Low zero-offset transducer apparatus

Claim 1

Transducer apparatus comprising: a first input terminal for connection to a source of voltage excitation; a second input terminal for connection to a source of a common reference potential; DC amplifier means having signal input terminals and a singleended output terminal, and power supply terminals respectively connected to said first and second input terminals; a bridge-type sensor having power supply terminals respectively connected to said first and second input terminals, and sensor output terminals respectively connected to said signal input terminals; a transducer output terminal; semiconductor means connected between said single-ended output terminal and said transducer output terminal, operable for providing a substantially unvarying potential difference between said output terminals such that the potential at said transducer output terminal approaches the common reference potential when the monitored condition is at a reference level; negative feedback means coupled between said transducer output terminal and one of said signal input terminals through a portion of said bridge-type sensor; variable resistor means connected between said transducer output terminal and said second input terminal, having a resistance range for maintaining operability of said semiconductor means, said range including a lower value for permitting the potential at said transducer output terminal to approach the common reference potential and an upper value for preventing excessive generation of current through said resistor means; and control means responsive to the potential at said transducer output terminal when said first and second input terminals are respectively connected to said sources, for controlling the resistance of said variable resistor means to vary in direct relation to the potential at said transducer output terminal.