Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Plural ranges – scales or registration rates
Patent
1994-06-01
1996-08-06
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Plural ranges, scales or registration rates
324123R, 324131, G01R 19165
Patent
active
055437060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for measuring small fluxes as well as a circuit for performing this process.
2. Discussion of the Related Art
In many measuring instruments such as, for example, mass spectrometers, vacuum gauges etc. the measurement values are produced on the basis of currents which are generated by positively or negatively charged particles impinging on an electrode. The dynamic range of the ion or electron currents which occur and have to be measured is very wide. It frequently spans from several hundred atto-Ampere to several micro-Ampere and thus covers over nine decades.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention is based on the objective of recommending a process for the measurement of currents in this order of magnitude as well as a suitable circuit for implementation of this method of measurement, by which it is possible to produce the measured values quickly, accurately and without interferences.
The method of measurement of the present invention is characterised by the features as herein described and claimed in the following method claims while the circuit of the present invention is characterised by the features described below and claimed in the apparatus claims.
The special advantage of the method of measurement of the present invention is the fact that all current range outputs exhibit the same transient response in parallel so that the measurement signals may be selected and read by a following multiplexer independently of the magnitude of the input currents. This makes logarithmic processing possible by software, for example. The measurement values are produced very quickly and this is supported by the advantage that the circuit can be made very fast (with small time constants). Due to the short time constants, the averaging period can be selected within a wide range through software by basing the average on many individual measurements. An offset can easily be accounted for by measuring all current range outputs at a point of time when no input current is flowing, and by subsequent subtraction of this value as the offset during the normal measurement process.
The circuit of the present invention is not complex and does not require much space. The circuit does not require any relays and is thus insensitive to interferences.
BRIEF DESCRIPTION OF THE DRAWING
Further objectives, advantages and details of the invention will become apparent from the following description taken in conjunction with the circuits in the drawing, wherein:
FIG. 1 is a first schematic representation of a circuit according to the present invention; and
FIG. 2 is a second schematic circuit diagram of the present invention showing specific values for the components thereof.
DETAILED DESCRIPTION OF THE INVENTION
In the schematic diagram according to drawing FIG. 1 the input of the circuit is marked 1. Input 1 is followed by an operational amplifier 2 with its feedback resistor 3. The output 4 of the operational amplifier 2 is connected via connection 5, into which a low pass filter 6 is inserted, to the multiplexer 7. Moreover, the output of low pass filter 6 is also connected to the input of amplifier 9, the output 11 of which is connected through connection 12 to the multiplexer 7. In addition, the output 11 of the amplifier 9 is connected to the input of amplifier 13, the output 14 of which is connected though connection 15 to the multiplexer 7.
Moreover, a connection line 17 with two anti-parallel connected diodes 18, 19 is connected to the signal input 1. This connection 17 leads to the input of a second operational amplifier 21 with its feedback resistor 22. The output 23 of this operational amplifier is connected to one of the inputs of a differential amplifier 25. The output 26 of this differential amplifier is connected through connection 27 to the multiplexer 7 and in addition through connection line 28 to the input of a further amplifier 29, the output 31 of which is connected through connection line 32 to
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patent: 3541462 (1990-11-01), Sarkisian
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patent: 3671931 (1972-06-01), Loofbourrow
patent: 3714569 (1973-01-01), Bruning, Jr. et al.
patent: 4131846 (1978-12-01), Stone
patent: 4876502 (1989-10-01), Verbanets et al.
patent: 5266888 (1993-11-01), Aslan
Do Diep
Leybold Aktiengesellschaft
Wieder Kenneth A.
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