RU2521752C1 - Product temperature and level measuring device - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device includes a measuring loop with a dielectric cover reinforced with two electrically conducting ropes that are used as sensors of a capacitance level indicator. Inside the dielectric cover an arrangement is made for temperature sensors and capacitance sensors, each of which consists of a sensitive element and a capacitance measurement module. Electrically conducting ropes, temperature sensors and outputs of capacitance sensors are connected to a processing unit containing signal processing modules of temperature sensors, capacitance sensors and capacitance level indicators. Automatic calibration of the device is performed from time to time considering dielectric permeability of temperatures of the product enveloping the measuring loop in arrangement zones of capacitance sensors.

EFFECT: reducing measurement error of a storage filling level.

3 cl, 4 dwg

Description

The invention relates to measuring equipment, in particular, to measuring the temperature and level of a product filling a store using a capacitive level gauge.

Known devices for measuring the temperature of the product filling the store [1] - [3] using temperature sensors distributed over the store. Known devices for measuring the level of the product [4] - [7] using capacitive sensors. In devices that measure the level of storage of the storage product [4] - [7], there is no function of measuring temperature. At the same time, level measuring devices have a disadvantage inherent in capacitive level gauges, namely the dependence of the results of measuring the storage level on the physical characteristics of the product.

To eliminate this drawback, the device [8] introduced reference sensitive capacitive elements, which allow one to obtain an estimate of the electrical characteristics of a product located near the reference sensitive capacitive elements, but this assessment can only be used when filling the entire storage with a product with fixed electrical characteristics, which is extremely rare. Most often, during the technological process of loading and unloading storage, humidity, density, and composition of the product change, which leads to a change in the dielectric constant of the product and, accordingly, to large level measurement errors.

In the device [9], the level measurement function is implemented by analyzing the temperature distribution along the sensitive element. This level measurement method has drawbacks that practically exclude its use for level measurement, namely:

- a significant difference in temperature of the layers of the product, the mixing of which is difficult or impossible, for example, for bulk products; this difference may significantly exceed the difference in temperature of the upper layer of the bulk product, the level of which is controlled, and the environment located above it;

- dependence on climatic conditions, as in some cases, there may be no temperature difference between the product, the level of which is controlled, and the medium above it, which completely excludes the possibility of measuring the level.

In [10], a device is presented that allows one to simultaneously measure the temperature of a product and the level of storage filling. It is described in more detail in [11].

The closest to the invention in terms of the result achieved and the combination of essential features (prototype) is a temperature and level measuring device [11], which contains a measuring cable inside the storage with a dielectric sheath reinforced with two metal cables isolated from each other and a processing unit for measuring results. Reinforcing metal cables are used as electrodes of a capacitive level sensor. Temperature sensors are located inside the dielectric sheath, and the processing unit for the measurement results includes a switch, a control and level calculation module, a capacitance measurement module, and a temperature measurement module. One metal cable is connected to the device ground, and the second to the input of the capacitance measurement module. The switch, temperature measurement module and capacitance measurement modules are controlled by a control and level calculation module.

The temperature of the controlled product is measured by temperature sensors located along the measuring loop.

The temperature measurement module periodically polls the temperature sensors and estimates the temperature distribution along the measuring loop.

Reinforcing cables form a capacitance, which is part of the generator timing circuit in the capacitance measuring module. The period of voltage fluctuations on the capacitance linearly depends on the size of the measured capacitance.

Before starting work, it is necessary to calibrate the device using two capacitance values and their corresponding levels.

The disadvantages of the device for measuring temperature and level [11] are:

- lack of correction of level values when changing the electrophysical characteristics of the product,

- a large level measurement error associated both with a change in the physical characteristics of the product and with the instability of the frequency of the generator in the capacitance measuring module.

The technical result to which the invention of the device is directed is to reduce the error in measuring the level of storage of the product with the product, due to both a change in the physical characteristics of the product and the instability of the parameters of the component elements in the device.

The technical result is achieved in that in a device for measuring temperature and product level, containing a measuring loop with a dielectric sheath, reinforced with two electrically conductive cables isolated from each other, inside which temperature sensors are placed, and also containing a measurement results processing unit, including a switch, a control module and calculating the level, the first output of which is connected to the first input of the switch, a temperature measurement module, in which the first input through the switch is connected nen with temperature sensors, the second input is connected to the second output of the control and level calculation module, and the first output is the first output of the device for measuring temperature and product level, and the capacitance measuring module, in which the first input is connected to the first cable, the second input is connected to the third the output of the control and level calculation module, and the output is connected to the first input of the control and level calculation module, while the second cable is connected to the ground of the device for measuring the temperature and level of the product, and the second exit The device for measuring temperature and product level is the fourth output of the control and level calculation module, in addition to the measurement processing unit, a second level measurement module is introduced, and capacitive sensors are placed in the measurement loop, placed along the measurement loop with the specified coordinates and connected to their outputs via a switch with the first input of the second level measurement module, in which the second input is connected to the fifth output of the control and level calculation unit, the third input is connected to orym output temperature measurement module, and an output connected to the second input of the control and calculating unit level.

