Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Balancing
Patent
1987-01-29
1988-09-13
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Balancing
324 73PC, 324123C, G01R 1900, G01R 1073
Patent
active
047712333
ABSTRACT:
An ammeter is used for measuring the current flowing through a lead on a printed circuit board having a four point probe contacting the printed wire under test. Each probe points is spring loaded and approximately one millimeter separates adjacent probe points. The center two probe points are coupled to the inputs of a high gain chopper stabilized operational amplifier which provides a signal related to the voltage between the center two probe points as a result of the line resistance. The operational amplifier must have a very low and stable input offset voltage. The amplifier signal is applied to the base electrodes of a bipolar current driver circuit, such as two opposite polarity Darlington circuits, which respectively have a source of positive and negative voltage coupled to flow through the collector emitter electrodes when the signal applied to the base renders the collector emitter conductive. The two sources of opposite polarity voltage are each coupled to a common point on the side thereof remote from the Darlington transistors. The emitters of the Darlington circuits are coupled together and to one of the outer probe points. The other outer probe point is coupled through a low resistance resistor to the common point and a meter and low pass filter are coupled in parallel with the low resistance resistor to obtain a voltage reading manifesting the current flowing therethrough. The above circuit connection allows the current flowing through the low resistance resistor to closely approximate the current flowing in the lead under test.
REFERENCES:
patent: 4175253 (1979-11-01), Pitegoff
"Meter Measures Current in Uncut PCB TRack", by Andrews, Elect. Engin. vol. 47, #574, p. 21, 12/75.
Barron Harry W.
Burns W.
Eisenzopf Reinhard J.
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