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RAVISANKAR G EMS INSTRUMENTS

RAVISANKAR G EMS INSTRUMENTS. THERMOCOUPLES, RTD’S AND PYROMETERS. THEMOCOUPLE TYPES. J - Fe-Cons 0-750 K - Cr -Al 0-1100 S- Pt-Pt Rh (10%) 0-1300 R- Pt-Pt Rh(13%) 0-1350 B- Pt-Pt Rh(30%) 0-1350 E-Cr-Cons 0-1100 T- Cu-Cons 0-750 N-Ni-NiCl 0-1400 .

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RAVISANKAR G EMS INSTRUMENTS

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  1. RAVISANKAR G EMS INSTRUMENTS THERMOCOUPLES, RTD’S AND PYROMETERS

  2. THEMOCOUPLE TYPES • J - Fe-Cons 0-750 • K - Cr -Al 0-1100 • S- Pt-Pt Rh (10%) 0-1300 • R- Pt-Pt Rh(13%) 0-1350 • B- Pt-Pt Rh(30%) 0-1350 • E-Cr-Cons 0-1100 • T- Cu-Cons 0-750 • N-Ni-NiCl 0-1400

  3. SELECTION OF THERMOCOUPLES • Cost • Resistance to corrosion • EMF output • Speed of response • Nature of medium

  4. THERMOCOUPLE CONSTRUCTION • Mineral Insulated thermocouples are popular now. • Exposed Type (with /without seal) • Non grounded type • Grounded type

  5. REFERENCE JUNCTION COMPENSATION • Temp versus EMF for a thermocouple is supplied by manufacturer. • Measurement is based on ref junction at 0. C • Ref Junction is at room temp in most cases. • So it is required to add the observed EMF with that EMF which T/C would develop if the ref junction were at 0. C. This is done using temp sensitive resistors.

  6. THERMOCOUPLE LAWS • Law of homogeneous Circuit: No current flows in th ckt made of a simple metal by application of heat alone • Law of Intermediate metals: If between any two points a no. of junctions appear, but all at same temp, EMF between these two points is independent of intermediate mmetals.

  7. THERMOCOUPLE LAWS • Law of Intermediate temp: EMF for a couple with junction temp t1 & t3 is sum of emfsof two couples of same metals having junction temp t1 & t2 and t2 & t3 resp. Extension wire & Compensating cable JPX, KPX, NPX, SPX, SNX etc

  8. RTD • PT: Accuracy: 0.01 .C; Costly, stable uniform & high resistance • Ni: Accuracy: 0.01 .C; Large change and high resistance. Not uniform • Cu : Accuracy: 0.01 .C; Uniform, stable, cheap, & low value of resistance.

  9. RTD • Thick and thin film RTD. -- Wire wound and thin pattern of pt metal alloy on ceramic substrate. • Two wire system • Three wire system • Four wire system

  10. RTD High accuracy Narrow Range No Compensation required. Expensive Up to 400 . C only Self heating may be a problem THERMOCOUPLE Moderate accuracy Stable & low cost Less output signal Calibration Drifts Electrical interface required Higher installation cost-extension wires RTD VERSUS THERMOCOUPLE

  11. PYROMETERS Radiation type : • Temp of continuously moving sheet of material can be measured. • High temp can be measured.(700-3000 . C ) • Stable, non contact output signal. • Thermopile, Photocell, Thermistor, LDR, Photodiode are common detectors.

  12. Thank you

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