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a) Pressure is used to measure other variables such as

Flow

Level

b) In process control, a pressure measuring devices needs a pressure transmitter that will produce an output signal for transmission.

c) Distillation column operated by

Manipulating pressure

Temperature

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• Absolute pressure: Measured relative to vacuum.

• Differential pressure: Difference between two pressures.

• Atmospheric Pressure: ~14.7 psi or 101.36 kPa at sea level.

• Vacuum Pressure: Below atmospheric.

• Total Vacuum: Zero pressure.

• Dynamic Pressure: Due to fluid motion.

• Static Pressure: Fluid at rest.

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1. Density (ρ)

• Mass per unit volume.

• Unit: kg/m³

2. Specific Weight (γ)

• Weight per unit volume.

• Unit: N/m³ or lb/ft³

3. Specific Gravity (SG)

• Ratio of the density of a substance to the density of water (dimensionless).

• No units (since it’s a ratio)

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Gauge pressure = pressure relative to the local atm or ambient pressure.

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-made from hard metal（bronze/brass）

-tube is bent into C-curve/spiral

-tube will deflect when there has a different between inside and outside pressure

-the tube will tend to straighten out if pressure is applied. The free end of the tube moves up, depending on magnitude of pressure

-Limitations:

·﻿﻿Low pressure

·Overload protection

·Critical media

-the displacement is caused by pressure changes and detected by a sensor（electrical signal）

-this signal then be displayed or recorded on an electrical device calibrated in terms of pressure

-Advantages：

·low cost

·simple construction

.safe for high pressure

- Disadvantages：

·sensitive to shock and vibration

.slow respond

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-rely on electrical properties of quartz crystals rather than resistive bridge transducer

- crystals will generate an electrical charge when they are strained

- electrodes transfer the charge from crystals to amplifier built into sensor

-the sensor are susceptible to shock and vibration

-Piezoelectric sensors are not normally suitable for measuring static pressure. The output signal will gradually drop to zero, even in the presence of constant pressure. They are, however, sensitive to dynamic changes in pressure across a wide range of frequencies and pressures.

-

-

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A U-shaped glass or plastic tube partially filled with liquid.

both ends of the tube are open

Measures pressure using the height difference (h) of the liquid.

Formula : ( gauge pressure )

Can measure pressure in both

a) liquids

b) gases

Advantages

a) low cost

b) provide direct

c) simple operation

d) low pressure & low differential pressure.

Disadvantages

a) limited in application

b) fragile

c) poor dynamic

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Strain Gauge Sensor (Simple Notes)

Function:

Measures strain (stretch/compression)

Converts mechanical force into electrical signal

How It Works:

1. Strain gauge changes resistance when stretched/compressed

2. Connected to a Wheatstone Bridge circuit

3. No pressure = balanced bridge (zero volts output)

4. Pressure unbalances bridge = voltage output

5. Output voltage proportional to pressure

Circuit Types:

Quarter-Bridge circuit commonly used

Voltage output changes with resistance due to pressure

Advantages:

High accuracy

Outputs electrical signal

Good for automation

Disadvantages:

Sensitive to temperature

May need calibration

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Bellows Sensor (Simple Notes)

Function:

Measures low differential pressure (0 to 1000 Pascals)

Converts pressure into mechanical movement

Construction:

Thin copper alloy tube, corrugated like a spring

One end sealed, one end has a hole for pressure

Expands/contracts when pressure applied

Working Principle:

Pressure moves the bellows

Movement connects to pointer or sensor for reading or signal

Advantages:

Low cost

Good for differential pressure

Disadvantages:

Cannot be repaired (replace if damaged)

Not for high pressure

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CHE HANIS SYAMILAH ( TH24025 )

NURHUDA ATHIRAH (TH24034)

NURBATRISYIA HUSNA (TH23045)

WONG SHU TING(TH23051)