DD301230A7 - CORROSION-RESISTANT SENSOR FOR MATERIAL HUMIDITY AND FLUID LEVEL - Google Patents

Abstract

Corrosion-resistant sensor for moisture content and liquid level for the determination of moisture in porous materials eg. B. in the ground or concrete, which is also to use for signaling levels heavily polluted, aggressive, boiling or foaming liquids and for leakage fuses. According to the invention the object is achieved so that at least two rod-shaped, cylindrical or cuboid plastic electrodes are used to detect the electrical impedance of a defined measuring path, which is used as a natural image signal of the material moisture or liquid level, the inside of an electrically conductive elastic material exist and are coated with an electrically insulating elastic material. The electrical resistance of the conductive material can be up to 100 kOhm / m. During the measuring process, a signal generator feeds a high-frequency pulse voltage to the series connection of the resistors of the electrodes and the resistance of the measuring path. The electronics used allow to evaluate impedance up to the order of magnitude of 1 Mohm.

Description

For this 1 page drawings

Field of application of the invention

The invention relates to a device for determining the moisture in porous solids, for. As soil or concrete, which is also to detect levels of dielectric or electrically conductive, aggressive, boiling, steaming or foaming liquids and for leakage fuses to use.

The device is in systems for automatic control of the humidity or the level or in warning and safety devices part of the measuring device whose electronics converts the electrical impedance of the measuring path between the electrodes of the device in an imaging signal (eg., DC voltage or frequency).

Characterization of the known prior art

Fs are known for obtaining a natural imaging signal for the measured material moisture content or liquid level devices that detect electrical variables of a test section.

According to DE 3439606, at least two antipolar electrodes of a good electrically conductive and non-corrosive material, e.g. Stainless steel or copper, placed at a distance of 10 to 50cm in a depth of 5 to 25cm in the layer to be moistened and with a DC voltage of 2 to 30 volts \ 'worries. The Gleichsuomwiderstand is evaluated in the medium to be humidified.

The disadvantages of this solution are:

The use of direct current leads to electrolysis processes which change the state of the measuring path.

The electrodes used are low-resistance. In order to obtain desired response thresholds, they must be attached locally separately.

The electrodes require mechanical fixations. The connection cables to the electronic part are loose.

The entire surface of the electrodes serves as a "conductor cross-section", a point-like measurement in any depth of the Voiumens is not possible.

From hardened Feststeffen the electrodes are not destructive removable.

Electrode arrangements according to DE 3439606 are also used for level measurements of liquids. The disadvantages of these arrangements are similar to those used in solids.

Pegelmessungsn of boiling or foaming liquids are not possible because the test section is low impedance and the power line over the entire electrode surface. As a result, it is not clear between steam and foam

and the liquid level. .

In aggressive liquids MetaMelektroden are only partially corrosion resistant.

In corresponding solutions, metal electrodes tend to become encrusted.

Metal electrodes are difficult to clean, under certain circumstances hygienic requirements can not be met.

Other known solutions (eg Offenlegungsschrift 2314902) use sinusoidal or pulsed alternating voltages and evaluate the electrical impedance of the measuring path, without fundamentally changing the type of electrodes. The electronic part can form a structural unit together with the electrode arrangement.

With DE 3046915 a stick electrode for capacitive level measurements has become known, preferably for use in the food industry. This electrode consists of a metal rod which is encapsulated in a plastic tube. It is fixed by a special fastening flange.

The disadvantages are the considerable production costs and the limited field of application. The electrode is only suitable for purely capacitive measurement in suitable media.

For use in leakage fuses, z. As for household washing machines, "water sensors" have become known (DE 3240868), which operate according to the above method and in which the electrode shape and size was adapted to the specific purpose.

In the patent DE 2339481 an electrical sensor in the form of a body with alternating conductive and insulating surface portions is described. These surface sections consist of plastic prepared with conductive or non-conductive filler. In principle, the sensor can be used both as a material moisture sensor and as a level sensor. Compared to other solutions, it is largely resistant to corrosion.

DBP 1039150 describes control probes for electrical equipment consisting of plate-shaped or tubular supports made of elastic insulating material which are firmly connected to non-metallic, elastic, electrically conductive layers.

A disadvantage of the last two solutions are the considerable effort for the production of the sensor structure, the complex contacting of the conductive sections.

The filler-rich strips embedded in the surface are not subject to wear and aging under mechanical, chemical and thermal stress. There is a risk of encrustation through appropriate media.

Object of the invention

The aim of the invention is a corrosion-resistant sensor for Mntei idlfeuchte and liquid level, which differs from the prior art by

- Temperature and pressure sensitivity

- Replaceability in aggressive, boiling, steaming and foaming media

- Resistance to pollution

- minimum size

- easy construction

- Maintenance free and

- low cost

characterized in that the sensor and the electronic transducer can form an initiator assembly.

When measuring the moisture of concrete or other water-hardening mixtures, the device must be non-destructively removable from the cured mass.

