SU828122A1 - Microwave device for measuring dielectric permittivity - Google Patents

Description

one

The invention relates to radio engineering and can be used in instrumentation technology for measuring the humidity of dielectric materials.

A microwave device for measuring the dielectric constant is known, comprising a generator connected to a radiating antenna, a detector and an indicator.

However, the known device does not provide sufficient measurement accuracy.

The purpose of the invention is to improve the measurement accuracy.

To do this, a thickness gauge and a series connected amplifier, a forming unit, a trigger and a key, the other input of which is connected to the output of the thickness gauge, while the detector input is rigidly connected, are inserted into the microwave device for measuring the dielectric constant, which contains a generator connected to the radiating antenna with the measuring tip of the thickness gauge at a distance that is a multiple of half the wavelength from the surface of the material under study, and its output is connected to the amplifier input, and the indicator is on li ne on key output.

The drawing shows a structural electrical circuit of the proposed device. The device contains a generator 1, a radiating antenna 2, a detector 3, an amplifier

4, forming block 5, trigger 6, key 7,

thickness gauge 8, measuring tip

9 thickness gauge, indicator 10.

A microwave device for measuring the dielectric constant works as follows.

Initially, the roller 11 of the thickness gauge 8 contacts the metal surface of the format drum 12. As the thickness of the asbestos cement rollout on the format drum 12 increases, the roller 11 moves away, dragging the detector 3 rigidly connected to the measuring tip 9, and its distance from the roll surface

all the time remains constant and a multiple of 1/2 the wavelength (in practice, half the wavelength). The readings of the thickness gauge 8 through the switch 7 pass to the indicator 10. From the radiating antenna 2 connected to the generator 1, the electromagnetic oscillations of the microwave with a flat front and the wavelength K propagate normally to the surface of the material 13 located on a metallic reflective substrate, which

particular case in the manufacturing process

The asbestos cement roll is the surface of a format drum 12 of a sheet-forming machine. Electromagnetic oscillations reflected from the surface of the material 13 are received by the detector 3. In the process of increasing the thickness of the material 13 from zero to a certain predetermined value for a certain thickness di, smaller than the predetermined thickness d, a standing wave is established. In this case, the thickness of the overrun is such that it contains an integer number of half-waves LU, where Ke is the wavelength

in material 13, i.e. d, A -,

where, 2, 3 (in practice we choose).

Since Ks is -7. , then d and I, you can determine the dielectric constant of the material from the dependence

 f-v

2dJ

At the time of the standing wave, the detector 3 enters the node of the standing wave and the signal at the amplifier 4 corresponds to an extreme value. From amplifier 4, the signal is fed to the shaping unit 5, which generates a signal at the time of the standing waves, triggering trigger 6. The signal from trigger 6 goes to the control input of switch 7, which opens the connection of thickness gauge 8 with indicator 10. The latter fixes the value corresponding to the thickness of the material di, which is associated with the dielectric constant given above dependence. The scale of the indicator 10 can be calibrated in units of dielectric permeability or directly in percent moisture. At a signal from the triggering unit 14, the device returns to its original position.

The described measurement cycle is performed during each loading cycle of the format drum 12.

The working wavelength is selected before measurements, based on the final thickness of the asbestos cement roll and the probable spread values of e.

Claims (1)

1. Brandt A. А. Investigation of dielectrics at microwave frequencies. M., “Physical and mathematical literature, 1963, p. 306-307 (prototype). / 2