Manometers

[Ref: KB Primary course May 2005]

Keypoints

Classification of manometers

A. Liquid

B. Mechanical

• Bourdon gauge
• Aneroid gauge
• Diaphragm gauge
  * Direct
  * Optical
  * Electromanometer (strain gauges and others)

Manometers - pressure measuring devices

Transducer - a device that changes energy from one form to another

Types of manometers

A. Liquid manometers

e.g. mercury manometer, U-tube manometer

Principle: the force of gravity on the molecules of a liquid gives rise to pressure that depends on the height of the liquid above the point of measurement

Sensitivity can be increased by wide bore tubing or tilting the tube

B. Mechanical pressure gauges

1. Bourdon gauge

Coiled tube with flattened cross-section. When pressure within the tube increases, it uncoils slightly.

• Advantage: Robust
• Disadvantage: Not very accurate
• Used to measure high pressure systems
• Also a type of aneroid gauge

2. Aneroid gauge

(without liquid)

Pressure changes cause movement of bellows

--> lever mechanism detects and magnifies changes

--> movement drives the pointer across a calibrated scale

3. Diaphragm gauge

Increased pressure causes movement of diaphragm, which is detected in 3 different ways

1. Direct
2. Optical
3. Electromanometers

Electromanometers

A. Strain gauges

When wire or silicon crystal is stretched or compressed, the electrical resistance changes
* stretched wire --> higher R

Two types:

• Wire strain gauge
• Silicon strain gauge

B. Others