The pressure transmitter is one of the most common instruments in any oil and gas facility - on wellheads, separators, pipelines, and tanks. It turns a physical pressure into a standard electrical signal a controller can read. This guide explains what a pressure transmitter is, how it works, the difference between gauge and absolute types, and how its signal reaches a SCADA system.
Pressure Transmitter in one line: A pressure transmitter is a field instrument that senses process pressure and converts it into a standardized output signal - usually a 4-20 mA analog current or a digital protocol like HART - that a PLC, RTU, or flow computer reads and reports to SCADA.
Inside a pressure transmitter, process pressure acts on a sensing element - most often a piezoresistive silicon diaphragm or a capacitance cell - that deflects slightly under load. That tiny mechanical change alters an electrical property (resistance or capacitance), which onboard electronics amplify, linearize, and temperature-compensate. The result is scaled to a proportional output over the instrument's calibrated range, for example 0-1,500 psi mapped to a 4-20 mA current.
The 4-20 mA current loop is the workhorse standard: 4 mA represents the low end of the range and 20 mA the high end. Because information is carried as current rather than voltage, the signal is immune to wire-length voltage drop and, usefully, a reading below 4 mA (a broken wire or dead transmitter) is detectable as a fault rather than mistaken for zero pressure.
Pressure is always measured relative to a reference, and the reference defines the transmitter type. A gauge pressure transmitter references atmospheric pressure, so it reads zero at ambient - the right choice for most vessel and line pressures. An absolute pressure transmitter references a sealed vacuum, so it reads full atmospheric pressure (about 14.7 psia) at sea level with no process applied; it is used where barometric changes must not affect the reading, such as in gas custody calculations.
A differential pressure transmitter measures the difference between two ports and underpins a huge range of measurements - flow across an orifice plate, level by hydrostatic head, and filter or strainer condition. It is a distinct instrument covered in its own guide.
A pressure transmitter is a field-level sensor: it does not talk to SCADA directly. Its 4-20 mA or HART signal is wired into an analog input on a PLC, RTU, or flow computer, which digitizes the reading into a tag - say WELLHEAD_PRESS. The SCADA platform then polls that controller over an industrial protocol and presents the value, trends it, and alarms on high or low limits.
Merobix, as a cloud-native SCADA, reads those digitized pressure tags from the PLC, RTU, or flow computer over Modbus, DNP3, OPC UA, or similar - it does not connect to the raw analog loop. The transmitter feeds the controller; the controller feeds Merobix. That chain is what lets an operator watch separator or line pressure from a browser anywhere.
It continuously measures pressure in a process - a wellhead, separator, pipeline, or tank - and converts it into a 4-20 mA or digital signal for a controller and SCADA system. That enables remote monitoring, alarming, and control based on live pressure.
A pressure gauge displays pressure locally on a dial for a person to read on site. A pressure transmitter converts pressure into an electrical signal so a controller or SCADA can read it remotely, trend it, and alarm on it. Many installations use both.
Most give a 4-20 mA analog current proportional to pressure, often with the HART digital protocol superimposed for configuration and diagnostics. Newer smart transmitters may output Foundation Fieldbus, PROFIBUS PA, or wireless (WirelessHART). The controller converts this into a numeric SCADA tag.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
Merobix reads your field devices into a cloud SCADA - the real thing behind these terms, live in days from any browser.