BECKHOFF FM33xx - Manual (Page 20)

Functional description
FM33xx 15
Peripheral data in the process image
One 16 bit value is supplied for each configured channel in the minimal
configuration. In addition to this value there is a 32 bit value for open
circuit, a 32 bit value for back voltage, and a 16 bit status word.
32 channels can be configured in the maximal configuration.
D0..D31 Temperature in 1/10 degree Celsius (16 bit signed integer per
channel)
Open circuit One bit is reserved for each channel. If the channel is deactivated this bit
will always have the value zero. If a channel is activated, this bit will be set
to 1 when an open circuit is detected, and this fact is indicated through the
channel data by the limit value of the implemented thermocouple:
Limit values of the
thermocouples for an open
circuit channel Type J: 900°C
Type K: 1370°C
Back voltage One bit is reserved for each channel, in a procedure similar to that for open
circuit. If excess voltage is detected at a channel, the corresponding bit is
set and the limit value of the implemented thermocouple is displayed.
Status word Each channel has a status word. The error bits in the status word are set
when an error is detected, and have the following meaning:
Error message Bit
OVERRANGE 0
UNDERRANGE 1
CHERROR 6
Underrange, Overrange and Error are all set if there is an open circuit.
Depending on whether the thermocouple is grounded or not, the ADC
value will go to 0x8000 or 0xFFFF.