GB2320763A

GB2320763A - Monitoring device

Info

Publication number: GB2320763A
Application number: GB9725025A
Authority: GB
Inventors: Paul Radmall; John Goldthorp
Original assignee: Rako Products Ltd
Current assignee: Rako Products Ltd
Priority date: 1996-11-29
Filing date: 1997-11-26
Publication date: 1998-07-01
Also published as: GB9624853D0; GB9725025D0

Abstract

A monitoring device comprises means for monitoring a signal and providing an indication when the signal level is above and/or below a predetermined range of values. The indiction provided may take the form of one or more visual and/or audible device. Data communication to and from the device may be implemented via radio transmissions or power supply line telemetry which may be used for remote programing of the device. Encoded signalling may be used to identify a particular device during such communication. The device may include an audible indication device with a piezoelectric element and an associated resonator with holes which are of a size which prevent water ingress. The device may be included within an electrical plug or socket termination. The device may monitor voltage or current or other signals from transducers and may be energised by a signal dependent or independent of the signal to be monitored.

Description

MONITORING DEVICE The present invention relates to a monitoring device. Such a device can be used to give an indication that a measured quantity, such as a supply voltage falls outside an acceptable range.

In some applications, such as the formation of a conveyor arrangement from a series of individual conveyor units, the long cable run may cause an unacceptable voltage drop to one or more of the units. This may result in poor performance. It is desirable to have a warning that the supply voltage has fallen outside an acceptable range of values.

According to the present invention there is provided a monitoring apparatus, comprising monitoring means for monitoring at least one input signal representative of a physical quantity and for indicating when the at least one physical quantity falls outside of an acceptable range of values, and an output device responsive to the monitoring means for indicating that the at least one physical quantity is outside the acceptable range.

Preferably the monitoring device is arranged to monitor a voltage, such as a supply voltage.

However other quantities such as current flowing in a conductor, magnetic field strength, temperature, illumination level, weight, or flow rate may be monitored.

The output device may provide one or more of a visual, audible or electrical indication of the voltage being out of range. A visual indicator may be a lamp, a light emitting diode, or a high intensity strobe light. An electrical indication may be a radio signal to a monitoring unit. Alternatively a signal may be transmitted along the power supply conductors which are being monitored by a voltage monitoring device. An encoded signal may be sent which uniquely identifies which monitoring device within a series of monitoring devices has detected an out of range condition. The electrical indication may be monitored by a central station which sets an alarm to takes some other action in response to the electrical indication.

Preferably the monitoring device has an audio output element and emits an audible signal in response to an out of range condition.

Advantageously, the audio output element is coupled to an acoustic resonator. The resonator may, for example, be a tuned volume or a Helmholtz resonator. The resonant frequency of the acoustic resonator and the operating frequency of the audio output element are substantially the same, or set such that they are harmonically related.

Advantageously, an output region of the resonator comprises at least one hole. In a preferred arrangement a plurality of holes are provided. The diameter of the or each hole may be selected such that the surface tension of water inhibits the ingress of water into the resonator. However, in the event that water does enter the resonator volume, the holes enable water to escape from the resonator by evaporation. Furthermore, the provision of a plurality of holes enables the output element to be heard if it is partially occluded, for example by debris.

Preferably the monitoring device is remotely programmable such that the acceptable ranges can be set remotely.

Preferably, the monitoring device is a voltage monitoring arrangement that derives its own power supply from the supply that it is monitoring. The voltage monitoring arrangement may include an averaging or timing circuit such that the alarm is only activated if the voltage remains outside the acceptable range for longer than a predetermined period.

Alternatively the alarm may sound when a product of the excursion outside the predetermined range and time exceeds a threshold. Advantageously, the alarm may include a temporary power store such that the alarm can continue to sound in the event of total supply failure.

Preferably, the monitoring device is included within a cable termination. The device may be included within a male cable termination (i.e. a plug) or a female termination (i.e. a socket).

It is thus possible to provide an audible out of range voltage alarm suitable for use in extension cables, control boxes, generators, transformer arrangements and conveyor systems, amongst other things.

The present invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a cable terminator incorporating a voltage waming device constituting a first embodiment of the present invention; Figure 2 schematically illustrates the resonator arrangement in greater detail; Figure 3 is a plan view of the end of the resonator; and Figure 4 is a schematic diagram of the alarm circuit.

The arrangement shown in Figure 1 comprises a plastic male plug body 2 which is intended, in use, to be connected to the remote end of an extension cable (i.e. the end electrically furthermost from the power supply). The plug 2 includes connector pins 4 for making electrical connection with a socket of the extension cable, a circuit board 6 carrying a voltage monitoring arrangement, and an audio output device held in a cap 8.

The cap 8 has a circular sleeve 10 which, in use, engages with a corresponding sleeve 12 to hold the cap attached to the plug body 2.

