초록 ▼

Automatic balancing circuits are provided for non-destructive testing systems such as eddy current systems in which an unbalance of a probe circuit including a test coil produces undesired deviations from a null indication. Error signal components are generated from a probe circuit output signal, st

Automatic balancing circuits are provided for non-destructive testing systems such as eddy current systems in which an unbalance of a probe circuit including a test coil produces undesired deviations from a null indication. Error signal components are generated from a probe circuit output signal, stored in storage means and then applied in a balancing direction to cancel the effect of the unbalance of the probe circuit. Preferably, the error signal components are generated by a pair of quadrature phase detectors and the storage means comprises either a capacitor or the combination of digital storage and digital-analog converter means. The balancing is performed either automatically, with a delay in the storage operation, or by operation of a switch means between a sample or null condition in which the error signals are stored and a hold condition in which the stored error signals are applied. In one embodiment, the stored error signals are used to modulate AC signal components in quadrature phase relation which are applied in a balancing direction. In another, the stored error signals are developed from phase detector output signals and then combined therewith. In both embodiments, balancing signals are combined with signals derived from the probe circuit output signal and applied at points preceding high gain amplification in signal processing circuitry.

대표청구항 ▼

In a non-destructive testing system comprising a probe circuit including probe means adapted to be placed in proximity to a part to develop an output signal according to characteristics of the part, indicating means, and signal processing means having input means coupled to said probe circuit to res

In a non-destructive testing system comprising a probe circuit including probe means adapted to be placed in proximity to a part to develop an output signal according to characteristics of the part, indicating means, and signal processing means having input means coupled to said probe circuit to respond to said output signal thereof and having output means coupled to said indicating means, said signal processing means including circuit means responsive to at least a component of said probe circuit output signal to apply a corresponding drive signal to said indicating means, a predetermined value of said drive signal being operative to produce a reference null indication by said indicating means, said circuit means including automatic balancing means for maintaining said drive signal at an average value equal to said predetermined value irrespective of relatively slow changes in the average value of said probe circuit output signal component while allowing changes in said drive signal in response to rapid changes in said probe circuit output signal component, said circuit means further including sample and hold means including a switch manually operable between a sample position and a hold position, sample means operative in said sample position of said switch to develop a voltage corresponding to the existing value of said probe circuit output signal component, and hold means operative upon operation of said switch from said sample position tO said hold position to store said voltage and to apply said stored voltage in said signal processing means in a direction to oppose said probe circuit output signal component and to produce said predetermined value of said drive signal and said reference null indication when said probe circuit output signal component has a value equal to said existing value, mode selector switch means manually operable between an automatic balance position and a sample and hold position, means operative in said automatic balance position for rendering said automatic balancing means operable and said sample and hold means inoperable, and means operative in said sample and hold position for rendering said sample and hold means operable and said automatic balancing means inoperable.