Moreover, each capacitive sensor contains a sensitive element with axial dimensions much smaller than the distances between the sensors and a capacitance measuring module, the input of which is connected to the sensitive element, and the output through the switch is connected to the first input of the second level measuring module. Moreover, the sensitive elements of capacitive sensors with their surface are pressed against the inner surface of the dielectric sheath.

The essence of the invention of the device lies in the fact that to reduce the error in measuring the level of the product in the store and to reduce the stability requirements of the characteristics of the electronic components that provide level measurement, the device is automatically calibrated periodically taking into account the dielectric constant and temperature of the product surrounding the measuring loop in the areas where capacitive sensors are located . For this, capacitive sensors are introduced into the measuring loop, connected by the outputs through the switch to the input of the second level calculation module, which is additionally introduced into the measurement results processing unit. In this case, the third input of the second level measurement module is connected to the second output of the temperature measurement module.

The analysis of the prior art, including a search by patent and scientific and technical sources of information and identification of sources containing information about analogues of the claimed invention, allows us to establish that the applicant has not found technical solutions characterized by features identical to all the essential features of the claimed invention. The definition from the list of identified analogues of the prototype made it possible to identify a set of essential (with respect to the technical result perceived by the applicant) distinctive features in the claimed object set forth in the claims. Therefore, the claimed invention meets the requirement of "novelty" under applicable law. The set of essential distinguishing features in the claimed object provides the device for measuring the temperature and level of the product with new qualities - the ability to automatically calibrate and, accordingly, the invariance to the dielectric constant of the product, climatic conditions and instability of the characteristics of the electronic components of the device. Information about the fame of the distinguishing features in the totality of the characteristics of the known technical solutions with the achievement of the same as the claimed device, there is no positive effect. Based on the fact that these differences do not follow explicitly from available scientific and technical sources, it is concluded that the claimed technical solution meets the criteria of the invention "inventive step".

The invention is illustrated by the diagram and drawing.

Figure 1 shows a simplified functional diagram of the inventive device.

Figure 2 shows the longitudinal and transverse sections of a segment of the measuring loop.

Figure 3 shows the simulation results of the device prototype and the proposed.

Figure 4 presents the test results of a prototype of the proposed device, placed in a granary.

A device for measuring temperature and product level (Fig. 1) contains a measuring loop with a dielectric sheath reinforced with two electrically conductive cables 1 and 2 isolated from each other, inside which temperature sensors 3 are placed, and also contains a measurement results processing unit, including a switch 4, a control and calculation module of level 5, the first output of which is connected to the first input of the switch, a temperature measurement module 6, in which the first input through the switch is connected to temperature sensors, the second the input is connected to the second output of the control and level calculation module, and the first output is the first output of the device for measuring temperature and product level, and the capacitance measuring module 7, in which the first input is connected to the first electrically conductive cable 1, the second input is connected to the third output of the control module and calculating the level, and the output is connected to the first input of the control module and calculating the level, while the second conductive cable 2 is connected to the ground of the device for measuring the level and the product, and the second output The fourth output of the control and level 5 calculation module is the property for measuring the temperature and level of the product. A second level 8 measuring module is introduced into the processing unit of the measurement results, and capacitive sensors 9 are placed in the measuring loop, placed along the measuring loop with specified coordinates and connected by their outputs through switch 4 with the first input of the second level 8 measurement module, in which the second input is connected to the fifth output of the control and level 5 calculation module, the third input is connected to the second output The module temperature measurement 6, and the output is connected to the second input of the control unit and calculating a level 5.

Each capacitive sensor 9 (Fig. 2) contains a sensitive element 10 with axial dimensions much smaller than the distances between the sensors and a capacitance measuring module 11, the input of which is connected to the sensitive element 10, and the output through the switch is connected to the first input of the second level measuring module 8.

The sensitive elements 11 of the capacitive sensors 9 are pressed with their surface to the inner surface of the dielectric sheath.

The practical implementation of the device is not difficult and is based on widely used electronic elements, for example, those produced by Analog Devices, MAXIM, Atmel, etc.

When using 3 MAXIM DS18B20 microcircuits as temperature sensors, and 11 Analog Devices capacitance meters AD7747 controlled by the Atmel microcontroller as the capacitance measuring module, it is advisable to reduce the number of connecting conductors between the measuring loop and the processing unit of the measurement results; data transmission between the sensors temperature 3, with capacitive sensors 9 of the measuring loop and the processing unit of the measurement results to produce on one data bus

As a switch, ADG736 chips from Analog Devices can be used. Atmel's ATtiny series chips can be used in the control and calculation module of level 5, in the temperature measurement module 6, and in the capacitance measurement module 7.

