EP1456631A2

EP1456631A2 - Methods and devices for erasing errors and compensating interference signals caused by gammagraphy in radiometric measuring systems

Info

Publication number: EP1456631A2
Application number: EP02792970A
Authority: EP
Inventors: Alecsandru Nistor
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2001-12-19
Filing date: 2002-12-11
Publication date: 2004-09-15
Also published as: CN1606690A; WO2003052396A3; WO2003052396A2; US7180054B2; AU2002358673A8; US20050116157A1; AU2002358673A1; DE10162703A1

Abstract

The invention relates to methods and devices for erasing errors and compensating interference signals caused by gammagraphy in radiometric measuring systems according to process measuring techniques. The inventive device comprises an input for measuring values Lm(t) of process variables L(t) measured by the detector, an input for at least one non-radiometrically measured and optionally monitored first process parameter P1 = P1(t-τ), whereby the modification thereof leads to a delay in a modification of Δ Lm = L(tj) Lm(tj + 1) of the radiometric measuring value Lm(t), amounting to a delay time τk, which can also be τk = 0; an output which is connected to a process control system, and a detection and error compensation device, which when an operational measuring mode determines the modification Δ Lm = L(ti) Lm(ti + 1) on the basis of radiometric measuring values Lm(ti) and Lm(ti + 1) detected by the detector at two consecutive random times ti and ti+1 and a comparision is effected by means of the mathematical interrelation Δ Lm = f (ΔP1,) with respect to a modification ΔP1 = P1(ti -τ) P1(ti+1-τ) of the first non-radiometric measured process parameter detected in the corresponding time interval.

Description

Method and device for error suppression and compensation of interference signals caused by gammagraphy in radiometric

measuring systems

The invention relates to methods and devices for suppressing errors and compensating for interference signals caused by gammagraphy in radiometric measuring systems.

Radiometric measuring systems have proven themselves for many years as a non-contact measuring method in process measuring technology. They are used where process parameters, e.g. Level of a medium in a container, a separating layer and / or a density of the medium under difficult conditions, such as e.g. at extreme temperatures and pressures. Known radiometric measuring systems usually include a radioactive radiator and a detector attached to or on a container or pipe, and an evaluation unit. Associated measurement methods are also known per se. In the chemical industry in particular, radiometric measurements are indispensable for difficult processes.

On the other hand, the integrity of pipes and containers and their connections is very important, especially in the plants of the chemical industry, and must therefore be checked from time to time. In the sense of non-destructive material testing of pipelines, welds and pressure vessels, gammagraphy is often used for this purpose, in which measuring procedure radioactive emitters and detectors are also used. If such a gammagraphy measurement is carried out in the vicinity of a radiometric measuring system, however, the radioactive emitter used in the gammagraphy can lead to interference in the radiometric measuring system, so that the measurement of the process variables is falsified.

In one of the currently customary methods of suppressing interference by gamma imaging on a radiometric measurement system, the affected radiometric measurement located near the grammage examination is stopped or stopped and the last measured value of the process variable is recorded, before the gamma analysis is started. ie saved, and quasi frozen. During the gammagraphy measurement, the measurement of the Process variables through the radiometric measuring system and is not available for process control. At the end of the gammagraphy examination, the radiometric measuring system is switched on again and the measurement of the process variables is started again. The disadvantages of this method are obvious: Either a process variable detected by the radiometric measuring system can no longer be measured and monitored for the duration of the gammagraphy, and this can have considerable effects on the process control. There is no need for a gammagraphy measurement and thus a check of the pipe and container walls or weld seams where no interruption of the acquisition of the process variables is permissible, and this is particularly problematic when radiometric measurements of the fill level of a medium in a container are made. where pumps are controlled depending on the current level measurement value. The other alternative, to shut down the process branch in which the gammagraphy measurement is to be carried out, is also problematic for most plant operators.

The invention is therefore based on the object of providing a method and a device which make it possible to enable or continue radiometric measurement of a process variable even during possible disturbances by simultaneous grammage measurements.

This object is achieved by a method for suppressing errors and compensating for interference signals caused by gammagraphy in a radiometric measuring system, with which a process variable _{(l) is} determined by means of a radioactive radiator and a detector, which method comprises the following steps:

a) in the course of the measuring operation, for two successive times t _t and t, ₊₁ per se, the change ALm - Lm _(ll) from the radiometric measured values Lm _{u) and Lm _{{tl + l) recorded} by the detector at these times - Lm _{(tl + X) is} determined and by means of a predefined arithmetic relationship ALm = / (ΔR,) with a change recorded in the corresponding time interval the first process parameter not measured radiometrically; b) if the change ALm = Lm _{u) -Lm _{(u + X) of} the radiometric measured value Lm _{(l) of} a previous change ΔR, = P _{l (u} _ _τ) - P _{+ l} _ _{τ) of} the first non-radiometrically measured Process parameters in the corresponding time interval and the mathematical relationship ALm = / (ΔR,), it is assumed that there is no malfunction of the radiometric measuring system, the associated process variable Z _{(/ l +} . From the last measured radiometric measured value Lm _{(ll + 1)} ₁₎ determined and sent to a bus connected to a process control system without an additional signal indicating a fault;

c) if the change ALm = Lm _{ü) -Lm _{{tl + Ϊ) of} the radiometric measured value Lm _{(l) of} a previous change ΔR, = R, ₍ , -_ _r) - R _{1 (r} , ₊₁ _ _r) does not correspond to the first non-radiometric process parameter in the corresponding time interval and the mathematical relationship ALm = / (ΔR.), it is assumed that there is a fault in the radiometric measuring system,

