Application Note

RTD Platinum Sensor

ATP_E2.1.10 | App Note | RTD Platinum Sensor 1/7

 Application Note
RTD Platinum Sensor
Content

1. General Information 3
2. Construction 3
3. Nominal Value and Temperature Coefficient 3
4. Long-term Stability 3
5. Temperature Characteristic Curve 3
6. Tolerance Classes IEC60751 Norm 4
7. Applied Current 4
8. Self-heating 4
9. Response Time 5
10. Dimensions Tolerances 5
11. Operating Conditions 6
12. Sensor Construction Examples 6
13. Additional Documents 7

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 Application Note
RTD Platinum Sensor

1. General Information
In many sectors, temperature is one of the most important physically defined parameters to determine product qua-
lity, security and reliability. Temperature sensors are produced with different technologies to fit specific application
requirements. IST AG has concentrated on the development and manufacturing of high-quality thin-film temperature
sensors. This know-how, partially derived from the semiconductor industry, allows IST AG to manufacture sensors in
very small dimensions. Thin-film temperature sensors exhibit a very short response time due to their low thermal mass.
The technologies and processes of IST AG thin-film sensors combine the positive attributes of traditional sensors -
accuracy, long-term stability, repeatability and interchangeability within a wide temperature range. The advantages of
thin-film mass-production create an optimal price/performance-ratio.

2. Construction
The temperature sensor consists of a high-purity platinum meander, structured on a ceramic substrate by the use of
photolithography. The resistivity is laser-trimmed and precisely adjusted to the final value. The resistive structure is
covered with a glass passivation layer protecting the sensor against mechanical and chemical damages. The welded
lead wires are covered with an additional fixation layer.

3. Nominal Value and Temperature Coefficent

The nominal value of the sensor is the defined value of the sensor resistance at 0 °C. The temperature coefficient α
(TCR) is defined as:
R100 - R0
α = 100 x R [K-1] according to the IEC60751, 2008-07 numerical value of 0.00385 K-1.
0

Generally, the value is defined in ppm/K.

This example defines 3850 ppm/K1).

R0 = resistance value in Ω at 0 °C
R100 = resistance value in Ω at +100 °C
1) Other TCRs available upon request

4. Long-term Stability
For all sensor types up to 7W (+750 °C), the change in ohmic value after 1000 hrs is less than 0.04 % at maximum
operating temperatures.

5. Temperature Characteristic Curve

The curve determines the relationship between the electrical resistance and the temperature.

R(T) = R0 (1 + A x T + B x T2) 0 °C to +850 °C

R(T) = R0 (1 + A x T + B x T2 + C x [T-100] x T3) -200 °C to 0 °C

Platinum (3850 ppm/K) Platinum (3911 ppm/K) Platinum (3750 ppm/K) Platinum (3770 ppm/K)
A = 3.9083 x 10 [°C ] -3 -1
A = 3.9692 x 10 [°C ]
-3 -1
A = 3.8102 x 10 [°C ]
-3 -1
A = 3.8285 x 10-3 [°C-1]
B = -5.775 x 10-7 [°C-2] B = -5.829 x 10-7 [°C-2] B = -6.01888 x 10-7 [°C-2] B = -5.85 x 10-7 [°C-2]
C = -4.183 x 10 -12
[°C ] -4
C = -4.3303 x 10 -12
[°C ] -4
C = -6 x 10-12
[°C ]
-4

R0 = resistance value in Ω at 0 °C
T = temperature in accordance with ITS 90

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 6. Tolerance Classes IEC60751 Norm
Temperature sensors are classified according to IEC60751, 2008-07.

Class ± deviations in °C Temperature range of IST AG reference

validity in °C*
IEC60751 F 0.1 0.10 + 0.0017 x |T| 0 to +150 Y
IEC60751 F 0.15 0.15 + 0.002 x |T| -30 to +300 A
IEC60751 F 0.3 0.30 + 0.005 x |T| -50 to +500 B
IEC60751 F 0.6 0.60 + 0.01 x |T| -50 to +600 C
1/5 IEC60751 F 0.3 0.06 + 0.001 x |T| upon request K
1/10 IEC60751 F 0.3 0.03 + 0.0005 x |T| upon request K
* Customer-specific temperature range available on request

|T| is the numerical value of the temperature in °C without taking leading signs into account.

