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page 163

+V

R5

R1

R3

-

+

Vout

R2

 

 

 

 

 

 

R4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

13.2 SENSOR TYPES

• A list of physical properties, and sensors to measure them is given below,

ELECTRICAL

 

 

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Voltage

 

voltage transducer

 

0-5V

 

lin.

 

<1%

 

Current

 

current transducer

 

0-5V

 

lin.

 

<1%

 

KW

 

power integrator

 

0-5V

 

exc./lin.

 

0.25%

 

power factor

 

transducers

 

0-5V

 

lin.

 

0.75%

 

KW-hr

 

pulse initiator

 

0-5V digital

 

exc.

 

0.1%

operation = excitation. lineation, compensation, offset

page 164

TEMPERATURE

 

 

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

temperature

 

thermistors

 

resistance

 

lin.

 

1%

 

 

 

thermocouple

 

0-80 mV

 

lin./comp.

 

0.5%

 

 

 

RTD

 

4-20 mA

 

exc./lin.

 

0.05%

 

 

 

IC sensor

 

BCD digital

 

exc./lin.

 

0.01%

 

 

 

 

 

 

 

 

 

 

ATMOSPHERIC

 

 

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

pressure

 

transducer/transmit.

 

0-5V,4-20mA

 

exc./lin.

 

0.5%

 

humidity

 

RH transmitter

 

4-20mA

 

exc./lin.

 

1% RH

 

precipitation

 

LVDT rain gauge

 

0-5V

 

exc./lin.

 

0.25%

 

solar radiation

 

pyranometer trans.

 

0-5V

 

exc./lin.

 

5%

 

wind direction

 

potentiometer

 

0-5V

 

exc./lin/off.

 

1%

 

wind velocity

 

pulse initiator

 

5V pulse

 

exc.

 

1%

 

 

 

 

 

 

 

 

 

 

FLUIDS

 

 

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

flow

 

transducer

 

0-5V

 

exc./lin.

 

0.3%

 

level

 

transmitter

 

4-20mA

 

exc./lin.

 

0.2%

 

 

 

 

 

 

 

 

 

 

MATERIAL PROPERTIES

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

strain

 

strain gauge

 

resistance

 

exc./lin.

 

0.5%

 

 

 

 

 

 

 

 

 

 

ELECTRONIC

 

 

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

frequency

 

pulse initiator

 

5V pulse

 

exc.

 

N.A.

 

 

 

 

 

 

 

 

 

 

page 165

SPATIAL (NEWTONIAN)

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

acceleration

 

accelerometer

 

 

 

 

 

 

 

position

 

transducer

 

 

 

 

 

 

 

velocity

 

velocity pickup

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPATIAL (PRESENCE)

 

 

 

 

 

 

 

Property

 

Sensor

 

Input

 

operation

 

typ. accuracy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

touching

 

contact switch

 

 

 

 

 

 

 

proximity

 

inductive

 

 

 

 

 

 

 

 

 

capacitive

 

 

 

 

 

 

 

 

 

laser reflection

 

 

 

 

 

 

 

between

 

optical

 

 

 

 

 

 

Common transducers,

-Ammeter - meter to indicate electrical current

-Bourdon tube - widely used industrial gage to measure pressure and vacuum

-Chromatographic instruments - laboratory-type instruments used to analyze chemical compounds and gases.

-Inductance-coil pulse generator - transducer used to measure rotational speed. Output is pulse train.

-Linear-Variable-Differential transformer (LVDT) electromechanical transducer used to measure angular or linear displacement. Output is Voltage

-Manometer - liquid column gage used widely in industry to measure pressure.

-Ohmmeter - meter to indicate electrical resistance

-Optical Pyrometer - device to measure temperature of an object at high temperatures by sensing the brightness of an objects surface.

-Orifice Plate - widely used flowmeter to indicate fluid flow rates

-Photometric Transducers - a class of transducers used to sense light, including phototubes, photodiodes, phototransistors, and photoconductors.

-Piezoelectric Accelerometer - Transducer used to measure vibration. Output is emf.

-Pitot Tube - Laboratory device used to measure flow.

-Positive displacement Flowmeter - Variety of transducers used to measure flow. Typical output is pulse train.

-Potentiometer - instrument used to measure voltage

-Pressure Transducers - A class of transducers used to measure pressure. Typical output is voltage. Operation of the transducer can be based on strain gages or other devices.

-Radiation pyrometer - device to measure temperature by sensing the thermal radiation

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