SU1283672A1 - Transducer of surface charges and potentials - Google Patents

Abstract

The invention relates to a measurement technique and can be used in reprography, flaw detection. electrical engineering. The aim of the invention is to increase the sensitivity of measurements while expanding the passband. To achieve a divi- sion in a device containing a metal electrode 1, an electrostatic screen 2 and a dielectric insert 3, the metal electrode 1 on the working side is made in the form of a corner with apex in the plane of the screen 2 face, and the dielectric insert 3; located between the generatrix of the cone and the side surface of the screen. The ratio of the height of the cone to the radius of the metal electrode 1 is selected in the range from 0.5 to 2. The dielectric constant of the insert is chosen equal to 3. The choice of these parameters was carried out experimentally. 2 Il. (L with:

Description

Yu

00 05 O)

sj

IS5

one

one

The invention relates to a measuring technique and can be used in reprography, flaw detection, electrical engineering.

The aim of the invention is to increase the sensitivity of measurements while simultaneously expanding the passband by making a metal electrode B in the form of a cone with a top in the plane of the screen butt and stirring a dielectric insert between the cone generator and the side surface of the screen and selecting the ratio of the height of the cone H to radius R the grounds

0.5 | 2

FIG. 1 shows the construction of the probe system in FIG. 2, a graph of the contrast-frequency characteristic of the device (CFC).

The sensor of surface charges and potentials contains a measuring metal electrode 1 located in a grounded electrostatic screen 2. The end of the metal electrode is made in the form of a cone with a top in the plane of the end of the screen. The dielectric insert 3 is located between the generator of the electrode and the side surface of the screen, and the ratio of the height of the cone to the half width of its base lies in the interval H R

le 0,5 5

2. Dielectric pro

6,

Nick insertion should be 1-3.

The limits of change - and the value of K

. selected experimentally. When determining the metrological characteristics of non-contact electrostatic induction systems, the probing field is usually used. The potential of the probing field is defined as the Laplace field arising in the probe system if a single potential is specified on the measuring electrode and the remaining conductors and shields are grounded. With

- 0.5 constant transfer ratio to

component, determining the sensitivity of the system, is

five

0

five

The bandwidth of the system at 0.5, determined from the QFH, is equal to O; 0.851 | 1 (Fig. 2, curve a). Thus, the bandwidth is O; 0.85 P defines the lower limit of the interval.

At - 2, i.e. with thin probes, to

the bandwidth expands to 0.3571, however, the sensitivity of the measurements in this case decreases by a factor of 3 compared with

,five.

In addition, as thin probes approach the carrier surface, the average noise power, i, caused by the surface irregularities of the carrier, sharply increases. The useful signal increases more slowly than noise, which eventually leads to a deterioration in resolution. .

The manufacture and operation of thin, pointed probes are also associated with technical difficulties. Therefore, it is advisable to choose an intermediate variant of the geometric shape of the probe - in the form of a cone, for which

thirty

0.5

H R

 2, For the call system with

- 3/2 QFC in FIG. 2 is represented by

H R curve

The device works as follows.

A circuit of a measuring electrode mounted above a test surface is induced by a signal Q. In this case, the transmission coefficient is recorded as follows:

K, o, QFC of the device

imi - 3 g 2 f-A2 ± 1,

 2 L2T V (2p + 1) 2

K (o)

L,

Ih (i) Ri oR.h

4 where T. (OR) is the Bessel function of the nth order;

TO,

 j H RS 21

h - distance to controlled

surface; 1 - distance to grounded

substrate.

As can be seen from FIG. 2, the passband level of 0.5 is 0; one; lATTJ, K (o) sensitivity

15 h 3 1

31283

Claims (1)

Invention Formula A surface charge and potential sensor, comprising a metal electrode placed in an electrostatic shield, and a dielectric insert, characterized in that, in order to increase the sensitivity when the passband is expanded, the metal electrode Q5 Jt the sides are made in the form of a cone with a top in the plane of the end of the screen, and the dielectric insert is located between the generator of the cone and the side surface of the screen, while the ratio of the height H of the cone to the radius R of the metal electrode corresponds to the expression 0.5 .f.a. tiJK eight 371 W