Explanation of the essence of the invention

The invention had the object of providing a producible with little technical effort device for signaling levels of hot, steaming, sometimes heavily polluted or aggressive dielectric or electrically conductive liquids to develop, which also for nearly point-like detection of Matenalfeuchte in voluminous, porous materials , preferably in the ground, concrete or anhydrite binder, is suitable.

According to the invention the object is achieved so that at least two rod-shaped, cylindrical or cuboid plastic electrodes are used to detect the electrical impedance, which is used as a natural imaging signal of the liquid jKeitspegels and the material moisture, which consist of an electrically conductive elastic material inside and with an electrically insulating elastic material are sheathed.

The specific electrical resistance of the conductive material can be up to 100kOhm / m.

The electrodes are led parallel at a distance of their lateral surfaces of 10mm.

The end faces of one end are connected via a suitable contact with an electronic part of the applicant, which consists of a standard signal generator, waveform converter and switching amplifier.

The electronoil can be cast together with the contacted ends of the sensor in synthetic resin.

The length of the electrodes intended for pouring is thermally structured along its jacket in order to fulfill the task of a strain relief and labyrinth seal.

Alternatively, the electrodes can be cast in a mounting flange and connected to a separate electronic part.

The measured value is recorded at the end faces of the free electrode ends, which can be sharpened conically and have a difference in length of 30 mm in order to make the formation of a closed liquid film by condensation or wetting impossible and to prevent encrustations.

If required, the free length of the sensor can be selected from a few millimeters up to one meter.

The electronic part can convert impedance up to the order of 1 Mohm into a voltage signal or a two-point signal with an adjustable threshold value. During the measuring process, the standard signal generator feeds a high-frequency pulse voltage to the resistor series circuit consisting of the resistance of the plastic electrodes plus the resistance of the measuring medium.

The invention will be described in more detail below with reference to two figures.

example 1

In the embodiment according to FIG. 1, the plastic electrodes consist of ignition cables for internal combustion engines

KWO NZÜ 2Y20. The inner conductive material consists of polyethylene with a high proportion of carbon black.

At the ends of the Zündkabelenden copper pins 6 are pressed into the conductive material 2 in the interior of the electrode and electrically connected to the electronic part 5 for contacting.

Electronic part 5 and the contacted ends of the electrodes are cast in a plastic housing 7 with epoxy resin 11.

The cast-in part of the electrode is thermally structured 3 in order to fulfill the functions strain relief and labyrinth seal. The free electrode tips 4 are tapered to prevent the formation of a closed liquid film by condensation or wetting.

The electrodes routed in parallel on their generatrix are welded together 12 and cast into a plastic tube 10.

About the connecting line 9, the power supply and the signal output can be realized.

With the fastening part 8, the arrangement can warn fixed.

The described sensor can be used for the Materialfouchtemessung in a defined depth z. B. irrigation systems in horticulture, but also for level controls z. B. be used in sump pumps od jr treatment plants under the harshest conditions,

Example 2

In the embodiment of Figure 2, two planar plastic electrodes 1 are attached from an electrically conductive material to an electrically insulating base plate 2 by gluing.

The contact is made by pressed into the electrode material copper pins 6, which are electrically connected to the electronic part 5.

Base plate 2 with electrodes 1 and electronic part 5 are cast in a plastic housing 7 with epoxy resin.

The connecting line 9 is the power supply and the signal output.

With the fixing part 8, the sensor can be fixed.

The plastic electrodes 1 are embedded in foam rubber 3.

This sensor design serves as a leak-proofing device for liquid leaking on the floor.

The foam rubber also absorbs small amounts of liquid. This activates the sensor and keeps the signal, even if the liquid z. B. flows through a slope.

Claims (6)

1. Corrosion-resistant sensor for moisture content and liquid level, consisting of at least two rod-shaped, cylindrical or cuboid Kunotstoffelektroden inside jus an electrically conductive elastic material and are coated with an electrically insulating elastic material, which together with a standard signal generator, a waveform converter and a Amplifier can form a structural unit, characterized in that the conductive material used for the sensor has an electrical resistance of up to 100kOhm / m and the elastic electrodes have a waxy surface in order to be able to be removed non-destructively from hardened substances. 2. Corrosion-resistant sensor according to claim 1, characterized in that the free electrode ends are tapered conically. 3. Corrosion-resistant sensor according to claim 1, characterized in that the electrodes are cast in a plastic tube with a suitable filler and the tube on the generatrix carries a length scale. 4. Corrosion-resistant sensor according to claim 1, characterized in that a conductive organic polymer is used as the electrode material. 5. Corrosion-resistant sensor according to claim 1, characterized in that a conductive plastic with filler carbon black is used as the electrode material. 6. corrosion-resistant sensor according to claim 1, characterized in that at least two planar, electrically conductive plastic electrodes of suitable geometry are attached to an electrically insulating base plate and that the electrodes are coated with an absorbent material.