MAX31865
RTD-to-Digital Converter
Table 10. Decoding RTD Faults for 2-Wire Setups When Fault Bit in RTD Data LSB
Register = 1
FAULT
STATUS
BꢀT SET
DESCRꢀPTꢀON OF POSSꢀBLE
CAUSE
DESCRꢀPTꢀON OF
RESULTꢀNG DATA
CONDꢀTꢀON DETECTED
Measured resistance greater than High Fault
Threshold value
D7
D6
Open RTD element
Full scale
Shorted RTD element
RTDIN+ shorted low
Open RTD
Measured resistance less than Low Fault
Threshold value
Near zero
Full scale
D5
RTDIN+ shorted high
RTDIN- shorted high
RTDIN- shorted low
RTDIN- shorted low
RTDIN+ shorted low
V
> 0.85 x V
Indeterminate
Indeterminate
Appear to be valid
Appear to be valid
Near zero
REFIN-
BIAS
D4
D3
D2
V
V
< 0.85 x V
< 0.85 x V
(FORCE- open)
(FORCE- open)
REFIN-
BIAS
RTDIN-
BIAS
Overvoltage or undervoltage fault Any protected input voltage >V
or <GND1
Indeterminate
DD
Table 11. Decoding RTD Faults for 3-Wire Setups When Fault Bit in RTD Data LSB
Register = 1
FAULT
STATUS
BꢀT SET
DESCRꢀPTꢀON OF POSSꢀBLE
CAUSE
DESCRꢀPTꢀON OF
RESULTꢀNG DATA
CONDꢀTꢀON DETECTED
Open RTD element
RTDIN+ shorted high and not
connected to RTD
Measured resistance greater than High Fault
Threshold value
D7
D6
Full scale
Force+ shorted high and
connected to RTD
RTDIN+ shorted to RTDIN-
RTDIN+ shorted low and not
connected to RTD
Measured resistance less than Low Fault
Threshold value
Near zero
Full scale
Force+ shorted low
Open RTD element
Force+ shorted high and
connected to RTD
D5
Force+ unconnected
V
- > 0.85 x V
- < 0.85 x V
REFIN
BIAS
Force+ shorted high and not
connected to RTD
Indeterminate
RTDIN- shorted high
RTDIN- shorted low
Force+ shorted low
D4
D3
D2
V
V
(FORCE- open)
(FORCE- open)
Appear to be valid
Near zero
REFIN
BIAS
RTDIN+ shorted low and
connected to RTD
- < 0.85 x V
RTDIN
BIAS
RTDIN- shorted low
Appear to be valid
Indeterminate
Overvoltage or undervoltage fault
Any protected input voltage >V
or < GND1
DD
Maxim Integrated
21
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