Knowing how full a tank, separator, or vessel is drives most oil and gas operations - from hauling schedules to overfill protection to custody accounting. A level transmitter is the instrument that measures that level continuously and reports it. This guide explains what a level transmitter is, the main measurement technologies, and how the level reaches a SCADA system.
Level Transmitter in one line: A level transmitter is a field instrument that continuously measures the height of liquid or solids in a tank or vessel and outputs a proportional signal - typically 4-20 mA or a digital protocol - that a controller and SCADA read as a level or volume tag.
Radar (non-contact) transmitters send a microwave signal down at the surface and time its reflection to compute distance and therefore level; they are accurate, unaffected by vapor, pressure, or temperature, and dominate crude and produced-water tanks. Guided-wave radar runs the signal down a probe for reliable readings in turbulent, foamy, or low-reflectivity liquids. Ultrasonic transmitters work similarly using sound pulses and are lower-cost, but vapor, foam, and temperature swings affect them, so they suit calmer, lower-stakes tanks.
Hydrostatic (pressure-based) transmitters infer level from the head pressure of the liquid column - the deeper the liquid, the higher the pressure at the bottom - and are simple and robust. Float and displacer devices use a buoyant element whose position tracks the surface; magnetostrictive float transmitters give high precision and are common on custody and interface measurement.
A level transmitter gives continuous level - a live percentage or height across the whole range - which is what SCADA trends and uses for volume calculations and haul-out decisions. A point level switch, by contrast, only detects whether the surface has reached one specific height, firing a discrete on/off signal. Point switches (float switches, vibrating forks, capacitance switches) are widely used as independent high-high overfill and low-low pump-protection trips that back up the continuous measurement.
Many tank installations pair both: a continuous transmitter for monitoring and inventory, plus an independent high-level switch wired to a shutdown for safety.
The transmitter's 4-20 mA or digital output is wired to a PLC, RTU, or tank-gauging controller, which converts it into a tag such as TANK_LEVEL and often into a calculated volume using a strapping table. SCADA polls that controller and shows the live level, trends fill and draw rates, and alarms on high and low limits.
A cloud SCADA like Merobix reads those level and volume tags from the controller over Modbus, DNP3, or OPC UA, giving operators tank inventory across many remote sites in one browser view. Merobix supervises the reported level; the measurement itself is done by the transmitter and controller in the field.
It continuously measures the level of liquid or solids in a tank, separator, or vessel and reports it as a signal to a controller and SCADA. Operators use it for inventory, hauling decisions, custody, and high/low level alarming.
Both measure the distance to a surface, but radar uses microwaves and ultrasonic uses sound. Radar is unaffected by vapor, temperature, and pressure and is more accurate for demanding tanks; ultrasonic is cheaper but degraded by vapor, foam, and temperature swings, suiting simpler applications.
A level transmitter gives a continuous reading across the full range for monitoring and inventory. A level switch only detects one specific point and fires an on/off signal, commonly used as an independent high or low safety trip.
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.