DM-513

**LABFACILITY THERMOCOUPLE & PLATINUM RESISTANCE THERMOMETRY – AT A GLANCE** ~~ee~~ **THERMOCOUPLE** 

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|SELECTING SENSOR CABLES: GUIDE TO INSULATION & COVERING|COLOUR CODES: THERMOCOUPLE CONNECTORS, EXTENSION AND|
|COMPENSATING WIRES AND CABLES|
|Which insulation|usable temperature|Application Notes|
|INSULATION COLOUR CODES|
|Material?|range|CABLE|
|Extension & Compensating Leads|CODE|
|PVC|-10°C to 105°C|Good general purpose insulation for ‘light’ environments.|FORMER STANDARD|IEC 60584-3(2007)|
|Waterproof and very flexible.|TYPE|CONDUCTORS +/-|BS1843: 1952BRITISH|ANSI/MC 96.1AMERICAN|DIN 43713 / 43714GERMAN|BS EN60584-3(2008)|
|PFA (extruded)|-75°C to 250°C|Resistant to oils, acids other adverse agents and fluids.|NICKEL CHROMIUM/CONSTANTAN|
|Good mechanical strength and flexibility. PTFE better for|EX|(Nickel Chromium/Copper Nickel,Chromel/Constantan, T1/Advance,|+–|+–|+–|EX|
|steam/elevated pressure environments|NiCr/Constantan)|
|foo|fo|YD|||
|PTFE|-75°C to 250/300°C|Resistant to oils, acids other adverse agents and fluids.|
|IRON*/CONSTANTAN|
|(taped & wrapped)|Good mechanical strength and flexibility.|J|(Iron/Copper Nickel, Fe/Konst|+–|+–|+–|+–|JX|
|Glassfibre|-60°C to 350/400°C|Good temperature range but will not prevent ingress of|||Iron/Advance, Fe/Constantan I/C)|Ss=_|oS|2|=|
|(varnished)|fluids. Fairly flexible but does not provide good mechanical|NICKEL CHROMIUM/NICKEL|
|protection.|K|ALUMINIUM*(NC/NA, Chromel/ Alumel, C/A,|+–|+–|+–|+–|KX|
|High temperature|-60°C to 700°C|Will withstand temperature up to 700°C but will not prevent|T1/T2, NiCr/Ni, NiCr/ NiAL)|
|||i|SB|fs|ff|
|glassfibre|ingress of fluids.|Fairly flexible, not good protection against|
|physical disturbance.|N|NICROSIL/NISIL|+–|+–|+–|NX|
|Ceramic Fibre|0 to 1000°C|Will withstand high temperature, up to 1000°C. Will not|NC|
|i|SS|Se|oe|
|protect against fluids or physical disturbance.|COPPER/CONSTANTAN|
|Glassfibre (varnished)|-60°C to 350/400°C|Good resistance to physical disturbance and high temperature|T|(Copper/Copper Nickel,|+–|+–|+–|+–|TX|
|stainless steel overbraid|(up to 400°C). Will not prevent ingress of fluids.|ae|Cu/Con, Copper/Advance)|oo|a|ke|
|Screened or unscreened?|With long cable runs, the cable may need to be screened and earthed at one|COPPER/CONSTANTAN|
|end (at the instrument) to minimise noise pick-up (interference) on the measuring circuit. Alternative|Vx|(LOW NICKEL) (Cu/Constantan)|+–|+–|+–|+–|KCB|
|Compensating for K (Cu/Constantan)|
|types of screened cable construction are available and these include the use of copper or mylar screening.|aa|a|
|Twisted pair configurations are offered and these can incorporate screening as required.|COPPER/COPPER NICKEL|
|Compensating for Platinum 10% or|
|U|13% Rhodium/Platinum (Codes SR|respectively) (Copper/Cupronic|&|+–|+–|+–|+–|RCASCA|
|THERMOCOUPLE ACCURACIES|ee|Cu/CuNi, Copper/No. 11 Alloy)|
|Tolerance classes for thermocouples to IEC 60584-2(1982) (Amend 1-1989) BS EN60584-2(1993)|* Magnetic, ( )|FOR THERMOCOUPLECONNECTORS body|FOR THERMOCOUPLECONNECTORS body|
|Fe-Con (J)|Class 1|- 40  +750°C:|±0.004|. t|or ±1.5°C|TL.|Alternative & Trade Name|colours are similar to outer sheath colours|colours are similar to outer sheath colours|
|Class 2|- 40  +750°C:|±0.0075|. t|or ±2.5°C|
|Class 3|-|-|-|
|Cu-Con (T)|Class 1|- 40  +350°C:|±0.004|. t|or ±0.5°C|CALIBRATION GUIDE|
|Class 2|- 40  +350°C:|±0.0075|. t|or ±1.0°C|Thermocouple|emf in absolute millivolts (IEC 584)|
|Class 3|-200  + 40°C:|±0.015|. t|or ±1.0°C|Type|100°C|400°C|800°C|1000°C|1200°C|1500°C|
|NiCr -Ni (K)|Class 1|- 40  +1000°C:|±0.004|. t|or ±1.5°C|T|4.279|20.872|-|-|-|-|
|and|Class 2|- 40  +1200°C:|±0.0075|. t|or ±2.5°C|E|6.319|28.946|61.017|76.373|-|-|
|NiCrSi-NiSi (N)|Class 3|-200  +  40°C:|±0.015|. t|or ±2.5°C|
|J|5.269|21.848|45.494|57.953|69.553|-|
|NiCr-Con (E)|Class 1|- 40  +800°C:|±0.004|. t|or ±1.5°C|K|4.096|16.397|33.275|41.276|48.838|-|
|Class 2|- 40  +900°C:|±0.0075|. t|or ±2.5°C|
|Class 3|-200  + 40°C:|±0.015|. t|or ±2.5°C|N|2.774|12.974|28.455|36.256|43.846|-|
|R|0.647|3.408|7.950|10.506|13.228|17.451|
|Pt10Rh-Pt (S)|Class 1|0  +1600°C:|±[1+(t-1000).0.003]|or ±1.0°C|
|and|Class 2|- 40 +1600°C:|±0.0025|. t|or ±1.5°C|S|0.646|3.259|7.345|9.587|11.951|15.582|
|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 +1700°C:|±0.0025|. t|or ±1.5°C|
|Class  3|+600 +1700°C:|±0.005|. t|or ±4.0°C|
|Note:|t = actual temperature|Use the larger of the two deviation values|
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|LABFACILITY 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)|
|The connection between the thermometer|that the length of cable is minimised to keep|Temp|Resistance|Tolerance|
|assembly and the instrumentation. The cabling|cable resistance to as low a value as possible.|Class A|Class B|
|introduces electrical resistance which is placed in|The use of  3 wires|, when dictated either by|(°C)|(|Ω|)|(±°C)|(±|Ω|)|(±°C)|(±|Ω|)|
|series with the resistance thermometer.|The two|probe construction or by the input termination of|-200|18.52|0.55|0.24|1.3|0.56|
|resistances are therefore cumulative and could|the measuring instrument, will allow for a good|-100|60.26|0.35|0.14|0.8|0.32|
|be interpreted as an increased temperature if|level of lead resistance compensation.|However|0|100.00|0.15|0.06|0.3|0.12|
|the lead resistance is not allowed for.|The|the compensation technique is based on the|100|138.51|0.35|0.13|0.8|0.30|
|longer and/or the smaller the diameter of the|assumption that the resistance of all three leads|200|175.86|0.55|0.20|1.3|0.48|
|cable, the greater the lead resistance will be and|is identical|and that they all reside at the same|300400|212.05247.09|0.750.95|0.270.33|1.82.3|0.640.79|
|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|
|For this reason,|a 2 wire arrangement is only|850|390.48|–|–|4.6|1.34|
|suitable for short cable lengths|. If it is essential|TT|
|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|
|For wire wound resistors|For film resistors|Tolerance value|[a]|
|Tolerance|Temperature range of|Tolerance|Temperature range of|°C|
|STEM CONDUCTION|SELF-HEATING|class|validity °C|class|validity °C|
|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|
|an apparent reduction or increase respectively in|passed through it. The measuring current|W 0.3|–196 to +660|F 0.3|–50 to +500|±|( 0.3 + 0.005 | t | )|
|measured temperature results. The|immersion|produces heat dissipation in the sensor. This|W 0.6|–196 to +660|F 0.6|–50 to +600|±|( 0.6 + 0.01 | t | )|
|depth|(the length of that part of the probe which|results in an increased temperature indication.|a|| 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.|

