WO2016124459A1

WO2016124459A1 - Measuring assembly for the radiometric density or filling level measurement of a medium in an explosive region

Info

Publication number: WO2016124459A1
Application number: PCT/EP2016/051652
Authority: WO
Inventors: Dieter Benz; Simon Weidenbruch
Original assignee: Endress+Hauser Gmbh+Co. Kg
Priority date: 2015-02-06
Filing date: 2016-01-27
Publication date: 2016-08-11
Also published as: DE102015101705B4; DE102015101705A1

Abstract

The invention relates to a measuring assembly for radiometric measurements in an explosive region. The photo-sensitive unit (5) of the detector (4) is configured in such a way that it is surrounded by an encapsulation (6). In this way, the encapsulation (6) both serves as explosion protection and is designed in such a way that it causes the conversion of the incident radioactive radiation into electromagnetic radiation. This is achieved in that the encapsulation (6) is formed by scintillating material at least in one region (7). This results in the advantage that, despite the explosion-safe encapsulation (6), the sensitivity of the photo-sensitive unit (5) is not reduced, rather it is increased. The in turn increased the potential measurement accuracy of the entire measuring assembly.

Description

Measuring arrangement for the radiometric density or level measurement of a medium in an explosive atmosphere

The invention relates to a measuring arrangement for the radiometric density or level measurement of a medium in a hazardous area.

In automation technology, in particular in process automation technology, field devices are often used which serve to detect and / or influence process variables. Sensors that are used, for example, in level gauges, flowmeters, pressure and temperature measuring devices, pH redox potential measuring devices, conductivity meters, etc., which contain the corresponding process variables level, flow, pressure, temperature, pH value, redox potential, resp Detect conductivity. to

Influencing process variables are used by actuators, such as valves or pumps, through which the flow of a liquid in one

Pipe section or the level can be changed in a container. In principle, all devices are called field devices, the

be used close to the process and deliver or process the process-relevant information. A variety of such field devices is manufactured and sold by the company Endress + Hauser.

In the case of density or level measurements, field devices whose measurement method is based on radiometry are often used. In the case of density determination, this measuring principle has proved particularly suitable for high-density media which are not of a purely liquid or gaseous nature but also contain high proportions of solids, such as, for example, sludges, oils or high-viscosity media in general. For level measurements, the medium may even be solid bulk materials such as gravel, sand or seeds. When handling such media, however, it must generally be borne in mind that the risk of explosion in the areas around the containers can arise due to oil vapors or the development of gas by the use of fuels, as well as the formation of dust by bulk materials. This makes it for measuring arrangements for Density or level measurement used in such potentially explosive atmospheres, necessary to be explosion proof.

The measuring method of radiometry uses radioactive radiation, preferably gamma radiation, which is emitted by a radiation source and passed through the container with the medium to be measured. After passing through the container, the transmitted radiation intensity is detected by a detector. By the evaluation of the detector signal of the transmitted portion of the emitted radiation intensity is determined, which can be deduced the density or the level of the medium.

However, the transmitted radiation intensity of the radioactive radiation can not be detected directly after passing through the container, it must first be converted by a suitable material into electromagnetic radiation in the optical range, before it can be detected by a photo-sensitive unit within the detector. Materials having this property are referred to as scintillating materials. Among others, polystyrene has this scintillating property. Only the radiation lying in the optical range can be detected by the photo-sensitive unit, such as an avalanche photodiode, for the operation of avalanche photodiodes only moderate voltages of usually 30 V are necessary, in contrast to Geiger-Müller counter tubes or photomultipliers , whose operating voltage can be several hundred volts to over a thousand volts. However, the operation of measuring arrangements which require high supply voltages is critical in potentially explosive atmospheres, since with increasing supply voltage the danger also increases that these devices act as a potential ignition source in potentially explosive atmospheres. In order to be able to carry out density or fill level measurements in potentially explosive areas, as can be found, for example, in process plants in the oil or gas industry, these must be particularly those

Components of the measuring arrangement, which require high supply voltages, be encapsulated for the purpose of protection against ignition. This will ensures that the necessary ignition energy, for example due to the high supply voltage, is not transferred to the hazardous area. Explosion-proof encapsulation can be implemented in a number of ways; this is specified for electronic components, for example in the EN 60079 series of standards. This includes an encapsulation whose ignition protection requirements are defined in the standard EN 60079-18.

From the patent US 20120132817 Vergusskapselungen for avalanche photodiodes are already known. However, here the Vergusskapselung serves only the protection of the avalanche photodiode from the outside

Environmental influences and not the explosion protection. Disadvantageous in the

However, encapsulation of avalanche photodiodes is also here that the

Radiation is absorbed when passing through the encapsulation. This reduces the measuring sensitivity of the avalanche photodiode and thus also the measuring accuracy of the entire measuring arrangement.

