6 Key Differences Between RTD's And Thermocouples - That .
6 key DifferencesBetween RTD’s and Thermocouples- that Might Change your PreferencesEllab White Paper - 02/19Validation Solutions
6 key Differences Between RTD’s and ThermocouplesValidation SolutionsWhat is the difference between a Resistance Temperature Detector (RTD) and a thermocouple (TC)? Both RTD’s andthermocouples are temperature sensors that can be used in a broad range of applications - their design and versatility,however, are completely different.This often raises the question: how do I choose between RTD’s and thermocouples? Each technology has its own advantages and disadvantages, which either makes them suitable or unsuitable for certain processes and applications.This paper highlights the 6 most important differences between RTD’s and thermocouples by delving into the technology-based advantages and disadvantages of each type of sensor. The various considerations that must be taken intoaccount before deciding on which type of sensor is right for your application will be explained and concluded.Page 2ellab.com
6 key Differences Between RTD’s and ThermocouplesValidation SolutionsTable of ContentsRTD Sensors.4RTD Sensor Highlights and Limitations.4Thermocouple Sensors.5Thermocouple Sensor Highlights and Limitations.5The 6 key Differences Between RTD’s and Thermocouples .6Measuring Range.7Accuracy.7Sensitivity.7Drift.7Measuring Area .7Cost.7Conclusion.8What Ellab Offers.8ellab.comPage 3
6 key Differences Between RTD’s and ThermocouplesValidation SolutionsRTD SensorsThe measuring principle of a Resistance TemperatureDetector, or RTD, can be described as follows: The electrical resistance of metals rise as heat increases and the metals become hotterThe electrical resistance of metals fall as heat decreases and the metals become colderRTD’s are therefore temperature sensors that use thechange in electrical resistance of metals to measure thechange in local temperature.All RTD sensor elements either consist of a fine coiledplatinum (Pt) wire wrapped around a ceramic core – or athin film of platinum in an element substrate. The elementis typically relatively fragile, so it is typically installed inside a sheath in order to protect it.RTD sensor elements are constructed from pure materials that have their resistance at various temperaturesdocumented. In other words, the material has a predictable change in resistance as the temperature varies. It isthis change that is used to determine the actual temperature.RTD principle (source: Electrical4you.com)RTD Highlights and LimitationsHighlights Very high accuracy Outstanding sensitivity Excellent stability and repeatability (low drift)Limitations Narrow temperature range High CostRTD’s are generally considered to be among the mostaccurate temperature sensors available. In addition to offering a very high accuracy, they provide excellent shortand long-term stability as well as repeatability.Page 4ellab.com
6 key Differences Between RTD’s and ThermocouplesValidation SolutionsThermocouple SensorsA thermocouple, or TC, consists of two dissimilar metalswelded together at one end. When the junction of the twometals is cooled or heated, a difference in voltage is produced that can be correlated directly back to the temperature,but only when the necessary cold junction compensationhas been considered.Thermocouples are manufactured in different combinationsof metals and/or calibration ranges. The most commontypes are J, K, T and E, whereas high temperature thermocouples include R, S and C. Each type has a differenttemperature range and environmental performance. Whilethe type defines the temperature range, the diameter of thethermocouple wire is also a factor.Since thermocouples measure wide temperature rangesand are relatively rugged, they can be used for industrialand process applications in which a high accuracy may bea less important factor.TypeJunctionTemperature Range CBPlatinum/Rhodium50 to 1800EChromel/Constantan-200 to 850JIron/Constantan-200 to 850KChromel/Alumel-200 to 1100RPlatinum/Rhodium0 to 1400SPlatinum/Rhodium0 to 1400TCopper/Constantan-250 to 400ellab.comThermocouple principle (source: PLC Academy.com)Thermocouple Highlights and LimitationsHighlights High measuring range Low costLimitations Lowered accuracy Less sensitive Relatively high drift-over-timePage 5