The temperature curves refer to IEC60751 standards. The values in the table are for informative purposes only.
Based on the assembly method and the different measurement conditions, accuracy, self-heating and response time
may vary.

The measurement point is 5 mm from the wire end. For long wires (> 20 mm) the resistance is compensated (mea­
sured at room temperature) to ensure the correct resistance at the chip edge.

The resistance compensation of long wires (direct soldered or extended wires) has always to be taken into considera-
tion for the end application. Exceptions are 3 or 4 wire solutions.

For 1/3 IEC60751, 1/5 IEC60751, 1/10 IEC60751 and 3- or 4-wire sensors please contact us.

7. Applied Current
The influence of the applied current is highly dependent on how the sensor is used in the application and can lead to
significant self-heating effects. In general, the applied current should be as low as possible in order to reduce self-he-
ating effects. The following values are typically used as measurement current:

100 Ω 500 Ω 1000 Ω 2000 Ω 10000 Ω

1 mA 0.5 mA 0.3 mA 0.2 mA 0.1 mA

Higher measurement currents can be applied as long as self-heating does not change the measurement value more
than the needed measurement accuracy. The maximum current for sensors between 750°C and 1000°C should not
exceed 1mA.

8. Self-heating
The electric current generates self-heating resulting in errors of measurement. To minimize the error, the testing
current should be kept as low as possible. The measurement error caused by self-heating is dependent on
temperature error ∆T = R x I2 / E.

E = self-heating coefficient in mW/K, R = resistance in kΩ, I = measuring current in mA

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 9. Response Time
The response time is defined as the time in seconds the sensor needs to detect the change in temperature. t0.63 descri-
bes the time in seconds the sensor needs to measure 63 % of the temperature change. The response time depends
on the sensor dimensions, the thermal contact resistance and the surrounding medium.

Dimensions number Response time in seconds Self-heating

Water (v = 0.4 m/s) Air (v = 1 m/s) Water (v = 0 m/s) Air (v = 0 m/s)

t0.5 t0.63 t0.9 t0.5 t0.63 t0.9 E in mW/K ∆T in [mK]
1)
E in mW/K ∆T in [mK]1)
161 0.05 0.08 0.18 1 1.2 2.5 12 8.3 1.8 56
308 0.08 0.1 0.25 1.2 1.5 3.5 15 6.7 2.2 46
232 (thin substrate) 0.09 0.12 0.33 2.7 3.6 7.5 40 2.5 4 25
202 0.11 0.16 0.38 3.6 4.9 10.2 32 3.1 3.2 31
216 0.12 0.18 0.42 4 5.4 11 36 2.8 3.6 28
232 0.15 0.2 0.55 4.5 6 12 40 2.5 4 25
325 0.25 0.3 0.7 5.5 7.5 16 90 1.1 8 13
516 0.25 0.3 0.7 5.5 7.5 16 80 1.3 7 14
520 0.25 0.3 0.75 6 8.5 18 80 1.3 7 14
525 0.33 0.4 0.85 6.5 9 19 90 1.1 8 13
538 0.35 0.4 0.90 7.5 10 20 140 0.7 10 10
505 0.4 0.5 1.1 8 11 21 150 0.7 11 9
102 0.33 0.4 0.85 7.5 10.5 20 140 0.7 10 10
281 2.5 4.5 8 10 15 28 60 1.7 5.5 18
281* 2 2.5 5.5 10 12 22 45 2.2 4 25
451 8 10 22 12 22 40 85 1.2 8 13
451* 5 6 14 16 18 37 60 1.7 6.5 15
SMD 1206 0.15 0.25 0.45 3.5 4.2 10 55 1.8 7 14
SMD 0805 0.1 0.12 0.33 2.5 3 8 38 2.6 4 25
FC 0603 0.08 0.1 0.25 1.8 2.2 5.5 25 4 2.5 40
1) Self-heating ∆T[mK] measured with Pt100 at 1 mA applied current at 0 ºC