- then, based on the previous change ΔP, = R. ₍ ,, _ _r) - R _{1 (} “ ₊₁ _ _{r) of} the first process parameter P _λ by means of the acquired mathematical relationship ALm = f (AP _l ) for the time t, ₊₁ a radiometric measured value c _{(r + 1) is} calculated;

- The associated process variable Z (.. ₊ i) is determined from the calculated radiometric measured value Lc _{{+ l)} and is sent to the bus connected to the process control system together with an additional signal indicating a fault; and

- In a subsequent detection of the change ΔR, = R _{1 (r} , ₊₁ _ _r) - R _{1 (r} , ₊₂ - _{r) of} the first non-radiometrically measured process parameter and the measurement, which takes place at a time t _{l + 1} of the radiometric measured value Lm _{(ll + 2)} from this and the calculated radiometric measured value Lc _{{n + X)} the change ALm = Lc _{{tl + l)} - Lm _{{tl + 2) is} determined and this in accordance with steps d) or e) is used to determine whether there is still a fault in the radiometric measuring system.

In a preferred embodiment of the method according to the invention, the following steps are carried out before the radiometric measuring system is started up and before the actual measuring operation is started:

a) To a measured by the detector of the radiometric measurement system measurement value Lm _{l) at least one non radiometrically measured and also monitored first process parameter R, = P _{l (l} _ _τ) identifies its change and t _{J + l} _ _τ and delayed by a possible delay time τ, which can also be τ = 0, leads to a change ALm = Lm _(tj) - Lm _{(tJ + X) of} the radiometric measured value Lm _t) ;

b) from the changes ALm of the radiometric measured value Lm _{l) determined under different operating and process conditions and at different times t, as a result of changes ΔR, the non-radiometrically measured first process parameter, a mathematical relationship ALm = / (ΔR,) is formulated and stored ;

In a further embodiment of the method according to the invention, it is provided that, before the signal indicating the malfunction of the radiometric measuring system is output, it is checked whether the change in the radiometric measured value ALm is smaller than a change δ = previously predetermined as the maximum permissible ; and that only in the case where ALm ≥ δ the signal indicating the interference of the radiometric measurement signal is sent to the bus.

The above-mentioned object is further achieved by a device for error suppression and compensation of interference signals caused by gammagraphy in a radiometric measuring system with a radioactive radiator and a detector, which device comprises:

an input for measured values Lm _{{t) of} a process variable L ₎ measured by the detector,

an input for at least one non-radiometrically measured and also monitored first process parameter R, = R _{1 (} , _ _r) , the change of which is delayed by a possible delay time τk, which can also be τk = 0, to a change ALm = Lm _{{IJ )} - Lm _{{tJ + l) of} the radiometric measured value Lm _{l) leads;

- An output, which is connected to a process control system, and

- an evaluation and error compensation device,

the changes in the running measuring operation for two successive times t, and t _{l + l} from the radiometric measured values Lm _(ll) and Lm _{(lnl) detected} by the detector at these times, its change ALm = Lm _(tl) - Lm _{( ll + l)} determined and by means of the mathematical relationship ALm = / (ΔR,) with a change ΔR, = R, _(/ , _ _r) - R _{1 ((/ + 1} _ _{r) of} the first, detected in the corresponding time interval, non-radiometrically compares measured process parameters; - the, if the change ALm = Lm _{ll) - Lm _{(tl +) of} the radiometric measured value Lm _{(l) of} a previous change ΔR, = R. ₍ "_ _r) - P _{Kll + x} . _{τ) of} the first non-radiometrically measured process parameter in the corresponding time interval and a predetermined arithmetic relationship ALm = / (ΔR,) corresponds, the associated process variable Z ₍ ,, _{+1) is} determined from the last measured radiometric measured value Lm _{(ll + X)} and this without an additional signal indicating a fault to the output and on a bus connected to a process control system;

- which, if the change ALm = Lm _w - Lm _{{ll + X) of} the radiometric measured value Lm _{{1) of} a previous change ΔR, = R _{1 (/} ._ _r) - P _{l (tl + l} _ _{τ) of} the first Process parameter not measured radiometrically in the corresponding time interval and does not correspond to the mathematical relationship ALm = / (ΔR,) detects a fault in the radiometric measuring system,

- Then, based on the previous change ΔR, = P _{X (ll} _ _τ) - R _{1 ((} , ₊ , _ _{r) of} the first process parameter R, by means of the acquired mathematical relationship ALm = f (AP _x ) for the time t _{l + x} a radiometric measured value Lc _{(l + X) is} calculated;

- Whereby the associated process variable Z ₍ .. ₊ i) is determined from the calculated radiometric measured value Lc _{(ll + X)} and gives this together with an additional signal indicating a fault to the output and to the bus connected to the process control system; and

- Wherein in a subsequent, at a time t _{l + 2} detection of the change ΔR, = R _{1 (} , ₍₊₁ _ _r) - R _{1 (} , _{. + 2} - _.) Of the first non-radiometrically measured process parameter and the measurement of the radiometric measured value Lm ₍₊₂₎ from this and the calculated radiometric measured value Lc _{{tl + X) determines} the change ALm = Lc _{(ll +)} - Lm _{(tl + 2) in} order to determine whether there is still a fault in the radiometric measuring system.

Further preferred embodiments of the invention relate to the measured value Lm _{t) measured by the detector of the radiometric system, which is a measure of a fill level of a medium in a container, a density of such a medium in a container or a separating layer of at least two phases of one or more media can be in a container or tube.

Other preferred embodiments of the invention relate to the first non-radiometrically measured process parameter R,, a pressure inside the container or in a pipe connected to the inside of the container,

- A temperature inside the container or in a tube connected to the inside of the container

- or is a flow value of a medium in a pipe connected to the inside of the container.

