Pressure Transducers

Types of Pressure Sensors

The demand for pressure measuring instruments arises with the advent of steam age. Mechanical methods of measuring pressure such as Bourdon tubes or bellows, where mechanical displacements were transferred to an indicating pointer were the first pressure instruments. Initially, these tubes were constructed of glass, and scales were added to them as per requirements. However, these mechanical motion balance pressure measuring arrangements were large, cumbersome, and not well suited for integration into automatic control loops. Consequently, as control systems evolve to become more centralized and computerized, these devices were replaced by analog electronic and, more lately, digital electronic pressure transmitters. Pressure transmitters or transducers are ready to use instruments employed for measurement of pressure. These are OEM transducers with

• pressure port
• integrated compensation resistors
• a cable or connector

The terms pressure gauge, sensor, transducer, and transmitter can be used interchangeably. Majority of modern pressure sensors operates on piezoresistance principle. Due to pressure, a material generates electricity at a certain rate, which leads to a specific level of charge flow related with a specific level of pressure. This charge is supplied to a wire which leads to a control panel and display for human analysis.

Pressure Transmitter

It is a standardized pressure measurement package which includes following three fundamental components:

• a pressure transducer
• its power supply,
• a signal conditioner/retransmitter used to transform the transducer signal into a standardized output
• In pressure transmitters, process pressures can be transmitted using
• an analog pneumatic (3-15 psig),
• analog electronic (4-20 mA dc),
• or digital electronic signal

When transducers are directly interfaced with digital data acquisition systems and are positioned at some distance from the data acquisition hardware, high output voltage signals are preferred and these signals must be guarded against both electromagnetic and radio frequency interference (EMI/RFI) when traveling longer distances.

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