Welcome Functionality and application of RTD Temperature Probes and Thermocouples Dipl.-Ing. Manfred Schleicher
This presentation informs about the basics of RTD Temperature Probes and thermocouples Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 2
Index RTD Temperature Probes General information Linearisation Connection types Tolerance classes Thermocouples thermo electrical effect Compensation Cable and connectors free of thermoelectric voltage External Temperature Compensation - Special Applications Tolerance classes Temperature transmitter and further information Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 3
RTD Temperature Probes General information
Operating Mode RTD Temperature Probes change the ohmic resistance if the temperature changes Platinum is the most common resistance material used for industrial measurements The PT 100 with a resistance of 100 Ω at 0 C is the most popular resistance thermometer Resistance values at temperatures from 0 100 C: Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 5
Operating Mode Furthermore the PT 1000 (basic resistance 1000 Ω), PT 500 (basic resistance 500 Ω) and the PT50 (basic resistance 50 Ω) are used In general all basic resistance are possible Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 6
RTD Temperature Probes Linearisation
Linearisation For the connection of a RTD Temperature Probes to a device, the RTD Temperature Probes is defined as the relevant input The device supplies the defined DC Based on the falling voltage and the ohmic law the resistance is determined In the device the different linearisations are filed; if - e.g. the linearisation Pt 100 is selected, the device determines the temperature which belongs to the resistance value I U Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 8
RTD Temperature Probes Connection types
Connection types 2-wire The measuring result incorporates the output resistance R L R L /2 I M U M R L /2 A temperature is measured which is higher than the real temperature at the RTD Temperature Probes The offset can be corrected either at the device or with the setup program As well after the zero point adjustment the output resistance changes if the ambient temperature changes and influences the measuring signal Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 10
Connection types 3-wire With a 3-wire connection the voltage drop at a conductor is determined (U L /2) R L /2 I M I 0 U L /2 U M R L /2 Due to high internal resistance (device) the current is supplied by the 3rd conductor 0 The double value U L /2 is deducted from the measured voltage U M By this means the voltage drop at the resistance thermometer is determined The actual resistance value is determined The 3-wire connection is the one which is used mostly in industry The pre-condition for an exact result is that both conductors have the same resistance value Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 11
Connection types 4-wire With a 4-wire connection the voltage drop is determined directly at the RTD Temperature Probes: I M I 0 I 0 U Resistor The resistance value can be determined directly by the voltage drop at the RTD Temperature Probes and the current The resistance values of the conductors and connectors can be differ The 4-wire connection offers the best measuring accuracy Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 12
RTD Temperature Probes Tolerance classes
Tolerance classes The following tolerance classes are defined for RTD Temperature Probes: Mostly RTD Temperature Probes class B are supplied Example: At a temperature of 0 C the thermometer has tolerance of: ±0,3 K At a temperature of 200 C the measuring tolerance is: ±(0,3 + 0,005x200)K=1,3K Devices in classes A and 1/3 class B are supplied in small quantities only Class 0,5 is used very seldom = Tolerance classes acc. to DIN EN 60 751 = Manufacturer tolerance classes Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 14
Thermocouples
Thermocouples Temperature measurements up to 600 C can be realized with RTD Temperature Probes Higher temperatures are mostly the reason for the application of thermocouples On the following pages we provide the most important basics concerning handling and application of thermocouples. Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 16
Thermocouples thermoelectric effect
Thermoelectric effect in a metal + - Due to heat supply the speed of the free electrons in a metal is increased The electrons move toward the colder wire Negative charge concentration at the cold end Positive charge concentration at the warm end Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 18
Thermoelectric effect in a metal Test measurement of the resulting voltage 0,00 mv Connection of cold end with measuring instrument Connection of copper cable with the warm end Reason: Same effect in the cable Same negative charge concentration on both ends No potential difference Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 19
Thermoelectric effect in a metal + Ni Cr 40,0 mv Ni Al - Use another metal for the cable: Now two different effects result in both cables The cold end of the nickel aluminum cable has a higher electric charge than the nickel chrome cable The electrons in the nickel aluminum cable are more flexible than the electrons in the nickel chrome cable Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 20
