JP4058063B2 - Surface potential detector - Google Patents

Description

  The present invention relates to a surface potential detection device that chops an electric field between a measurement object and a detection electrode with a vibrator and converts the electric field into an alternating voltage, and detects the surface potential of the measurement object from the voltage.

  A conventional surface potential detection device of this type corresponds to the period of a vibrator drive signal (pulse) of a vibrator as disclosed in Patent Document 1 (Japanese Patent No. 3518809) relating to the application of the present applicant. After the AC voltage detected in this manner is amplified, it is simply synchronously rectified by a synchronous detection rectifier circuit and converted into a DC voltage, and potential determination and polarity determination are performed by the DC voltage.

Therefore, it takes time for the smoothing operation for rectification in the synchronous detection rectifier circuit, and it takes time to output the results of potential determination, polarity determination, and the like, and high-speed detection cannot be performed.
Japanese Patent No. 3518809

  An object of the present invention is to provide a surface potential detection device that can output results such as potential determination and polarity determination at high speed without performing smooth operation, and can increase the detection response speed. .

  The present invention includes a detection electrode, a vibrator that chops an electric field between the detection electrode and the object to be measured, and a vibrator driving circuit that vibrates the vibrator. In the surface potential detection device for detecting the surface potential of the sensor, the sampling means for sampling the AC voltage from the detection electrode with a sampling signal having a frequency much higher than the frequency, and the peak of the sampled signal, the transducer drive circuit And a peak detecting means for detecting each pulse of the vibrator drive signal from the above.

  The peak detecting means detects the peak of the sampled signal from the rising point to the falling point of the pulse of the transducer driving signal.

  In the case of polarity discrimination, there is provided polarity output means for outputting an AC voltage polarity discrimination signal after a predetermined number of samplings from the time of peak detection.

  In addition, when determining a failure, a failure determining means for determining a failure based on the presence or number of sampled signals is provided.

  According to the present invention, after the alternating voltage from the detection electrode is sampled with a sampling signal having a frequency much higher than that frequency, the peak of the sampled signal is detected for each pulse of the transducer driving signal. Due to the smoothing operation in the conventional synchronous detection rectification, no output delay occurs, and the detection response speed can be increased.

  According to the second aspect of the present invention, the peak of the sampled signal is detected from the rising point to the falling point of the pulse of the transducer driving signal, so that peak detection is facilitated.

  According to the third aspect of the invention, since the polarity determination signal of the AC voltage is output after a predetermined number of samplings from the time of peak detection, the polarity determination can also be speeded up.

  According to the fourth aspect of the present invention, since the failure is determined from the presence or absence or the number of the sampled signals, the presence / absence of the failure can be determined easily and accurately.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of the surface potential detection device according to the present invention, and FIG. 2 is a timing chart of its operation.

  In this surface potential detection device, a vibrator driving signal by self-excited oscillation with a vibrator driving circuit 2 is applied to a tuning fork type vibrator 1. FIG. 2 (2) shows a pulsed transducer drive signal output from the output end of the transducer drive circuit 2, and this pulsed transducer drive signal is input to the AND circuit 3. The AND circuit 3 receives the sampling pulse shown in FIG. 2 (6) from the sampling pulse generator 4. The frequency of the sampling pulse is much higher than the frequency of the pulse-like vibrator drive signal, and the AND circuit 3 shows that when the vibrator drive signal shown in FIG. As shown in 4), a sampling pulse is output.

  On the other hand, the electric field generated between the detection electrode 5 and the object to be measured is detected as an AC voltage by the impedance conversion circuit 6 by chopping in synchronization with the vibration of the vibrator 1 and amplified by the amplifier 7. Thus, it is extracted as an AC analog signal corresponding to positive and negative polarities as shown in FIG. This analog signal is separated into a positive component and a negative component as shown in FIG. 2 (3) by the polarity discrimination circuit 8, and is sampled by the sampling pulse shown in FIG. 2 (4) output from the AND circuit 3. The circuit 9 samples the positive and negative separately. FIG. 2 (5) shows sampled positive and negative sampling analog signals.

  These positive and negative sampling analog signals are, as shown in FIG. 2 (7), the peak (maximum potential) between the start and stop, with the rise of each pulse of the transducer drive signal as the start signal and the fall as the stop signal. Are detected separately by the peak detection circuit (peak hold circuit) 10. FIG. 2 (8) shows the timing of peak detection, and peak detection is performed for each pulse of the transducer drive signal. FIG. 2 (9) shows the output timing of the polarity discrimination result, and the output is performed for each pulse of the transducer drive signal and delayed from the peak detection time. FIG. 2 (10) shows an enlarged output timing of the peak detection and polarity discrimination results between the start signal and the stop signal.

  The peak (maximum potential) detected in this manner is converted to digital by the A / D conversion circuit 11 and then input to the CPU 12 to measure the maximum potential separately for positive and negative.

  The sampling pulse output for each pulse of the transducer drive signal from the AND circuit 3 is input to the failure determination circuit 13, where the transducer drive signal is obtained by counting the presence or absence of the sampling pulse or the number of pulses. It is determined whether or not the transducer drive circuit 2 is outputting normally. A signal indicating the determination result is also input to the CPU 12.

It is a block diagram which shows the structure of the surface potential detection apparatus by this invention. It is a timing chart of the operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vibrator 2 Vibrator drive circuit 3 AND circuit 4 Sampling pulse generator 5 Detection electrode 6 Impedance conversion circuit 7 Amplifier 8 Polarity discrimination circuit 9 Sampling circuit 10 Peak detection circuit 11 A / D conversion circuit 12 CPU
13 Fault determination circuit

Claims (4)

  A detection electrode, a vibrator for chopping an electric field between the detection electrode and the object to be measured, and a vibrator driving circuit for vibrating the vibrator, and the surface potential of the object to be measured from the AC voltage generated from the detection electrode In the surface potential detection device for detecting, sampling means for sampling the AC voltage with a sampling signal having a frequency much higher than the frequency, and the peak of the sampled signal from the vibrator driving signal from the vibrator driving circuit A surface potential detection device comprising: peak detection means for detecting each pulse of the above.   2. The surface potential detection apparatus according to claim 1, wherein the peak detection means detects the peak of the sampled signal between the rising point and the falling point of the pulse of the transducer driving signal.   3. The surface potential detection device according to claim 1, further comprising a polarity output unit that outputs an AC voltage polarity discrimination signal after a predetermined number of samplings from the time of peak detection.   4. The surface potential detection apparatus according to claim 1, further comprising failure determination means for determining a failure from the presence or absence or the number of sampled signals.

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