process instrumentation i module code: eipin1b study ... - Home Mweb
process instrumentation i module code: eipin1b study ... - Home Mweb
process instrumentation i module code: eipin1b study ... - Home Mweb
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EIPINI Chapter 5: Temperature Measurement Page 5-22<br />
Example 5-14<br />
The following equations are provided for a type K thermocouple, to calculate<br />
temperature (t in °C) from emf (v in μV) in the temperature range 0 °C to 500 °C:<br />
t = (2.508355×10 -2 )v + (7.860106×10 -8 )v 2 - (2.503131×10 -10 )v 3<br />
+ (8.315270×10 -14 )v 4 – (1.228034×10 -17 )v 5 + (9.804036×10 -22 )v 6<br />
- (4.413030×10 -26 )v 7 + (1.057734×10 -30 )v 8 – (1.052755×10 -35 )v 9 ,<br />
Equation (a)<br />
and to calculate emf (v in μV) from temperature (t in °C) in the temperature range<br />
0 °C to 1372 °C:<br />
v = -17.600413686 + 38.921204975t + (1.8558770032×10 -2 )t 2<br />
- (9.9457592874×10 -5 )t 3 + (3.1840945719×10 -7 )t 4<br />
- (5.6072844889×10 -10 )t 5 + (5.6075059059×10 -13 )t 6<br />
- (3.2020720003×10 -16 )t 7 + (9.7151147152×10 -20 )t 8<br />
− 4<br />
2<br />
– (1.2104721275×10 -23 )t 9 + 118.5976e<br />
−1.183432×<br />
10 (t −126.9686)<br />
Equation (b)<br />
a) Use Equation (a) to calculate the temperature when the emf is 2602 μV.<br />
b) Use Equation (b) to calculate the emf when the temperature is 20 °C.<br />
a) t = (2.508355×10 -2 )×2602 + (7.860106×10 -8 )×2602 2 - (2.503131×10 -10 )×2602 3<br />
+ (8.315270×10 -14 )×2602 4 – (1.228034×10 -17 )×2602 5 + (9.804036×10 -22 )×2602 6<br />
- (4.413030×10 -26 )×2602 7 + (1.057734×10 -30 )×2602 8 – (1.052755×10 -35 )×2602 9<br />
= 65.26740 + 0.5321609 – 4.409664 + 3.811584 – 1.464694 + 0.3042627<br />
- 0.03563592 + 0.002222464 – 0.05755631<br />
= 63.95 °C<br />
b) v = -17.600413686 + 38.921204975×20 + (1.8558770032×10 -2 )×20 2<br />
- (9.9457592874×10 -5 )×20 3 + (3.1840945719×10 -7 )×20 4<br />
- (5.6072844889×10 -10 )×20 5 + (5.6075059059×10 -13 )×20 6<br />
- (3.2020720003×10 -16 )×20 7 + (9.7151147152×10 -20 )×20 8<br />
− 4<br />
2<br />
– (1.2104721275×10 -23 )×20 9 + 118.5976e<br />
−1.183432×<br />
10 (20 −126.9686)<br />
= -17.600414 + 778.4241 + 7.423508 – 0.7956607 + 0.05094551<br />
- 0.001794331 + 35.88804×10 -6 – 409.8652×10 -9 + 2.487069×10 -9<br />
- 6.197617×10 -12 + 30.61899<br />
= 798.1 microvolt<br />
(Compare these answers to those of Example 5-11)<br />
5.10.6 Compensating leads<br />
Thermocouple thermometers are normally installed some distance away from the<br />
voltmeter or computer that measures the emf generated by the thermocouple. For<br />
this purpose, cheaper and lower grade thermocouple wires, called extension wire or<br />
compensating leads, are used to connect the thermocouple to the measuring device<br />
at the reference junction. Compensating leads have the same thermoelectric