The capacitance measuring module 7 can be made on the basis of a controlled generator, similar to the prototype device, or using a PCapOl microcircuit from Acam-messelectronic gmbh, which allows obtaining a digital capacitance value of up to hundreds of nanofarads.

Without changing the essence of the invention, a variant of the software implementation of the functions of several modules of the processing unit of the measurement results using one more powerful microcontroller, for example, ATmegal28, is possible.

Figure 2 shows the longitudinal and transverse sections of the design variant of the measuring loop, in which data are exchanged between the temperature sensors 3, the capacitive sensors 9 of the measuring loop and the processing unit of the measurement results via one data bus. In this case, MAXIM DS18B20 microcircuits can be used as temperature sensors, and Analog Devices AD7747 controlled by Atmel ATtiny84 controller can be used as capacitance measurement modules 11. The sensitive elements 10 of the capacitive sensors 9 can be made, for example, in the form of multi-element springs with a common contact, in the form of metal pipes mounted in a dielectric sheath, and other elements that provide mechanical contact of their outer surface with the inner surface of the dielectric sheath, for example, due to the elastic properties of the elements.

A device for measuring temperature and product level works as follows.

After mounting the device on an empty storage, using the command on the control module and calculating level 5, the operator confirms the absence of a product in the storage, the level and temperature of which are subject to control. By this command, the device measures the capacitance between the reinforcing conductive cables 1, 2 - C0x, corresponding to the initial value of the level H0x, as well as the initial capacitances of the sensitive elements 10 of the capacitive sensors 9 - CS01 ... CS0k. The measured values C0x and CS01 ... CS0k are stored respectively in the memory of the control and calculation module level 5 and the second measurement module level 8. After that, the device is ready for operation. Interrogation of temperature sensors 3 and fixing the results of temperature measurements by temperature measuring module 6 allows you to get the temperature distribution along the storage. A survey of capacitive sensors 9 gives a preliminary (rough) estimate of the level of product in the store. The exact value of the level is estimated by the device based on the capacitance between the reinforcing cables 1, 2. Thus, there are two independent channels for level measurement, the joint operation of which can significantly reduce the error of the device when measuring the level. Consider the interaction of channels in more detail.

Based on a priori information about the noise of capacitance measuring modules 11 of capacitive sensors 9, preliminary threshold levels of capacitance of sensitive elements are established for all capacitive sensors 9 Ср01 ... Ср0к, the excess of which indicates the appearance of the product at the location of the capacitive sensor 9. Subsequently, based on the values of the capacitance of the sensitive elements 11 capacitive sensors 9 located below the level of the product Cf1 ... Cfj (immersed in the product), the threshold values of the capacitances of the sensing elements are adjusted 11 all x capacitive sensors 9 Cp1 ... Cpk. Thus, the device adapts to a specific product, which fills the storage and reduces the influence of the noise of the modules for measuring the capacitance 11 of the capacitive sensors 9 on the operation of the device. Increasing or decreasing the capacitance of the sensitive element of the j-th capacitive sensor Csj located at a known level Hsj, leading to the passage of a value equal to the threshold Cpj, allows you to adjust the level readings of the device and estimate the dielectric constant of the product for further level calculations

ε = 1 + (Cx-C0x); Hm / C0x-Hsj,

where Cx - the value of the capacitance between the cables 1 and 2, measured by module 7,

Hm - the maximum possible level value (length of the measuring loop),

Hsj is the level at which the j-th sensor is located, while the level value is taken equal to the level of placement of the j-th capacitive sensor Hsj.

When correcting the level readings, the effect on the error of the device is eliminated not only of changes in the dielectric constant of the product, but also of the instability of the characteristics of the component parts in the device, affecting its level readings.

At the same time, the level gauge channel based on cables 1 and 2 makes it possible to eliminate false alarms of capacitive sensors 9 located at a great distance from the level of the product measured by the device.

In addition, for capacitive sensors 9 located above the product level, the initial values of the capacitances of the sensitive elements of the sensors 9 are determined, taking into account possible contamination of the measuring loop.

In the second module for measuring level 8, in addition to the capacitance values of the sensitive elements of the capacitive sensors 9, temperature measurement data are received from temperature sensors 3 located near the capacitive sensors 9, which are used for temperature correction of all capacities.

The temperature dependence of the capacitance of the sensitive elements 10 of the capacitive sensors 9 is measured and recorded in memory before mounting the device in storage.

