New Universal Impedance Bridge With Simplified Semiautomatic Tuning

By using feedback to adjust one bridge element automatically, a bridge requiring only one balancing control is achieved.

Universal bridges have considerable versatility, being able to measure not only resistance, capacitance, and inductance over wide ranges, but also the Q of inductances and the dissipation factor (1/0 of capacitors. This versatility, however, has led to complicated control panels, oftentimes making it not so simple for the casual user to make bridge measurements without recourse to study of the instruction manual.

A new universal bridge has been designed to remove the confusing

Impedance Bridge Parallel Capacitor

Fig. 2. Typical impedance bridge configuration, this one for measuring unknown capacitor C,-R, in which capacitor loss factor is considered as resistance Rx in parallel with pure capacitance Cs. Besides adjustment of R<rl, Una must be adjusted to match time constant of Cr-Rna to time constant of Cr-Rr if balance is to be achieved. 7?UQ and Rcrl are interacting as far as indication on detector is concerned.

Fig. 2. Typical impedance bridge configuration, this one for measuring unknown capacitor C,-R, in which capacitor loss factor is considered as resistance Rx in parallel with pure capacitance Cs. Besides adjustment of R<rl, Una must be adjusted to match time constant of Cr-Rna to time constant of Cr-Rr if balance is to be achieved. 7?UQ and Rcrl are interacting as far as indication on detector is concerned.

elements that have been associated with bridge operation. For example, the readout is direct. Measurement results are displayed by an in-line digital readout and the decimal point is placed automatically by the RANGE switch. The unit of measurement, as selected by the FUNCTION and RANGE switches, is shown in a window. There is no need for applying multiplication factors to the readings and, as shown by the panel arrangement in the photo of Fig. 1, there is no ambiguity in making read-

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FUNCTION

UNKNOWN UNE Cs rCpi R rLsi lp SENSiTIVtTY

FUNCTION

UNKNOWN UNE Cs rCpi R rLsi lp SENSiTIVtTY

Fig. 1. New Universal Bridge has digital read-out, automatic decimal placement, non-ambiguous range indication, and other features that simplify measurement of resistance, capacitance, inductance, Q, and loss factor. Bridge design eliminates prolonged balancing procedures formerly caused by sliding null in measurements of lossy reactive components. Control circuitry automatically brings DQ resistor to correct value as CRL dial is adjusted for a null.

RESISTANCE BRIDGE (R)

To Detector (de) Unknown

RESISTANCE BRIDGE (R)

To Detector (ac) known

Dj. = (üCt Rc CAPACITANCE BRIDGE (Cs, Low D) (Series loss)

RANGE Iii IMSl

To Detector (ac) Unknown

RANGE Iii IMSl

To Detector (ac) Unknown

CAPACITANCE BRIDGE (<Cp, HIGH D) (Parallel loss)

CAPACITANCE BRIDGE (<Cp, HIGH D) (Parallel loss)

To Detector (ac) Unknown

INDUCTANCE BRIDGE (Ls, Low Q) (Series loss)

To Detector (ac) Unknown

Fig. 3. Bridge circuits selected by FUNCTION switch in new Universal Bridge. In auto mode measurement of low Q or high D components, DQ resistor (Rc) is replaced by servo-controlled variable resistance.

INDUCTANCE BRIDGE (Lp, High Q) (Parallel loss)

INDUCTANCE BRIDGE (Ls, Low Q) (Series loss)

INDUCTANCE BRIDGE (Lp, High Q) (Parallel loss)

ings of resistance, capacitance, or inductance.

As a further step toward removing conf usion factors, the only terminals on the front panel of the new instrument are those for the unknown component. All other terminals, those for bias insertion and for external detectors and generators, are on the rear panel.

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