Instruments - Pressure

Question 1

How does a pressure transmitter work?

Answer 1

A sensing diaphragm flexes under pressure; one side is vented to atmosphere (via a vented reference or breather), and the sensor (often silicon piezoresistive or capacitive) converts the diaphragm’s strain to an electrical signal.

Question 2

How does a DP transmitter work?

Answer 2

Two isolation diaphragms and oil-filled cavities transmit pressure to a central sensing element measuring ΔP. Static pressure is common to both sides and largely cancels, leaving the difference.

Question 3

What are the three measuring sensor types used in pressure transmitters?

Answer 3

• Piezoresistive (silicon strain gauge)
  The diaphragm strain changes resistance in a Wheatstone bridge; robust, compact, widely used for gauge/absolute/DP with oil isolation.
• Capacitive
  Pressure changes the gap between a diaphragm and fixed electrode; excellent stability and resolution, common in many premium DP units.
• Resonant (quartz or resonant silicon)
  Pressure alters a resonant frequency of a vibrating element; inherently digital signal, very stable for high-accuracy DP/PA applications