RU10464U1 - HUMIDITY MEASUREMENT DEVICE - Google Patents

Abstract

1. A device for measuring humidity, comprising a capacitive sensor immersed in a controlled environment, an autonomous transducer block containing a controlled rectangular pulse generator, the output of which is connected to the first capacitive sensor electrode, and a first emitter follower, the input of which is connected to the second capacitive sensor electrode, a timer connected to a square-wave generator of a measuring transducer, a peak detector consisting of two series-connected amplifiers DC, to the inputs of which are connected the first and second charging capacitors, respectively, while parallel to the second charging capacitor, the capacity of which is much larger than the capacity of the first charging capacitor, a timer-controlled discharge key is connected, and a humidity detection unit connected to the output of the peak detector, characterized in that a differential amplifier, a second emitter follower and a compensating capacitor, the input of the second emitter follower are inserted into the measuring transducer connected to the output of the rectangular pulse generator through a compensating capacitor, and the output to the inverting input of the introduced differential amplifier, the non-inverting input of which is connected to the output of the first emitter follower, and the output is connected to the input of the peak detector, while the first and second electrodes of the capacitive sensor are respectively made in the form internal and external hollow coaxial cylinders mounted on the insulating wall of the housing of the autonomous measuring transducer block. 2. At

Description

Humidity meter

The invention relates to measuring equipment, in particular, to instruments for measuring humidity using a capacitive sensor, and is intended for use in a variety of industries, in particular in the energy sector, with express control of moisture in transformer oils or in other viscous media, where it is mainly high precision is required when determining small amounts of moisture.

A device for measuring the water / oil ratio (PCT application 8501352, IPC G01N 27/22, 03/28/85) containing a coaxial capacitor with an inner rod electrode, the outer tube electrode of which is connected in series with the pipeline through which the test mixture flows, is known. The inner and outer electrodes are connected to a temperature-compensated generator circuit, at the output of which the frequency is proportional to the capacitance of the coaxial capacitor. There are also means for converting the frequency into a digital code and a digital computer, in the memory of which the dependencies between the digital codes and the corresponding humidity values are stored.

The analyzed parameter in this device is the generation frequency, which depends on the dielectric constant of the medium between the capacitor plates.

However, this parameter at low moisture contents does not track its changes quite sensitively, which does not allow for accurate determination of the amount of moisture at a low moisture content.

Also known is a device for determining the moisture content of oil (US Pat. RF 2055354, IPC G01N27 / 22, 02.27.96), containing a sensing element made of two capacitors operating under the same conditions, some of which plates are directly connected to each other and others through corresponding managed key, switch, youMPK G01N27 / 22

the passages of which are connected to the control inputs of the indicated keys, the capacitance measuring unit of the indicated capacitors, also connected to the switch sync output, the information processing unit and the oil moisture determination unit, in the memory of which there is a calibration curve.

This device maintains accuracy during long-term operation by taking into account the emerging contaminants on the sensitive elements.

However, when measuring such a sufficiently generalized parameter as capacitance, it is difficult to distinguish small changes in the dielectric constant due to insignificant changes in moisture in the medium, which reduces the accuracy of monitoring small values of moisture content.

A device for remote determination of oil moisture (US Pat. RF No. 2092825, M1ZH G01N 27/22, dated 12.26.94), containing a series-connected microcontroller, digital-to-analog converter, voltage-controlled generator, resonant sensor, amplitude detector, delay element, memory element and a comparator. The microcontroller is also connected to a digital indicator and a frequency meter, and the resonant sensor is an oscillating circuit made of an inductance coil, capacitor, capacitive electrodes and two communication coils.

The information parameter in this device is the resonant frequency of the circuit, depending on the value of the capacitance between the capacitive electrodes. The disadvantage of this device is the low sensitivity of the device (and, therefore, accuracy), because the discreteness of measurement provided by it is approximately an order of magnitude larger than required.

The prototype of the claimed device selected device, the scope of which is limited to measuring the humidity of substances (US Pat. RF No. 2030739, from 11.02.92, IPC G01N27 / 22). Nevertheless, this device is the closest to the claimed by the totality of the common essential features and the principle of action. The known device comprises a capacitive sensor immersed in a controlled environment, an autonomous transducer block containing a square-wave pulse generator, and a first emitter follower, the input of which is connected to the second capacitive sensor electrode, a timer connected to a square-wave transducer, a peak detector consisting of two series-connected DC amplifiers, the inputs of which are connected, respectively, the first and second charging capacitors in this case, parallel to the second charging capacitor, the capacity of which is much larger than the capacity of the first charging capacitor, a timer-controlled discharge key is connected, and a humidity detection unit connected to the output of the peak detector, the input of which is connected to the second electrode of the capacitive sensor, a timer connected to a rectangular generator pulses, a peak detector, consisting of two series-connected DC amplifiers, the inputs of which are connected, respectively, the first and second charge capacitors, in parallel with the second charging capacitor, the capacitance of which is much greater capacitance of the first charging capacitor, controlled by a timer connected bit key, and a determination unit humidity vsholnenny a registrar.

