LABFACILITY THERMOCOUPLE & PLATINUM RESISTANCE THERMOMETRY AT A GLANCE THERMOCOUPLE COLOUR CODES: THERMOCOUPLE CONNECTORS, EXTENSION AND SELECTING SENSOR CABLES: GUIDE TO INSULATION & COVERING COMPENSATING WIRES AND CABLES Which insulation usable temperature Application Notes INSULATION COLOUR CODES Material range CABLE Extension & Compensating Leads CODE FORMER STANDARD PVC -10C to 105C Good general purpose insulation for light environments. IEC 60584-3(2007) BRITISH AMERICAN GERMAN BS EN60584-3(2008) Waterproof and very flexible. TYPE CONDUCTORS +/- BS1843: 1952 ANSI/MC 96.1 DIN 43713 / 43714 PFA (extruded) -75C to 250C Resistant to oils, acids other adverse agents and fluids. NICKEL CHROMIUM/CONSTANTAN + + + (Nickel Chromium/Copper Nickel, Good mechanical strength and flexibility. PTFE better for EX Chromel/Constantan, T1/Advance, EX steam/elevated pressure environments NiCr/Constantan) PTFE -75C to 250/300C Resistant to oils, acids other adverse agents and fluids. IRON*/CONSTANTAN + + + + (taped & wrapped) Good mechanical strength and flexibility. (Iron/Copper Nickel, Fe/Konst J JX Iron/Advance, Fe/Constantan I/C) Glassfibre -60C to 350/400C Good temperature range but will not prevent ingress of NICKEL CHROMIUM/NICKEL (varnished) fluids. Fairly flexible but does not provide good mechanical ALUMINIUM* protection. + + + + K (NC/NA, Chromel/ Alumel, C/A, KX High temperature -60C to 700C Will withstand temperature up to 700C but will not prevent T1/T2, NiCr/Ni, NiCr/ NiAL) glassfibre ingress of fluids. Fairly flexible, not good protection against NX physical disturbance. + + + NICROSIL/NISIL N NC Ceramic Fibre 0 to 1000C Will withstand high temperature, up to 1000C. Will not protect against fluids or physical disturbance. COPPER/CONSTANTAN (Copper/Copper Nickel, + + + Glassfibre (varnished) -60C to 350/400C Good resistance to physical disturbance and high temperature + TX T Cu/Con, Copper/Advance) stainless steel overbraid (up to 400C). Will not prevent ingress of fluids. COPPER/CONSTANTAN Screened or unscreened With long cable runs, the cable may need to be screened and earthed at one + + (LOW NICKEL) (Cu/Constantan) + + KCB end (at the instrument) to minimise noise pick-up (interference) on the measuring circuit. Alternative Vx Compensating for K (Cu/Constantan) types of screened cable construction are available and these include the use of copper or mylar screening. COPPER/COPPER NICKEL Twisted pair configurations are offered and these can incorporate screening as required. Compensating for Platinum 10% or + + + RCA 13% Rhodium/Platinum (Codes S & + U R respectively) (Copper/Cupronic SCA Cu/CuNi, Copper/No. 11 Alloy) THERMOCOUPLE ACCURACIES FOR THERMOCOUPLE FOR THERMOCOUPLE * Magnetic, ( ) Tolerance classes for thermocouples to IEC 60584-2(1982) (Amend 1-1989) BS EN60584-2(1993) CONNECTORS body CONNECTORS body colours are similar to colours are similar to Fe-Con (J) Class 1 - 40 +750C: 0.004 . t or 1.5C Alternative & Trade Name outer sheath colours outer sheath colours Class 2 - 40 +750C: 0.0075 . t or 2.5C Class 3 - - - CALIBRATION GUIDE Cu-Con (T) Class 1 - 40 +350C: 0.004 . t or 0.5C Class 2 - 40 +350C: 0.0075 . t or 1.0C Thermocouple emf in absolute millivolts (IEC 584) Class 3 -200 + 40C: 0.015 . t or 1.0C Type 100C 400C 800C 1000C 1200C 1500C NiCr -Ni (K) Class 1 - 40 +1000C: 0.004 . t or 1.5C T 4.279 20.872 - - - - and Class 2 - 40 +1200C: 0.0075 . t or 2.5C E 6.319 28.946 61.017 76.373 - - NiCrSi-NiSi (N) Class 3 -200 + 40C: 0.015 . t or 2.5C J 5.269 21.848 45.494 57.953 69.553 - NiCr-Con (E) Class 1 - 40 +800C: 0.004 . t or 1.5C K 4.096 16.397 33.275 41.276 48.838 - Class 2 - 40 +900C: 0.0075 . t or 2.5C N 2.774 12.974 28.455 36.256 43.846 - Class 3 -200 + 40C: 0.015 . t or 2.5C R 0.647 3.408 7.950 10.506 13.228 17.451 Pt10Rh-Pt (S) Class 1 0 +1600C: 1+(t-1000).0.003 or 1.0C S 0.646 3.259 7.345 9.587 11.951 15.582 and Class 2 - 40 +1600C: 0.0025 . t or 1.5C Pt13Rh-Pt (R) Class 3 - - - B 0.033 0.787 3.154 4.834 6.786 10.099 Pt30Rh- Class 1 - - - Pt6Rh (B) Class 2 +600 +1700C: 0.0025 . t or 1.5C Class 3 +600 +1700C: 0.005 . t or 4.0C Note: t = actual temperature Use the larger of the two deviation valuesLABFACILITY THERMOCOUPLE & PLATINUM RESISTANCE THERMOMETRY AT A GLANCE PLATINUM RESISTANCE THERMOMETER PRACTICAL BRIDGE CIRCUITS FOR 2, 3 AND 4 WIRE THERMOMETERS RESISTANCE V TEMPERATURE AND TOLERANCES FOR PLATINUM RESISTORS TO IEC 751(1995)/BS