Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1991-11-01
1995-11-21
Peng, John K.
Communications: electrical
Condition responsive indicating system
Specific condition
340635, 340679, 388820, 388921, G08B 2100
Patent
active
054691486
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a frequency monitoring device for monitoring a frequency for longer lasting deviations from a desired value.
Such frequency monitoring devices are required for the most varied purposes. One example is the monitoring of the frequency in a linked system. If the frequency has deviated from its desired value for a given time a correction must take place, but not before this.
Another use is in the field of communications and computers. In this case the equipment is ventilated with the aid of so-called equipment fans, so as to dissipate the heat therefrom to the outside. The prerequisite is that the fans operate at the given speed, e.g. 2000 min.sup.-1 (=2000 r.p.m.). If the speed of such a fan briefly drops below this level, e.g. for 5 seconds, this is not normally harmful. However, if it takes place for a longer time, cooling is no longer reliably ensured, because there is e.g. bearing damage in the fan and then an alarm signal must be issued, so that the fan can be replaced.
US-A-4 544 852 discloses an analog technology monitoring circuit, which fulfils these requirements and which has proved satisfactory in practice. This circuit responds to deviations from the desired speed, but only after a delay of e.g. 10 seconds. Therefore it is e.g. possible for an equipment fan to start without giving an alarm. An alarm is only triggered if the speed drops below a predetermined value for more than 10 seconds. However, this proven circuit suffers from the disadvantage that relatively large components are required for it and in particular large RC elements. However, equipment fans are very compact and have standardized external dimensions and consequently it is difficult to house such components in such an equipment fan. Deviations from the desired times can also result from the tolerances of the individual components.
The problem of the invention is therefore to bring about an improvement, particularly with respect to the construction volume and/or precision.
In a frequency monitoring device for monitoring a frequency for longer lasting deviations from a desired value, according to the invention this problem is solved in that a digital comparator is provided for comparing the cycle duration of said frequency with a predetermined time, said comparator being activated by a storage element in the case of a deviation from the predetermined time and triggers the emission of at least one deviation signal and that said at least one deviation signal can be supplied to a monitoring means, which monitors the time of the occurrence of said deviation signal and deactivates the storage element again if said time interval is smaller than the predetermined time interval. Thus, a very compact device is obtained, which can e.g. be constructed as an IC and which operates with digital precision.
With particular advantage a timer is associated with the storage element and triggers an alarm signal on exceeding a predetermined storage element activation time interval. This alarm signal makes it possible to e.g. switch off an equipment, or a signal of random type can be triggered.
Further details and advantageous developments of the invention are described in greater detail hereinafter relative to non-limitative embodiments, together with the subclaims, as well as the drawings, wherein show:
FIG. 1 a circuit diagram of a first embodiment of the inventive device.
FIG. 2 a detail of FIG. 1.
FIGS. 3 and 4 diagrams for illustrating the operation of the device according to FIG. 1.
FIG. 5 a circuit diagram of a second embodiment of an inventive device.
FIG. 6 a view of the comparator used in the device of FIG. 5.
FIG. 7 a view of the multiplexer used in FIG. 6 and a table of digit
ally preselectable release or trigger speeds.
FIG. 8 a view of a means for switching from two to four pole motors in the device of FIG. 5.
FIG. 1 shows the construction of a first embodiment of an inventive frequency monitoring device 20. It operates with three binary counters 21,22, 23, e.g. of type CD 4060 B as shown in FIG. 2, in order to faci
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patent: 4507591 (1985-03-01), Kelleher
patent: 4513233 (1985-04-01), Giammarrusco
patent: 4521894 (1985-06-01), Moffat
patent: 4544852 (1985-10-01), Moosman et al.
patent: 4695779 (1987-09-01), Yates
C. Veloyudhan et al., "An Electronic Frequency Deviation Transducer", International Journal of Electronics, vol. 52, No. 3, Mar. 1982, pp. 283-289 (Taylor & Francis Ltd.).
Intel Corp. Component Data Catalog, Jan., 1982 "8253/8253-5 Programmable Interval Timer" and 8254 Programmable Interval Timer.
Baumann Hans-Martin
Muller Rolf
Lefkowitz Edward
Papst Licensing GmbH
Peng John K.
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