connector prong 30 with a friction fit and supports pressure plate 28 for axial motion in response to applied fluid pressure a printed circuit board 40 carries sensing and control circuits 42 surge suppressing circuits 44 are coupled to a dc supply 46 a digital circuit regulator 48 and analog circuit regulator 50 feed digital circuits 56 and differential amplifier 52 respectively the differential amplifier 52 is coupled to strain gauge 34 via connectors 34 a movement of the plate 28 in a first direction in response to increasing fluid pressure generates a signal of a first polarity at amplifier 52 movement of plate 28 in the opposite direction in response to decreasing fluid pressure generates a signal of the opposite polarity at amplifier 52 digital control circuits 56 include a programmable processor or computer 58 a and associated storage random access memory eeprom and flash memory indicated generally at 58 b software or control programs stored in eeprom or flash memory can be executed by processor 58 a in carrying out the above described switching process circuits 56 can be accessed via a programming interface 58 e a factory calibration port 58 f is also provided digital output circuits 58 c are respectively coupled to triac driver 62 a and triac 62 b and relay driver 64 a and relay 64 b as described above electrical energy from connector 22 is.