In still other embodiments of the invention it is provided that a plurality of process parameters P _k are monitored for (k = 1, 2, ...), the change ΔR _t = P _klv - _Λ) - P _{klt + l} . _Λ) for any time _tj _ _τk and t _{J + x} _ _Λ and by a possible delay time τk, which can also be τk = 0, delayed to a change ALm = Lm _{IJ) - Lm _{{lj + X of} the radiometric measured value Lm _(l) leads;

- where, based on measurements under different operating and process conditions, a mathematical representation of the dependence of the change in the radiometric measured value Lm _{t) on a change in each or more of the process parameters P _k to ALm = f (AP _x , AP ₂ , ... .) is formulated; and it is checked in the ongoing measuring operation by means of the calculated relationship ALm = f (AP _x , AP ₂ , ....) whether there is a fault in the radiometric measuring system.

The advantage of the invention is that the process control is not impaired, in particular under safety, since the process variable to be measured can be monitored without interruption.

In addition, the invention offers the possibility of creating a device with which, in the sense of a retrofit kit, older and already installed radiometric measuring systems can be upgraded.

Such a retrofit kit is usually to be arranged between the radiometric measuring system and the process control system. The invention is described in more detail below with reference to various embodiments of the invention and with reference to the accompanying drawings. Show:

1: a schematic representation of a part of a process monitored by a radiometric measuring system; Fig. 2: a schematic representation of a radiometric

Measuring system monitored part of a process with a gammagraphy measuring system operating in their vicinity;

Fig. 3: a schematic diagram of a device for evaluation and

Error suppression and compensation according to the invention;

Fig. 4: a flowchart of a preferred first embodiment of a

Process for evaluation, error suppression and compensation after the

Invention;

Fig. 5: a flowchart of a preferred second embodiment of a

Process for evaluation, error suppression and compensation after the

Invention;

Fig. 6: a schematic representation of a conventional connection of a radiometric measuring system and others for the detection of others

Measuring devices serving process parameters to a process control system; and

Fig. 7: a schematic representation of a connection of a radiometric

Level measuring system and other measuring systems for the detection of others

Process parameters with a process control system with the interposition of a

Fault masking and compensation device according to the invention.

For simplicity and clarity, the same elements, assemblies or parts of the different embodiments of the invention are provided with the same reference numerals.

1 shows an example of part of a conventional industrial plant of a so-called process. A radiometric measuring system 14 is attached to a container 10, which contains a medium 12 inside, which comprises a radioactive radiator 16 and a detector 18. As shown in FIG. 1 and as is customary in such systems, the radioactive emitter 16 and the detector 18 are arranged on opposite sides of the container 10. A beam path of the radiation emitted by the radioactive radiator 16 and incident on the detector 18 is illustrated by dashed lines, but is not described in more detail here. The radiometric measuring system 14 also includes evaluation electronics 20, in which a signal for the detected process variable L _{(t) is} formed from a measured value Lm _(t) measured at any time t by the detector 18. The process variable E ₍ described here and below) is preferably the fill level of the medium 12 in the container 10. In principle, however, it can also be any other Act process variables that can be recorded with a radiometric measuring system, such as the density of a medium in a container or tube or the interface between two phases of one or more media in the container or in a tube.

Often, the evaluation electronics 20, as shown in FIG. 1, are arranged separately from the detector 18 and connected to the latter by a cable. However, it can also be accommodated in a housing of the detector 18 or in a housing common to it. In most cases, the evaluation electronics 20 is connected to a bus line 22, via which the process variables obtained from measurement signals are sent to a process control system, not shown here. Instead of the bus line 22 shown in FIG. 1, a wireless bus is also conceivable as a connection to a process control system or a corresponding central control center.

In addition to the radiometric measuring system 14, in the example of a process illustrated in FIG. 1, further measuring devices are shown with which process parameters which are not recorded radiometrically are determined, which have an influence on or are influenced by the measured value Lm _(t) recorded by the radiometric measuring system 14. In short: Changes to the process parameters are an indication of possible changes to the process variables.

In or on a first pipeline 24, which opens into the interior of the container 10 and is used for filling with the medium 12, a flow measuring device 26 is installed, with which a flow as the first process parameter P _x = P _{(l) of} the medium 12 can be detected by the first pipeline 24. Due to the medium 12 flowing through the first pipeline 24 into the container 10, the measured value Lm _{{t) of} the process variable fill level L _(t) in the container 10 changes, unless an equal volume of the medium flows out in the same time period.

To monitor a pressure in the vapor or gas layer above the medium 12 in the container 10, a pressure measuring device 28 is used, which is attached in or on a second pipeline 30, which opens into the interior of the container 10 from above. The pressure measuring device 28 detects the pressure in the container 10 in the vapor or gas layer above the medium 12 in the container 10 as the second process parameter P ₂ = P _m . Changes in the pressure can indicate changes in the fill level Z ^, _{(/) of} the medium in the container 10. In the Fig. 1 selected representation of the pressure gauge 28 in or on the second pipe 30 is not mandatory and not a limitation of the invention. It is known to the person skilled in the art that the pressure measuring device 28 can also be arranged in the container 10 in the region of its cover.

In a third pipeline 32, which opens into the bottom or sump of the container 10, a valve 34 is arranged, by means of which the outflow of the medium 12 from the container 10 can be controlled. The position of the valve 34 or its actual degree of opening is recorded as the third process parameter R ₃ = R _{3 (} changes in this third process parameter R ₃ , which increase the opening or closing of the valve 34 and thus increase, less or no outflow of the medium 12 mean the container 10, lead to a change in the fill level L _{{t) of} the medium 12 in the container 10, unless there is a corresponding inflow of the medium 12, the inflow is, as described above, by changing the first process parameter R, with the flow rate Measuring device 26 controls.