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This is the mechanism by which heat is conducted from or to the process medium by the probe itself; an apparent reduction or increase respectively in measured temperature results. The **immersion depth** (the length of that part of the probe which is directly in contact with the medium) must be such as to ensure that the “sensing” length is exceeded (double the sensing length is recommended). Small immersion depths result in a large temperature gradient between the sensor and the surroundings which results in a large heat flow. 

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|Temperature range of validity|
|Tolerance class|°C|Tolerance values|[a]|
|Wire wound resistors|Film resistors|°C|
|AA|–50 to +250|0 to +150|±|( 0.1 + 0.0017 | t |)|
|A|–100 to +450|–30 to +300|±|( 0.15 + 0.002 | t | )|
|B|–196 to +600|–50 to +500|±|( 0.3 + 0.005 | t | )|
|C|–196 to +600|–50 to +600|±|( 0.6 + 0.01 | t | )|

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If the sensor is immersed in flowing liquid or gas, the effect is reduced because of more rapid heat removal. Conversely, in still gas for example, the effect may be significant. The self-heating coefficient E is expressed as: 

The ideal immersion depth can be achieved in practice by moving the probe into or out of the process medium incrementally; with each adjustment, note any apparent change in indicated temperature. The correct depth will result in no change in indicated temperature. For calibration purposes 150 to 300mm immersion is required depending on the probe construction. 

> E = L t / (R – I[2] ) 

> Where L t = (indicated temperature) – (temperature of the medium) 

> a | t | = modulus of temperature in °C without regard to sign. For any value of R° 

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RECOMMENDED TERMINATION COLOUR CODES IEC 751(1995)<br>**----- End of picture text -----**<br>


R = Pt resistance 

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Red White Red Red White Red Red White White<br>2 Wire 3 Wire 4 Wire<br>**----- End of picture text -----**<br>


I = measurement current