Bridge with Automatic Zero (Patent No: 772307)

Inventor: Arksey, Graydon W.

Location: Edmonton

Comments: N/A

Description:
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A zero-compensated bridge, including an impedance network having energizing terminals and output terminals and condition-sensing means including at least one component whose impedance varies as a function of the departure of the sensed condition from the normal condition thereof, said network being proportioned to yield substantially zero output at said network output terminals in response to said normal condition, said network being subject to drift so that some departure from zero output tends to develop over a period of time, and means for compensating said bridge for zero drift-error, said compensating means including an operational amplifier having first and second load resistors connected together at a network output point, said first and second resistors being connected in series in the load circuit of the amplifier, one of said resistors being interposed between an output terminal of said network and an output terminal of said bridge, a negative feedback circuit connected between an input terminal and an output terminal of the operational amplifier, said feedback circuit having a storage capacitor, and switching means operable periodically to connect the input terminals of said amplifier to the bridge output terminals.

2. A zero-compensated bridge, including a four-armed network of resistors having energizing terminals and output terminals and including a condition-responsive sensing resistor, said network being proportioned to yield substantially zero output at said network output terminals in response to a normal condition of said sensing resistor, said network being inherently subject to drift that causes deviation from zero output over a period of time, and means for compensating said bridge for such deviation, said compensating means including an operational amplifier having a load resistor interposed between an output terminal of said network and an output terminal of said bridge, a negative feedback circuit including a storage capacitor connected between input and output points of the operational amplifier, and switching means operable periodically to impress the potential appearing at the bridge output terminals on the input end of said amplifier.

3. A zero-compensated bridge including a normally balanced resistor network subject to zero drift and having a direct-current energizing circuit, main output terminals, and zero-compensating means between said output terminals and said resistor network, said compensating means including a high-gain direct-current-responsive amplifier having an input circuit, an output circuit and a negative feedback circuit between said input and output circuits, and said amplifier including a drift-signal storage capacitor connected to said input circuit, and means including a switching device for at times connecting said amplifier input circuit to said main output terminals, said amplifier including a load resistor interposed in a circuit between one of said main output terminals and said resistor network for injecting zero-drift compensation into the bridge output.

4. A zero-corrected bridge, including a normally balanced resistor network subject to drift and having direct-current energizing terminals, main output terminals, and means
for injecting a zero-correcting signal between said resistor network and said main output terminals, said zero-correcting means including a high-gain direct-current amplifier having selectively operable input circuit connections to said main output terminals, and a negative feedback circuit between respective input and output terminals of said amplifier, said operational amplifier including a storage capacitor connected to the input circuit thereof, said zero-correcting signal injecting means including a load resistor of said amplifier interposed between a portion of the normally balanced resistor network and one of said main output terminals.

5. A zero-corrected bridge, including a normally balanced resistor network subject to drift and having direct-current energizing terminals, main output terminals, and means for injecting a zero-correcting signal between said resistor network and said main output terminals, said zero-correcting means including a high-gain direct-current amplifier having selectively operable input circuit connections to said main output terminals and a negative feedback circuit between respective input and output terminals of said amplifier, said feedback circuit including a storage capacitor, said zero-correcting signal injecting means including a load resistor of said amplifier interposed between a portion of the normally balanced resistor network and one of said main output terminals.

6. A zero-corrected bridge, including a normally balanced resistor network subject to drift and having direct-current energizing terminals, main output terminals, and means for injecting a zero-correcting signal between said resistor network and said main output terminals, said zero-correcting means including a high-gain direct-current amplifier having selectively operable input circuit connections to said main output terminals, and a negative feedback circuit between respective input and output terminals of said amplifier, said feedback path including a storage capacitor and a first resistor connected in series, the first resistor being additionally connected to an input terminal of the amplifier, and a circuit including a second resistor in series with a switching device connected between the junction of said first resistor with said capacitor and a reference point at the input of the amplifier, said amplifier including a load resistor interposed between a portion of the normally balanced resistor network and one of said bridge output terminals.

7. A zero-compensated bridge including a normally balanced resistor network subject to zero drift and having a direct-current energizing circuit, a pair of main output terminals, and zero-compensating means between said main output terminals and said resistor network, said compensating means including an inverting operational amplifier having input terminals including a reference terminal connected to one of the main terminals and including switching means for connecting another amplifier input terminal to the other of said main output terminals, said amplifier also having an output circuit and having a negative feedback circuit between said other amplifier input terminal and said output circuit, a drift signal storage capacitor interposed in said feedback circuit as a part thereof, and said amplifier including a load resistor interposed in a circuit between said one main output terminal and said resistor network for injecting zero-drift compensation into the bridge output.

8. A zero-compensated bridge, in accordance with claim 7, further including a resistor between said other input terminal of the amplifier and said storage capacitor, and a circuit including a resistor and a switching device connected between said reference terminal of the amplifier and a point in the feedback circuit between said resistor and said capacitor, and coordinated operating means for closing and opening both said switching device and said switching means.