The cap contains a piezoelectric transducer disc 14 which is held in position by a retaining ring 16. An aperture plate 18 forms an outwardly facing face of the cap 8. The aperture plate and the piezoelectric transducer disc define a cavity 20 therebetween. The cavity is coupled to the surrounding environment via a plurality of holes 19 in the aperture plate. The front face of the aperture plate is illustrated in Figure 3. In the embodiment, forty-nine holes are provided in a seven column by seven row matrix. Each hole has a diameter of lmm. Such an arrangement can form a Helmholtz resonator. This gives rise an effective increase in the strength of the audible signal. The holes are sufficiently small to inhibit the ingress of water into the resonator volume 20, by virtue of utilizing the surface tension of water which tends to bridge the holes rather than enter them.

However, if water does enter the cavity 20, for example, due to condensation, the series of holes provide sufficient ventilation for the water to escape by evaporation. The front face of the piezoelectric transducer disc may contain a protective layer (not shown) to prevent moisture damage. Alternatively a waterproof membrane may be included within the cavity 20.

Figure 4 schematically illustrates the circuit of a voltage warning device constituting an embodiment of the present invention. A power supply unit 30 is connected to the supply rails 33 and 34 which are being monitored. The power supply unit 30 generates a stabilised supply which is provided to operate a measurement circuit 32 and an integrator and output stage 36. The power supply unit 30 may be arranged to accommodate wide fluctuations in the supply voltage on the rails 33 and 34. The precise implementation of the supply 30 is a matter of design choice, and need not be described further. The measurement circuit 32 is also connected to the supply rails 33 and 34. The measurement circuit 32 may be implemented as an under voltage and/or over voltage detector, or simply as an under voltage detector (as shown). In the event that the potential difference between the supply rails 33 and 34 falls outside an acceptable range, an error signal is sent to the integrator and output unit 36. The measurement circuit 32 may be arranged to supply the error signal if the supply voltage deviates by more than a predetermined amount, for example by more than 10% from the nominal supply voltage.

The integrator and output stage 36 monitors the error signal and checks that the error signal has been asserted for a predetermined period before sounding the alarm. The unit 36 may be arranged not to sound the alarm until the error signal has been asserted from three seconds or so. This avoids triggering the alarm in response to transient voltage drops, such as may occur when devices on a very long extension cable are powered up. The integrator and output stage may be implemented as part of the measurement circuit 32.

It is thus possible to provide a reliable an inexpensive voltage alarm. The alarm unit may be incorporated within plugs or sockets at any point within an extension cable, and on devices connected to a power supply. The provision of a termination plug at the end of a extension cable has the advantage that the voltage is monitored at the point furthest from the connection to the source of power, and consequently, is at the point most liable to suffer from under voltage conditions.

Claims

1. A monitoring device, comprising monitoring means for monitoring at least one input signal representing a physical quantity and for indicating when the at least one physical quantity falls outside a range of acceptable values.

2. A monitoring device as claimed in claim 1, in which the output element provides one or more of a visual, audible or electrical indication of the voltage being out of range.

3. A monitoring device as claimed in claim 2, in which the output element is a visual indicator, and is a lamp, a light emitting diode or a high intensity strobe light.

4. A monitoring device as claimed in claim 2, in which the output element sends a radio signal to a monitoring unit.

5. A monitoring device as claimed in claim 2, in which the output element transmits a signal along power supply conductors which are in use, monitored by the device.

6. A monitoring device as claimed in claim 4 or 5, in which an encoded signal is sent which uniquely identifies which monitoring device within a series of monitoring devices.

7. A monitoring device as claimed in claim 2, in which the device has an audio output element coupled to an acoustic resonator.

8. A monitoring device as claimed in claim 7 in which the resonant frequency of the acoustic resonator and the operating frequency of the audio output element are substantially the same, or harmonically related.

9. A monitoring device as claimed in claim 7 or 8, in which an output region of the resonator comprises at least one hole.

10. A monitoring device as claimed in claim 9 in which a plurality of holes are provided.

11. A monitoring device as claimed in claim 9 or 10, in which the diameter or the or each hole is selected such that a surface tension of water inhibits ingress of water into the resonator.

12. A monitoring device as claimed in any one of the preceding claims, further comprising an averaging or timing circuit such that the alarm is only activated if the at least one measured quantity remains outside the acceptable range for longer than a predetermined period.

13. A monitoring device as claimed in any one of the preceding claims in which the device includes a temporary power store such that the alarm can continue to sound in the event of total supply failure.

14. A monitoring device as claimed in any one of the preceding claims, in which the device is remotely programmable.

15. A monitoring device as claimed in any one of the preceding claims, in which the device is a voltage monitoring device and it derives its own power supply from the supply that it is monitoring.

16. A monitoring device as claimed in any one of claims 1 to 14 arranged to monitor at least one voltage.

17. A monitoring device as claimed in any one of claims 1 to 14 arranged to measure at least one of a voltage, magnetic field strength, current, temperature, illumination, weight or flow rate.

18. A device as claimed in any one of the preceding claims in which the alarm is activated when the product of the excursion of a monitored valve outside of the acceptable range and time exceeds a threshold valve.

19. A device as hereinbefore described with reference to accompanying drawings.