So what is the differences between conversion time and response time for thermocouples?

Conversion time refers more to the electronics. This would be your Analog to Digital converter. Response time of the thermocouple is defined in the link I provided. When we choose a thermocouple for an intended application we have several considerations, for example temperature range and how linear will our thermocouple output be over that range. Then the environment, does our thermocouple need a protection tube? If we choose a sheath then what sheath material? Inconel sheath, maybe a stainless sheath? Unless you can define in detail exactly what you want or need to do then you can't even begin to choose the best thermocouple. Saying fast response is not quite good enough, there are other considerations. It all starts with choosing a thermocouple.

Ron

 

Ron and ebeowulf17 thank you for your answers and patients. I misunderstood about analog compensator. So what is the differences between conversion time and response time for thermocouples? I want to build a thermocouple circuit that measure temperature and its measurement speed is important. Where do I can begin to build it? Firstly I choose thermocouple that response fast. Then I can use compensator and adc .

What are you trying to measure the temperature of? Air, water, boiling acid, slabs of metal? Give us some information.

In general terms, as shown by the information in the link above, the smaller the probe, the faster the response. The smallest, fastest ones aren't sheathed or shielded in any way. They are vulnerable to mechanical stress, corrosion, etc. but they are fast. Sheathed probes that can handle liquid immersion are necessarily slower. Larger diameters with thicker walls to withstand high pressure are even slower. Etc, etc...

But this is all relative. What are you trying to measure, and how fast do you think you need to measure it? And why is speed so important?

 

The application is Thermal atomic force microscopy. It will measure the temperature of different types of specimen at the nanometer scale .( https://en.wikipedia.org/wiki/Scanning_thermal_microscopy - http://appnano.com/wp-content/themes/appnano/pdf/VERTISENSETM-THERMAL-IMAGING-AMP.pdf ). So speed is important for that application.

 

EDIT:
Disregard the comment I had put here about thread splitting and merging. I must've been hallucinating!

 

ebewoulf17, I didnt open new thread, I dont want to continue on this thread because there are similar thermocouple applications. If the mods doesnt permit that, I can open new thread

 

The application is Thermal atomic force microscopy. It will measure the temperature of different types of specimen at the nanometer scale .( https://en.wikipedia.org/wiki/Scanning_thermal_microscopy - http://appnano.com/wp-content/themes/appnano/pdf/VERTISENSETM-THERMAL-IMAGING-AMP.pdf ). So speed is important for that application.

Wow. That's fascinating stuff! Thanks for sharing the links.

Are you planning to use an existing AFM thermocouple and just wanting to build your own data acquisition electronics? I can't imagine this technique working with any conventional thermocouple that I'm familiar with. The size of the TC junction is amazingly small in the links you shared. It seems like you'd have to have something along those lines for the technique to work.

It looks like complete systems already exist doing exactly what you want. Why build your own system? What are you wanting to do differently? Given the precision, both in temperature and in spatial dimensions, I think this would be a challenging design even for very experienced engineers. But maybe I'm overestimating that - I'm certainly not an experienced engineer.

Anyway, I really look forward to hearing Ron's take on all this. He knows TCs far better than I.

 

ebewoulf17, I didnt open new thread, I dont want to continue on this thread because there are similar thermocouple applications. If the mods doesnt permit that, I can open new thread

I'm confused now. Maybe me memory is playing tricks on me. Oh well. No matter.

Regardless, the AFM stuff is really interesting.

 

Actually I want to build my own system, I dont know that conventional cold junction compensation ICs work for that.

 

Actually I want to build my own system, I dont know that conventional cold junction compensation ICs work for that.

Swap thermocouple polarity during measurement to eliminate cold junction.
This allows you to calculate the real cold junction. ( All cable (cold) junctions are vulnerable to temperature)

Simple solution and easy to implement.

Picbuster

 

One possibility as base system -

http://www.cypress.com/documentatio...psoc-5lp-temperature-measurement-thermocouple

http://www.cypress.com/documentation/code-examples/ce95382-thermocouple-psoc-35lp

For lower T range applications -

http://www.cypress.com/documentatio...-4-and-psoc-5lp-temperature-measurement-diode

And RTD approaches -

http://www.cypress.com/documentatio...oc-4-and-psoc-5lp-temperature-measurement-rtd


Regards, Dana.

 

Sorry as I literally lost the thread. My email notifications stopped working for about a week and I was simply clicking on alerts and managed to literally lose this thread.

I read the links and just plain wow. The whole concept is really pretty cool and a long way from a conventional thermocouple. I really can't imagine building a simple home brew version of what I read. This is all new to me.

Ron

 

Thinking more about this I will make a suggestion. It was about 30 years ago i wrrkrf with some thermo environment chambers where we did some shake and bake as well as thermal shock Tenny and a few other chambers. One trick was to operate boards and alternator control units as used in the Tomahawk cruise missile system. One test included running a board and monitoring its operation up to something like 250 Degrees F, They ran there for awhile and then the heaters were shut down and two huge compressors were turned on to make cold and in addition several solenoid valves were turned on allowing LN (Liquid Nitrogen) to pour into the chambers We went from 250 F down to -250F literally in seconds. My sensors were just not fast enough so I finally called Omega Engineering and got an applications enjineer. They suggested I try a tiny ribbon design thermocouple After kicking dimension and slope time they sent me a few "practice suggestions" Took a few attempts but it worked out well. The junctions were bare hairlike ribbons and in my cased on the chamber airflow stream.

You may want to talk to a thermocouple applications engineer from Omega Engineering or Marlin Manufacturing or large scale temperature sensing manufacturer. This sort of work is what they do.

RON