The main advantage of such a meter is its high accuracy, due to the use of the most informative parameter when measuring: the maximum charging current of the capacitive sensor, as well as the use of the pulse sequence supplied to the capacitive sensor to average the result, which neutralizes the possible spread in the amplitudes of the pulses supplied to the capacitive sensor. However, if it is necessary to measure very small amounts of moisture in the medium to be measured, which occurs when measuring the moisture content in transformer oils, where the moisture content should be no more than 50 g / t, this device does not have the necessary accuracy. This is due to the fact that small amounts of moisture make such a small change in the amount of charge

current, that this change against the background of the main signal is not monitored by the measuring part of the circuit.

The problem solved by the claimed utility model is to create a device that can quickly and accurately determine small amounts of water in a viscous medium, in particular in transformer oils, and track their small changes.

The problem is solved as follows. In a device for measuring humidity, containing a capacitive sensor immersed in a controlled environment, an autonomous transducer block containing a controlled rectangular pulse generator, the output of which is connected to the first capacitive sensor electrode, and a first emitter follower, the input of which is connected to the second capacitive sensor electrode, a timer, connected to a square-wave generator of a measuring transducer, a peak detector consisting of two series-connected amplifiers direct current, to the inputs of which are connected, respectively, the first and second charging capacitors, while parallel to the second charging capacitor, the capacity of which is much larger than the capacity of the first charging capacitor, a timer-controlled discharge key is connected, and a humidity detection unit connected to the output of the peak detector, according to of the claimed utility model, a differential amplifier, a second emitter follower and a compensating capacitor are introduced into the measuring transducer block, the capacity of which equal to the capacitance of the capacitive sensor in an environment with zero humidity, the input of the second emitter follower is connected to the output of the rectangular pulse generator through a compensating capacitor, and the output to the inverting input of the introduced differential amplifier, the non-inverting input of which is connected to the output of the first emitter follower, and the output is connected to the input peak detector, while the first and second electrodes of the capacitive sensor are respectively made in the form of internal and external hollow coaxial cylinders replicated on the insulating wall of the corne of the measuring transducer.

The technical result achieved in this case is the automatic exclusion from the signal received for amplification and processing of the non-informative part corresponding to a medium with zero moisture content and constituting a significant part of the total signal. Using the coaxial shape of the electrodes makes it possible to eliminate edge effects on the plates of the capacitive sensor, which, being commensurate with the magnitude of the monitored parameter, neutralize small changes in the output signal.

In addition, the capacitive sensor can be equipped with an additional external coaxial electrode connected electrically to the internal one. This provides an additional increase in the accuracy of measuring small amounts of water by increasing the sensor’s own capacitance and, as a result, increasing the values of recorded increments as a function of capacity. This, in turn, will make it possible to reduce its dimensions at the optimum value of the capacitance of the sensor, thereby further reducing the influence of edge effects.

In Fig. 1 is a diagram of the inventive device for measuring humidity, in Fig. 2 - timing diagrams.

