GB2279210A - Monitoring remote signal sensors - Google Patents

Abstract

A sensor monitoring system, comprising one or more remote sensors (14) which are positioned to respond to the condition of a variable quantity to be monitored, such as the level of liquid fuel in a storage tank (10) means for transmitting output signals from the sensor or sensors (14) to a base unit (22) which is coupled via the public telephone network (26) to a central controller (30), and means for controlling transmission of monitoring signals via the telephone network such that interference with voice communications is minimal, e.g. by transmitting the signals at specified times of the day or night. <IMAGE>

Description

DESCRIPTION MONITORING REMOTE SIGNAL SENSORS The present invention relates to the monitoring of the status of signalling sensors disposed at a remote site or sites from the monitoring location.

There are many situations when it is required to monitor the status of signal-producing sensors and where the monitoring location is remote from the location of the sensor(s).

By way of example, there is a requirement for a method of monitoring at a central location a remote stock of fuel disposed at a customer's premises.

In accordance with a first aspect of the present invention there is provided a sensor monitoring system, comprising one or more remote sensors which are positioned to respond to the condition of a variable quantity to be monitored, means for transmitting output signals from the sensor or sensors to a base unit which is coupled via the public telephone network to a central controller, and means for controlling transmission of monitoring signals via the telephone network such that interference with voice communications is minimal.

Advantageously, when it intends to communicate with the CCS, the base unit is arranged to generate and apply to the telephone network a short burst dial and then to remain passive until the CCS signals that point to point connection has been made.

Preferably, the system includes a means of generating a warning signal at the CCS if no sensor monitoring signal is transmitted within a specified period, indicating that a manual check of the variable being monitored should be made.

The remote sensor or sensors preferably pass status information to the CCS with a specified maximum time between signals, this time being known to the CCS. The status signalling may occur on specific events, eg. tank nearly empty, as well as at fixed time intervals. The CCS can have a count down alarm timer for each RSD known to its database. If the time overruns then the CCS reports a fault condition. CCS reporting may be either for system fault conditions or for normal reporting of the external system monitored by the RSD. CCS reporting may be by textual and/or audible output, or by signalling another system directly which will take action automatically.

The system signals down wires of a PSTN and the line(s) so used may be dedicated to this application, or may be shared with normal voice use or any other system capable of using the PSTN network.

The remote sensor or sensors (RTSD) may be a battery powered unit signalling via radio or hard wiring to the base unit which in turn relays the signal via the PSTN to the CCS.

A typical application might include a system to monitor level or weight of liquid in a tank in order to automatically replenish the stock of liquid by one or more suppliers. The data transferred to the CCS might include, amongst other items, the status of level switches or load cells, indicating the urgency for replenishment, together with the status of the battery if used, such that the battery might be replaced, possibly at the same time as the tank stock is replenished. Data may also be transferred to the RSD from the CCS which might include accurate absolute time information to enable timed transmission of further data or control of events local to the RSD.

One proposed method of operation when the RSD shares a PSTN line with other users of same, is that the RSD signals by DTMF (dual-tone, multi-frequency) tone and then gives no other interference with the other line operation, until a response is heard from the CCS, indicating that it has a point to point link.

This may then be arranged to result in perhaps only a 1 second noise disturbance to the other channel traffic, and thus be unlikely to give significant disruption. The RSD may delay by a time, for example 3 minutes, if no contact is made such that the other channel user is not unduly disturbed. The RSD may signal only at times of day when a potential channel sharer is unlikely to be using the channel. The RSD may be able to test a shared channel and only act if it is not otherwise being used. The RSD could then make use of the channel only when it becomes free, or even only when it had been made free for a time. The RSD may have a system or algorithm for becoming more competitive for use of a shared channel based on its signal inputs and time.

In accordance with a second aspect of the present invention, there is provided a sensor monitoring system wherein signals from one or more remote sensors are transmitted to a base unit which is coupled via the public telephone network to a central control system (CCS), the system being arranged to restrict transmission of monitoring signals via the telephone network to specified times of the day/night where interference with voice connections will be minimal.

A system in accordance with the present invention has the advantages that it can: be fail safe by virtue of the action of the CCS in the event of no signalling from the RSD within the time expected; remove the problem of wiring to an outlying monitoring point by using a mixture of radio and conventional wire communication channels; solve the problem of managing a remote stock of liquid product; completely automate a liquid stock management system which previously required human intervention or prediction; and eliminate the problem of stock running out by a failsafe monitoring system.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic illustration of one embodiment of the monitoring system in accordance with the present invention; Fig. 2 is a diagrammatic illustration of one embodiment of a remote signal monitoring device (RSD); and Fig. 3 is a diagrammatic illustration of one embodiment of a central control system (CCS).

Referring to Fig. 1, a fuel tank 10 disposed adjacent to a customer's premises 12 is provided with a fuel level sensing device 14 containing one or more switches (not shown) whose switching status is dependent upon the prevailing liquid fuel level in the tank 10. The fuel tank supplies fuel to one or more appliances 16 via a fuel supply line 18. Connected to the switch or switches of the sensing device 14 is a radio transmitter which transmits a low level radio signal 20 representative of the switching position of said switch(es) and hence indicative of the fuel level status of the fuel in the tank 10. (The radio transmitter corresponds effectively to the handset of a cordless telephone.) A base unit 22 for receiving the radio signal 20 is disposed in the customer's premises 12 and is plugged into a conventional telephone socket 24 connected to the public telephone network 26. At the fuel supply premises 28, a central control system 30 is also connected to the telephone network 26 so that it can be brought into communication with the base unit 22 upon the two being connected.

