Technische Alternative CAN-EZ2, Manual

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56
NTC sensors
For evaluating the NTC sensors, the R25 value and the beta value must be
specified.
The nominal resistance R25 is always based on 25 °C.
The beta value refers to the characteristic of an NTC sensor in relation to
2 resistance values.
Beta is a material constant and can be calculated from the manufacturer's resistance table using the
following formula:
As the beta value is not a constant over the total temperature curve, the anticipated limits of the
measuring range must be determined (e.g. for a cylinder sensor from +10 °C to +100 °C or for an out -
side sensor from -20 °C to +40 °C).
All temperatures in the formula must be given as
absolute temperatures in K (Kelvin) (e.g. +20 °C =
273.15 K + 20 K = 293.15 K)
ln
Natural logarithm
R1
(NT)
Resistance at the minimum temperature of the temperature range
R2
(HT)
Resistance at the maximum temperature of the temperature range
T1
(NT)
Minimum temperature of the temperature range
T2
(HAT)
Maximum temperature of the temperature range
PTC sensors
The R25 value is also required for the evaluation of PTC sensors. The
nominal resistance R25 is based on 25 °C.
In addition, the
Alpha (x10^-3) and Beta (x10^-6) values are required. The
Alpha and Beta values are normally taken from the PTC sensor datasheet
and entered after applying the adjacent formula.
To calculate the Alpha and Beta values, any two resistance values and
their associated temperatures are selected according to the resistance ta -
ble of the respective PTC sensor.
Beta should be calculated first, as that value is necessary to calculate Alpha .
R
1 ...
Resistance value 1 (Ohm) T
1
... Temperature at resistance R
1
(°C) ΔT
1
= T
1
– 25 °C
R
2
... Resistance value 2 (Ohm) T
2
... Temperature at resistance R
2
(°C) ΔT
2
= T
2
– 25 °C