EN60751(1996) that the length of cable is minimised to keep The connection between the thermometer Temp Resistance Tolerance assembly and the instrumentation. The cabling cable resistance to as low a value as possible. Class A Class B (C) () (C) () (C) () introduces electrical resistance which is placed in The use of 3 wires, when dictated either by series with the resistance thermometer. The two -200 18.52 0.55 0.24 1.3 0.56 probe construction or by the input termination of resistances are therefore cumulative and could -100 60.26 0.35 0.14 0.8 0.32 the measuring instrument, will allow for a good 0 100.00 0.15 0.06 0.3 0.12 be interpreted as an increased temperature if level of lead resistance compensation. However 100 138.51 0.35 0.13 0.8 0.30 the lead resistance is not allowed for. The the compensation technique is based on the 200 175.86 0.55 0.20 1.3 0.48 longer and/or the smaller the diameter of the assumption that the resistance of all three leads 300 212.05 0.75 0.27 1.8 0.64 cable, the greater the lead resistance will be and is identical and that they all reside at the same 400 247.09 0.95 0.33 2.3 0.79 the measurement errors could be appreciable. In ambient temperature this is not always the case. 500 280.98 1.15 0.38 2.8 0.93 the case of a 2 wire connection, little can be Optimum accuracy is therefore achieved with a 600 313.71 1.35 0.43 3.3 1.06 done about this problem and some measurement 4 wire configuration. 650 329.64 1.45 0.46 3.6 1.13 error will result according to the cabling and 700 345.28 3.8 1.17 input circuit arrangement. 800 375.70 4.3 1.28 850 390.48 4.6 1.34 For this reason, a 2 wire arrangement is only suitable for short cable lengths. If it is essential to use only 2 wires, ensure that the largest NEW TOLERANCE CLASSES FOR RESISTORS to IEC 60751(2008) possible diameter of conductors is specified and a For wire wound resistors For film resistors Tolerance value Tolerance Temperature range of Tolerance Temperature range of C class validity C class validity C STEM CONDUCTION SELF-HEATING W 0.1 100 to +350 F 0.1 0 to +150 ( 0.1 + 0.0017 t ) This is the mechanism by which heat is conducted In order to measure the voltage dropped across W 0.15 100 to +450 F 0.15 30 to +300 ( 0.15 + 0.002 t ) from or to the process medium by the probe itself the Pt sensing resistor, a current must be W 0.3 196 to +660 F 0.3 50 to +500 ( 0.3 + 0.005 t ) an apparent reduction or increase respectively in passed through it. The measuring current W 0.6 196 to +660 F 0.6 50 to +600 ( 0.6 + 0.01 t ) measured temperature results. The immersion produces heat dissipation in the sensor. This a depth (the length of that part of the probe which results in an increased temperature indication. t = modulus of temperature in C without regard to sign. For any value of R is directly in contact with the medium) must be It is necessary to minimise the current flow as such as to ensure that the sensing length is much as possible 1mA or less is usually NEW TOLERANCE CLASSES FOR THERMOMETERS to IEC 60751(2008) exceeded (double the sensing length is acceptable. Temperature range of validity recommended). Small immersion depths result in a If the sensor is immersed in flowing liquid or Tolerance class C Tolerance values a large temperature gradient between the sensor gas, the effect is reduced because of more Wire wound resistors Film resistors C and the surroundings which results in a large rapid heat removal. Conversely, in still gas for AA 50 to +250 0 to +150 ( 0.1 + 0.0017 t ) heat flow. example, the effect may be significant. The A 100 to +450 30 to +300 ( 0.15 + 0.002 t ) The ideal immersion depth can be achieved in self-heating coefficient E is expressed as: B 196 to +600 50 to +500 ( 0.3 + 0.005 t ) practice by moving the probe into or out of the 2 E = t / (R I ) C 196 to +600 50 to +600 ( 0.6 + 0.01 t ) process medium incrementally with each a adjustment, note any apparent change in Where t = (indicated temperature) t = modulus of temperature in C without regard to sign. For any value of R indicated temperature. The correct depth will (temperature of the medium) result in no change in indicated temperature. R = Pt resistance RECOMMENDED TERMINATION COLOUR CODES IEC 751(1995) For calibration purposes 150 to 300mm immersion WhiteWhite Red White Red Red WhiteRReded I = measurement current is required depending on the probe construction. 2 Wire 3 Wire 4 Wire