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Datasheets and User Guides

App Notes

Software & Driver

 

18.0 Internal Temp Sensor [T-Series Datasheet]

Overview By Device

T4

 

T4 Temperature Sensor Location

Sensor Range: -50°C to 150°C

T4 Operating Range: -40°C to 85°C

Accuracy (20°C to 40°C): ±1.5°C*

Accuracy (-20°C to 50°C): ±2.0°C*

Accuracy (-45°C to 85°C): ±3.5°C*

The T4 has an LM94021 temperature sensor (with GS=10) connected to an internal analog input. The sensor is physically located on the top of the PCB behind the VS screw terminal of the FIO4 and FIO5 screw terminal block.

T7

 

T7 Temperature Sensor Location

Sensor Range: -50°C to 150°C

T7 Operating Range: -40°C to 85°C

Accuracy (20°C to 40°C): ±1.5°C*

Accuracy (-20°C to 50°C): ±2.0°C*

Accuracy (-45°C to 85°C): ±3.5°C*

The T7 has an LM94021 temperature sensor (with GS=10) connected to internal analog input channel 14 (AIN14). The sensor is physically located on the bottom of the PCB between the AIN0/1 and AIN2/3 screw-terminals.

 *Accuracy of measuring device temperature, which is typically warmer than ambient air temperature.  Includes error from LM94021 specifications and error due to linear equation fit.

Device Temperature

Read TEMPERATURE_DEVICE_K to get the device temperature:

Name Start Address Type Access
TEMPERATURE_DEVICE_K 60052 FLOAT32 R
TEMPERATURE_DEVICE_K
- Address: 60052
Takes a reading from the internal temperature sensor using range=+/-10V and resolution=8, and applies the formula Volts*-92.6+467.6 to return kelvins.
  • Data type: FLOAT32  (type index = 3)
  • Read-only
  • Minimum firmware version: 0.2020
  • T7-specific details: The internal temperature sensor, AIN14, is internally connected to an LM94021 (U24) with GS=10 which is physically located on the bottom of the PCB between the AIN0/1 and AIN2/3 screw-terminals.
  • T4-specific details: The internal temperature sensor is internally connected to an LM94021 (U24) with GS=10 which is physically located on the top of the PCB behind the VS screw terminal of the FIO4 and FIO5 screw terminal block.

T7 only:

 

AIN14 Temperature Sensor Voltage

Alternatively, reading from AIN14 returns the temperature sensor voltage, which can be converted to device temperature using the formula:

Device temperature K = volts * -92.6 + 467.6

Stream Mode

You can read the raw temp sensor voltage from AIN14 in stream mode, but cannot read TEMPERATURE_DEVICE_K or TEMPERATURE_AIR_K since the internal math that is required for them is too slow.  If streaming, use AIN14 to get volts and use the above formula to get device temperature in K.  For an estimate of air temperature, see the following "Air Temperature" section.

Air Temperature

TEMPERATURE_AIR_K is an estimate of the ambient air temperature outside the device:

Name Start Address Type Access
TEMPERATURE_AIR_K 60050 FLOAT32 R
TEMPERATURE_AIR_K
- Address: 60050
Returns the estimated ambient air temperature just outside of the device in its red plastic enclosure. This register is equal to TEMPERATURE_DEVICE_K - 4.3. If Ethernet and/or WiFi is enabled, subtract an extra 0.6 for each.
  • Data type: FLOAT32  (type index = 3)
  • Read-only
  • Minimum firmware version: 0.2020

It is calculated depending on whether Ethernet and/or WiFi is enabled as follows:

  • USB                               TEMPERATURE_AIR_K = TEMPERATURE_DEVICE_K - 4.3
  • USB & Ethernet               TEMPERATURE_AIR_K = TEMPERATURE_DEVICE_K - 4.9
  • USB & WiFi                     TEMPERATURE_AIR_K = TEMPERATURE_DEVICE_K - 4.9
  • USB & Ethernet & WiFi     TEMPERATURE_AIR_K = TEMPERATURE_DEVICE_K - 5.5

These offsets were determined from measurements with the enclosure on and in still air.  We noted that the time constant was about 12 minutes, meaning that 12 minutes after a step change you are 63% of the way to the new value.

Note on thermocouples - T7 Only:

 

The value from TEMPERATURE_DEVICE_K best reflects the temperature of the built-in screw-terminals AIN0-AIN3, so use that for cold junction compensation (CJC) if thermocouples are connected there.

The internal sensor has a specified accuracy of ±2.0 °C across the range of -20 to +50 °C.  Allowing for a slight difference between the sensor temperature and the temperature of the screw-terminals, expect the returned value minus 3 °C to reflect the temperature of the built-in screw-terminals with an accuracy of ±2.5 °C.

If thermocouples are connected to the CB37, you want to know the temperature of the screw-terminals on the CB37.  The CB37 is typically at the same temperature as ambient air, so use the value from register TEMPERATURE_AIR_K for CJC.  Better yet, add a sensor such as the LM34CAZ to an unused analog input on the CB37 to measure the actual temperature of the CB37.