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What is the response time of mineral insulated thermocouples?

Home » Thermocouples » Thermocouples 101 » Introduction to Thermocouples » What is the response time of mineral insulated thermocouples?
Read further about Thermocouples:
  • What do thermocouple letter designations mean?
  • What are thermocouple color codes?
  • What letter of calibration should I use?
  • What is the initial accuracy of temperature sensors?
  • Is there a maximum length for thermocouples and thermocouple wiring?
  • What sheath material is the best for my application?
  • What are the maximum temperatures of thermocouples?
  • What type of junction should I use?
  • What is the response time of mineral insulated thermocouples?
  • Where should my sensor be placed?
  • What should the thermocouple resistance measure?
  • The sensor appears to be reading incorrectly. What might be wrong?
9

What is the response time of mineral insulated thermocouples?

The smaller the diameter, the faster the thermocouple will respond. Grounding the junction will also improve the response time by approximately 50 percent. This is based on the sensor achieving 63.2 percent of the final reading, or to the first time constant. It will take about five time constants to obtain steady state readings. Since you are actually interested in the temperature of the surrounding medium, accuracy depends on the ability of the sensor to conduct heat from its outer sheath to the element wire.

Several factors come into play:

The most commonly noted is “time constant” (thermal response time). Time constant, or thermal response time, is an expression of how quickly a sensor responds to temperature changes. As expressed here, time response is defined as how long it takes a sensor to reach 63.2 percent of a step temperature change.

Response is a function of the mass of the sensor and its efficiency in transferring heat from its outer surfaces to the wire sensing element. A rapid time response is essential for accuracy in a system with sharp temperature changes.

Time response varies with the probe’s physical size and design.

Average Response Time Still Water (seconds)
Readings are to 63.2% of measured temperature.
Sheath Diameter Grounded Junction Ungrounded Junction
1/2 0,500 15 20
3/8 0,375 8 11
5/16 0,313 5 7
1/4 0,250 2,2 4,1
3/16 0,188 1 2,3
1/8 0,125 0,5 1,1
1/16 0,062 0,22 0,4
1/25 0,040 0,04 0,13
Temperature Response Time Of Still Water At 80 Celcius
Measured with a Thermocouple having a .250″ Sheat Diameter.
Time Constant Response Time Step Change Measured Temperature
Grounded Ungrounded
1 2,2 4,1 63,2% 50,6
2 4,4 8,2 86,5% 69,2
3 6,6 12,3 95,0% 76,0
4 8,8 16,4 98,2% 78,6
5 11,0 20,5 99,3% 79,4
6 13,2 24,6 99,8% 79,8
9

What is the response time of mineral insulated thermocouples?

The smaller the diameter, the faster the thermocouple will respond. Grounding the junction will also improve the response time by approximately 50 percent. This is based on the sensor achieving 63.2 percent of the final reading, or to the first time constant. It will take about five time constants to obtain steady state readings. Since you are actually interested in the temperature of the surrounding medium, accuracy depends on the ability of the sensor to conduct heat from its outer sheath to the element wire.

Several factors come into play:

The most commonly noted is “time constant” (thermal response time). Time constant, or thermal response time, is an expression of how quickly a sensor responds to temperature changes. As expressed here, time response is defined as how long it takes a sensor to reach 63.2 percent of a step temperature change.

Response is a function of the mass of the sensor and its efficiency in transferring heat from its outer surfaces to the wire sensing element. A rapid time response is essential for accuracy in a system with sharp temperature changes.

Time response varies with the probe’s physical size and design.

Average Response Time Still Water (seconds)
Readings are to 63.2% of measured temperature.
Sheath Diameter Grounded Junction Ungrounded Junction
1/2 0,500 15 20
3/8 0,375 8 11
5/16 0,313 5 7
1/4 0,250 2,2 4,1
3/16 0,188 1 2,3
1/8 0,125 0,5 1,1
1/16 0,062 0,22 0,4
1/25 0,040 0,04 0,13
Temperature Response Time Of Still Water At 80 Celcius
Measured with a Thermocouple having a .250″ Sheat Diameter.
Time Constant Response Time Step Change Measured Temperature
Grounded Ungrounded
1 2,2 4,1 63,2% 50,6
2 4,4 8,2 86,5% 69,2
3 6,6 12,3 95,0% 76,0
4 8,8 16,4 98,2% 78,6
5 11,0 20,5 99,3% 79,4
6 13,2 24,6 99,8% 79,8
Read further about Thermocouples:
  • What do thermocouple letter designations mean?
  • What are thermocouple color codes?
  • What letter of calibration should I use?
  • What is the initial accuracy of temperature sensors?
  • Is there a maximum length for thermocouples and thermocouple wiring?
  • What sheath material is the best for my application?
  • What are the maximum temperatures of thermocouples?
  • What type of junction should I use?
  • What is the response time of mineral insulated thermocouples?
  • Where should my sensor be placed?
  • What should the thermocouple resistance measure?
  • The sensor appears to be reading incorrectly. What might be wrong?

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