Burkert Type 8620 - Manual (Page 69)

mxCONTROL Type 8620
Page 69
12.2.2 Pt100 Inputs
Figure 19: Pt100 Input
A/D-Conversion
The enabled analog Pt100 inputs are sampled every 50ms with a resolution of 10 bit in order to
convert the analog input signal to a digital value.
Additionally the enabled analog inputs are checked after each sampling process on
• input fault (detected temperature < approx. -22 °C)
• sensor fault (detected temperature > approx. +155 °C)
• AD-fault (fault during sampling process).
• A calibration data fault is treated as an input fault.
Scaling
The measuring range of the Pt100 inputs depends on the hardware:
-20 °C ... +150 °C or -4 °F ... 302 °F .
Each Pt100 input is configured separately, available engineering units are:
Degree Celsius (°C), degree Fahrenheit (°F), degree Rankin (°R) and Kelvin (K).
The unit is used at the same time for the scaling values, the alarm and warning limits of this input and
for certain parameters of associated modules.
The reference span for the alarm and warning hysteresis of this input as well as for specific
parameters of associated modules (e.g. deadband) are defined by the setting of the low and high
scaling value. Furthermore, the value range of some input parameters and certain module parameters
(e.g. set point) is determined by the low and high scaling value.
Correction Value
The temperature measurement with platinum resistors of type Pt100 is based on the changing
resistance of platinum in dependence on the changing of the temperature. In the factory calibration
data of the Pt100 Inputs the constant resistance of the cable used for calibration is included.
If such a fault occurs, the common alarm output is activated.
Additionally, the safety output value will be activated in the corresponding modules, which
support the safety output function and which are linked with the faulty input.
If the safety output value is activated the manual output value will be reset to “0”!
If the scaling unit of a Pt100 input was changed, the corresponding alarm and warning
limits
and the set points of the corresponding modules have to be changed manually to the
value corresponding with the new engineering unit of the input (no automatic conversion from
one unit to a different one!).
The process value is not limited by the low and high scaling value.
When changing the scaling values, the corresponding alarm and warning limit as the set
points of the corresponding modules should be examined for their relevance!