Figure 3 shows the simulation results of the device prototype and the proposed. During the simulation, together with a change in the level, the dielectric constant of the product changed within 2.2 ± 15%. When modeling the proposed device, five capacitive sensors were used, located at levels of 2, 6, 10, 14, and 18 meters, respectively. Dotted line 12 shows the change in product level. The dash-dotted line 13 gives an estimate of the level of the device with a prototype that does not take into account the change in its dielectric constant. Level readings may exceed the physical size of the vault. Solid line 14 gives an estimate of the level of the proposed device. On it, correction points of the device readings are clearly visible when the product level reaches the coordinates of the location of the capacitive sensors 9. Moreover, it is clear that the nature of the correction is different. At the bottom three correction points, the level estimate reaches the location coordinates of the capacitive sensors 9 faster than the actual level (i.e., the previous dielectric permittivity estimates are lower than the dielectric constant of the product filling the storage). And at the points located at the levels of 14 and 18 meters, the nature of the correction changes, a product with a dielectric constant lower than that used in level calculations comes into the storehouse.

It should be noted that in addition to the correction of the dielectric constant used in the proposed device, upon reaching the product level, the location coordinates of the capacitive sensors 9 also take into account the instability of components based on the exactly known levels (coordinates) of the location of the capacitive sensors 9.

Thus, the accuracy of level measurement is improved not only by evaluating the characteristics of the product, but also by evaluating the characteristics of the device.

Figure 4 presents the test results of the prototype of the device, placed in a grain storage, which was used in the preparation of animal feed. During the working day, from 8 a.m. to 11 p.m., grain from various suppliers with different physical characteristics was constantly supplied to the storage and at the same time the grain was unloaded in the tank where the compound feed was prepared. Here, as well as during modeling, correction points 15 are clearly visible when loading the storage with grain with various physical characteristics. During the trial operation (about 1.5 months), the level readings were periodically monitored using a measuring lot, the difference in the level readings did not exceed 0.3 m, while the error was 6-14 times lower than the error of the known device.

Thus, the feasibility of the invention is confirmed by the manufacture of a prototype and the act of its trial operation at the elevator.

Information sources

1. http://www.liroselectronic.com/gw/sensor_lines.html

2. http://www.rolfesatboone.com/index.cfm?fuseaction=cEcommerce.Product& ProductID = 1000

3. http://www.cimbria.com/files/filer/Solutions/Brochures/Temperature_Momitoring_ System_GB.pdf

4.http: //www.dinel.cz/uploads/pdf/080901024831-clm-36-dat-en.pdf

5. http://www.hawker-electronics.co.uk/files/flexicap_data_sht_254_iss_e_2.pdf

6. https://eb.automation.siemens.com/goos/catalog/Pages/ProductData.aspx71anguage-en&nodeid=10017044&tree=CatalogTree&regionUrl=/#activetab=product&

7. http://www.vegacontrols.co.uk/product_details.asp?productID=78&fixedRangeID=04

8. http://www.emo.org.tr/ekler/b7cleabb2baa803_ek.pdf

9. Patent RU2079818 "Method for measuring the level of grain or feed in silos", IPC G 01 F 23/22, publ. 05/20/1997

10. Berestnev E.V., Petrichenko V.E., Novitsky V.O. Recommendations on the organization and conduct of the process at flour mills. M .: DeLi print, 2008, p.164 (prototype).

11. http://www.kontakt-l.ru/pdf/tur01.pdf (prototype).

Claims (3)

1. A device for measuring temperature and level of a product, comprising a measuring loop with a dielectric sheath, reinforced with two electrically conductive cables isolated from each other, inside which temperature sensors are placed, and also containing a unit for processing measurement results, including a switch, a control and level calculation module, the first the output of which is connected to the first input of the switch, a temperature measurement module, in which the first input through the switch is connected to temperature sensors, the second input with is single with the second output of the control and level calculation module, and the first output is the first output of the device for measuring the temperature and level of the product, and the capacitance measuring module, in which the first input is connected to the first cable, the second input is connected to the third output of the control and level calculation module, and the output is connected to the first input of the control and level calculation module, while the second cable is connected to the ground of the device for measuring temperature and product level, and the second output of the device for measuring temperature and the product level is the fourth output of the control and level calculation module, characterized in that a second level measurement module is introduced into the processing unit of the measurement results, and capacitive sensors are placed in the measurement loop, placed along the measurement loop with predetermined coordinates and connected by their outputs through the switch with the first input the second level measurement module, in which the second input is connected to the fifth output of the control unit and calculating the level, the third input is connected to the second output of the tempo measurement module the output, and the output is connected to the second input of the control and level calculation module. 2. The device according to claim 1, characterized in that each capacitive sensor contains a sensitive element with axial dimensions much less than the distances between the sensors and a capacitance measuring module, the input of which is connected to the sensitive element, and the output through the switch is connected to the first input of the second level measurement module . 3. The device according to claim 2, characterized in that the sensitive elements of capacitive sensors with their surface are pressed against the inner surface of the dielectric sheath.

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