In summary, it can be stated that changes in one or more process parameters R 1, R ₂ , R ₃ mean a change in the radiometric measurement value Lm _{{t) of} the fill level L _{t) . A relationship existing between the changes in the process parameters R 1, R ₂ , R ₃ and a change in the radiometrically recorded measured value Lm _(t) is preferably according to the invention under different operating and process conditions and at different, successive times t, and t _{ι +1 recorded} before the actual, regular commissioning of a special system or used as a function that is previously known and possibly adapted from a comparable system.

The functional relationship is determined as changes ALm of the radiometric measured value Lm _(l) as a result of changes in the process parameters ΔR,, ΔR,, ΔR ₃ , a mathematical relationship ALm = / (ΔR ,, ΔR ₂ , ΔR ₃ ) being formulated and stored , If a change in one or more process parameters R,, R ₂ or R by a possible delay time τ, which can also be τ = 0, delays to a change ALm = Lm _(IJ) - Lm _{(IJ + X) of} the radiometric measured value Lm _{( l)} leads to this when determining the mathematical relationship ALm = Lm _tJ - Lm _{tJ + x} = / (ΔR ,, ΔR ₂ , ΔR ₃ )

ARL ⁼ ° 2 « _/ -r) ~ ° 2 (/ j + lr) ^{Ur |} ΔR ₃ = R _{3 ((;} _ _r) ^~ R3 «, + l-.) Is taken into account. This mathematical connection ALm = Lm _tJ - Lm _{lj + X} = / (ΔR ,, ΔR ₂ , ΔR ₃ ) is preferably stored in a memory of the evaluation electronics 20 or in a memory connected to it, where it stands for the suppression and compensation of errors caused Interference signals available.

For the embodiment of the invention shown in FIG. 1 and described here, three process parameters have been selected. However, it is clear to the person skilled in the art that in other plants and under different conditions there may be more or fewer process parameters, the changes of which lead to changes in the process variables and which are to be monitored and processed according to the invention.

In Fig. 1 also connecting lines from the flow meter 26 and from the pressure meter 28 to the bus line 22 are indicated. The process parameters measured by the flow measuring device 26 and by the pressure measuring device 28 are also passed to the evaluation electronics 20 of the radiometric measuring system 14 for further evaluation and processing.

2 shows schematically and simplified the container 10 shown in FIG. 1 and the radiometric measuring system 14 for determining the filling level of the medium 12, as well as a gamma-graphing measuring system 36 which is used in the vicinity in the area of an adjacent pipe bend 38 for its examination becomes. A radioactive radiation emanating there from a radiator 40 and directed onto the pipe bend 38 is also received as interference 42 by the detector 18 of the radiometric measuring system 14 and interferes with or falsifies the measurement signals used to determine the fill level of the medium 12. This additional external radiation received by the detector 18 means that a lower fill level is displayed than is actually present in the container. But this is highly undesirable and dangerous.

Fig. 3 shows a schematic diagram of a device 44 for evaluation, error suppression and compensation according to the invention. This device 44 comprises an input 46 for radiometric measured values Lm _(t) measured by the detector 18 and for the further process parameters P _x = P _m , P ₂ = R _{2 (()} and / or R ₃ = R _{3 (/ )} , an evaluation and error compensation device 48 in the actual sense and an output 50. An energy supply which is a matter of course for the device 44 for evaluation, error suppression and compensation is not shown here for reasons of simplicity and clarity.

In the ongoing measuring operation, the evaluation and error compensation device 48 determines the change for two successive times t, and t, ₊₁ from the radiometric measured values Lm _(tl) and Lm _{(tl + X)} detected by the detector at these times ALm = Lm _(tl) - Lm _{(ll +)} and checks by means of the predefined and stored arithmetic relationship ALm = f (AP _x , AP ₂ , AP ₃ ) based on the changes in the process parameters ΔR,, ΔR ₂ or ΔR recorded in the corresponding time interval, whether there is a fault in the radiometric measuring system 14, as shown in FIG. 2, or not. In the event that a fault is assumed, a value to be output for the process variable L _{(t) is} determined in the evaluation and error compensation device 48 according to the method for fault suppression and compensation of interference signals, which is described in more detail below, which value together with a corresponding one , a signal indicating a fault, for example an alarm signal, is output from output 50 to bus line 22 (see FIG. 1). In the event that no fault is assumed, a value to be output for the process variable L _{l) is} determined in the evaluation and error compensation device 48 for the last measured radiometric measured value Lm _(t) and from the output 50 - without an alarm signal - to the Given bus line 22.

4 illustrates in a flowchart a preferred first embodiment of a method according to the invention for evaluation, error suppression and compensation according to the invention. Here, an example of a time segment from an ongoing measurement operation is shown for two successive times t, and t _{l + x} . The radiometric measured value Lm _(t) and several process parameters are measured. The exemplary embodiment shown here is three, process parameters R 1, R ₂ , R ₃ , which are preferably the process parameters shown in FIG. 1 and the description associated with it. For the sake of simplicity, it is assumed that the arithmetical relationship ALm = / (ΔR ,, ΔR ₂ , ΔR ₃ ) previously determined and determined under various operating and process conditions has already been formulated for further processing and in a suitable form in a memory 60 of the device Fault masking 44 (see also FIG. 3) is stored. It is further assumed that at time t _{l + x} , at which the process of the method shown in FIG. 4 begins (again), the measured values Lm _{ll) , P _{X (ll)} , R ₂ acquired at the previous time t _{(/ 1)} , R _{3 (} , _{() are} also stored in a suitable form in a memory 58 of the device for fault suppression 44 and are available for further processing.

