Method for determining a remaining operating period of a detector unit

Abstract

The present disclosure relates to a method for determining a remaining operating period of a detector unit for a radiometric, density- or fill-level measuring device. The detector unit includes a photomultiplier. In such method, the control voltage of the photomultiplier is registered over at least one predetermined time period, a time rate of change function is ascertained based on control voltage registered during the predetermined time period, and the remaining operating period until reaching a maximum control voltage is calculated by means of the time rate of change function and a current control voltage, which is present at the current operating time. The method of the present disclosure permits approximation of the remaining operating period of the detector unit and, thus, timely learning of when required maintenance measures, especially aging related replacement of the photomultiplier, must be performed.

Claims

1. A method for determining a remaining operating period of a detector unit of a radiometric, density or fill level measuring device, the method comprising: providing a radiometric, density or fill level measuring device including a detector unit, which includes a photomultiplier having a controllable amplification factor, and a control-evaluation unit configured to control the photomultiplier using a control voltage such that the amplification factor is constant; registering the control voltage over a predetermined time period; ascertaining a time rate of change function based on the control voltage registered during the predetermined time period; and calculating a remaining operating period of the detector unit using the time rate of change function and a current control voltage at a current operating time, wherein the remaining operating period is a period until the current control voltage exceeds a maximum control voltage.

2. The method of claim 1, wherein the time rate of change function is ascertained using a regression of the control voltage over the predetermined time period.

3. The method of claim 2, wherein a least squares method is used for the regression and/or for ascertaining a suitable regression type.

4. The method of claim 2, further comprising creating a report when at least one parameter of the time rate of change function changes beyond a predefined limit value or when the regression type of the rate of change function changes.

5. The method of claim 1, wherein the control voltage is registered temperature compensated.

6. The method of claim 1, wherein the predetermined time period extends over an entire operating time of the detector unit to the current operating time.

7. The method of claim 1, wherein the predetermined time period is constant and ends with the current operating time.

8. The method of claim 1, wherein the registering of the control voltage is performed at least within the predetermined time period in predefined time intervals.

9. The method of claim 1, wherein the predefined time intervals are greater than one day.

10. The method of claim 1, further comprising displaying the calculated remaining operating period via a display unit.

11. A detector unit for a radiometric, density or fill level measuring, comprising: a scintillator; a photomultiplier optically coupled with the scintillator and having a controllable amplification factor; and a control-evaluation unit configured to: control the photomultiplier using a control voltage such that the amplification factor is constant; register the control voltage over a predetermined time period; ascertain a time rate of change function based on the control voltage registered during the predetermined time period; and calculating a remaining operating period of the detector unit using the time rate of change function and a current control voltage at a current operating time, wherein the remaining operating period is a period until the current control voltage exceeds a maximum control voltage.

12. The detector unit of claim 11, further comprising a display unit configured to display the calculated remaining operating period.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will now be explained based on the appended drawing, the two figures of which show as follows:

(2) FIG. 1 shows an arrangement of a detector unit of the present disclosure at a container, and

(3) FIG. 2 shows a schematic diagram for calculating the remaining operating period according to the disclosure.

DETAILED DESCRIPTION

(4) Shown in FIG. 1 is a detector unit 1 of the invention for a radiometric, density- or fill-level measuring device 2. Besides the detector unit 1, the density- or fill-level measuring device 2 includes a radioactive radiation source 3. FIG. 1 shows how the radiometric, density- or fill-level measuring device 2 is typically arranged at a container containing a fill substance, whose fill level or density is to be determined.

(5) The radiation source 3 is placed such that it sends radioactive radiation in the direction of the container containing the fill substance to be measured. In the case of fill level measurement, the radioactive radiation is differently greatly absorbed as a function of the fill level, so that after passage through the container a corresponding intensity of the radioactive radiation strikes the detector unit 1. In support of this, the detector unit 1 is arranged with reference to the radiation source 3, for instance, on the oppositely lying side of the container, such that it is located roughly in the center of the radiation lobe of the radiation source 3. In the case of density measurement, the radiation intensity at the detector unit 1 results based on the density of the fill substance (at least in the case of vertically arranged containers, the proviso for this is that in the case of non-gaseous fill substance the fill level exceeds the heights, to which the radiation source 3 and the detector unit 1 extend).

(6) The detector unit 1 includes a scintillator 11 for receiving the radioactive radiation and for converting it into light in the optical- or near infrared region. For transmitting the light, the scintillator 11 is coupled (for example, via a window transparent for the light) to a photomultiplier 12. Via a control-evaluation unit 13 arranged (with reference to the scintillator 11) on the rear side of the photomultiplier 12, light power incoming to the photomultiplier 12 is, on the one hand, evaluated. On the other hand, the control-evaluation unit 13 controls the amplification factor A of the photomultiplier 12 by means of a control voltage V.sub.a, which can be a number of hundred volts to more than a kV. In such case, the amplification factor A of the photomultiplier 12 is that factor, with which the light power incoming to the photomultiplier 12 is amplified into an electrical output power. The control of the photomultiplier 12 by means of the control voltage (V.sub.a) proceeds in such a manner that the amplification factor (A) is held as constant as possible (apart from a possible additional compensating of the temperature effect) over the operating time t.sub.B of the detector unit 1.

(7) For electrical connection of the detector unit 1, the control-evaluation unit 13 is, additionally, connectable (for example, via an electrical cable connection, such as a multipoled plug) to a superordinated unit, for example, a process control room.

(8) Depending on field of application, the detector unit 1 can meet certain explosion protection specifications. This can occur, for example, by encapsulating the detector unit 1 by means of a corresponding pressure resistant housing (especially according to the series of standards EN 60079-1.

(9) The diagram of FIG. 2 illustrates the method of the invention, by means of which the probable remaining operating period t.sub.B,r of the detector unit 1 can be calculated (starting from its current operating time t.sub.B,a): The abscissa of the chart gives the progressing operating time t.sub.B of the detector unit 1, while the ordinate provides the required control voltage V.sub.a. As can be seen from the diagram, the control voltage V.sub.a from the control-evaluation unit 13 must be increased with increasing operating time t.sub.B, in order to keep the amplification factor A of the photomultiplier 12 constant. The reason is its aging behavior. Permitted to be applied to the photomultiplier 12, however, is, at most, a maximum control voltage V.sub.a,max. This limit can, on the one hand, result from the photomultiplier 12 itself. On the other hand, the limit can, however, also be brought about by explosion protection specifications that need to be met.

(10) According to the invention, in the vicinity of the operating time t.sub.B, the control voltage V.sub.a is registered over a predefined time period dt. Thereupon, a time rate of change function dV.sub.a/dt is ascertained based on control voltage V.sub.a registered over the predetermined time period dt. Both the registering and the ascertaining are performed by the control-evaluation unit 13 in the case of the example of an embodiment shown in FIG. 1. In the schematic diagram of FIG. 2, ascertainment of the rate of change function dV.sub.a/dt occurs based on a linear regression of registered control voltage V.sub.a. The so obtained rate of change function dV.sub.a/dt is applied, using the current control voltage V.sub.a,a, in order to calculate a probable remaining operating period t.sub.B,r until the reaching of the maximum control voltage V.sub.a,max.