The invention is therefore based on the object to provide a measuring arrangement for operation in a hazardous area, in which the explosion-proof encapsulation of the photosensitive unit increases the sensitivity of the photo-sensitive unit.

The invention solves this problem by a measuring arrangement for

radiometric determination or monitoring of the density or the

Level of a medium in a container, which is in a

explosive area is located. The measuring arrangement comprises

a radioactive radiation source for emitting radioactive radiation,

- a detector with

a photo-sensitive unit that converts electromagnetic radiation into a measurement signal,

- An explosion-proof encapsulation enclosing at least the photosensitive unit, and at least in one defined subregion consists of a scintillating material.

Here, the detector and the radiation source are such to each other

arranged that the radioactive radiation after passing through the container to the scintillating material impinges and electromagnetic

Radiation generated, wherein the photo-sensitive unit receives the electromagnetic radiation. Furthermore, a control / evaluation unit is provided which determines the density or the level based on the measurement signal. In addition, a higher-level unit is provided which is arranged outside the potentially explosive area and which supplies the detector with energy via an electrical connecting line.

Due to this design of the explosion-proof enclosure, at least in a partial area, a conversion of the incoming

radioactive radiation takes place in electromagnetic radiation, the electromagnetic radiation can enter directly into the photo-sensitive unit

be coupled. As a result, on the one hand, an additional scintillator unit becomes superfluous. On the other hand, the direct sensitivity of the photo-sensitive unit or the entire measuring arrangement can be increased by the direct coupling of the electromagnetic radiation. As a scintillating material, for example, a plastic having scintillating properties such as polystyrene or polyvinyltoluene can be used. Likewise, however, inorganic scintillating materials such as cesium iodide, lanthanum chloride, bismuth germanate or comparable materials with scintillating

Properties conceivable.

An advantageous embodiment of the measuring arrangement provides that the control / evaluation unit is also enclosed by the explosion-proof enclosure. In this advantageous embodiment, the control / evaluation unit is in the immediate vicinity of the photo-sensitive unit, for example, on the same board, so that the evaluation of the data or the control of the photo-sensitive unit in

explosion-proof area can be performed. A preferred development of the measuring arrangement provides that the explosion-proof enclosure consists of scintillating material. In this case, where not only a portion of the explosion-proof encapsulation of scintillating material exists, the radioactive radiation is converted over the entire surface of the encapsulation in electromagnetic radiation and hereby further increases the sensitivity of the detector.

According to a further preferred embodiment of the measuring arrangement, the explosion-proof enclosure is a

Encapsulation. This can be realized, for example, by using polystyrene, since polystyrene has, on the one hand, scintillating properties, and, on the other hand, it can, by virtue of its thermoplastic properties, be formed by primary shaping processes, e.g. in the form of a potting, processed. In the geometrical design of the encapsulation are aspects of

Explosion protection, as set out, for example, in the standard EN 60079-18 (or an equivalent standard).

In an advantageous development of the measuring arrangement, the electrical connection line is an intrinsically safe connection cable. This ensures that even by this cable, which is primarily intended to power the detector, no danger of ignition of the hazardous area emanates. It goes without saying that over such a cable not only the

Energy supply must take place. So can in addition also

Data exchange via this cable connection. Alternatively, the data exchange can also take place via a wireless connection. In this case, the detector includes an additional transceiver unit for wireless data transmission. According to a preferred embodiment of the measuring arrangement has

the explosion-proof enclosure a protective layer to protect against environmental influences, in particular ambient light on. Ambient light can lead to a falsified measurement of the detector, since the photo-sensitive Unit also detects parasitic ambient light and this can not distinguish from the actual measurement signal. Therefore one increases

Protective layer the reliability of the measuring arrangement. Such

Protective layer may for example consist of a metallic reflection layer, which by means of a coating method, such as. B. physical sputtering is applied. It can also be a light-absorbing lacquer layer.

In an alternative development of the measuring arrangement to the latter embodiment, the explosion-proof enclosure has a housing for

Protection against environmental influences, such as ambient light, on. It thus assumes an equivalent function as the protective layer. Suitable materials are again, for example, light-absorbing or reflective metals or plastics. This can also provide protection against others

Environmental influences such as water spray, corrosive media or mechanical effects can be achieved.

In an advantageous form of the measuring arrangement, the photosensitive unit is a photodiode or an array of several

Photodiodes. In this case, an arbitrary array can assume any desired shapes, for example a rectangular area comprising a large number of photodiodes arranged side by side for enlarging the photosensitive area. Above all, avalanche photodiodes for detecting electromagnetic radiation in the optical range are very suitable among photodiodes.

According to the invention, however, any type of photodiode capable of converting the electromagnetic radiation emanating from the scintillating material into measuring signals can in principle be used.

