LTC2983
31
2983fc
For more information www.linear.com/LTC2983
APPLICATIONS INFORMATION
Fault Reporting – RTD
Each sensor type has unique fault reporting mechanism
indicated in the most significant byte of the data output
word. Table 31 shows faults reported in the measurement
of RTDs.
Bit D31 indicates the RTD or R
SENSE
is open, shorted, or not
plugged in. This is a hard fault and –999°C or °F is reported.
Bit D30 indicates a bad ADC reading. This can be a result
of either a broken (open) sensor or an excessive noise
event (ESD or static discharge into the sensor path). This
is a hard error and –999°C or °F is reported. In the case of
an excessive noise event, the device should recover and
the following conversions will be valid if the noise was a
random infrequent event. Bits D29 and D28 are not used
for RTDs. Bits D27 and D26 indicate over or under tem-
perature limits (see Table 32). The calculated temperature
is reported, but the accuracy may be compromised. Bit
D25 indicates the absolute voltage measured by the ADC
is beyond its normal operating range. If an RTD is used
as the cold junction element, any hard or soft error is also
flagged in the thermocouple result.
Table 32. Voltage and Resistance Ranges
RTD TYPE MIN Ω MAX Ω LOW TEMP LIMIT °C HIGH TEMP LIMIT °C
PT-10 1.95 34.5 –200 850
PT-50 9.75 172.5 –200 850
PT-100 19.5 345 –200 850
PT-200 39 690 –200 850
PT-500 97.5 1725 –200 850
PT-1000 195 3450 –200 850
NI-120 66.6 380.3 –80 260
Custom Table Lowest Table Entry Highest Table Entry Lowest Table Entry Highest Table Entry
Table 31. RTD Fault Reporting
BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT
D31 Sensor Hard Fault Hard Open or Short RTD or R
SENSE
–999°C or °F
D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F
D29 Not Used for RTDs N/A Always 0 Valid Reading
D28 Not Used for RTDs N/A Always 0 Valid Reading
D27 Sensor Over Range Soft T > High Temp Limit (See Table 32) Suspect Reading
D26 Sensor Under Range Soft T < Low Temp Limit (See Table 32) Suspect Reading
D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • V
REF
/2 Suspect Reading
D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 Valid Reading
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