Transmitter sensor operating temp

[helpyou]

Hi

In some pressure transmitter manuals ..its written that minimum temperature for its sensors is for example is - 40 C.. but they are actually installed in a line of - 160 C (Liquified gas process) and it gives correct reading .. my question is how is this possible ?

 

[IRstuff]

Can you cite an example?

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[danw2]

It is important that a cryogenic liquid not make contact with the sensing element of the common industrial pressure transmitter to avoid damage. There is an aerospace transmitter rated to -350 Deg F that I ran into once, its sensor is remote from its electronics.

The typical method of isolating the transmitter from the liquid is to mount the transmitter above the process and use the heat of an impulse line to vaporize the liquid to maintain a gas pocket in the impulse line.

Details in the attached doc

 

[Woody4000]

As danw2 stated if you can keep the cryogenic liquid from touching the sensor they typically will function because they wont get down to the actual Cryo fluid temperature. I have seen the setup danw2 shows and I have seen users install what's called a dry leg or pigtail device. Data sheet for one here:

https://blueribboncorp.com/wp-content/uploads/2018/06/BR5SL-A-003_Siphon_RwA-2.pdf.

This keeps a dry portion of this leg near the sensor. We do offer Cryo transmitters with a 4-20 mA signal but typically they are very high cost and a dry leg or impulse line is much more cost effective and does a good job.