METHOD FOR FILL LEVEL MEASUREMENT

Abstract

Disclosed is a method for measuring a fill level of a fill substance in a container. The method includes: transmitting a first signal toward the fill substance; receiving a first received signal after reflection of the first signal in the container; transmitting a second signal toward the fill substance, wherein the second signal has at least one defined property deviating from the first signal; receiving a second received signal after reflection of the second signal in the container; ascertaining a first fill level value based on the first received signal and a second fill level value based on the second received signal; and determining the first fill level value or the second fill level value as fill level when the first fill level value and the second fill level value agree. In this way, the fill level is determined in redundant manner.

Claims

1-12. (canceled)

13. A method for measuring a fill level of a fill substance in a container, the method comprising: transmitting a first signal in a direction of the fill substance; receiving a corresponding first received signal after reflection of the first signal in an interior of the container; transmitting a second signal in the direction of the fill substance, wherein the second signal has at least one defined property deviating from the first signal; receiving a corresponding second received signal after reflection of the second signal in the interior of the container; ascertaining a first fill level value based on the first received signal and ascertaining a second fill level value based on the second received signal; and determining the first fill level value or the second fill level value as the fill level when the first fill level value and the second fill level value agree.

14. The method as claimed in claim 13, further comprising: outputting a failure signal when the first fill level value and the second fill level value do not agree.

15. The method as claimed in claim 13, further comprising: calculating a difference value by subtracting the first fill level value from the second fill level value when the first fill level value and the second fill level value do not agree.

16. The method as claimed in claim 13, wherein the second signal is transmitted with a power that differs from a power of the first signal.

17. The method as claimed in claim 13, wherein the second signal is transmitted with a frequency that differs from a frequency of the first signal.

18. The method as claimed in claim 13, wherein the first signal and the second signal are both radar signals.

19. The method as claimed in claim 18, wherein the first signal is transmitted according to the FMCW principle, and the first fill level value is determined based on the FMCW principle, and wherein the second signal is transmitted according to the pulse travel time principle, and the second fill level value is determined based on the pulse travel time principle.

20. The method as claimed in claim 13, wherein the first signal is transmitted as a radar signal, and wherein the second signal is transmitted as an ultrasonic signal.

21. The method as claimed in claim 13, wherein the first signal and the second signal are both ultrasonic signals.

22. The method as claimed in claim 13, wherein the first signal and/or the second signal are/is optical.

23. A radar-based, fill level measuring device, comprising: a signal production unit designed to transmit a first signal and a second signal, in each case, as a radar signal in a direction of the fill substance; a receiving unit designed to receive after reflection of the first signal in an interior of a container, a corresponding first received signal and further designed to receive after reflection of the second signal in the interior of the container, a corresponding second received signal; and an evaluating unit, configured to: ascertain a first fill level value based on the first received signal; ascertain a second fill level value based on the second received signal; and output the first or second fill level value as the fill level when the first fill level value and the second fill level value agree.

24. The fill level measuring device as claimed in claim 23, further comprising: an interface by means of which the first fill level value, the second fill level value, and/or the fill level is transmittable.

Description

[0029] Based on the appended drawing, the invention will now be explained in greater detail. The sole figure of the drawing shows as follows:

[0030] FIG. 1 a typical arrangement of a radar- or ultrasonic based fill level measuring device.

[0031] For providing a basic understanding of the invention, FIG. 1 shows a typical arrangement of a radar- or ultrasonically based fill level measuring device 1 mounted on a container 2. Located in the container 2 is a fill substance 3, whose fill level L is to be determined by the fill level measuring device 1. To this end, the fill level measuring device 1 is mounted on the container 2 at a location above the maximum allowable fill level L. Depending on field of application, the installed height h of the fill level measuring device 1 can amount to more than 100 m above the container floor.

[0032] As a rule, the fill level measuring device 1 is connectable via an interface 11, which is based on a corresponding bus system, such as, for instance, “Ethernet”, “PROFIBUS”, “HART” or “wireless HART”, to a superordinated unit 4, for example, a process control system, a decentral database or a handheld device, such as a mobile radio device. In this way, on the one hand, information with reference to the operating condition of the fill level measuring device 1 can be communicated. However, also the fill level L can be transmitted via the interface 11, in order, in given cases, to control incoming or outgoing flows of the container 2.

