CS242909B1 - Insulator thickness indicator with compensator - Google Patents

Abstract

The insulator thickness indicator with compensator is designed for measuring the thickness of electrically non-conductive objects based on the measurement of the electrical capacitance between electrodes placed on both sides of the measured objects. The advantage of the indicator is its wide range of application, i.e. even in cases of inhomogeneous structures of the measured insulators, or curvature, non-parallelism or roughness of their surfaces.

Description

The present invention relates to an insulator thickness indicator with a compensator which determines the thickness of an insulator by measuring its capacity.

The previously known mechanical measurements using calipers and mirometers or other mechanical indicators have a very limited field of application, since they are not suitable for measuring large-area boards, vessel walls, etc.

In addition to these gauges, ultrasonic measuring devices are known which are very costly and, moreover, they fail on a number of articles, in particular some plastic products manufactured by special technologies. By way of example, it is not possible to measure polyethylene containers produced by rotary sintering by ultrasound.

Other known devices for measuring the thickness of non-conductive materials are based on radioactive or Roentgen radiation. The use of this measuring technique creates a harmful environment, requires dosimetric monitoring of the operator and, as a consequence, very costly equipment in the workplace.

Thickness measurement by means of a capacitive sensor has not been possible in the prior art, because it is necessary to measure a very small capacity, of the order of tens of picofarads, in the presence of approximately the same large parasitic capacity.

The purpose of the present invention is to provide a capacitive sensor and an associated evaluation device so that the wall thickness of the capacitive sensor can be measured.

The aforementioned drawbacks are solved by a measuring device according to the invention, consisting of an electrical voltage evaluating element, to whose first input a compensating voltage source is connected and to the second input an integrator is connected to a monostable flip-flop connected to an astable flip-flop. a probe with the measuring electrodes between which it is located, the thickness of which is determined.

In particular, the measuring device according to the invention has the following advantages over known devices:

- high accuracy even when measuring insulators with uneven surface,

- very low dependence of the measurement results on the internal structure of the measured objects,

- the measuring equipment has no harmful effect on human operators.

The attached drawing shows a block diagram of one particular embodiment of the device. The individual function blocks are interconnected as follows: the electrodes 1, 2 are placed against each other on the insulator 2, the thickness of which we measure and connected to one input of the monostable flip-flop by means of electrical wires

It is an input that determines the pulse length. At the second, synchornization input of the monostable flip-flop is connected an astable flip-flop. The output of the monostable flip-flop 2 is connected to the input of the integrator 8, the output of which is connected to one input of the electrical voltage evaluating element 6, to the other input of which the output of the compensation voltage source 1 is connected.

The principle of operation of the device is as follows: On both surfaces of the insulator 2, whose thickness is determined, two surface electrodes 1, 2 are placed against each other, so that the capacitance of the capacitor they create is directly proportional to the thickness of the insulator 2 ·

This capacity then determines the pulse length of the monostable flip-flop whose frequency is determined by the astable flip-flop 2. circuit £.

The pulses are adjusted to have a constant amplitude at all times and are then integrated into the integrator 6. At the output of the integrator 8, we then receive a voltage proportional to the total capacitance between the electrodes J and £.

However, since many parasitic influences, such as lead capacities, electrode scattering capacities, etc., contribute significantly to this capacitance, it is possible to compensate for this effect by not setting the compensating voltage on the second input of the compensating voltage source 1 at zero measured capacitance. so that at the output of the voltage evaluation element g there is a zero value in this state.

The insulator thickness indicator with compensator was realized in the national company Plastimat with the purpose to measure large-volume plastic containers (600 to 2,000 liters) produced by rotary sintering technology. The walls of said containers have an inhomogeneous structure and therefore their thickness cannot be measured by ultrasonic devices.

Claims (1)

SUBJECT OF THE INVENTION Insulator thickness indicator with compensator, characterized in that a compensating voltage source (7) is connected to a voltage input member (8) and an integrator (6) is connected to a second input to which a monostable flip-flop (5) is connected; an electrically stable probe (4) containing an insulator (3) whose thickness is detected.