After the actually measured values Lm _{{ll + X)} , P _{X {tl + X)} , R _{2 (} ,, ₊₁₎ , R _{3 (} ,, ₊₁₎ in the evaluation electronics 20 (see also FIG. 1 ) are present, a determination 62 of their changes compared to the values Lm ₍₎ , R, ₍₍₁₎ , acquired at the previous time t, and read out from the memory 58,

Pι _W ^■ P ^{ZU ALm} = ^Lm W - ^Z "Vi) '^ i = K <0 ~ ^P K" + i)' ^ 2 = ^ 2 (.) - (., ₊ I) And

ΔR ₃ = R _{3 (h)} - R _{3 (/ I + 1)} performed. A comparison 64 is then carried out, in which the change in the radiometric measured value ALm = Lm _(tl) - Lm _{{ll + l) is} compared with the changes ΔR, .DELTA.R ₂ , .DELTA.R ₃ detected in the corresponding time interval and in which means of the calculated relationship ΔZ w = / (ΔR ,, ΔR ₂ , ΔR ₃ ) read out from the memory 60, it is checked whether the actually measured change ALm = Lm _(tl) - Lm _{{tl + X) is} a result of the calculated relationship ΔZw = / (ΔR ₁ , ΔR ₂ , ΔR ₃ ) resulting change. The values of the process parameters R 1, R ₂ , R ₃ measured for the time t _{1 + x} are loaded into the memory 58 and stand for the subsequent measurement time t, _{+ 2} as comparison values for determining the changes ΔR,, ΔR ₂ , ΔR ₃ available for the following period t _{l +} to t _{l + 2} .

If the actually measured change ALm = Lm _{ll) - Lm _{(+ X) of} the radiometric measured value Lm _(t) corresponds to the changes ΔR,, ΔR ₂ , ΔR _{3 of} the measured process parameters, it is assumed that there is no interference with the radiometric measurement system , The associated process variable L _{{ll + X) is} determined from the last measured radiometric measured value Lm _{(tl + X)} and applied to the bus line 22 connected to the process control system without an additional signal indicating a fault. The measured radiometric measured value Lm _{(tl + X)} is loaded into the memory 58 and is available for the subsequent measurement instant tl _{+ 2} as a comparison value for determining the change ALm for the period tl _{+ x} to t, ₊₂ .

If the change ALm = Lm _{ll) - Lm _{{ll + X) of} the radiometric measured value Lm _l) the changes ΔR,, ΔR ₂ , ΔR _{3 of} the non-radiometrically measured process parameters does not correspond to the corresponding time interval and the arithmetical relationship ALm = /(ΔR., ΔR ₂ , ΔR ₃ ), it is assumed that a fault in the radiometric measuring system, for example due to external radiation from a nearby gamma-graphic measuring system (see also FIG. 2), is present. In this case, by means of the known mathematical relationship ALm = / (ΔR ,, ΔR ₂ , ΔR ₃ ), a calculation 66 is carried out for the period t, to t _{l +} under consideration, which calculates a measured value Lc _{t for the time t _{l + x} _{+ γ)} returns. In practice, a change ΔZc ₍₊₁₎ , which is permissible for the relevant period according to the mathematical relationship ALm = f (AP _x , AP ₂ , AP _i _{), is} determined, so that a measured value Lc _{(tl + X)} from Lc _{{tl + X)} = Lm _{ll) + ALc _(lt ,, _{+1) is} calculated. The associated process variable! (., + -) is determined for this calculated radiometric measured value Lc _{(ll + X)} and, together with an additional signal 68 indicating a fault, is passed to the bus line 22 connected to the process control system. The calculated radiometric measured value Lc _{(ll +)} is loaded into the memory 58 and stands for the subsequent measurement time t _{l + 2} as a comparison value for determining the change ALm = Lc _{(ll + X)} - Lm _{(ll + 2)} for a subsequent period t, ₊₁ to t _{l + 2} are available.

At a subsequent time t _{l + 2} (and to further subsequent time points) method illustrated 4 runs the described and in Fig. According to the invention again from, wherein the place of the time t _{l + x} measured process parameters R _{1 (l +1)} , R _{2 (} ,, ₊₁₎ , R _{3 (} , _{l + 1)} those process parameters R, ₍ ,, ₊₂₎ , R _{2 (} „ _{+2) recorded} at the new point in time. R _{3 (.. + 2)} kick. The time indices of the individual steps of the procedure must be adjusted accordingly. The above-described determination 62 of the changes .DELTA.R, .DELTA.R ₂ , .DELTA.R ₃ is carried out accordingly for the new period under consideration.

The determination 62 of the change ALm in the measured value of the process variables for the period t _{l + x} to t _{l + 2} depends on whether a fault in the radiometric measuring system was previously determined or not. If there is no disturbance, the method runs as described above for the period t _{l + x} to t _{l + 2} to be considered. In the event of a fault, the calculated radiometric measured value Lc _{{tl + X) takes} the place of the measured measured value Lm _{(tl +)} , so that the change ALm of the radiometric measured value in the period from t _{l + x} to t _{l + 2} from ALm = Lc _{(tl + X)} - Lm _{(ll + 2) is} determined. Should the change ALm = Lc _{(tl + X)} - Lm _{{tl + 2)} determined for the period from t _{l + x} to t _{l + 2} not be the detected one If changes ΔR, ΔR ₂ , ΔR ₃ for the new period under consideration correspond to the known mathematical relationship ALm = / (ΔR ,, ΔR ₂ , ΔR ₃ ), then the radiometric measured value Lc _{{ll + 2)} for the time t _{l +2} with the aid of the mathematical relationship ALm = / (ΔR ,, ΔR ₂ , ΔR ₃ ) and the associated process variable Z (., ₊ 2) calculated and given to the output 50 together with the alarm signal 68.

