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Process Enginering Equipment Handbook - Claire W.

Claire W. Process Enginering Equipment Handbook - McGraw-Hill, 2002. - 977 p.
ISBN 0-07-059614
Download (direct link): processengineeringequipmenthandbook2002.pdf
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RT = R0 (1 + AT + BT2)
(M-1)
R = R0ek
(M-2)
(M-3)
Measurement M-5
TABLE M-3 Typical Characteristics of Resistance Thermometers
Noble Metal Nonmetallic
Precision Industrial Thermistor
Sensitivity 0.1W/C 0.22W/F Varies with units
Precision 0.001C 0.3F 0.02F up to 200F
Accuracy 0.01C 3.0F standard 0.5F standard
1.5F special 0.2F special
Response: bare 15 s Fast
Response: with well 30 s
Resistance 25.5W at 0C 25W at 32F Varies with units
Linearity 70.1C/50C span 70.1C/50C span Exponential
Range -452.2 to -297.3 to -100 to 500F
1,168.3F 1,950F (-75 to 260C)
(-269 to (-182.96 to
630.74C) 1,064C)
Base Metal
10 W Copper, 100 W Nickel, 100 W
Sensitivity 0.22 W/F 0.22W/F 0.186W/F (0.213W/F)
Precision 0.1F 0.1F 0.1F
Accuracy 0.5F standard 0.5F standard 0.5F standard
0.2F special 0.2F special 0.2F special
Response: bare 20 s 40 s 40 s
Response: with well 60s 90 s 90 s
Resistance 10 W at 77F 100W at 77F 100 W at 77F
Linearity Excellent Excellent Excellent
Range -100 to 300F -325 to 300F -100 to 300F
(-75 to 150C) (-200 to 150C) (-75 to 140C)
resistance properties and the nonlinearity of the resistivity curve limits the use of thermistors.
Information on important characteristics of different classes of resistance thermometers is included in Table M-3.
Accessories. Some forms of Wheatstone-bridge circuits are used for the measurement of temperature with base-metal or industrial platinum resistance thermometers, while the Mueller bridge is used with precision platinum resistance thermometers.
Thermocouple thermometer
A thermocouple thermometer is a temperature-measuring instrument in which the electromotive force developed in a circuit composed of two dissimilar metals is used as a means of temperature measurement. It consists of a device for measuring electromotive force, a sensing element (thermocouple), and electrical conductors operatively connecting the two.
The thermocouple thermometer operates on the principle that an electric current will flow in a closed circuit of two dissimilar metals when the junctions of the metals are at two different temperatures. Thermocouple materials are available for use within the approximate limits of -300 to 3200F. Platinum is the generally accepted standard material to which the thermoelectric characteristics of other materials are referred. The emf-temperature relations of conventional thermoelements versus platinum are shown in Fig. M-2. Reference tables of
M-6 Measurement
40
30
20
10
0
-10
-20
-30
-40
CHR0l\ CL^-
Pt 87-Rh 13-
/C0PF ER IF ON___
Pt 90- Rh 10
ATINUM
AlUMEL


^CONS' 'ANTAN

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200
TEMPERATURE, F
FIG. M-2 emfs of various materials versus platinum. (Source: Demag Delaval.)
TABLE M-4 Limits of Error of Thermocouples
Limits of Error
Temperature Range,
Thermocouple Type C Standard Special
T (copper-Constantan) -184 to -59 1%
-101 to -59 2% 1%
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