Gefran has released a series of extrusion sensors filled with NaK rather than Mercury. Nak is defined as GRAS – safe under the RoHS guidelines. The performance and price are almost the same as the previous M versions, and NaK is the standard offering in Europe. It has yet to be accepted in Australia.
In the recent past, extrusion sensors were filled with mercury to transmit pressure at high temperature, from the measuring diaphragm to the sensing element.
A European directive has banned the use of Mercury in the applications, and other ‘fill’ materials are used. Many use food grade silicon oils, and these are successful, but have limits on the temperature and temperature coefficient. NaK is 22% sodium and 78% Potassium, and it is stable and safe even at extreme temperatures
The NaK series extrusion sensors with inconel diaphragm material are rated for continuous use at 538C. Whilst most applications use standard 15-5PH diaphragms, considerable extensions of life are possible by using alternative materials such as inconel718 and hastelloyC276.
Also, special coatings can extend life through hardness or chemical resistance and Gefran GTP, their latest and most advanced diaphragm coating, is offered as standard.
The K series extrusion sensors are available from ECEFast .