Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1994-07-18
1998-02-10
Hofsass, Jeffery
Communications: electrical
Condition responsive indicating system
Specific condition
340618, 340620, 73290V, 73290R, 310318, 310319, G08B 2100
Patent
active
057173834
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for determining and/or monitoring a predetermined level of contents in a container, comprising a sensor which is so arranged on the container at the contents level to be monitored that it comes into contact with the contents when the same reach the predetermined level, an exciting arrangement which excites the sensor to mechanical vibrations at its natural resonant frequency, and an evaluating circuit for causing indicating and/or switching operations dependent on whether the frequency of the mechanical vibrations of the sensor is above or below a switching frequency.
A device of this type is for example disclosed in the German patent specification 3,336,991. In the case of this known device the sensor possesses two oscillating rods, which are mounted at a distance apart on a diaphragm and are caused to perform opposite vibrations transversely in relation to their longitudinal direction. However devices of this type have also been suggested in the case of which the sensor comprises only a single oscillating rod or, according to another design, are made entirely without oscillating rods. In all cases the manner of functioning of the device is based on the principle that the natural resonant frequency of the sensor changes when the sensor comes into contact with the contents of the container. When the sensor is covered with the contents, its natural resonant frequency is lower than when the sensor is clear of the contents. The switching frequency is so selected that it is between the lower natural resonant frequency with the sensor covered and the higher natural resonant frequency when the sensor is cleared. When the evaluating circuit determines that the frequency of oscillation of the sensor is below the switching frequency, this will be an indication that the sensor is covered by the container contents, i.e. the contents level in the container is above the monitored level. If on the contrary the evaluating circuit determines that the oscillation frequency of the sensor is above the switching frequency, this will be an indication that the sensor is clear of the container contents, i.e. the contents level in the container is below the monitored level. Sensors of this type are more especially suitable for monitoring the level of liquids, since in such case the change in the natural resonant frequency, which occurs on changing over from the free to the covered state and vice versa, can always be distinctly detected.
Owing to manufacturing conditions such sensors have different resonant frequencies. Since on the other hand in particular in the case of liquids of low density the natural resonant frequencies of the covered and uncovered sensor are relatively close together, the switching frequency for each sensor must be individually set. The evaluating circuit is then necessarily matched with the sensor; if it is to be employed in connection with another sensor, it must be rematched to suit the other sensor, for which purpose the natural resonant frequency of the other sensor must be known. Such matching may not normally be readily performed on the site of application of the equipment. This impairs the performance of repair and servicing operations for the equipment.
An object of the invention is the provision of an apparatus of the type initially mentioned which permits to employ each evaluating circuit with any desired sensor without an individual matching of the evaluating circuit being necessary to suit the respective sensor.
In accordance with the invention this object is attained in that an electrical circuit element is associated with the sensor, which electrical circuit element has a characteristic parameter whose value bears an unambiguous relationship to the natural resonant frequency of the sensor, and that in the evaluating circuit the switching frequency is set in accordance with the value of the characteristic parameter of the electrical circuit element.
During the manufacture of the device in accordance with the invention all evaluating circuits are made identica
REFERENCES:
patent: 2927301 (1960-03-01), Booth et al.
patent: 3625058 (1971-12-01), Endress et al.
patent: 4540981 (1985-09-01), Lapetina et al.
patent: 4594584 (1986-06-01), Pfeiffer et al.
patent: 4594891 (1986-06-01), Benz et al.
patent: 4864856 (1989-09-01), Ichikawa et al.
patent: 5060484 (1991-10-01), Bush et al.
patent: 5155472 (1992-10-01), Dam
patent: 5191316 (1993-03-01), Dreyor
patent: 5264831 (1993-11-01), Pfeiffer
patent: 5400376 (1995-03-01), Trudeau
patent: 5408168 (1995-04-01), Pfandler
PCT/EP93/02557 Search Report, Jun. 1, 1994.
Dreyer Volker
Pfandler Martin
Schrock Arthur
Endress & Hauser GmbH & Co.
Hofsass Jeffery
Mannava Ashok
LandOfFree
Device for determining and/or monitoring a predetermined level o does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for determining and/or monitoring a predetermined level o, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for determining and/or monitoring a predetermined level o will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2080318