LTC2983
23
2983fc
For more information www.linear.com/LTC2983
Table 15. Thermocouple Fault Reporting
BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT
D31 Sensor Hard Fault Hard Open Circuit or Hard ADC or Hard CJ –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 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error –999°C or °F
D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading
D27 Sensor Over Range Soft Thermocouple Reading Greater Than High Limit Suspect Reading
D26 Sensor Under Range Soft Thermocouple Reading Less Than Low Limit Suspect Reading
D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • V
REF
/2 Suspect Reading
D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading
APPLICATIONS INFORMATION
Fault Reporting – Thermocouple
Each sensor type has a unique fault reporting mechanism
indicated in the upper byte of the data output word. Table 15
shows faults reported in the measurement of thermo-
couples.
Bit D31 indicates the thermocouple sensor is open (broken
or not plugged in), the cold junction sensor has a hard
fault, or the ADC is out of range. This is indicated by a
reading well beyond the normal operating range. 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). Either of these
are 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 event
was a random, infrequent event. Bit D29 indicates a hard
fault occurred at the cold junction sensor and –999°C
or °F is reported. Refer to the specific sensor (diode,
themistor, or RTD) used for cold junction compensation.
Bit D28 indicates a soft fault occurred at the cold junction
sensor. A valid temperature is reported, but the accuracy
may be compromised since the cold junction sensor is
operating outside its normal temperature range. Bits
D27 and D26 indicate over or under temperature limits
have been exceeded for specific thermocouple types, as
defined in Table 16. Bit D25 indicates the absolute voltage
measured by the ADC is beyond its normal operating range.
This fault reflects a reading that is well beyond the normal
range of a thermocouple.
Table 16. Thermocouple Temperature Limits
THERMOCOUPLE TYPE LOW TEMP LIMIT °C HIGH TEMP LIMIT °C
J-Type –210 1200
K-Type –265 1372
E-Type –265 1000
N-Type –265 1300
R-type –50 1768
S-Type –50 1768
T-Type –265 400
B-Type 40 1820
Custom Lowest Table Entry Highest Table Entry
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