Davidson Measurement Tech Tips

Protecting transducers from high (or low) temperature pressure media

We often advise customers to mount transducers on a length of small bore pipe to protect them from temperature extremes of the pressure media.

Providing the pressure vessel is insulated to limit radiant heat transfer, and that there is no flow of fluid through the transducer mounting pipe, the major source of thermal input to the transducer can only be due to conduction through the connecting pipe.

Assuming the ambient temperature around the connecting pipe and transducer is 40°C (100°F), the curves shown below illustrate the temperature drop/length of pipework for various materials and pipe dimensions.

The curves are based upon the following constants:

a) Heat transfer rate (convection) from the tubing in still air is 1.44 BTU/FT/HR/°F.
b) The thermal conductivity of the media is less than 0.4 BTU/hr/ft/°F (applicable to most liquids and gases).
c) The temperature of the transducer will be between -17°C to +93°C.

Pipework: Material and size:

(1) Stainless steel: 3 mm O.D. x 0.18 mm I.D.
(2) Stainless steel: 6.4 mm O.D. x 4.5 mm I.D.
(3) Brass: 6.4 mm O.D. x 4.6 mm I.D.
(4) Stainless steel: 6.4 mm O.D. x 4.6 mm I.D.