Temperature Indicator -urgent

What does the procurement specification say?

Or, what does TI say?

I say you are not right. Does the probe take two readings and add them together?

Procurement spec says that TI is measuring process temperature ..not atmospheric temperature. My question is If some portion of the stem(20mm) exposed to the atmosphere ..does this portion effect the temperature value?

tell me how can i add picture here? i would like 2 attach photo for clear view.

Hi, Guest

Send your instrument to the machinish to add socket to cover the 20mm exposed to atmospher.

Regard's

newbie

GA for pointing out that the sensinsg element is at the tip.

The TI will not be mechanically coupled to the thermowell (as was pointed out by a Irs)and therefore it is likely (depending on the application) that the TI will become loose and measurements will be compromised. There is only so much heat transfer paste that can go into a thermowell and this alone may not be sufficient to maintain the mechanical stability.

I saw your suggestion about the compression fitting and this is not a bad idea but perhaps for the the long term succes of this application the Op should just simply purchase the correct TI.

While the air space will permit heat to be transferred by convection a little easier, the temperature reading will always be of the bi-metallic sensor. The small amount of heat lost to heating the air that is permitted to leave the cavity will likely not be a significant loss. Now if there is no seal at all you might lose a considerable amount of you HC gas.

I agree with those who explain that the measurement is made in the 50mm near the tip of the bimet, so that the influence of 25mm exposed stem is not signficant.

But as I understand it, it seems that there is no means of securing the bimet in the thermowell, because the threaded process connection does not screw into the internal threads on the thermowell:

How is the bimet secured from falling out of the thermowell?

You might be able to screw a compression fitting into the female thermowell threads.

sir kindly give me a clear picture ...what should i do.....

should i fix a compression fittings to cover the expose part or else?

or any other method is there

A compression fitting would cover almost all of the exposed 20mm of the probe stem, which already doesn't really matter.

is it really true that of 50mm from bimet probe tip contains the sensing part?

upper portion of the probe doesnt contain sensing part.

i didnt find this in the vendor catalog

model :Baumer TBI130/264.160 RANGE : (-) 50 TO 400 DEG F

All bimets have similar construction. The helical or spiral bimetallic element is anchored at the tip. The length of the bimetallic element depends on range and model.

The article's author at the link provided below cites a study that shows that a bimet's element averages the temperature gradient across the element.

http://www.hi-tm.com/Documents2001/hamburger-temp.pdf

OK, so put lagging round it, then.

Conventional wisdom is that thermowell length should be at least 10 times the sensor diameter. Your system exceeds this criteria which means you should be okay. If you want to test this conclusion, measure the temperature at different insertion depths and plot the data. If the measured temperature doesn't change over the last 10 mm of insertion, the length is okay.

thanks to all those who spent time for me and replyed .

i will verify it by measuring temp.

I am in the process industry for last 10 years and we are purchasing usually from WIKA INSTRUMENTS.i never found such cases.thats why i asked to alll.

thanks to all again

Happens all the time. We manage to get at least two sensors too long for the thermowell that was installed in a new tank every year. Then one has the following choices

1. if the well and the sensor are NPT a nipple or a coupling can be added - whatever works.

2. if not, perhaps an extension can be welded to the thermowell

3. none of the above work - order a proper length sensor

And, always point fingers at someone as the culprit for not correlating the two dimensions correctly, unless it was you, then have a good excuse ready.

Most processes use one thermocouple for process control and one for over temperature alarms. If your system is set up this way simply compare the two readings. If the readings are both the same or close you should be OK.

As was mentioned earlier in this post the sensing is done at the tip of the thermocouple and if the installation is vertical the sensing tip will be in physical contact with the bottom of the thermowell if it is unsupported. This may cause process overshoot if the system is tuned with the thermocouple not in contact with the thermowell. If the installation is horizontal or the gland nut can secure the thermocouple off of the bottom you should be OK.

The only other thing to consider is mechanical damage. If the thermocouple sticks out of the thermowell too far it may get damaged by objects or persons moving around in the area.

It's best to use the proper length thermocouple if possible. We have in the past been able to shorten ours but they may not be the same design as yours.

Good Luck