6 key Differences Between RTD’s and ThermocouplesValidation Solutions6 key DifferencesBetween RTD’s and ThermocouplesBecause RTD’s and thermocouples are designed differently, having specific characteristics for each makes itimpossible to conclude whether RTD’s or thermocouplesare the superior choice for a specific application.Instead, it is far more useful to compare the performanceof RTD’s and thermocouples by using other qualities,such as their measuring range, accuracy, sensitivity, driftand cost in order to facilitate an appropriate decisionbased on the specific needs.Page 6ellab.com
6 key Differences Between RTD’s and ThermocouplesValidation Solutions1. Measuring Range4. DriftThe main advantage of thermocouples is their range.Most RTD sensors are limited to temperatures of up to400-500 C, and in some cases higher, whereas certainthermocouples can be used to measure above the 1400to 1800 C range, which makes them suitable for a largerange of applications.The RTD sensors drift is small due to their design, whichmakes them produce stable readings for longer durationsthan thermocouples can. Unlike RTD sensors, a thermocouple has a relative high drift-over-time, which is typically caused by inhomogeneity of the conductor wires resultingfrom heat- and chemical exposure or mechanical damage,such as having been bent, tugged or squeezed during use.Due to this, frequent calibrations and adjustments are mandatory for thermocouples.2. AccuracyRTD’s provide the highest accuracy and may be the preferred solution when a temperature measurement accuracy isrequired to be around 0.05 to 0.1 C.Thermocouples in comparison, have a lowered accuracyaround 0.2 to 0.5 C.5. Single Point Measurements3. SensitivityAlthough a thermocouple sensor system usually has afaster response time due to the changing temperature at itspoint of contact, it generally takes longer to reach thermalequilibrium. This is largely due to the presence of the coldjunction compensation, which does not respond to the change in temperature as quickly as the hot junction located atthe tip of the sensor does. In comparison an RTD sensor isdesigned to be more durable and react faster to temperaturechanges (naked tip).Due to the design of a thermocouple, it is possible to narrowthe measuring point down to the exact spot where the twometals are welded together. This point can then be definedvery accurately when operating thermocouples with “nakedtips”. For RTD sensors however, measurements are calculated by taking the average value along the entire surface ofthe PT (platinum) element itself. This is mainly a disadvantage for large elements like PT100, whereas smaller elementslike the PT1000 rarely have this issue, as some leading suppliers can provide PT1000 elements as small as 1x1.5 mm.6. CostWhen it comes to cost, thermocouples are generally lessexpensive than RTD sensors, as most thermocouples costbetween half to one third of an RTD. As mentionedhowever, thermocouples require regular adjustments andcalibration, which in addition to the longer installation andSensor ComparisonParametersetup times, adds to the long-term costs of the product.RTDThermocouple-240 to 650 C-270 to 2,320 CLong-term StabilityExcellentPoor to FairAccuracyExcellentGood to MediumRepeatabilityExcellentPoor to FairGoodMedium to ExcellentTypical Measuring RangeResponse TimeLinearityUndesirable Self-HeatingTip Sensitivityellab.comGoodFairMedium to ExcellentExcellentFairExcellentPage 7
6 key Differences Between RTD’s and ThermocouplesValidation SolutionsConclusionThe conclusion is based exclusively on the advantages and disadvantages of the sensor types, and does notconsider the features and benefits of the measuring equipment.For applications that require a high accuracy and operate at temperatures below 500 C, the RTD temperaturesensors are often the right choice. Thermocouples, on the other hand, are ideal for simply constructed processes thatrequire a wider temperature range, faster response time and the ability to measure highly specific points of interest.Looking at the 6 key differences, the RTD sensor is more accurate, stable and repeatable. They also drift far less.RTD’s also offer a more robust output signal, resulting in an increased sensitivity and linearity. However, they have anarrower operating range, lower maximum operating temperature and are generally more expensive.Thermocouples are less expensive, are more durable and can measure a wider range of temperatures. However, theyhave a lowered accuracy and a high drift-over-time, making frequent calibrations mandatory, adding to overall costs.The conclusion is that RTD’s and thermocouples