Again, the actually measured process parameters R _{1 (/ I + 2)} , R _{2 (} " ₊₂₎ , R _{3 (} " ₊₂₎ and the measured value of the process variable, whether as the actually measured value Lm _{{ ll + 2)} or as calculated measured value Lc _{{tl + 2)} , stored in the memory 58 for further processing in subsequent measurements and kept ready.

In the previous description of the method for error suppression and compensation according to the invention shown in FIG. 4, it has been assumed that changes in the process parameters R 1, R ₂ , R ₃ for the period under consideration also result directly in a change in the measured value Lm show the process variables for this period. However, in the case where a change in a process parameter P by a possible delay time τ, which can also be τ = 0, delays a change in ALm = Lm _(tJ) - Lm _{(tJ + X) of} the radiometric measured value Lm _(l) , it is recommended in the method according to the invention to change the relevant process parameter, for example ΔR, for a time period corrected by the delay time τ from t _{j →} to t _{J + x} _ _τ for y ^' = 7, ..., /, i + 1, i + 2, .... to be used, especially if the mathematical relationship ALm = f (AP _x , AP ₂ , AP ₃ ) should depend on the period under consideration.

So it can happen that, as in the part of a conventional industrial process plant shown in FIG. 1, changes in the process parameter 'flow rate', which are recorded with the flow rate measuring device 26, are delayed by a certain time in a change in those with the radiometric measurement system Show 14 measured level measured value.

The method according to the invention does not change by taking into account the delay time τ, only the indices of the method shown in FIG. 4 are to be adapted accordingly. Proceed in the same way if there are different delay times with different process parameters. 5 illustrates in a flow chart a further preferred embodiment of the method according to the invention for evaluation, error suppression and compensation according to the invention, which largely corresponds to the method shown in FIG. 4 and described above and method steps. FIG. 5 also shows an example of a temporal section from an ongoing measuring operation for two successive times t ₁ and t _{1 + x} . As with the method shown in FIG. 4, the measured values P _{X (tl)} , R _{2 (} , ₍₎ , R _{3 (1)} and Lm _m (or Lc _(tl) stored for the time t _t in the case of a Disturbance) and the measured values R. ₍ ,, ₊₁₎ , R _{2 (r} , ₊₁₎ , R _{3 (/} , ₊₁₎ and Lm _{(tl + X)} measured at time t _{l + x make} a determination 62 of the respective Changes ALm = Lm _(tl) - Lm _{{tl + X)} and ΔR,, ΔR ₂ , ΔR ₃ instead. It is also checked here in a comparison 64 whether the change in the radiometric measured value ALm = Lm _{ll) - Lm _{{ll + X)} corresponds to the changes ΔR, .DELTA.R ₂ , .DELTA.R ₃ detected in the corresponding time interval in the sense of the from the Memory 60 reads the arithmetical relationship ALm = / (ΔR ,, ΔR ₂ , ΔR ₃ ) or not, ie whether or not there is a fault.

If no malfunction is found, the process variable _{(H + 1)} belonging to the radiometric measured value Lm _{{ll + X} _{) is} formed, and is passed to the bus line 22 via the output 50.

If, however, a malfunction is detected, a check 70 is carried out, in deviation from the method according to FIG. 4, in which a check is made as to whether the change in the radiometric measured value ALm is smaller in magnitude than a deviation δ from the arithmetical relationship ALm = previously predetermined as the maximum permissible / (ΔR ,, ΔR ₂ , ΔR ₃ ). If the change in the radiometric measured value ALm is less than δ and the amount is still within a tolerable variance range, the actually measured radiometric measured value Lm _{(tl + X) is} considered acceptable. As described above, the process variable J ₍ ,, ₊₁₎ belonging to the radiometric measured value Lm _{1 + X)} is then formed and passed to the bus line 22 via the output 50.

In the case where | ΔIm | > δ and the amount of change in the radiometric measured value ALm thus deviates by more than the amount allowed from the mathematical relationship ΔZ.m = / (ΔR ,, ΔR ₂ , ΔR ₃ ), becomes a fault accepted. As described above, a calculation 66 is now carried out using the known mathematical relationship ALm = / (ΔR ,, ΔR ₂ , ΔR ₃ ) for the period t until t _{l + x} under consideration, which calculates one for the time t _{l + x} Measured value Lc _{(l + X)} delivers. For this purpose, the associated process variable -. (., + 1) is determined and, together with an additional signal 68 indicating a fault, applied to the bus line 22 connected to the process control system.

According to the method according to FIG. 4, in the method according to FIG. 5 the measured value directed to the output 44, be it the calculated radiometric measured value Lcl _{+ X)} in the event of a fault or the actual measured measured value Lm _{{ll + X) is} loaded into the memory 58, where it is used for the subsequent measurement instant t _{l + 2} as a comparison value for determining the change ALm = Lc _{l + X)} - Lm _{(ll + 2)} or ALm = Lm _{{ll + X)} - Lm _{ll + 2) is available} for a subsequent period t, ₊₁ to t _{l + 2} .

In order to illustrate the simple manner in which the device according to the invention can be integrated into an existing, already installed plant for process measurement technology in the sense of retrofitting, FIG. 6 shows a conventional connection of a radiometric measurement system and other process parameters that are not recorded radiometrically serving measuring devices to a process control system shown schematically. For the sake of simplicity, the n already exemplified in FIG. 1 is assumed (see also FIG. 1 with the corresponding description text). As can be seen from FIG. 6, the evaluation electronics 20 of the radiometric measuring system 14, the flow measuring device 26 and the pressure measuring device 28 are usually connected directly to the bus line 22. The wiring itself is shown in Fig. 6 for a conventional so-called two-wire system, for example according to the so-called HARD Communication Foundation.

