Apparatus for detecting contamination on probe surface

Details Apparatus for detecting contamination on probe surface Apparatus for detecting contamination on probe surface

1989-06-08

1990-05-01

Eisenzopf, Reinhard J.

Electricity: measuring and testing

A material property using electrostatic phenomenon

Frictionally induced

324 711, 324 713, G01N 2760

Patent

active

049222058

ABSTRACT:
An apparatus for detecting contamination on probe surface which comprises a sweep voltage generator for generating sweep voltage which is applied to a probe or probes in plasma, a probe current detection circuit for detecting probe current which flows in accordance with the sweep voltage applied, an amplitude discriminator for comparing the probe current with a predetermined threshold and generating an output signal when the probe current becomes equal to the predetermined threshold, a first sample-hold circuit for sampling and holding the sweep voltage upon reception of the output signal from the amplitude discriminator while the sweep voltage is increasing, a second sample-hold circuit for sampling and holding the sweep voltage upon reception of the output signal from the amplitude discriminator while the sweep voltage is decreasing, and a subtracter for providing a difference between the sweep voltages holded in the first and second sample-hold circuit. Degree of the contamination on the probe surface can be evaluated from the difference.

REFERENCES:
patent: 4006404 (1977-02-01), Szuszczewicz et al.
patent: 4023931 (1977-05-01), Wolfgram
Langmuir and Mott-Smith, Jr., "Studies of Electric Discharges in Gases at Low Pressures", General Electric Review, vol. XXVII, No. 7, Jul. 1924, pp. 449-455.
Wehner and Medicus, "Reliability of Probe Measurements in Hot Cathode Gas Diodes", Journal of Applied Physics, vol. 23, No. 9, Sep. 1952, pp. 1035-1046.

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