Thermoelectric effect in a metal Ni Cr + The thermoelectric voltage in the nickel chrome cable and the nickel aluminum cable remains unidentified The difference between the charge concentrations is measured The measured thermoelectric voltage is an indicator of the temperature difference mv? Ni Al mv? - Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 21
Measurement of temperature difference A thermocouple always measures a temperature difference (T 1 -T 2 ) To measure the temperature T 1, temperature T 2 must be measured as well and ad up to the temperature difference Fe T 1 T 2 CuNi Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 22
Measurement of terminal temperature T 2 is the temperature measured with an additional temperature sensor (PT100) on the terminals of the field devices The terminal temperature T 2 is added on the calculated temperature difference This is called internal temperature compensation Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 23
Configuration analog input For the used input, only the kind of probe thermocouple and the relevant linearization must be chosen: Please select thermocouple Please select the relevant linearization for the device The field device calculates the temperature at the thermocouple from the determined voltage at the thermocouple and the defined linearization Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 24
Thermocouples Compensation Cables and connectors free of thermoelectrical voltage
Thermocouples Compensation Cable The described function (internal temperature compensation) is granted only, if the additional thermovoltage arises at the clamps of the field device For this reason a compensation cable is used which has the same thermoelectrical behaviour as the metals of the thermocouple: Metal 1 Reference junction U 100 C V Metal 2 Compensation cable The appropriate compensation cables must be used for each thermocouple (polarity to be considered) See data sheet 90.3735 Compensation and connection cables Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 26
Colour marking of the compensation cable If the thermocouples are produced acc. to DIN EN 60584, the colours of the compensation cable enable to identify the kind of thermocouple and as well sheath, plus and minus The following table shows the colouring: Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 27
Colours Compensation cable - international Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 28
Thermocouples connectors free of thermoelectric voltage When the extension wires are divided and connected via e.g. terminal strips, this results in new thermocouples U U Extension wire part 1 Extension wire part 2 The voltages are canceled by each other when different parts have the same temperature When the temperatures differ, you have to use connectors free of thermoelectric voltage (e.g. when the wire is directed through the housing): The connectors are made of the same material like the thermocouples or of materials with the same thermoelectric behavior - Connectors depend on the used thermocouple - Consider the polarity Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 29
Thermocouples Connection Wires - Plug assignment and Colour Codes Plug assignment and the used colour codes of the connection wires for resistance thermometers and thermocouples are standardised Please refer to the overview in our data sheet 90.0002: Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 30
Thermocouples External Temperature Compensation - Special Applications
External Temperature Compensation Basically thermocouple and device can be connected by a copper wire Metal 1 Copper U 100 C PT100 V Metal 2 Input 2 Reference junction The reference junction arises at the connection clamps of the thermocouple The device measures the voltage of thermocouple minus the voltage at the connection clamps The temperature must be measured at the connection clamps and ad up Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 32
External Temperature Compensation Configuration at the device: Thermocouple with external temperature compensation (Only some JUMO devices offer this function) Which input provides the temperature of the reference junction? Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 33
Tolerance classes
Thermocouples Tolerance classes Three tolerance classes are defined: Example: Element Fe-CuNi J Class 2, Measuring temperature 200 C Tolerance: ±0,0075 x 200 C = ±1,5 C or ± 2,5 C Basis is always the max. value; thus it must be reckoned with a measurement tolerance of ± 2,5 C. Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 35
Temperature transmitters and literature
Temperature transmitters Transmitter realizes standard signals (e.g. 4...20 ma) Controller Screen recorde Resictance Thermometer / Thermocouples Standard signal PLC etc. Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 37
Temperature transmitter JUMO offers a big assortment of transmitters for head or rail installation Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 38
Further information Reference Book Electrical Temperature Measurement Free Download (PDF document) available under: http://literatur.jumo.info Functionality and application of RTD Temperature Probes and Thermocouples/ Manfred Schleicher (2012-01-03) 39
Thank you for your attention.