What is the cause of the "RTD FAULT" message in Sepam relays?
Sepam 20, 40, 80
MET 148, 1482
The message " DEFAUT SONDE" or " RTD FAULT " corresponds to a physical fault on the temperature sensor.
The resistance being read by the RTD must be within the expected bounds. For example:
In this example we will use a PT 100 sensor (PT 100 means that the sensor is made of Platinum and its resistance is of 100 ohms at 0°C )
The sensor PT 100 Equation is:
RPT100 = 100(1 + AT+ BT2)
Constants : A = 3,90802 10-3 et B= - 5,80195 10-7
Below 35°C we will consider the sensor input to be a shortcircuit, and above 205°C we will consider the input sensor to be an open circuit.
R sensor being the Internal resistance of the sensor.
35°C => R sensor = 86,25 ohms
+ 205°C => R sensor = 177,68 ohms
We will have the "DEFAUT SONDE "or "RTD' FAULT "if R sensor < 86,25 ohms or > 177,68 ohms