eFunda: Introduction to Diaphragm Pressure Gages
engineering fundamentals Diaphragm Pressure Gages: Introduction
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Overview

The Diaphragm Pressure Gage uses the elastic deformation of a diaphragm (i.e. membrane) instead of a liquid level to measure the difference between an unknown pressure and a reference pressure.

A typical Diaphragm pressure gage contains a capsule divided by a diaphragm, as shown in the schematic below. One side of the diaphragm is open to the external targeted pressure, PExt, and the other side is connected to a known pressure, PRef,. The pressure difference, PExt - PRef, mechanically deflects the diaphragm.

Typical Diaphragm Pressure Gage

The membrane deflection can be measured in any number of ways. For example, it can be detected via a mechanically-coupled indicating needle, an attached strain gage, a linear variable differential transformer (LVDT; see the schematic below), or with many other displacement/velocity sensors. Once known, the deflection can be converted to a pressure loading using plate theory.

LVDT-Based Diaphragm Pressure Gage
Pros and Cons

  • Pros:
  - Much faster frequency response than U tubes.
  - Accuracy up to ±0.5% of full scale.
  - Good linearity when the deflection is no larger than the order of the diaphragm thickness.
  • Cons:
  - More expensive then other pressure sensors.

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