Electrical bridge balancing circuit
AssigneeGoring Kerr Limited
InventorBruce G. Kerr
Life of this patent
Estimating the term…
Abstract
An electric sensing circuit, typically a metal detector includes a bridge including inductors. The out of balance condition of the bridge is stored on a capacitor and a balancing signal is fed to balance the bridge in dependence upon the stored value of the charge. The stored value of the charge is only updated in response to relatively slow changes in the out of balance condition of the bridge. Relatively rapid changes in the out of balance condition are used to provide an output signal for alarm or measuring purposes, and the arrangement is thereby so arranged that the balancing signal does not attempt to automatically balance out the output signal giving the alarm or measurement.
Claims12
An electrical sensing circuit comprising:
- bridge circuit means including an electrical bridge and sensing means for producing an output signal which is a function of the in or out of balance condition of the bridge;
- storage means for storing the value of said output signal;
- balancing means responsive to said storage means for applying a balancing signal to said bridge circuit means for tending to cause said output signal to represent a balanced condition of the bridge, the value of said balancing signal being a function of the value of said output signal stored by said storage means;
- threshold means responsive to said output signal for producing a switch control signal which assumes a first state when the value of said output signal changes at less than a predetermined rate to exceed a predetermined threshold;
- switching means responsive to said switch control signal for applying said output signal to said storage means when said control signal is in said first state to modify the stored value of said storage means;
- and
- alarm means for providing an alarm signal in response to said output signal changing at a rate greater than said predetermined rate to exceed a given level.
An electrical sensing circuit comprising:
- bridge circuit means including an electrical bridge and first and second sensing means for producing first and second output signals which are a function of the in or out of balance condition of inductive and resistive components of the bridge respectively;
- first and second storage means for storing the values of said first and second output signals respectively;
- first and second balancing means responsive to said first and second storage means respectively for applying to the bridge first and second balancing signals respectively for tending to cause said first and second output signals to indicate a balanced condition of the inductive and resistive components of the bridge, the values of said first and second balancing signals respectively being a function of the values of said first and second output signals stored by said storage means;
- combining means for combining together said first and second output signals to provide a combined output signal;
- threshold means responsive to said combined output signal for providing a switch control signal which assumes a first state when the value of said combined output signal changes at less than a predetermined rate to exceed a predetermined threshold;
- first and second switching means responsive to said switch control signal for respectively applying the first and second output signals to the first and second storage means when said control signal is in said first state to modify the stored values thereof;
- and
- alarm means for providing an alarm signal in response to said combined output signal changing at a rate greater than said predetermined rate to exceed a given level.
Dependencies are inferred from the claim text.