Compensate for Measurement Error due to Long Leads
Compensate for Measurement Error due to Long Leads
Wire
Resistance
A Pt100 sensor changes resistance with temperature and thus the base unit can measure
the resistance to calculate the temperature. The wiring from the system to the sensor
and back adds resistance to the measurement and causes an error — the temperature
value shown will be higher than the actual temperature. The longer and thinner the wires,
the larger the error in the measurement.
The wire resistance is proportional to the wire length and inversely proportional to the
cross section:
Resistance = Resistivity x (2 x Length of sensor cable) / Wire cross section
The resistivity of copper is 0.0172
Ω
mm²/m.
Measurement
Error Example
If the distance between the pump and the cabinet is 50 meters and the Subcab cable is
used (1,5 mm² cross sectional area), the error in the temperature measurement will be:
• +4,5 °C (8,1°F) for Temp main bearing and Temp stator ph 1 (using a common return
lead)
• +3 °C (5,4 °F) for Stator ph 2, Stator ph 3, Support bearing (using separate leads)
Note!
The error is proportional to the distance so a distance of 100 meters doubles the
error.
Compensation
Method
The compensation method used is software compensation and does not require any
additional leads. The software compensation method requires that the lead resistance is
estimated (measured or calculated) and entered into the system. The system will then
simply reduce the measured resistance values by the lead resistance prior to calculating
the temperature.
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