SU1265570A1 - Capacitive pickup of moving sheet material humidity - Google Patents

Abstract

This invention relates to moisture measurement and can be used to measure the moisture content of sheet materials. The purpose of the invention is improving the accuracy of measurements. The sensor includes a housing on which three fixed electrodes and a movable rod are fixed, which rigidly connects two movable electrodes. These electrodes create a measuring and two. compensating capacitor. The accuracy is improved by taking into account the second compensating capacitor and the additional capacitors changing the NIN sensitivity of the measuring capacitor, depending on the thickness C of the object under study. 2 Il.

Description

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The invention relates to moisture measurement and can be used to measure the moisture content of sheet materials and fabrics in the textile, chemical, rubber and other industries.

The aim of the invention is to improve the accuracy of measurements by automatically reducing the influence of the measurement of the proportion of the moving material on the sensitivity of the instrument.

Figure 1 shows the design of the sensor; in fig. 2 shows the priker for switching the sensor into the measuring circuitry.

The sensor (Fig. 1) U contains a moving electrode 15 which, together with the base 2, forms measuring ones; A co-sensor C c i. Between which the moving test mass 3 is located. With the electrode 1, the moving electrode 5 forming the fixed electrode through the insulating rod 4 b first compensation capacitor rc. The electrodes 6 and 7 are fixed through insulators 8 and 9 on the bracket 10, which is movably fixed on the axis 11.

Capacities Su and C c, (FIG. 2) are powered from the first output of the generator 12 of high-frequency voltage and are included in the first comparison circuit of capacitances 3. Capacitance C 2 is connected in series with the capacity of the additional capacitor Cd ,, powered from it 12 and is included in the second tank comparison circuit 14.

“Exit. the first and second comparison circuits are connected to the input of the voltage multiplier, and the outputs of the multiplier Tz of the voltage and the first circuit 13 of the comparison are connected to the input of the oyiMMaTopa 1 voltage,

The device works as follows

With a change in the moisture content of the material, the capacitance of the measuring capacitor changes, and at the output of the first capacitance comparison circuit, a voltage Ug, proportional to the humidity, appears. A change in the thickness of the material at a constant humidity leads to a change in the distance between the electrodes 4 and 2, Zib, 5 and 7 of the sensor of the first compensating capacitor. Due to the differential inclusion C c, and Sc-nepbj, To, the capacitance comparison circuit does not change the voltage at its output,

In the case of a simultaneous change in moisture and material thickness, a measurement error occurs due to a change in the sensitivity of the measuring capacitor. To eliminate it, the second compensating capacitor, the capacitance of which increases with increasing material thickness and decreases with decreasing it, is lowered.

At the output of the second capacitance comparison circuit, a voltage appears that is proportional to the change in the thickness of the material with a positive polarity in the case of an increase in thickness, and with a negative polarity in the case of its decrease

The output voltages of the first and second capacitance comparison circuits are multiplied by a voltage multiplier 15, the output of which is the voltage applied to the input of the voltage adder 16, where it is summed with the output voltage of the first comparison circuit of capacitance 13, due to which is voltage.

. tg Uebu + ALUM ,. Ug ,,,, where Um, j, (is the voltage at the output of the first capacitance comparison circuit;

 voltage at the output of the second capacitance comparison circuit;

K is a scalable coefficient, the value of which is chosen such that it corresponds to E-alo to a specific value of the moisture content of a material regardless of its thickness.

By implementing the formula, a voltage is added or subtracted to the output voltage VQ to compensate for the decrease or increase in the sensitivity of the sensor / sensor as the thickness of the material placed between its plates changes.

Thus, due to the inclusion in the device of a second compensating and additional capacitors, it was possible to improve the measurement accuracy by automatically compensating for changes in the sensitivity of the sensor when the thickness of the moving controlled material changes.

Claims (1)

Invention Formula Capacitive humidity sensor for moving sheet materials, containing