Glossary · Process instrumentation and analytical measurement
Orifice plate
Also known as: Orifice meter, Measuring orifice
German: Blende
In flow measurement, an orifice plate is a differential-pressure primary element: a thin plate with a precisely machined hole installed in a pipe, which creates a pressure drop from which the flow rate is calculated according to ISO 5167.
- Process instrumentation
- Standards
- Process industry
In one sentence
An orifice plate is a plate with a precise hole in a pipe; the pressure drop across it is used to calculate flow per ISO 5167.
Example
An orifice plate with flange taps and a differential-pressure transmitter measures the natural gas flow to a boiler.
How it applies
- Engineering: The flow is proportional to the square root of the differential pressure. ISO 5167-2 defines geometries, tapping arrangements, straight-length requirements and the equations, which allows flow calculation without flow calibration when the requirements are met.
- Operation: The square-root relationship limits the usable turndown; at low flow, small differential pressures produce large relative errors. Orifice plates cause a permanent pressure loss.
- Maintenance: Worn or damaged inlet edges and deposits change the discharge coefficient and cause errors. Inspect the plate at defined intervals.
- Documentation: Keep the orifice calculation sheet with the bore diameter, pipe diameter, fluid data and design flow. After any process change, these data decide whether the plate still fits.
Orifice plate vs. flowmeter
An orifice plate is a primary element, not a complete flowmeter. Together with a Differential-pressure transmitter and the flow calculation, it forms the measuring system.