Pressure Transmitter Product

Overview

A pressure transmitter is a robust instrument converting hydrostatic or dynamic fluid pressure into a standard electronic signal (4–20 mA analog or digital) suitable for process monitoring and control. It isolates the delicate electronic circuitry from harsh process media using a Sensing Diaphragm that separates the measuring cavity from the process; a Fill Fluid inside transmits the diaphragm deflection to the Piezoresistive Cell, a piezoresistive silicon chip whose internal Wheatstone bridge output changes with strain. The Electronics Module amplifies and scales this bridge voltage, and a Current Output Stage drives the 4–20 mA loop. A Process Manifold provides isolation valves, damping, and bleed points for safe installation and maintenance.

How it works

Pressure at the Process Manifold inlet pushes against the stainless diaphragm, deflecting it inward. The deflection compresses the silicone Fill Fluid beneath, transmitting force to the Sensing Diaphragm face of the sensing die. The Silicon Die is a micromachined piezoresistive element: stress in its material changes the electrical resistance of diffused boron or phosphorus resistors arranged in a Wheatstone bridge configuration.

The Bridge Amplifier excites the bridge with a stable reference voltage and amplifies the output voltage proportional to pressure. Integrated resistors allow Offset Adjust (zeroing at atmospheric pressure) and Span Adjust (scaling the full-scale pressure range) through manual trim pots. For remote configuration, newer transmitters replace trim pots with digital potentiometers accessible via a two-wire current loop protocol (HART) or Modbus serial connection.

The Current Output Stage converts the amplified voltage to a 4–20 mA output compatible with older process control systems: 4 mA indicates zero pressure, 20 mA indicates full scale. The current source is active and self-powered from the loop supply (24 V DC), so no additional power is required. A Damping System with a sintered brass or plastic orifice attenuates pressure spikes and pulsations that would degrade measurement stability in processes like pump discharge or compressor outlet.

The Process Manifold isolates the transmitter during maintenance without shutting down the process: the Isolation Ball Valve is closed, the Vent/Bleed Valve is cracked to vent trapped pressure, and the transmitter can be removed and replaced. Transmitters are calibrated at the factory for their specified range (e.g., 0–50 bar), but field trim capability allows re-zeroing after years of drift.