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Technical Notes Precision Resistors Pt100
Technical data of Precision Resistors Pt100
Pt - resistance sensor
The most exact temperature measurement can be made by using platinum sensors. With the Pt100 sensor for example (platinum sensor with 100 Ohm nominal resistance at
0 °C) you can measure temperatures from -254,3 °C up to 850 °C. With the latest platinum sensors the temperature range can even reach up to +1100 °C. The combination of the
right measurement method and the excellent physical properties of platinum enables the achievement of an excellent accuracy (which can be less than 0,03 °C, depending on the
sensor used. In addition Platinum sensors have an excellent long-time stability, reproducibility and inter- exchangeability. They are also resistant against corrosion and chemical
influences. The measurement is based on the fact that the electrical resistance of the platinum depends strongly on the temperature. The resistance variation of the platinum
behaves on average to 0,385 Ohm/K and is not linear. The nonlinearity can be compensated by using the suitable Measuring / Computing method.
Connection of Pt - resistance sensor
The temperature measurement with Pt – resistance sensors is based on the strong dependence of their resistance on the temperature. The resistance variation is measured by
powering the resistor with a constant electrical current and the measurement of the potential difference arising between the ends of the resistor ( U (Volts) = R (Ohms) x I (Amperes)).
Because of the self heating effect caused by the electrical current (Ohm’s Law), the measurement current has to be kept as low as possible (in practice between 1µA and
1mA). From the measured resistance value, the temperature is determined in an inverse polynomial computation. The extension of Platinum resistance sensors to the evaluation
devices is made in 2-, 3- or 4-wires execution. Because the resistance change of Pt in dependence of the temperature is just about 0,385 Ohms/ °C the intrinsic resistance of the
extension cable or wires, has to be taken in account, especially when using the 2-wires connection. The use of the 4-wires connection eliminates fully the influence of the cable
resistance.
Specifications / Norms
Platinum resistances were defined according to ITS-90 temperature scala as primary standard. All over the world either the IEC 751 norm or the British Standard of 1964 BS
1904/JISC 1604 is valid. According to IEC 751 all platinum sensors nominal resistance can be calculated as follows:
R(t) = R(0 °C) (1+At+Bt 2 +C (t-100)t 3 ) for -200 °C at 0 °C
R(t) = R(0 °C) (1+At+Bt 2 ) for 0 °C at 850 °C
A = 3,9083x10 -3 / °C -1 B = -5,775x10-7 / °C -2 C= -4,183x10-12 / °C -4
Specifications Pt100
Sensor Pt100 (platinum precision resistor, wound or film) in or on ceramic material
Nominal resistance at 0 °C 100,00 Ohm
Tolerances class A: ∆t = ∆t(0,15 °C + 0,002xltl)
class B: ∆t = ∆t(0,3 °C + 0,005xltl)
Limited tolerances 1/3, 1/5, 1/10 DIN class B
Other standards BS 1904, BS2G. 148, JIS C 1604
Measuring range T90 Thin film technology -70...+500 °C
Ceramic wound -200...+600 °C
at +850 °C on request
Thermal response time The thermal response time depends on the diameter of the ceramic tube and is therefore different for each sensor. The response time is
between 0,03 sec and 2,2 sec for a sudden temperature change of 10 K in flowing water.
Long-term stability Above ±0,05 % / year
Already as a component of the manufacturing an artificial aging process takes place. Between -50 and +450 °C the temperature stability of
ceramic sensors are unreachable. The value of 0 °C shows a maximum discrepancy of 0,04 % after 10 temperature shocks of -200
up to +600 °C.
Recommended measuring current: Max. 1mA at Pt100/100-300 μA at Pt 500/1000 at Pt1000 0,1-0,3 m²
Self heating Min. 0,2 K/mW at 0 °C
Shock and vibration Max. 30 g of 10 Hz up to 1 kHz (when inserted correctly)
Winding method Bifilar (therefore minimal capacities and inductivities)
Calibration All precision resistors are checked with 8 mm distance to the ceramic tube at 0 °C and 100 °C. (calibration point: 8 mm distance to ceramic
material)
Norms The characteristic curve of Pt100 sensors correspond to IEC 751 (DIN 43760). Other norms on request.
Options Double Pt100 (double wounded in ceramic material), triple Pt100, Pt500, Pt1000, extended connection wires.
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