high measurement accuracy platinum thin film rtd
TRANSCRIPT
HIGH MEASUREMENT ACCURACY PLATINUM THIN FILM RTD TEMPERATURE SENSORS
Dave Boylan
23.07.2020
Common methods for measuring temperature include:
• Thermocouples
• Thermistors
• Resistance temperature detector (RTD)* Best for stability in production, and ability to be calibrated to very high sensitivity levels with very low drift
in the specified temperature range
https://www.ist-ag.com/en/products-services/temperature-sensors
• Pyrometer
• Infrared
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RTD sensors can be thin-film, wire-wound, or coiled elements
Advantages of platinum resistance thermometers:
• High accuracy
• Low drift
• Wide operating range
• Suitability for precision applications.
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Fundamentals of Pt thin film RTD temperature sensors
• Platinum RTDs are the most common metal based RTDs used in industrial
applications. This is because platinum offers corrosion resistance, long-
term stability, low drift, low hysteresis and measures across a wide range
of temperature,
(-200…+850°C).
• Thin film RTDs are mass-produced and cost less than the other RTD types.
They are smaller, have a mechanical robust construction and have a faster
response time than other types (wire-wound, coiled), which is desirable in
many applications. They are made by depositing a thin pathway
(meander) of platinum on a ceramic base.
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IST AG Pt Thin Film RTD Construction
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Al2O3 for chemical and temperature robustness
Pt Thin film RTD Parameters
• Sensor is basically described by the following parameters:• – TCR – Temperature coefficient of resistance usually 3850 ppm/K
• – R0 – base resistance at 0°C
• - Tolerance
• The real characteristics of the resistance in regards to the temperature is defined by
the• – Polynomial or characteristic curve
• – With values A,B,C
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R0 is the nominal ohmic value at 0°CCommon is 100 Ohm, 500 Ohm, 1000 OhmSometimes:
– 50 Ohm (mostly for heaters)– 200 Ohm (mostly automotive)– 2000 Ohm– 10000 Ohm
Pt100 or Pt1000?
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Previously, wire-wound RTDs with R0 = 1000Ohm were expensive and fragile (long Pt wires with small diameter)• Pt100 was mostly used for wire-wound RTDs
However using thin-film technology, Pt1000 R0 could be a better choice:• Higher resistance change• Less influence of connecting wires• Less influence of contact resistances• Same price as Pt100
However using Pt100 could be a good choice for• Small Die sizes and/or high temperature die, as lower ohmic resistances are better
IEC 60751 standard for Pt thin film RTDs
• Platinum RTDs generally conform to the IEC 60751 standard. In a typical industrial
application, the RTD is protected by inserting it into a stainless steel sheath.
• The standard describes the behaviour of the sensor in regards to the temperature
• All sensors according to the standard can be interchanged without recalibration
• The standard defines the measurement accuracy tolerance bands and tolerance ranges
• It also regulates the differences between temperature sensing elements and probes
Limitation: Standards can be limiting and forbid product differentiation based on performance
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- 1/5 DIN (F 0.3) : ±(60mK +1 mK/K)- 1/10 DIN (F 0.3): ±(30mK +0.5 mK/K)*
Unofficial norms:
* Best in class today
1/10 DIN Class B => Limited Range of Validity ~
30degC
Accuracy deviations increase with increasing
Temperature
Highly priced due to tight selection criteria
IEC
Question: How Can I get the very best Accuracy calibrated Sensor?Solution: Individually Calibrated Sensors from IST AG for high measurement accuracies
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High accuracy RTDs generally do not exactly
match the IEC 60751 R:T curve. To further
improve measurement accuracy, IST AG can
very precisely characterize an RTD based on
more than 25 years experience. This is done
by carefully measuring the RTD resistance at
a different temperatures and then using that
data to derive the polynomial A, B, and C
coefficients.
Method: Each Thin-film RTD sensor is individually measured in the normal IST AG manufacturing process
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• Temperature Characteristic Curve (Polynomial) is calculated from multiple measurement points
• +/- 50mK measurement accuracy possible across the full range -40degC to +100degC T Range extension possible) => No increase of measurement uncertainty with temperature!
• +/- 30mK measurement accuracy also possible (More measurement points necessary )
• Ro A, B & C Polynomial values for each serialised sensor provided in Spreadsheet (Look-up values), Data-Matrix or QR code on packaging
Individual calibrated Sensor Benefits:
• High Volumes possible
• 4 – Wire options available
• Reasonably priced
• Pre-compensated (shifted) tolerance band is also possible
[mostly customers add offset and drift while assembling
IST AG sensors.]
Contact us to discuss ➔ https://www.ist-ag.com/en/contact
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Example: Pt1000 Thin Film RTD
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P1K0.1206.1K.K.SResistance: 1000 Ohm at 0°CTolerance: individual polynomial values for accuracy: +/- 50mK between -10°C and +60°CIEC 60751 F0.3 in rangeT.-Range: -20°C - +100°CPackage: single packaged and numbered, delivered with electronic and paper versions of polynomial values R0, A & B
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Example: New Glass Sealed RTD with Class A (IEC 60751 F0.15) Accuracy to 400degC
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Resistance: 100 Ohm at 0°CTolerance: IEC 60751 F 0.15 from -200°C to +400°CTCR: 3850 ppm/KT.-Range: -200°C - +400°CDimension: 2.4 x 1.4 x 0.8 mm (LxWxH, element)Contacts: Pt-wire, Ø 0.2 mm, 10 mm longSpecial: in round glass housing 8 x 2.25 mm (LxD)
PW0K1.216.4K.A.010.S (Order # 151495)
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Application Example: High Accuracy RTD that can be used as both heater and temperature sensor in a Heated Razor
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Option 1:Panel / area heater (uniformly distributed oversurface) • Heater size about 35 x 2.5 mm
Solution:1. Ceramic heater (Thick- or Thinfilm)
Directly integrate the heater on the ceramic?
2. Heater direcly processed on metalNo assembly needed to heat spreaderNo thermal bridge to the spreaderVery fast response time (<<1 sec)
3. FlexPrint or stainless steel heater with additional temperature sensors (as in fig. 2)
* Replaces NTC’s
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Application Example: High Accuracy RTD that can be used as both heater and temperature sensor in a Heated Razor
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Option 2:• Local heating spots (in orange)• Heater size about 2.1 x 1.2 mm • Sensor backside in contact with the heat
spreader• Very low cost solution• Fast response time ~<1Sec
* Replaces NTC’s
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Customised assemblies also available from IST AG
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https://www.ist-ag.com/en/contact
Contact
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Innovative Sensor Technology IST AG
Stegrütistrasse 14
9642 Ebnat-Kappel
Switzerland
Phone: +41 71 992 01 00Fax: +41 71 992 01 [email protected]
THANK YOU!
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