The moisture measuring device comprises a measuring transducer 1, which includes a direct-coupled impulse generator 2 located in a common housing, a compensating capacitor 3 made in the form of a tuning capacitor, the first emitter follower 4, the second emitter follower 5, differential amplifier 6. On the electrical insulation the wall 7 of the housing of the Converter 1 is fixed coaxial cylindrical electrodes 8,9 and 10 of the capacitive sensor 11. The device also contains a timer 12, a peak detector p 13, consisting of a first DC amplifier 14, a second DC amplifier 15 with a feedback circuit in the form of a voltage divider across resistors 16 and 17, a nerve and second charging capacitors 18 and 19, a discharge switch 20, and a moisture detection unit 2L Generator output 2 rectangular pulses, the control input of which is connected to the output of the timer 12, is connected to the first lining of the compensating capacitor 3 and to the inner electrode 8 of the capacitive sensor 11, combined with an additional outer electrode 10 of the sensor. The intermediate electrode 9 of the capacitive sensor 11 is connected to the input of the first emitter follower 4, the output of which is connected to the non-inverting input of the differential amplifier 6. The second lining of the compensating capacitor 3 is connected to the input of the second emitter follower 5, the output of which is connected to the inverting input of the amplifier 6. The output of the differential amplifier 6 using communication lines connected to the input of the peak detector 13, which is a non-inverting input of the first DC amplifier 14, included a voltage follower circuit. The output of the amplifier 14 is connected to the non-inverting input of the DC amplifier 15, connected according to the scheme of the non-inverting voltage amplifier, the gain of which is determined by the ratio of the resistors 16 and 17. The first charging capacitor 18 is connected in parallel with the input of the amplifier 14, and the second charging capacitor 19 is connected in parallel with the input of the amplifier 15 , the capacity of which In parallel with the same capacitor, a bit switch 20 is activated, controlled by a timer 12. The output of the detector 13 is connected to the humidity determination unit 21, which minutes may be particularly vsholnen a microcontroller in whose memory is stored humidity values corresponding to the outputs of the peak detector.

The device operates as follows.

closing the bit key 20, which causes the discharge of the capacitor 19 "zeroing the peak detector. At the same time, a rectangular pulse generator 5 is started (Fig. 2d), the duration of which is set by the pulse duration from the output of the timer 12. From the output of the generator 2, a sequence of rectangular pulses of stable amplitude is supplied to a capacitive sensor 11 included in the measuring circuit, formed by two pairs of 8.9 and 9 , 10 parallel coaxial electrodes. At the same time, a sequence of rectangular pulses is applied to a compensation capacitor 3, the capacitance of which is selected equal to the total capacity of the capacitive sensor 11 immersed in the test medium at a zero moisture content in it. From the capacitive sensor 11, a sequence of signals whose amplitude is determined by the moisture content of the test oil is fed through the emitter follower 4 to the non-inverting input of amplifier 6 (Fig. 2e), to the inverting input of differential amplifier 6 through an emitter follower 5 with an amplifying capacitor 3 receives a sequence of pulses, the amplitude of which eo corresponds to zero moisture content in the test material (Fig, 2E). Differential amplifier 6, subtracting these sequences, selects useful signals whose amplitude Umi and Um2 depends only on the amount of moisture in the sample (Fig. 2g). From the output of the differential amplifier 6, the signals are transmitted through the communication line to the input of the peak detector 13, which stores the amplitude Uni2 of the maximum of the signals during the measurement cycle (Fig. 2h). Memorization is as follows. Each of the incoming pulses is stored for a short time on the capacitor 18 of small capacity C1. The capacitance C1 is selected such that its charge is realized during the duration of the pulse front. Then, the capacitor 18 is discharged through an amplifier 14 connected in accordance with a voltage follower circuit to a capacitor 19c with a capacity that stores the voltage until a pulse with a large amplitude arrives. In this case, the capacitor 19 is recharged and the voltage stored on it is equal to the maximum of the pulse amplitudes in this measurement cycle. This parameter is saved until the next measurement step, and after amplification by a factor of 15, the amplifier 15 enters the input of the humidity determination unit 21 (Fig. 2i). Before the start of the next measurement step, the signal from the timer output is reset to zero and the process starts again.

Claims (2)

1. A device for measuring humidity, comprising a capacitive sensor immersed in a controlled environment, an autonomous transducer block containing a controlled rectangular pulse generator, the output of which is connected to the first capacitive sensor electrode, and a first emitter follower, the input of which is connected to the second capacitive sensor electrode, a timer connected to a square-wave generator of a measuring transducer, a peak detector consisting of two series-connected amplifiers DC, to the inputs of which are connected the first and second charging capacitors, respectively, while parallel to the second charging capacitor, the capacity of which is much larger than the capacity of the first charging capacitor, a timer-controlled discharge key is connected, and a humidity detection unit connected to the output of the peak detector, characterized in that a differential amplifier, a second emitter follower and a compensating capacitor, the input of the second emitter follower are inserted into the measuring transducer connected to the output of the rectangular pulse generator through a compensating capacitor, and the output to the inverting input of the introduced differential amplifier, the non-inverting input of which is connected to the output of the first emitter follower, and the output is connected to the input of the peak detector, while the first and second electrodes of the capacitive sensor are respectively made in the form internal and external hollow coaxial cylinders mounted on the insulating wall of the housing of the autonomous measuring transducer block. 2. The device according to claim 1, characterized in that the capacitive sensor is equipped with an additional external coaxial cylindrical electrode electrically connected to the internal one.