The invention will be explained in more detail with reference to the following figure. It shows:

Fig. 1: A preferred embodiment of the invention

Measuring arrangement for the radiometric determination or monitoring of the level in the hazardous area. In Fig. 1, a measuring arrangement for the radiometric determination or monitoring of the level of a medium 13 in a container 2, which is located in a hazardous area, shown.

It can be seen with reference to FIG. 1 how the individual components of the measuring arrangement are arranged relative to one another:

A radiation source 3 emits radioactive radiation in the direction of the container 2 with the medium 13 to be measured. When the level of the medium 13 in the container 2 is above the radioactive radiation, the radiation is conducted through the medium 13 and consequently absorbed more strongly, so that after passage through the container 2 results in a lower intensity of the radioactive radiation. In Fig. 2, the level is below the course of the radioactive radiation.

After passing through the container 2, the radioactive radiation strikes a subregion 7 of a scintillating material

explosion-proof enclosure 6 of a detector 4.

The partial area 7, in which the radioactive radiation is converted into electromagnetic radiation, is followed by a photo-sensitive unit 5 within the enclosure 6. The photo-sensitive unit 5 detects the electromagnetic radiation and converts it into a dependent of the intensity of the electromagnetic radiation measurement signal. This can be further processed by a rule / evaluation unit 8. In the present

Embodiment, the control / evaluation unit 8 is also within the explosion-proof enclosure. 6

On the basis of the detected by the photo-sensitive unit 5 intensity of the radioactive radiation can be concluded that the level is above the radioactive radiation. In the simplest case can therefore be detected on the basis of the measuring arrangement, whether the level falls below or exceeds a certain limit level. The limit level is the height at which the radioactive radiation passes through the container.

For ignition protection in potentially explosive atmospheres, it is also important that all components of the measuring arrangement that are not explosion-proof, located outside the hazardous area. Therefore, the power supply of the detector 4 is performed by the parent unit 9 in the illustrated embodiment from outside the hazardous area. In this case, the detector 4, the energy is supplied via an intrinsically safe cable 10 in order to ensure the power supply to the explosion-hazardous area in explosion-proof.

1, it can be seen that the photo-sensitive unit 5, which is preferably an avalanche photodiode, is protected in an explosion-proof manner and at the same time has scintillating properties in the critical subarea 7 of the encapsulation 4, thereby improving the sensitivity of the photodiode. sensitive unit 5 is effected.

LIST OF REFERENCE NUMBERS

1 measuring arrangement

2 containers

3 radiation source

4 detector

5 Photo-sensitive unit

6 encapsulation

7 subarea

8 control unit / unit

9 Parent unit

10 connection line

1 1 protective layer

12 housing

13 medium

Claims

claims

1 . Measuring arrangement for the radiometric determination or monitoring of the density or the level of a medium (13) in a container (2), which is located in an explosive atmosphere, comprising

- a radioactive radiation source (3) for emitting radioactive

Radiation,

- A detector (4) with

a photo-sensitive unit (5) which converts electromagnetic radiation into a measuring signal,

- an explosion-proof enclosure (6), which surrounds at least the photosensitive unit (5), and which consists of a scintillating material at least in a defined portion (7),

wherein the detector (4) and the radiation source (3) are arranged in such a way that the radioactive radiation, after passing through the container (2) impinges on the scintillating material and generates electromagnetic radiation,

wherein the photo-sensitive unit (5) receives the electromagnetic radiation,

wherein a control / evaluation unit (8) is provided which determines the density or the level based on the measurement signal, and

wherein a superordinated unit (9) is provided, which is arranged outside the hazardous area and which supplies the detector (4) via an electrical connecting line (10) with energy.

2. Measuring arrangement according to claim 1, wherein the control / evaluation unit (8) of the explosion-proof enclosure (6) is enclosed.

3. Measuring arrangement according to claim 1 or 2, wherein the explosion-proof enclosure (6) consists of scintillating material.

4. Measuring arrangement according to at least one of the preceding claims, wherein it is in the explosion-proof enclosure (6) to a

Vergusskapselung acts.

5. Measuring arrangement according to at least one of the preceding claims, wherein the electrical connection line (10) is an intrinsically safe connection cable.

6. Measuring arrangement according to at least one of the preceding claims, wherein the explosion-proof enclosure (6) has a protective layer (1 1) for

Protection against environmental influences, in particular ambient light having.

7. Measuring arrangement according to at least one of claims 1 to 6, wherein the explosion-proof enclosure (6) has a housing (12) for protection against environmental influences, in particular ambient light.

8. Measuring arrangement according to at least one of the preceding claims, wherein the photo-sensitive unit (5) is a photodiode or an arrangement of a plurality of photodiodes.