If, for example, the device 44 for error suppression and compensation according to the invention shown in FIG. 3 is provided in the form of a retrofit kit 72 (see FIG. 3 and the associated descriptive text), such a retrofit kit 72, such as 7, in the system for process measurement technology shown in FIG. 6, switch between the measuring devices 14 or 20, 26 and 28 and the bus line 22. The retrofit kit 72 preferably comprises a housing and not shown here housed therein the same modules and components as the device 44 for error suppression and compensation shown in FIG. 3. In a two-wire system according to the so-called HARD Communication Foundation, the inputs and outputs are connected in the manner shown in FIG. 7.

Claims

claims

1. A method for error suppression and compensation of interference signals (42) caused by gammagraphy in a radiometric measuring system (14), with which a process variable L _{(l) is} determined by means of a radioactive radiator (16) and a detector (18), which method includes the following steps:

a) In the ongoing measuring operation, for two successive times *> and ^{t, + i, the change} from the radiometric measured values ^(r,) and ⁽ " ⁺¹⁾ detected by the detector (18) at these times ^{~ (} ">) <" ⁺¹⁾ determined and by means of a predetermined mathematical relationship

ALm = / (ΔR,) _m j _te j _ner j _m corresponding time interval detected change

.DELTA.R ι = P κ, - ^{^r.)} - P ^{i (,} + ^ι-r) _e j not _nes first measured radiometrically

Process parameters R, = R _{1 (} _ _r) compared;

b) if the change ^{~ (} '° ⁽ " ^{+1) of} the radiometric measured value ⁽

ΔR = R - R of a previous change ^{1 1 (} " ^_r) K" ⁺ - ^.) Of the first process parameter R, = R, ₍ ,

Time interval and the calculative relationship ^Δ ^ ^{W =} ^(Δ) corresponds to, it is assumed that no interference of the radiometric measuring system is present, which is determined from the last measured radiometric measurement value ⁽ ^"+1), the associated process variable ^(" ⁺¹⁾ and without a additional one

Signal (68) indicating a fault is applied to a bus (22) connected to a process control system;

c) if the change ^{~ (} " ^{} (} " ^{+1)) of} the radiometric measurement ^w

ΔR = R - R of a previous change ' ^{1 (} " ^_r > - ⁽ -' ⁺ --- ^{■) of} the first non-radiometric process parameter R, = R _{1 (} ,. In the corresponding

Time interval and the mathematical relationship ^Δ ^ ^W = / (ΔR ₁ ) does not correspond, it is assumed that a disturbance of the radiometric

Measuring system (14) is present,

- Then, based on the previous change ΔR, = R, ₍ "_ _r) - R, ₍ " ₊ , _ _{r) of} the first process parameter R, by means of the computed arithmetic

Relationship ΔJ = / (ΔR,) for the time / _{/ +} , a radiometric measured value

Lc _{{l + l) is} calculated; - wherein the associated process variable Z (.. + i) is determined from the calculated radiometric measured value Lc _{(tl + X)} and, together with an additional signal (68) indicating a fault, is passed onto the bus (22) connected to the process control system; and

- Wherein in a subsequent, at a time t _{l + 2} detection of the change ΔR, = R _{1 (/} , ₊₁ _ _τ) - R _{1 (} " ₊₂ _ _{τ) of} the first non-radiometrically measured process parameter and the measurement of radiometric measured value Lm _{(ll + 2)} from this and the calculated radiometric measured value Lc _{{ll + X)} the change ALm = Lc _{{ll + X)} - Lm _{{tl + 2) is} determined and this in accordance with steps d) or e ) is used to determine whether there is still a fault in the radiometric measuring system (14).

2. The method according to claim 1, in which the following method steps are carried out before the radiometric measuring system (14) is started up: a) At least one non-radiometric measured value is measured for a measured value Lm ₍₁₎ by the detector (18) of the radiometric measuring system (14) and also monitored first process parameter R, = R _{1 (} , _ _r) identified, whose change ΔR, = P _{x J} _ _τ) - R _u , ₇₊ , _ _r) for arbitrary times t _} _ _τ and t _{] + x} _ and delayed by a possible delay time τ, which can also be τ = 0, leads to a change ALm = Lm _{lJ) - Lm _{(lJ + X) of} the radiometric measured value Lm _(l) ; and

b) from the changes ALm of the radiometric measured value Lm _(l) determined at different operating and process conditions and at different times t, as a result of changes ΔR, the non-radiometrically measured first process parameter, a mathematical relationship ALm = / (ΔR,) is formulated and stored ;

3. The method according to claim 1 or 2,

- Before the output of the signal indicating the malfunction of the radiometric measuring system (68) it is checked whether the amount of the change in the radiometric measured value ALm is smaller than a previously predetermined maximum deviation δ from the mathematical relationship ALm = f (AP _x ) and

- in which only in the case where \ ALm \ ≥ δ a signal (68) indicating the disturbance of the radiometric measured value is transmitted to the bus (22).

4. The method according to claim 1, 2 or 3, wherein the measured value Lm _{t) measured by the detector (18) of the radiometric system (14 _{) is} a measure of a fill level of a medium (12) in a container (10), a density of such a medium in a container or a separation layer of at least two phases can be one or more media in a container or pipe.

5. The method according to claim 4, wherein the first non-radiometrically measured process parameter R,

a pressure inside the container or in a pipe connected to the inside of the container,

6. The method according to claim 5,

- whereby several process parameters P _k (k = 1, 2, ....) are monitored, their change ΔR, = P _tte _ _Λ) - P _{kilJ + x →)} for any time _t] _ _τk and t ₇₊ , _ _Λ and delayed by a possible delay time τk, which can also be τk = 0, leads to a change ALm = Lm _(t]) - Lm _{{tJ + X) of} the radiometric measured value Lm _{l) ;

- where, based on measurements under different operating and process conditions, a mathematical representation of the dependence of the change in the radiometric measured value Lm _{t) on a change in each or more of the process parameters P _k to ALm = / (ΔR ,, ΔR ₂ , ... .) is formulated; and in the ongoing measuring operation according to steps c) to e) according to claim 1, by means of the calculated relationship ALm = f (AP _x , AP ₂ , ....), it is checked whether there is a fault in the radiometric measuring system (14).

