Overview By Device
T4
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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.
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T7
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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.
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*Accuracy of measuring device temperature (TEMPERATURE_DEVICE_K). Includes error from LM94021 specifications and error due to linear equation fit.
Read TEMPERATURE_DEVICE_K to get the device temperature:
| Name |
Start Address |
Type |
Access |
|
TEMPERATURE_DEVICE_K
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.
|
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)
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Read-only
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T7:
- 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.
- Minimum firmware version: 1.0105
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T4:
- 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.
- Minimum firmware version: 0.2020
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T7 only:
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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.
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TEMPERATURE_AIR_K is an estimate of the ambient air temperature outside the device:
| Name |
Start Address |
Type |
Access |
|
TEMPERATURE_AIR_K
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.
|
60050 |
FLOAT32 |
R
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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)
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Read-only
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T7:
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T4:
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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.
T7 or T7-Pro: TEMPERATURE_AIR_K and TEMPERATURE_DEVICE_K always use Range = 10 and ResolutionIndex=8. Which means they take about 1.09 ms per reading from Table A.3.1.1.
T4: TEMPERATURE_AIR_K and TEMPERATURE_DEVICE_K always use ResolutionIndex=5. Which means they take about 0.8 ms per reading.
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.
If thermocouples are connected to an LJTick-Amp (typical with the T4), you want to know the temperature of the screw-terminals on the LJTIA, which we would expect to be close to ambient, so use the value from register TEMPERATURE_AIR_K for CJC.
