1. INTRODUCTION TO ELECTRONIC INSTRUMENTATION
INTC 1305 – 01
Vern Wilson
Chapter 2

2. PRESSURE GAUGE

3. PRESSURE
P = F / A

4. FORCE IS AFFECTED BY
SPEED – Molecules are separate in gases and together in liquids – they bounce off each other according to T
MASS – The amount of matter (MW) in an object – depends on the amount of atoms in a molecule
DENSITY – Total number of molecules per unit volume
SPECIFIC GRAVITY – Relative to water or air
WATER GRADIENT = PSI PER FOOT
1 PSI = 27.7 INCHES OF WATER
1 BAR = 14.5 PSIA

5. PRESSURE
Measuring and controlling pressure allows for safer and more qualitative control
PSI – psig or psia
Atmospheres
Inches of water – 27.7 in H2O = 1 psi
Inches of Hg – 2.04 in Hg = 1 psi
Bars = 14.5 psia (metric)
14.7 psia = 1 atmosphere = bars = 407” H2O = 29.92” Hg

6. MEASURING PRESSURE MANOMETERS - water or mercury
GAUGES – Bourdon tubes
Tranmitters are transducers??? A sensor measures and influences an electronic circuit – sends 4 – 20 ma output
DIFFERENTIAL PRESSURE CELLS – Measures two signals and determines the difference
STRAIN GAUGES – group of wires – resistance changes – most popular
CAPACITANCE TRANSDUCERS – DP cell with capacitor – plates get closer capacitance increases

7. Bourdon Tube

8. Manometer

9. Differential Pressure Cell

10. Differential Pressures

11. Differential Pressure Cell
VEGADIF 35.jpg

12. Capacitance Transducers
As the space changes or as the area of overlap changes

13. Capacitance Transducer Schem.

14. PROBLEMS Convert pressures: 13 Bars to psia
14,500 feet to water pressure on bottom
76” of Hg is the same as ? ”of water
Is the pressure at the bottom of a 10” well the same as the pressure at the bottom of a 4 ½” well?