Null-balance servo system

Claim 2

A null-balance servo system comprising an adjustable circuit element for restoring balance wherein the position of said adjustable circuit element represents a measurement of said unknown signal, a detector responsive to the unbalance of said adjustable circuit element, and a motor for adjusting said adjustable circuit element in a direction to restore balance to said servo system, the improvement residing in said detector comprising: means for controlling the input for said motor including amplifying means; means for producing an error signal proportional to the difference between said input signal and a position feedback signal; means for altering said error signal by a small velocity feedback signal for damping; means for further altering said error signal by a large velocity feedback signal for dampiNg when the rate of adjustment of said adjustable circuit element exceeds a threshold; means for applying the altered error signal to said means for controlling the input to said motor, and means for constraining current through said motor to a tolerable level and applying a signal representative of the constrained current to said amplifying means to dominate control of said motor and returning control to said motor to said altered error signal when current constraint is no longer needed.

Claim 3

The null-balance servo system of claim 1 wherein said means for further altering said error signal by a large velocity feedback signal comprises a large velocity feedback circuit connected between said adjustable circuit element and said detector including means for establishing a velocity threshold.

Claim 4

The null-balance servo system of claim 2 wherein said means for constraining current comprises a motor current feedback circuit between said motor and said detector including means for establishing a motor current threshold.

Claim 5

The null-balance servo system of claim 3 wherein said means for establishing a velocity threshold comprises a pair of oppositely poled diodes, one of which is conductive when the threshold level is exceeded.

Claim 6

The null-balance servo system of claim 4 wherein said means for establishing a motor current threshold comprises a pair of oppositely poled diodes, one of which is conductive when the motor current threshold level is reached so as to conduct a current limiting feedback signal to said amplifying means.

Claim 7

The null-balance servo system of claim 4 wherein said means for establishing a motor current threshold comprises a pair of parallel-connected FET''s connected between the output and the input of said amplifying means and gate control means connected between said FET''s and the output of said motor, one of said FET''s being conductive when the motor current threshold level is exceeded so as to reduce the gain of said amplifying means thereby constraining current applied to said motor to said tolerable level.

Claim 8

A null-balance servo system for measuring an unknown electrical quantity as an input signal comprising an adjustable circuit element for restoring balance wherein the position of said adjustable circuit element represents a measurement of said unknown signal, a detector comprising amplifying means responsive to the unbalance of said adjustable circuit element, and a motor for adjusting said adjustable circuit element in a direction to restore balance to said servo system, the improvement residing in said detector comprising: means for producing a position feedback signal substantially proportional to the position of said adjustable circuit element; means for producing an error signal substantially proportional to the difference between an input signal and said position feedback signal; means for driving said motor in response to said error signal; means for producing a velocity feedback signal proportional to the rate of adjustment of said adjustable circuit element; means for reducing said error signal by a small velocity feedback signal for damping; means for further reducing said error signal by a large velocity feedback signal for damping when the rate of adjustment of said adjustable circuit element exceeds a threshold; and means for limiting said error signal in response to the current through the motor when said current reaches a threshold so as to constrain said current to a tolerable level.

Claim 9

A null-balance servo system for measuring an unknown electrical quantity as an input signal comprising an adjustable circuit element for restoring balance wherein the position of said adjustable circuit element represents a measurement of said unknown signal, a detector comprising amplifying means responsive to the unbalance of said adjustable circuit element, and a motor for adjusting said adjustable circuit element in a direction to restore balance to said servo system, the improvement residing in said detector comprising: means for producing a position feedback signal substantially proportional to the position of said adjustable circuit element; means for producing an error signal substantially proportional to the difference between an input signal and said position feedback signal; means for driving said motor in response to said error signal; means for producing a velocity feedback signal proportional to the rate of adjustment of said adjustable circuit element; means for reducing said error signal by a small velocity feedback signal for damping; means for further reducing said error signal by a large velocity feedback signal for damping when the rate of adjustment of said adjustable circuit element exceeds a threshold; and means for limiting said error signal in response to the current through the motor when said current reaches a threshold so as to constrain said current to a tolerable level.

Claim 10

The improved servo system of claim 7 wherein said means for further reducing said error signal comprises a large velocity signal feedback circuit from said adjustable circuit element for further reducing the error signal in response to the velocity of said adjustable circuit element.

Claim 11

The improved servo system of claim 8 wherein said means for constraining current comprises a current limiting feedback circuit from said motor for limiting said error signal in response to the mOtor current.

Claim 12

The improved servo system of claim 9 wherein said large velocity feedback circuit comprises a pair of parallel oppositely poled diodes for establishing a threshold, one of said diodes being conductive when a velocity threshold is exceeded.

Claim 13

The null-balance servo system of claim 7 wherein said current limiting feedback circuit comprises a pair of parallel oppositely poled diodes for establishing a motor current threshold, one of said diodes being conductive when the motor current threshold is exceeded.

Claim 14

The null-balance servo system of claim 7 wherein said means for constraining current further comprises a pair of complementary FET''s connected in parallel relationship between the input and the output of said amplifying means and having gate electrodes connected to said current limiting feedback circuit so as to render one of said FET''s conductive when the motor current threshold is exceeded.