* Two sensing elements in the same round ceramic housing

L: Sensor length (without connections) H: Sensor height (without connections)

W: Sensor width H2: Sensor height (incl. connections and strain relief)

10. Dimensions Tolerances

Sensor width (W) ±0.2 mm Wire length ±1 mm (up to 30 mm)
Sensor length (L) ±0.2 mm Wire length > 30 mm, tolerances according ISO 2768-1,
Sensor height (H2) ±0.3 mm tolerance class V (very coarse): see table below
Sensor height (H) ±0.1 mm

Wire length in mm 31-120 121-400 401-1000 1001-2000 2001-4000

ISO 2768-1, tolerance class V (very coarse): ±1.5 mm ±2.5 mm ±4 mm ±6 mm ±8 mm

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 11. Operating Conditions
Platinum temperature sensors are built on the basis of very robust materials: a high temperature glass protects the
meander, the substrate is mainly based on densely sintered high-purity alumina and the wire fixations enable a relia-
ble strain relief of the welding points.

Unfortunately it is not possible to test the sensor behavior in all application and installation conditions. Therefore the
customer needs to test the compatibility of the sensor element with the application and/or the installation condi-
tions. With certain ceramic casting compounds for instance there can occur chemical reactions between the passi-
vation glass and the fixation glass. Potential problems can also arise due to strong creeping polymers (e.g. uncured
silicones) or because of the reaction between plastic-based casting compounds with the plastic-based wire fixations,
used for directly welded wires. The use of bare sensors in long-term humid environment as well as in aggressive
atmospheres has to be avoided; the same applies to the direct dipping of the sensor into liquids. Furthermore me-
chanical pressure on the sensors, e.g. caused by hard or strong post-curing casting compounds should be avoided.
Some epoxy-based casting compounds might become conductive above Tg and therefore cause a bypass via the
sensor wires, which can lead to a lower resistance reading.

For sensors at higher temperatures (> +600 °C) oxygen access should be guaranteed in order to counter post-oxida-
tion-effects in stainless steel housings. Alternatively the construction should be chosen in a way that no significant
decrease of the oxygen partial pressure might occur in the installation. In principle, stainless steel parts should be
carefully cleaned and pre-oxidized.

IST AG also offers special (customer-specific) sensors for various applications. Please don’t hesitate to contact us and
ask for your suitable sensor solution.

12. Sensor Construction Examples

Wire

SIL

FlipChip and SMD

Minisens and Slimsens

Long wire, insulated wire and insulated stranded wire

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 Inverted wire and perpendicular wire

Round ceramic housing

13. Additional Documents

Document name:
English: German:
Data Sheets: DTP150_E DTP150_D
DTP200_E DTP200_D
DTP300_E DTP300_D
DTP400_E DTP400_D
DTP600_E DTP600_D
DTP750_E DTP750_D
DTP850_E DTP850_D
DTP1000_E DTP1000_D
DTPPW_E DTPPW_D
DTPPW_4-Wire_E DTPPW_4-Leiter_E
DTPPG_E DTPPG_D
DTPSMD_E DTPSMD_D
DTPFC_E DTPFC_D
DTPBondSens_E DTPBondSens_D
DTPRPT_E DTPRPT_D
DTP_Round_Housing_E DTP_Rundes_Gehaeuse_D

Innovative Sensor Technology IST AG, Stegrütistrasse 14, 9642 Ebnat-Kappel, Switzerland
Phone: +41 71 992 01 00 | Fax: +41 71 992 01 99 | Email: info@ist-ag.com | www.ist-ag.com
All mechanical dimensions are valid at 25 °C ambient temperature, if not differently indicated • All data except the mechanical dimensions only have information purposes and are not to be understood as assured characteristics • Technical
changes without previous announcement as well as mistakes reserved • The information on this data sheet was examined carefully and will be accepted as correct; No liability in case of mistakes • Load with extreme values during a longer
period can affect the reliability • The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner • Typing errors and mistakes reserved • Product
specifications are subject to change without notice • All rights reserved
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