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Pressure Measurements. Absolute, Gauge, and Differential Barometers Manometers Low/High Level Analog Output Calibration. Pressure Ranges. Ref. Press. Absolute Pressure. P abs = 0 : When all molecular action stops. P abs = P gage + P ambient.

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Pressure Measurements

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Pressure Measurements

• Absolute, Gauge, and Differential

• Barometers

• Manometers

• Low/High Level Analog Output

• Calibration

Ref. Press

Absolute Pressure

Pabs = 0 : When all molecular action stops.

Pabs = Pgage+ Pambient

Pabs – Pressure that is used in thermodynamics to determine the state of a substance.

Pgage – It is the pressure relative to the local ambient air pressure

Differential pressure – Diff. Pressure is simply the diff. In pressure between two points

P2

P1

Manometerdifferential

P1

P2

P2 – P1 = (m- s) g h

m Density of manometer fluid

s -Density of sensed fluid

(P/ g) – height of fluid-(height of Hg)

Density vs temperature

Thermal expansion

For gases, s is zero

P1 A

A

h

h

P2 A

P1

P1 A

A

h

P2

h

P2 A

Inclined Manometerdifferential

For low pressure differentials, use

Inclined manometer

Increased sensitivity and accuracy

P1

P1 A

hr

h

P2

g

A

P2 A

Barometerabsolute

0

• Well type manometer with one leg evacuated (to make it Hg vapor pressure)

• Pabs = gh

•  density

• g acceleration due to gravity

• h height of the fluid

P=0

A

h

h

Patm

Patm A

Patm

P2

SPECIFICATIONS:

Excitation: 10 Vdc (15Vdc max)

Output: 3 mV/V ±0.25%

Input Resistance: 350 Ω±5 PΩ

Output Resistance: 350 ±5 Ω

Linearity: ±0.05%FS

Hysteresis: ±0.05% FS

Repeatability: ±0.05% FS

Zero Balance: 1.0% FS

Agency Approvals: Standard:

FM Intrinsically Safe IS/I.II.III/1/CDEFG

Optional: FM Hazardous Location

S/I/1/ABCD

Shunt Calibration:

Value specified on Calibration sheet

Sensing Element:

4 active-arm bridge, using thick film

strain gages in a hermetically sealed

chamber

Operating Temp Range:

-73 to 163°C (-100 to 325°F)

Compensated Temp Range:

16 to 71°C (60 to 160°F)

Thermal Effects:

Span: 0.0025% Rdg/°F

Zero: 0.0025% FS/F

SPECIFICATIONS:

Excitation: 8 Vdc Regulated

(6 to 12 Vdc at 20 mA)

PX163-120BD5V use 10Vdc

Output: 1 to 6 Vdc

Linearity: ±1.0% FS BFSL at specified

voltage

Hysteresis & Repeatability:

±0.25% full scale

Zero Balance: 1 Vdc ± 0.05

(3.5± 0.05 Vdc PX163 series)

Operable Temperature Range:

-40 to 185°F (-40 to 85°C)

Compensated Temperature Range:

PX161 and PX162:

0 to 145°F (-18 to 63°C)

PX163 and 164:

41 to 113°F (5 to 45°C)

Operable Overpressure: 5 psi

Media Compatibility

P1: Dry Gases Only

Block Diagram

Data Acquisition Card

Vex

Computer

Breakout

Mux

Amp

A/D

PX01-MV

PX160 Series

+Vex

Patm

Transducer

Patm

P1

h

Patm

Transducer

Patm

P1

h

Transducer

Patm

P=0

P1

h1

hatm

Patm

hg

Bourdon gauge

Piezo-resistive pressure sensors

Pressure causes stress

Stress changes resistance