[0033] Independently of the implemented measuring principle, the fill level measuring device 1 is so developed that it transmits corresponding signals S.sub.1, S.sub.2 from an antenna 12 in the direction of the fill substance 3. In such case, the signals S.sub.1, S.sub.2 are, depending on signal type (radar, ultrasound) and the implemented measuring method (pulse travel time or FMCW), generated in a corresponding signal production unit of the fill level measuring device 1.

[0034] On the surface of the fill substance 3, the transmitted signals S.sub.1,2 are reflected, so that the corresponding, received signals E.sub.1,2 are received by a receiving unit of the fill level measuring device 1 after a corresponding signal travel time. The fill level L can be determined from the received signals E.sub.1,2, since the signal travel time of the signals S.sub.1,2, E.sub.1,2 depends according to d=h−L on the distance d of the fill level measuring device 1 from the fill substance surface. Accordingly, an evaluating unit of the fill level measuring device 1 designed for this determines the fill level L based on the received signals E.sub.1,2.

[0035] Depending on character of the fill substance 3 or condition of the fill level measuring device 1, the fill level L can, in given cases, not be determined correctly with sufficient safety, for example, when due to chemical processes in the container 2 a foam formation occurs. Also, an accretion formation on the antenna 12 of the fill level measuring device 1 can, depending on type of the transmitted signal S.sub.1, S.sub.2, prevent a correct fill level measurement. In order that the fill level measuring device 1 can have a high degree of device safety, for example, corresponding to “Safety Integrity Level 3 (SIL3)” conforming to the standard IEC61508, the fill level measuring device 1 must, however, at least be able to output a failure message, when the ascertained fill level L is not valid.

[0036] In order to assure this, according to the invention, two signals S.sub.1, S.sub.2 with mutually differing properties are transmitted by the fill level measuring device 1. In such case, it is not relevant within the scope of the invention, whether the first signal S.sub.1 is transmitted simultaneously with, or alternately to, the second signal S.sub.2. Based on each of the two signals S.sub.1, S.sub.2, the fill level measuring device 1 receives separate received signals E.sub.1, E.sub.2, such that, based on each of the at least two different received signals E.sub.1, E.sub.2, separate fill level values are determined. When the first fill level value, which is ascertained based on the first received signal E.sub.1, agrees with the fill level value based on the second received signal E.sub.2, such fill level value is output as valid fill level L. Because of the transmitting of the signals S.sub.1, S.sub.2 of the invention with different properties, the fill level measuring device operates, thus, redundantly. In the unsafe case, when the first fill level value does not agree with the second fill level value, the fill level measuring device 1 can, for example, output a corresponding failure message through the interface 11 or display such on a display.

[0037] The deviation of the properties according to the invention between the two signals S.sub.1, S.sub.2 to be transmitted can be achieved in different ways. Thus, for example, the first signal S.sub.1 can be radiated as a radar signal, while the second signal S.sub.2 is transmitted as an ultrasonic signal. The two signals S.sub.1, S.sub.2 can also be transmitted as radar signals, wherein in the case of the first (received-) signal S.sub.1, E.sub.1, and thus for ascertaining the first fill level value, the FMCW method is applied, while the second signal S.sub.2 is transmitted with pulse shape, so that the fill level measuring device 1 ascertains the second fill level value based on the pulse travel time method.

[0038] Independently of the implemented signal type or the applied measuring method, the signals S.sub.1, S.sub.2 can, however, also be produced only with differing transmitting powers and/or differing transmitting frequencies, in order to produce redundancy. Another option would be to transmit one of the two signals S.sub.1, S.sub.2 as a laser signal and to ascertain the corresponding fill level value by means of interferometry or another, travel time method.

[0039] Based on the method of the invention, the fill level measuring device 1 can, additionally, be supplemented in such a way that it subtracts the fill level value ascertained by the first signal S.sub.1, E.sub.1 from the second fill level value and, as a result, calculates a difference value, when the first fill level value and the second fill level value lie significantly apart. This can be an indicator of foam formation, such that the difference value represents the foam thickness, or an interface thickness between two phases of the fill substance. The ascertained difference value can, in this case, in turn, be output via the interface 11 or a possible display of the fill level measuring device 1.

LIST OF REFERENCE CHARACTERS

[0040] 1 fill level measuring device

[0041] 2 container

[0042] 3 fill substance

[0043] 4 superordinated unit

[0044] d measured distance

[0045] E.sub.1, E.sub.2 received signals

[0046] h installed height, or measuring range

[0047] L fill level

[0048] S.sub.1, S.sub.2 transmitted signals