i do my research on measurement of temperature during electron beam welding.
In most fields the response time corresponds with the time it takes to get a measurement you can already trust. In most cases it corresponds with 63% of the time passed after an instantaneous temperature change occurs for the input of the sensor. It can be also seen as the time you need to wait to acquire a meaningful measurement with your thermocouple. I guess for your application this response time will be directly coupled with the diameter of your thermocouple, most likely you will have a higher response time the higher your thermocouple diameter.
I confirm the previous answer and want to add one point. It's important to know that thermocouples don't measure the temperature surrounding, but its own temperature. So diameter could have not negligible effect as well as the contact between your thermocouple and your material : welded TC or embedded in a hole. If possible, it will be better to use small TC for accurate measurements.
It is often reasonable to consider that the output signal of the thermocouple is affected by a first-order delay. This delay causes a temperature error, that results from identifying the corresponding measured temperature (Tmeas) with the actual (real) temperature (Treal). The following ordinary differential equation represents the dynamic response of the temperature sensor: τ·dTmeas/dt + Tmeas = Treal (*), where τ stands for the 'time constant' of the thermocouple sensor, often identified its 'response time'. However, this later expression is also sometimes used as including other possible causes of delay, unrelated with the temperature sensor (e.g. data buffering delay), which, therefore, do not contribute to its time constant. A step temperature change imposed to the temperature sensor may, in principle, allow for the estimation of the time constant.
(*) Cf. (e.g.) R.J. Ord-Smith, J. Stephens, "Computer Simulation of Continuous Systems", Cambridge University Press, 1975.
response time it is a measurement of speed of response of thermocouple to temperature change and it is may be called (time constant)
the first question would be what do you want to measure and also where?
As it was already said thermocouples measure their OWN temperature so that you should consider :
- the heated surface / surface which is not heated and which transfers heat to the environment and the own mass which has to be heated= device own time constant
- the "quality" of the contact between thermocouple and hot part.(there are sevarl good papers on it)
- the thermal diffusibility of the stuff between the EB and the thermocouple and the distance between the beam and the contact position = contact delay
All those "delays" are in series and lead to the total delay.
One important remark : the measured temperature even after several time constants can be far from the real temperature at the EB spot since there several thermal resistances in series between heat zone and environment. Result will depend on the ratio between inlet and outlet resistances.
Nick hamburger sir....nice to hear the suggestion from you...
Sir i am measuring temperature using thermocouple during electron beam welding. So i have to attached the thermocouple on the stainless steel plate then pass the beam near the thermocouple. so thermocouple read the temperature . kindly provide me related papers and suggest me related journal name.
Thanking you
Lord jaykishannayak
SRF,IIT Kharagpur, India
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