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Daviteq Thermocouple Node
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Daviteq Thermocouple Node

TCK

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1. Introduction

Daviteq Thermocouple Node (TCK) is a device to connect to external thermocouple sensor to measure a large temperature range for kilns, gas turbine exhaust, diesel engines, other industrial processes and fog machines.... in various applications, including industrial processes, household appliances, safety devices, medical equipment, and research settings. Thermocouple sensor include different types ( type B, E, J, K, N, R, S, T) with various measurement range and accuracy.

The TCK node can be integrated into the wireless transmitter from Daviteq, such as Sub-GHz WS433, LoRaWAN WSLRW, and Sigfox WSSFC, to build the complete wireless thermocouple node.


Specifications

Input: Thermocouple Temperature Sensor Type B, E, J, K, N, R, S, T

Resolution: 0.1 oC

Accuracy: +/- 1 oC

2. Principle of Operation

A thermocouple comprises two distinct electrical conductors, typically made of different metals or metal alloys. These conductors are joined at both ends to form an ‘electrical junction’. The junction can be created through welding, twisting, or soldering. The fundamental phenomenon behind thermocouples is the ‘Seebeck effect’. When the junction experiences a ‘temperature gradient’ (with one end hotter and the other colder), it generates an ‘electromotive force (EMF)’. This EMF results in a ‘voltage’, known as the ‘Seebeck voltage’ or ‘thermoelectric voltage’. The magnitude of the Seebeck voltage is directly proportional to the ‘temperature difference’ between the hot and cold junctions.



To accurately measure temperature, a reference point is essential. One end of the thermocouple (usually the cold junction) is maintained at a known reference temperature (often room temperature). The voltage across the thermocouple is measured using a ‘voltmeter’. By referencing calibration tables or employing specific equations tailored to the thermocouple type, the actual temperature can be determined.


While the Seebeck voltage is approximately linear with temperature over a limited range, this linearity is not perfect, especially at extreme temperatures. Thermocouples are characterized by their ‘thermoelectric coefficients’, which describe the relationship between temperature and voltage. Since the reference junction (cold junction) is not always at a fixed temperature, compensation techniques are necessary. Modern thermocouples incorporate ‘cold junction compensation’ methods, such as using a ‘thermistor’ or an ‘IC-based sensor’ to measure the reference temperature


Daviteq thermocouple node measures the mV output of thermocouple, compensate the cold junction mV, and convert to the temperature

3. Calibration

To calibrate a complete thermocouple temperature device (Daviteq thermocouple node and thermocouple sensor), follow these steps:

  1. Isolate the sensor (thermocouple) from the process.

  2. Immerse the sensor fully into a dry-well or bath that can cover the required temperature range.

  3. Change CONSTANT_A = 1 and CONSTANT_B =0 on Daviteq thermocouple node memory by offline tool or downlink

  4. Adjust the temperature of the bath or dry-well to each of the test points. At each test point, record the readings of the standard temperature and thermocouple device's temperature. Record 2 test points (calibrated minimum temperature point and calibrated maximum temperature point)

  5. Calculate CONSTANT_A and CONSTANT_B based on the standard temperature and thermocouple device's temperature at minimum temperature point and maximum temperature point.


    Standard Temperature = CONSTANT_A * thermocouple device's temperature + CONSTANT_B

  6. Change calculated CONSTANT_A and CONSTANT_B on Daviteq thermocouple node memory by offline tool or downlink

4. Application Notes

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5. Installation Notes

Thermocouple Installation Guidelines

  • Location and Depth Selection:

Carefully choose the installation location and insertion depth where the temperature accurately represents the process conditions.

Avoid stagnant areas with non-representative temperatures.

Position the thermocouple so that the hot end is visible for visual confirmation of the junction location.


  • Depth of Immersion:

Immerse the thermocouple sufficiently to include the measuring junction entirely within the temperature zone to be measured.

A depth approximately ten times the diameter of the protection tube is recommended.

Heat conducted away from the hot junction can lead to lower readings due to “stem loss.”


  • Cold Junction and Connecting Head:

Keep the connecting head and cold junction in the coolest ambient temperature available.

Prevent thermal shock by gradually preheating ceramic tubes during installation.


  • Protection Tube:

Avoid direct flame impingement on the protection tube.

Impingement shortens tube life and affects temperature accuracy.

For high-temperature measurements, consider vertical installation to minimize tube sagging.


Extension Wire Installation Guidelines

  • Wire Selection:

Ensure you choose the correct type of extension wire based on the thermocouple calibration.

Use the color coding of individual wires as a guide

  • Avoiding EMF Interference:

To prevent spurious electromotive force (EMF) caused by electrostatic and electromagnetic noise:

Never run thermocouple extension wire in the same conduit as power sources.

Keep the thermocouple wire at least 12 inches away from any power source.

Avoid running the extension wire parallel to the conduit or near power lines.

  • High-Noise Areas:

In environments with high noise levels:

Use thermocouple extension wire with:

Twisted and shielded conductors: This minimizes interference.

A drainwire for additional protection.

  • Insulation Selection:

Choose the proper insulation material based on specific operating conditions. \


6. Troubleshooting

1. The measured value is not within the expected value

  • The thermocouple sensor is drifted over time: Re-calibrate the sensor.

  • The thermocouple sensor was spoiled due to some reasons. Replace the new sensor


2. HW_Error = 1

  • The thermocouple node got a problem: Please consult the manufacturer for a warranty or replacement.

7. Maintenance

Implement monthly check and maintenance as below:


  • Visual Inspection:

Cable and Connections: Examine the thermocouple cable for any signs of wear, fraying, or damage. Check the connectors (if detachable) for tightness and cleanliness.

Junction Area: Inspect the junction (where the two dissimilar metals meet) for any corrosion, oxidation, or physical damage. Clean it gently if needed.


  • Electrical Continuity:

Use a multimeter to measure the electrical continuity of the thermocouple. Connect the multimeter leads to the thermocouple terminals and verify that the resistance matches the expected values for the specific type (e.g., type K, type J).


  • Temperature Verification:

Compare the thermocouple reading with a known reference temperature. You can use a calibrated thermometer or another reliable temperature sensor. Ensure that the thermocouple accurately reflects the actual temperature.


  • Calibration Check:

If possible, perform a calibration check using a certified reference source. This ensures that the thermocouple maintains its accuracy over time.

Note any deviations from the expected values and take corrective action if necessary.


  • Environmental Factors:

Consider the environmental conditions where the thermocouple is installed. Check for exposure to chemicals, moisture, or extreme temperatures.

Inspect any protection tubes (if used) for cracks or damage.

8. Default Configuration