Thus, fuel status signals transmitted by the fuel level sensing device(s) 14 are ultimately received at the central control system 30 by way of the radio link 20 and telephone network 26.

A typical base unit 22 is illustrated in Fig. 2 and comprises a battery 32 connected to a timing unit 34 and a control and transmission unit 36 via a power sharing control 38. The control and transmission unit 36 is connected to the telephone network 26.

The power sharing control 38 is controlled by the timing unit 34 and is adapted to permit current to flow from the battery to the control and transmission unit 36 only when necessary, for example, when it is time for the control and transmission unit to transmit a signal.

An alternative embodiment of the present invention uses a microprocessor and associated circuitry to perform the functions of the timing unit 34 and the control and transmission unit 36, and the power saving control 38, which is then unnecessary, is dispensed with.

In alternative systems, the fuel level sensing device 14 could be hard-wired to the base unit 22 which in that case is then adapted to translate the fuel level signals into signals (eg signal pulses) recognisable by the central control system 30.

Further details of one possible central control system (CCS) 30 for the present system are shown in Fig. 3. The CCS 30 of Fig. 3 comprises a control unit 40 connected by a bi-directional link 41 to a plurality of pairs of units 42,44, one for each remote sensor being monitored. Each unit 42 comprises a timer and each unit 44 comprises a status and history log for the associated remote sensor 14. The control unit 40 is coupled to the telephone network 26 by lines 43, and is also coupled by lines 45 to a report generator 46 and printer 48. Ongoing data can be passed to other linked systems via a unit 50 and communication lines 51.

Advantageously, the system is arranged such that the remote sensor signals are only transmitted to the CCS via the telephone network in a short burst or bursts, eg. 1 second, and at a time of day/night when it is unlikely that the telephone line will be needed from voice communication (eg. at 0.200 hr).

Advantageously, the system is arranged so that if the telephone line 26 is being used for voice communication to other telephone sets 54 at the customer's premises 12, then the system will wait until the line becomes free. An audible indication may be made to the person using the handset 54 that the system has tried to send its monitoring signals.

The CCS can be arranged so that if no monitoring signal is received from the remote sensor(s) 14 within a specified period (eg 24 hours) then an alarm/fault condition is generated at the CCS using the timer(s) 42 and a call is put out automatically for the fuel tank to be checked manually.

For obtaining minimised possibility of interference with normal use of the telephone line, the system can generate a short (eg 1 second) dualtone, multi-frequency DTNF burst dial, and it can then remain passive until the central control system 30 signals that point to point connection has been made.

Shared use of an existing PSTN line is obviously possible.

Thus, the present invention provides a solution to the problem of monitoring a remote stock of liquid fuel at a customer's premises. The invention can provide a system which can signal a central control and result in (from the customer's point of view) an automatic replenishment of liquid stock. In this way, the customer can have a continuous supply of, for example, liquid fuel without any effort on his part, in the same way that people connected to the Gas Main supply have.

From the supplier point of view, not only can order entry be automated, but their vehicle routing can be planned in a more efficient manner.

Claims (10)

1. A sensor monitoring system, comprising one or more remote sensors which are positioned to respond to the condition of a variable quantity to be monitored, means for transmitting output signals from the sensor or sensors to a base unit which is coupled via the public telephone network to a central controller, and means for controlling transmission of monitoring signals via the telephone network such that interference with voice communications is minimal.

2. A system as claimed in claim 1, wherein the base unit includes a clock/timer arrangement which permits transmission of monitoring signals to the central control system only at a specified time or times of the day/night, when interference with voice communications on the telephone network will be minimal.

3. A system as claimed in claim 1 or 2, wherein the base unit is arranged to generate and apply to the telephone network a short burst dial and then to remain passive, without transmission of monitoring information, until the CCS signals that point to point connection with the base unit has been made.

4. A system as claimed in claim 1, 2 or 3 in which the central control system includes a timer arrangement which generates a warning signal at the CCS end if no remote monitoring signal is transmitted from the or each remote sensor within a specified period.

5. A system as claimed in any of claims 1 to 4, in which the base unit is arranged to seek to transmit information to the central control system either on the occurrence of specific events or at fixed time intervals, or both.

6. A system as claimed in any of claims 1 to 5 wherein the remote sensor, or sensors communicates with the base unit by radio, or infra-red.

7. A system as claimed in any of claims 1 to 5 wherein the remote sensor, or sensors, communicates with the base unit by hand-wired link.

8. A sensor monitoring system wherein signals from one or more remote sensors are transmitted to a base unit which is coupled via the telephone network to a central control system, the system being arranged to restrict transmission of monitoring signals via the telephone network to specified times of the day/night where interference with voice connections will be minimal.

9. A sensor monitoring system substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 of the accompanying drawings.

10. A sensor monitoring system substantially as hereinbefore described with reference to, and as illustrated in, Figs. 1 to 3 of the accompanying drawings.