Process temperature & thermocouples

[@ChemEngWeekly]

This is a great demo on how thermocouples work, and the demonstration with the fridge and the oven was great! Good job Pat 👍

[@naturalnewbie98]

Please point out that modern input devices have CJC built into them, and that in the software or hard dip switches will have selections for different thermocouple types, and that any extension wire must be of the same type as the thermocouple . Also note that corrosion at any connection points can skew the reading, and that CJC can go bad. Any critical thermocouple channels should be tested with a traceable calibrator. And that's just the basics :)

[@brendan714]

Some hilarious parts in this video like 1:05 had me laughing out loud and I love the good technical content, as usual. But I have to say I'm most impressed with the fact that your fridge and freezer just look like regular kitchen cabinet doors. My fridge stands out in my kitchen like a sore thumb (or tooth operation), it really messes with my interior design schemes

[@ProcesswithPat]

Glad you enjoyed it! Funny you mention the fridge door! We actually don’t like it (doesn’t help that the fridge is rubbish), so I wouldn’t mind one with just brushed stainless steel.

[@skunkjobb]

In my branch, we don't use thermocouples for process temperature measurement, only Pt-100 resistive measurement which don't need ambient temperature compensation. That might be because we're in a moderate temperature regime seldom over 150 °C and thermocouples work better at more extreme temperatures, just a guess. Further, the sensitive Pt-100 "signal" is converted in the field instrument to a more robust 4-20 mA signal (or some data bus signal) so the cable to the control equipment can be very long without disturbance.

[@coolminded850]

Great demonstration. Really helpful to develop clear understanding. Keep it up.

[@rasmussverdrup7479]

This video has great potential.

[@magarlai-dado]

Thanks for this video. Trying to get my head around something. If I can calculate temperature using a millivolt meter and coefficient table: why do we need a cold-junction meter? As in, you measured your voltage whilst the thermocouple was disconnected from the cold-junction meter. Should it not have been connected to the cold-junction meter while you measured voltage?

[@ProcesswithPat]

The table only gives you the voltage under the assumption that the cold end of the thermocouple is at 0 degrees, which most of the time, it isn’t. So the further away from zero the cold junction actually is, the more inaccuracy you’d have in your reading. Think of it this way… Imagine you were looking at a ten story building, and you knew each story was exactly 3m in height. Imagine you wanted to work out the ALTITUDE of the top of the building. Given only this information your only numerical guess is that the altitude is 30m. But this is only true if your building is at sea level (sea level is 0 Celsius in the analogy). If you were 100m above sea level then the altitude of the top is actually 130m. So the further away from sea level your building is, the more inaccurate your “reading”. You need to know the height above sea level of the bottom of the building to “compensate”. Not sure if that helps or just makes things worse for you! Let me know…

[@magarlai-dado]

Thanks so much!

[@dounutkiller]

such a great video, appreciate the work.

[@pavithraa2915]

Very good demonstration...Please do video on PSV sizing

[@ProcesswithPat]

You know, PSV sizing is one of those things I never went into extensive detail myself. Given the criticality and the thorough API standards that exist, I think I need to give this one a pass for the moment!