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A thermocouple has low response time when

A thermocouple has low response time when Correct Answer Both (1) and (2)

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A thermocouple is an electrical device containing junctions of two dissimilar metal joints. It is used as temperature sensors.

It works on the principle of Seebeck effect which states that temperature difference between two dissimilar electric conductors produces a voltage difference between them. This potential difference is used to measure temperatures.

Construction:

  • A thermocouple basically comprises of wires (called thermoelement), Insulation, Sheath and means for external connection.
  • One end of thermoelement made up of two different metals are welded together to form a junction.
  • The thermoelement is housed in a rigid metal sheath, generally made of Inconel.  Measuring junction is formed at the bottom of the housing.
  • Magnesium Oxide filling surrounds the thermoelement. This filling acts as a shock absorber and prevents the wire form vibrational damage. It also acts as a heat dissipating medium of hot junction.

 

Response:

  • The use of sheath slows the response appreciably as the increase the mass of the thermocouple.
  • However, in applications where response time is the primary consideration, bare or thin sheathed thermocouples are used.
  • The sensitivity of thermocouple can be increased by reducing the mass of the measuring junction.

Related Questions

A thermocouple junction in the form of 4 mm radius sphere is to be used to measure the temperature of a gas stream. The junction is initially at 35 degree Celsius and is placed in a gas stream which is at 300 degree Celsius. The thermocouple is removed from the hot gas stream after 10 seconds and kept in still air at 25 degree Celsius with convective coefficient 10 W/m2 K. Find out the time constant of the thermocouple. Assume the thermos-physical properties as given below h = 37.5 W/m2 K p = 7500 kg/m3 c = 400 J/kg K
The following data pertains to the junction of a thermocouple wire used to measure the temperature of the gas stream. Density = 8500 kg/m3, specific heat = 325 J/kg K, thermal conductivity = 40 W/m K and the heat transfer coefficient between the junction and gas = 215 W/m2 K. If thermocouple junction can be approximated as 1 mm diameter sphere, determine how long it will take for the thermocouple to read 99% of the initial temperature difference
“The response of a thermocouple is defined as the time required for the thermocouple to reach the surrounding temperature when it is exposed to it”.
Below are given two sets, Set - I which gives modalities of operant conditioning and Set - II which provides the types of reinforcement, the types of responses (responses made or withheld) and the presence or absence of cue. Match the two sets and indicate your answer by choosing from the code : Set - I (Modalities of operant conditioning procedures) Set – II           (Conditions and contexts) (a) Reward training (i) Positive reinforcement, response made, with cue present (b) Escape training (ii) Positive reinforcement, response withheld with cue absent (c) Discriminated omission training   (iii) Positive reinforcement, response made with cue absent (d) Active avoidance   (iv) Negative reinforcement, response made with training (e) Punishment training (v) Positive reinforcement, response withheld with cue present   (vi) Negative reinforcement, response withheld with cue absent  
A low value of time constant can be achieved for a thermocouple by (i) Increasing the wire diameter (ii) Increasing the value heat transfer coefficient (iii) Use light metals of low density and low specific heat
A J-type thermocouple has an output voltage Vθ = (13650 + 50 θx) μV, where θx is the junction temperature in Celsius (°C). The thermocouple is used with reference junction compensation, as shown in the figure. The Instrumentation amplifier used has a gain G = 20. If θRef is 1 °C, for an input θx of 100 °C, the output Vo of the instrumentation amplifier in millivolt is
A thermocouple junction of spherical form is to be used to measure the temperature of the gas stream. The junction is at 20 degree Celsius and is placed in a gas stream which is at 200 degree Celsius. Make calculations for junction diameter needed for the thermocouple to have thermal time constant of one second. Assume the thermos-physical properties as given below k = 20 W/ m K h = 350 W/m2 K c = 0.4 k J/kg K p = 8000 kg/m3
The sensitivity of thermocouple is defined as the time required by thermocouple to reach how much percentage of its steady state values?
A thermocouple junction of spherical form is to be used to measure the temperature of the gas stream. The junction is at 20 degree Celsius and is placed in a gas stream which is at 200 degree Celsius. Make calculations for time required by the thermocouple to reach 197 degree Celsius temperature. Assume the thermos-physical properties as given below k = 20 W/ m K h = 350 W/m2 K c = 0.4 k J/kg K p = 8000 kg/m3
Consider the following statements: 1. The delay time is the time required to reach 50% of the final value in the first time. 2. The rise time is the time required for the response to rise from 10% to 90% of its final value for underdamped systems. 3. The rise time is the time required for the response to rise from 0 to 100% for the underdamped systems. Which of these statements are correct?