Remote probe differential pressure transducer

A differential pressure transducer assembly for measuring low range pressure differentials with a minimum shift of zero under changing temperature conditions where the measurement is to be made across a restriction in a pipe carrying a flowing fluid which contains solids, is dirty or highly viscous comprising:

• first and second probes each of which has an insertable end designed for insertion into said pipe at different points as required to detect a differential pressure therebetween, said insertion ends of said probes each having
• a cavity of substantially the same volume containing a fill fluid, and
• identical barrier diaphragms of minimum but equal thickness mounted at that end of the cavities to be inserted into said flowing fluid for isolating the flowing fluid in the pipe from the fill fluid;
• two substantially identical capillary tubes containing fill fluid and connected to the respective cavities of said probes;
• a pressure receiving body having first and second pressure receiving sections each having a cavity containing fill fluid, said cavities each being connected by way of said fill fluid to the fill fluid in the cavity of one of said probes by way of the fill fluid in said capillary tubes, said body cavities each being filled by an insert which fits its cavity to close tolerance so as to minimize the volume of fill fluid in said cavities, said inserts being of a material which has a thermal coefficient of expansion which is lower than that of said body and said inserts also being of a volume such that the volumes of fill fluid in said body cavities is substantially equal and such that a change in volume of the fill fluid in each of the body cavities due to temperature changes of the body and the inserts is substantially equal to the change in volume of the fill fluid for such a temperature change without a change in fill fluid pressure;
• and
• a differential pressure measuring transducer having a diaphragm sandwiched and bonded between two support plates to form on opposite sides of said diaphragm cavities of minimum and substantially equal volumes containing fill fluid, said transducer being placed so that opposite diaphragm cavities communicate through a minimum volume of fill fluid with corresponding body cavities so that said diaphragm will deflect in response to the differences in pressure exerted by the flowing fluid on the barrier diaphragms.