Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
1999-12-21
2001-11-13
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S096000
Reexamination Certificate
active
06316930
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention concerns a direct current meter with passive input and galvanic insulation, particularly for high voltage.
2. Prior Art and Other Considerations
The measurement of the intensity of a direct current that is produced by a high voltage source notoriety creates problems with insulation. This is the case, for instance, of the measurement of the anode current of a photomiltiplier tube with earthed cathode and anode supplied at high voltage.
An object of the present invention is provision of a direct current meter that is capable of measuring a direct current flowing in a conductor that is at high voltage, as for instance the anode voltage of a photomultiplier tube operating in the above indicated way.
SUMMARY
According to the invention such object is solved with a current meter characterized in that it is made up of a passive input part of an active outer part that is optically coupled to the passive part and electrically insulated from it.
In particular the passive part comprises a parallel circuit supplied with the current to be measured and including a photo-emitter diode and a photo-receiver diode that are connected in anti-parallel, whereas the active part comprises a photo-receiver transistor that is optically coupled to said photo-emitter diode of the passive part in order to form an electrically insulated current amplifier with high open-loop gain and, in series with said photo-receiver transistor, an additional photo-emitter diode optically coupled to said photo-receiver diode of the passive part in such a way so as to form an electrically insulated feedback for said amplifier and, in a symmetrical way, to an additional photo-receiver diode of the active part that produces an output signal substantially proportional to the current that flows through said photo-receiver diode of the passive part.
In other words, the current meter according to the invention is thus made up of a feedback amplifier sensitive to the current, that comprises an open-loop amplifier and a feedback, both electrically insulated. The open-loop amplifier comprises the photo-emitter diode of the passive part and the photo-receiver transistor of the active part, as well as preferably a bipolar transistor or any other circuit structure that is capable to further increase the current gain determined by the high-gain current amplifier. The feedback comprises in turn the photo-emitter diode of the active part and the photo-receiver diode of the passive part.
Even more in particular, the photo-emitter diode of the passive part and the photo-receiver transistor of the active part are implemented in the form of an optocoupler chip with high current gain at low input current, for example of the type known on the market as Toshiba TLP-127, while the photo-emitter diode of the active part and the two photo-receiver diodes are implemented in the form of a linear optocoupler chip, for example of the type known on the market as Siemens IL388 or IL300.
In this way a current meter is obtained in which the high voltage to ground present at the input affects only the passive part of the meter while the active part can be supplied with low voltage and, owing to the high gain of the current amplifier and to the symmetrical optical coupling between the photo-emitter diode of the active part and the two photo-receiver diodes, is capable to provide an output signal proportional to the current to be measured and substantially independent from the working temperature. In particular this last feature is guaranteed by the monolithic structure of the chip used used for feedback.
A current meter made in this way has proven to be particularly, though not exclusively, suitable to measure the anode current of a photomultiplier tube with earthed cathode. For such use the input part of the current meter according to the invention is connected in series with the last resistance on the anode side of the bias resistive network of the photomultiplier tube and its output together with the cathode of the photomultiplier tube is connected to an input of an operational amplifier with feedback. Due to this connection, as it will be better explained hereinafter, a voltage proportional to the anode current of the photomultiplier tube is thus produced at the output of the operational amplifier.
REFERENCES:
patent: 3772514 (1973-11-01), Sunderland
patent: 4070572 (1978-01-01), Summerhayes
patent: 4316141 (1982-02-01), Adolfsson et al.
patent: 5107202 (1992-04-01), Renda
patent: 5389578 (1995-02-01), Hodson et al.
patent: 5654559 (1997-08-01), Spaeth et al.
patent: 6166816 (2000-12-01), Blake
Patent Abstracts of Japan, vol. 007, No. 051 (P-179), Feb. 26, 1983 & JP 57 199961 A (Mitsubishi Demki KK), Dec. 8, 1982.
Istito Nazionale di Fisica Nucleare
Metjahic Safet
Nixon & Vanderhye P.C.
Sundaram T. R.
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