Resistance Temperature Detectors

Resistance Temperature Detector Specifications

Unless otherwise specified, Durex's RTD assemblies include photo-lithographically structured, high-purity platinum thin-film elements laser trimmed to precise resistance values. These sensors feature brief response times, excellent long term stability, low self heating and excellent resistance to vibration and temperature shocks.

Thermal Response Time
The response time T_0.63 is the time the sensors need to respond to 63% of the change in temperature. The response time depends on the sheath dimensions, but can be as low as 1.2 seconds.

Long Term Stability
The change of ohmage after 1,000 hours at maximum operating temperature amounts to less than 0.03%.

Self Heating
To measure the resistance, an electric current has to flow through the element, which will generate heat energy resulting in errors of measurement. To minimize error, the testing current should be kept low (approximately 1mA for Pt-100).
Temperature error ΔT = RI²/E with:
E = self-heating coefficient in mW/K
R = resistance in kΩ
I = measuring current in mA
The self-heating coefficient (E) for the standard elements used in Durex RTD assemblies is 4 mW/K in air and 40 mW/K in water.

Measuring Current
Measurement current causes heating of the platinum thin-film sensor. The resulting temperature error is given by:
ΔT = P/E with the power loss P = I²R, and the self-heating coefficient E in mW/K.
The amount of thermal transfer from the sensor in the application determines how much measuring current can be applied. There is no bottom limit of the measurement current with platinum thin-film. The measurement current depends highly on the application in use.
We recommend at:
100Ω: typically 1mA, maximum 5mA
500Ω: typically 0.5mA, maximum 3mA
1000Ω: typically 0.3mA, maximum 2mA
2000Ω: typically 0.2mA, maximum 1mA

Nominal Values
The nominal or rated value of the sensor is the target value of the sensor resistance at 0°C. The temperature coefficient α is defined as
α = R100 - R0
      100 - R0
 (K^-1) and has the numerical value of 0.00385 K^-1 according to DIN IEC 751.

In practice, a value multiplied by 10⁶ is often entered: TCR = 10⁶ x R100 - R0
                                                                                                           100 - R0 x (ppm/K)

In this case, the numerical value is 3850 ppm/K.

Temperature Characteristic Curve
The temperature characteristic curve determines the dependence of the electrical resistivity on the temperature. The following definition of the temperature curve according to DIN EN 60751 standard applies:

Tolerance Classes

Class	± limit deviations in °C (K)	IST AG designation	Temperature range
DIN 60751, class B	0.30 + 0.005 x |T|	B	-200°C to 850°C
DIN 60751, class A	0.15 + 0.002 x |T|	A	-90°C to 300°C
⅓ DIN 60751, class B	0.10 + 0.0017 x |T|	Y	-50°C to 150°C

|T| is the numerical value of the temperature °C without taking into account either negative or positive signs.
Special selection of sensors upon request (pairings, groupings, special tolerances).

Calibration Services
Durex RTD calibrations are fully traceable to the National Institute of Standards and Technology (NIST) and are useful for defining the exact temperature coefficient of the sensor. For sensor applications below 32°F (0°C), a cryogenic range calibration is recommended. Certificates are supplied with all calibrations. Printed tables of interpolated values are only supplied with cryogenic range calibrations.

Style: R1L, R2L, R3L, R4L - The maximum rated temperature for these four styles is 500°F. Typically they are constructed with Teflon leads and the lead end is protected with an epoxy seal. This epoxy seal provides a moisture resistant barrier.

Style: R1M, R2M, R3M, R4M - The maximum rated temperature for these next four styles is 900°F. They are constructed with high temperature fiberglass insulated conductors. The lead end is sealed and protected with a high temperature cement.

Style: R1P, R2P, R3P, R4P - The maximum rated temperature for these last four styles is 1200°F. Their construction features highly compacted magnesium oxide insulation. Nickel conductors provide for extended temperature ratings and harsh environments.

 

Available Resistance Temperature Detector Elements

Code	Element Type	Temperature Coefficient	Tolerance at 0°C
A	100 ohm Platinum	.00385	.1%
B	100 ohm Platinum	.00385	.06%
C	100 ohm Platinum	.00385	.03%
D	500 ohm Platinum	.00385	.1%
E	1000 ohm Platinum	.00385	.1%
F	2000 ohm Platinum	.00385	.1%
G	100 ohm Platinum	.00392	.1%
H	100 ohm Platinum	.00392	.03%
J	120 ohm Nickel	.00392	.5%
K	604 ohm Nickel Iron	.00392	.5%

RTD Wiring Diagrams

 

Custom Options Available - Contact us for Engineering Assistance.