differential pressure Transmitter Installation hookup diagram

  • Hookup diagram for Liquid  and steam service pressure Transmitter  
  • Hookup diagram for Gas service  pressure Transmitter

Pressure Transmitter manufacturer list:

Invensis (Foxboro)
Emerson Process Control (Rosemount)
Endress + Hauser

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