7. A device (44) for suppressing errors and compensating for interference signals (42) caused by gammagraphy in a radiometric measuring system (14) with a radioactive radiator (16) and a detector (18), which device comprises:

- an input (46) for measured values Lm _{(l) of} a process variable Z ₍ ,) measured by the detector (18) - An input (46) for at least one non-radiometrically measured and also monitored first process parameter R. = P _{x (l} _ _τ) , the change of which is delayed by a possible delay time τk, which can also be τ / c = 0 ALm = Lm _(lJ) - Lm _{(t] + X) of} the radiometric measured value Lm _{l) leads;

- An output (50) which is connected to a process control system, and

- an evaluation and error compensation device (48),

- The change in the running measuring operation for two successive times t _t and t _{l + x} from the radiometric measured values Lm _(ll) and Lm _{(ll + X)} detected at these times by the detector (18) ALm = Lm _w - Lm _{ll + X)} determined and not radiometrically by means of the mathematical relationship ALm = / (ΔR,) with a change ΔR, = P _{X (} _ _τ) - R, ₍ , ₊₁ _ _{T) recorded} in the corresponding time interval measured process parameter R, = R, ₍ , _ _{r) is} compared; - the, if the change ALm = Lm _(h) - Lm _{(u +) of} the radiometric measured value L ₍ a previous change ΔR, = R _{1 (/ (} _ _r) - R _{1 (/ I + 1} _ _{r) of} the first Process parameter R, = R, ₍ , _ _r) measured in a non-radiometric manner in the corresponding time interval and having a predetermined mathematical relationship ALm = f (AP _x ), the associated process variable Z ₍ “ ₊₁₎ from the last measured radiometric measured value Lm _{{tl +} ₎ determined and this is given without an additional signal (68) indicating a fault to the output and to a bus (22) connected to a process control system;

- the, if the change ALm = Lm _(tl) - Lm _{{ll + X) of} the radiometric measured value Lm _{{t] of} a previous change ΔR, = R _{1 (} "_ _r) - R, _{(I +} , _ _{r) of} the first Process parameter R, = R _{1 (/} _ _r) not measured radiometrically in the corresponding time interval and does not correspond to the mathematical relationship ALm = f (AP _x ), detects a fault in the radiometric measuring system (14),

- Then, based on the previous change ΔR, = P _{x (ll} _ _τ) - R _{1 (/ 1 + 1} _ _{r) of} the first process parameter R, by means of the detected mathematical relationship ALm = f (AP _x ) for the point in time t _{l +} a radiometric measured value Lc _{u + X) is} calculated;

- Whereby the associated process variable Z, ₍ .. ₊ i) is determined from the calculated radiometric measured value Lc _{{tl + X)} and this, together with an additional signal (68) indicating a fault, on the output (50) and on the one with the process control system connected bus (22) there; and

- In a subsequent detection of the change ΔR, = R, _{(/; +} , _ _r) - R _{1 (/} , ₊₂ _ _{r) of} the first non-radiometrically measured process parameter and the measurement, which takes place at a time t _{l + 2} the change of the radiometric measured value Lm _{(ll + 2)} from this and the calculated radiometric measured value Lc _{(ll + X)} ALm = Lc _{{ü + X)} - Lm _{{tl + 2)} determined to determine whether there is still a fault in the radiometric measuring system (14).

8. The device according to claim 7, in which, before the signal (68) indicating the malfunction of the radiometric measuring system is output, it is checked whether the change in the radiometric measured value ALm is smaller than a change δ = predetermined beforehand as the maximum permissible ; and

- in which only in the case where ALm ≥ δ the signal (68) indicating the disturbance of the radiometric measurement signal is given to the bus (22).

9. Device according to one of claims 7 or 8, wherein the measured value Lm _(t) measured by the detector (18) of the radiometric system (14 _{) is} a measure of a fill level of a medium (12) in a container (10), a Density of such a medium in a container or a separation layer of at least two phases can be one or more media in a container or tube.

10. The device according to claim 9, wherein the first non-radiometrically measured process parameter R,

11. The device according to claim 9, on the input (46) several

Process parameters P _k (k = 1, 2) are given, their change

ΔP _k = P _k - * - Pn _ι , ₊ ι- * ₎ for any time _t] _ _τk and t _{] +} _ _Λ and by a possible delay time τk, which can also be τk = 0, delays to a change ALm = Lm _(lJ . - Lm _{(lJ + X) of} the radiometric measured value Lm _(l) leads; in the ongoing measurement operation from the evaluation and error compensation device according to claim 7 by means of a predetermined mathematically determined relationship ALm = f (AP _x , AP ₂ , ....) it is checked whether there is a fault in the radiometric measuring system (14).

12. Device according to one of claims 7 to 11, which is part of an evaluation electronics to be assigned to the radiometric measuring system (14).

13. Device according to one of claims 7 to 11, which is accommodated in a housing independent of the detector (18) of the radiometric measuring system (14).

14. Device according to one of claims 7 to 13, which is connected in an already installed radiometric measuring system in the sense of a retrofit kit (72) between the measuring system (14) and the process control system.

15. The device according to one of claims 7 to 14, in the arithmetic context for representing the dependence of the change in the radiometric measured value Lm _(t . On a change in each or more of the non-radiometric process parameters P _k to

ALm = f (AP _x , AP ₂ , ....) is obtained on the basis of measurements under various operating and process conditions.