How does a differential pressure transmitter differ from a flow meter?

A differential pressure (DP) transmitter measures the pressure difference between two points — such as across an orifice plate, venturi, or across a chiller evaporator — and outputs a 4–20mA or 0–10V signal proportional to ΔP, but it does not inherently compute flow. A flow meter either (a) combines a DP transmitter with a primary element and square-root extraction to calculate flow (Q ∝ √ΔP), or (b) uses a direct flow-sensing technology like electromagnetic, ultrasonic, or Coriolis that outputs a signal directly proportional to flow rate. In HVAC, DP transmitters are commonly used for pump differential pressure control (maintaining ΔP at a remote sensor), filter status monitoring (pressure drop across filters), and for building static pressure control. For energy measurement applications, modern devices like the Belimo Energy Valve or Siemens SITRANS F flow meters provide direct flow and energy output as BACnet objects, eliminating the manual square-root calculation and accuracy issues that plague DP-based flow measurement at low flows.