Overview - T7/T8
This feature is only supported on the T7 and T8.
AIN#_EF_INDEX values:
20: Thermocouple type E
21: Thermocouple type J
22: Thermocouple type K
23: Thermocouple type R
24: Thermocouple type T
25: Thermocouple type S
27: Thermocouple type N
28: Thermocouple type B
30: Thermocouple type C
This Thermocouple Extended Feature automatically performs calculations for the thermocouple types listed above.
The thermocouple AIN-EF acquire two primary measurements: thermocouple voltage measured on the analog input(s), and the temperature from a CJC (cold junction compensation) sensor.
For more information, see the Thermocouples App Note.
Configuration
To configure, write to the following registers.
AIN#_EF_CONFIG_A - Options: Select temperature units for AIN#_EF_READ_A and AIN#_EF_READ_C:
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0 = K
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1 = °C
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2 = °F
AIN#_EF_CONFIG_B - CJC Modbus address: The Modbus address that will be used to acquire the CJC sensor reading.
T7: Default is 60052 (the TEMPERATURE_DEVICE_K register address).
T8: Default is the address for TEMPERATURE#_CAPTURE. For example, 702 (the TEMPERATURE1_CAPTURE register address) is the default value for AIN1_EF_CONFIG_B.
Note: The Modbus address for AIN channels are always 2*AIN#. For example, AIN2 is at address 4.
AIN#_EF_CONFIG_D - CJC Slope: A slope to be applied to the CJC reading.
This value is always in units of K/volt, regardless of AIN#_EF_CONFIG_A. When using an internal temperature sensor this value should be 1.00. When using an LM34 sensor it should be set to 55.56.
Default is 1.0.
AIN#_EF_CONFIG_E - CJC Offset: An offset to be applied to the CJC reading.
This value is always in units of K, regardless of AIN#_EF_CONFIG_A. When using an internal temperature sensor this value should be 0.0. When using an LM34 sensor it should be set to 255.37.
Default is 0.0.
Remarks
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The normal analog input registers are used for negative channel, resolution index, settling, and range.
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Differential thermocouple readings help mitigate ground loop and ground offset problems. See the Thermocouples App Note for more information.
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T7 Only - If the channel range setting is set to ±10V, this AIN_EF will automatically reconfigure the range to ±0.1 V. Otherwise, the specified range will be used.
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T8 Only - If the channel range setting is set to any range greater than ±0.15 V, this AIN_EF will automatically reconfigure the range to ±0.15 V. Otherwise, the specified range will be used.
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The thermocouple calculations require that the CJC temperature is provided in Kelvin. This does not change if the output units are changed using AIN#_EF_CONFIG_A.
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The internal temperature sensors (f.e. TEMPERATURE_DEVICE_K) will return Kelvin.
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When applying a slope and offset to measurements from the internal sensor, the result must be in units of Kelvin.
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When using an external CJC sensor the measurement will almost certainly be in volts, therefore the slope and offset must be used to convert that voltage reading to Kelvin.
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Results
Results are read from the following registers. Only reading AIN#_EF_READ_A triggers a new measurement.
AIN#_EF_READ_A - Thermocouple Temperature: Final calculated temperature of the remote end of the thermocouple. -9999 will be returned when the measured thermocouple voltage is outside of the valid thermocouple voltage range. This commonly occurs when the analog input is floating.
AIN#_EF_READ_B - Measured Thermocouple Voltage: The voltage measured on the AIN; it should be the same value as returned by AIN#.
AIN#_EF_READ_C - CJC Temperature: The temperature of the CJC sensor, calculated using the CJC slope and offset configuration values.
AIN#_EF_READ_D: CJC Equivalent Thermocouple Voltage: The equivalent thermocouple voltage calculated at the CJC sensor temperature.
Example
Assume a type K thermocouple is connected to AIN3/GND. To configure:
AIN3_EF_INDEX = 22 // feature index for type K thermocouple
AIN3_EF_CONFIG_B = 60052 // TEMPERATURE_DEVICE_K for CJC address
AIN3_EF_CONFIG_D = 1.0 // slope for CJC reading
AIN3_EF_CONFIG_E = 0.0 // offset for CJC reading
Read AIN3_EF_READ_A to get the calculated temperature. If the remote end is at room temperature, it will read as approximately 298 kelvin.
For a more detailed walkthrough, see the tutorial for your device in the Thermocouples App Note.