each have their own advantages and disadvantages. When choosing between the two types of temperature sensors, all 6 key differences should be taken into consideration and beheld against the important factors of the process. Finally, size is also an important factor to consider, as RTD sensorsremain relatively large by comparison to thermocouples.What Ellab OffersEllab offers complete validation solutions, in which theIn other words, time is money and working with a wirelesssensors themselves only consist as a small part of thesystem generally saves operators a highly considerableoverall measuring equipment. This means that there areamount of time.additional considerations before making a final choice.Ellab has also developed a highly unique hybrid solution,Several studies have shown that purchasing wired cablein which a thermocouple sensor is attached to one of oursystems, may initially be cheaper from an investmentTrackSense Pro wireless data loggers. This solutionpoint of view. But when it comes to operating the twoenables a wide range of alternatives for applications likedifferent systems (TrackSense and E-Val Pro), one bigLyophilization and UHT/HTST pasteurization.and operate RTD’s via wireless data loggers, makingIf you wish to learn more about Ellab, we recommend thatthe initial purchase price considerably less importantyou take a closer look at the various thermocouple andwhen compared to the total running costs.RTD based validation systems available at ellab.comEllab A/S Trollesmindealle 25 3400 Hillerød Denmark ellab.com Ellab A/S, 2019factor stands out – it is generally a lot faster to install
RTD sensor elements are constructed from pure mate-rials that have their resistance at various temperatures documented. In other words, the material has a predic-table change in resistance as the temperature varies. It is this change that is used to determine the actual tempera-ture. RTD
The previous equations define the RTD resistance as a function of its temperature, R. RTD (t). However, to implement an RTD sensor interfacing circuit, the RTD temperature must be deter-mined, instead, as a function of its resistance, T. RTD (r). This may be less straightforward, given the
The RTD Series Precision RTD (Resistance Temperature Detector) Simulator provides a very broad-range of absolute resistance values that replace RTD’s,thermocouples. Thermocouples present a re-sistance that depends on the temperature. The RTD simulator effectively replaces an RTD to test, analy
Accounting Differences There are no differences. System Management Differences There are no differences. Execution/Call Processing Differences There are no differences. Client Application Differences There are no differences. Deployment/Operational Differences There are no differences. System Engineering Differences There are no differences.
Table 2 lists the coefficients used in this equation for each of the TCR values that the [c]FP-RTD-124 supports. If you have a nonstandard RTD that does not match one of these linearization curves, measure the resistance with the [c]FP-RTD-124 and convert the resistance to temperature in the manner suggested by t
TX92 RTD Transmitter. The TX92 Two-Wire RTD Transmitter will produce a standard 4-20 mA output signal proportional to that produced by its RTD input temperature sensor. Transmission of the proportional current output may be accomplished by using copper wires. The TX92 RTD Transmitter accepts 100 Ohm, Plat
About the Excel RTD app The Excel RTD app lets you do two things: Put real-time data into Excel using only Excel's RTD() function. No macros; no . MT4/5: the app will report all the symbols which are included in the MT4/5 market watch . 2.2 Excel formula Once the RTD app is running, you can use the following formula in Excel to insert a .
4-wire RTD and ohms T/Cs and millivolts RTD with compensation loop (2) (1) Emerson provides 4-wire sensors for all single-element RTDs. You can use these RTDs in 3-wire configurations by leaving the unneeded leads disconnected and insulated with electrical tape. (2) Transmitter must be configured for a 3-wire RTD in order to recognize an RTD with a
4-Wire RTD or 3-Wire RTD (100 W platinum [PT100], D100, F100, PT385, PT3916, or user 0 W to 10 kW) (Selectable Offset compensation On or Off) For 3-wire RTD, dmm.connect dmm.CONNECT_FOUR_WIRE, 0.1 W lead resistance mismatching in Input HI and LO. Add 0.25 C/0.1 W of lead resistance mismatch. 4-Wire RTD –200 to 630 C 0.01 C 0.06 C 0 .
