Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Thermal
Patent
1991-01-03
1993-02-23
Harvey, Jack B.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Thermal
324706, 324725, G01R 2102
Patent
active
051893622
ABSTRACT:
A circuit for measuring the R.M.S. voltage of a high frequency signal (e.g. 100MHz) comprises two series-connected ntc thermistors (TH1, TH2) in a bridge circuit which is energized by a current source (1). The unknown signal is applied across one (TH1) of the thermistors and the resulting change in the resistance causes a D.C. output voltage to appear across the balanced terminals (T3, T4) of the bridge. This output voltage is proportional to the square of the R.M.S. voltage of the A.C. signal. In another embodiment, two ptc thermistors are connected in parallel in a bridge circuit which is energized by a voltage source, and are used to measure R.M.S. current. In each case, the thermistors are preferably operated in a negative slope resistance portion of their voltage-current characteristic. In a further embodiment two balanced bridges, each incorporating two thermistors, are connected in series in one arm of a bridge circuit, and a compensating signal is applied by a feedback circuit to one bridge so as to match the heating effect of the unknown A.C. signal applied to the other bridge.
REFERENCES:
patent: 3093732 (1963-06-01), Clark
patent: 3624525 (1971-11-01), Smith
patent: 3626290 (1971-12-01), Aslan
patent: 3723845 (1973-03-01), Duckworth
patent: 3911359 (1975-10-01), Metcalf
patent: 4023099 (1977-05-01), van Kessel et al.
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