GB2145550A

GB2145550A - Remote monitoring radio link

Info

Publication number: GB2145550A
Application number: GB08320383A
Authority: GB
Inventors: Dr Maurice Bloch; Harry Ainsworth Haskell
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-07-28
Filing date: 1983-07-28
Publication date: 1985-03-27
Also published as: GB8320383D0

Abstract

In a radio link for remote monitoring of a condition or conditions, a transmitter 10, 11, 12, 13 radiates regular repetitive sequences of radio frequency pulses, each sequence comprising a predetermined number of groups of pulses, which groups of pulses are followed by an interval of predetermined duration. Each group comprises one or more pulses followed by an interval such that the total duration of pulse or pulses and subsequent interval is the same for each of the groups. A condition monitor 23 is operative to suppress radiation of pulses if a condition change is to be notified. At a distant receiver the pulses are received and checked and if the suppression of a pulse is detected, an output indication is given. <IMAGE>

Description

SPECIFICATION Remote monitoring radio links This invention relates to a radio link for remote monitoring.

There are many circumstances in which a condition or conditions at a remote point have to be monitored. It is known to use radio links for this purpose. It is an object of the present invention to provide an improved form of radio link for such a monitor system.

According to the present invention a radio link for a condition monitor comprises a transmitter arranged to radiate regular repetitive sequences of radio frequency pulses, each sequence comprising a predetermined number of groups of pulses, which groups of pulses are followed by an interval of predetermined duration, each group of pulses comprising one or more radio frequency pulses followed by an interval such that the total time of the pulses and subsequent interval in each group is the same for each of the groups, and means controlled by a condition monitor operative to suppress radiation of pulses when a condition change is to be notified and, at a distant point, a receiver for receiving said repetitive sequences of groups of pulses, means checking the number of pulses in each group and the number of groups of pulses and operative to give an output indication or signal if the predetermined groups are not received.

The transmitter and/or the receiver may be at fixed locations or may be mobile.

With the arrangement described above the absence of a transmitted pulse or pulses provides the required information at the receiving station and hence any interference with the transmitter or the power supply will in general cause the receiver to indicate a change in the monitored condition.

The transmitted pulses may have a pulse duration which is very short compared with the overall time between successive sequences. Typically each pulse is a few cycles, for example 10 cycles, at the radio frequency of the transmitter. Each group of pulses may comprise a predetermined number of pulses, which may be different for different groups and hence may be regarded as representing a digital number. The successive groups thus represent a sequence of numbers and hence give a coded identification. The transmitter may incorporate a read-only memory, conveniently a programmable read-only memory, which is set to control the code carried by the transmission from that transmitter. Any failure at the receiver to receive the correct code results in an output indication or signal being given.

Conveniently the transmitter includes logic means comparing the output of counting means counting pulses from a pulse bit and space generator with a code programme in the read-only memory, the comparator controlling gating means gating the signals from a radio frequency oscillator to be transmitted.

A condition monitor such as for example an intruder detector may be arranged to inhibit transmission when a condition is detected about which information is to be transmitted.

Using a VHF radio frequency, and with pulses of the order of 10 cycles of radio frequency, it is readily possible, in the manner described above, to transmit a multi-digit code signal in a fraction of a m.sec. The interval between transmissions of successive repetitive coded signals conveniently is very much longer than this. The transmitter may thus have a very low duty ratio and it is therefore readily possible to obtain a high peak power in the pulses.

In such an arrangement, the transmitter may incorporate a timer for controlling the repetitive transmission of the coded signals.

The condition monitor may be arranged to inhibit the timer output controlling the transmitter so as thereby to prevent transmissions.

With a transmitter having a high peak power as described above, the receiver may conveniently be a simple tuned radio frequency receiver with a crystal detector. The detected pulses may be fed to a bit counter giving an output which is compared in a digital comparator with information stored in a memory conveniently a programmable readonly memory. By this means it is possible to check the correct number of bits for each digit hence whether the correct digits are received.

A missing pulse detector may be arranged to operate an alarm.

The following is a description of one embodiment of the invention, reference being made to the accompanying drawings in which: Figure 1 comprises four timing diagrams for explaining the signals transmitted by a transmitter in one embodiment of the invention; Figure 2 is a block diagram illustrating a transmitter; and Figure 3 is a block diagram illustrating a receiver.

The transmitter radiates a series of blocks of pulses, each pulse, in this particular embodiment, comprising 10 radio frequency cycles at a VHF radio frequency which might typically be of 35 Mhz. Between successive pulses in a group there is an interval of 5-cycle duration without any radiation. Referring to Fig. la, which is a waveform diagram illustrating four of the pulses, a pulse of 10 cycles would occupy 286 nanoseconds. The interval between such pulses occupies 1 43 nanoseconds. There are between 1 and 1 5 pulses in a group. The number of these pulses thus represents a code indicating a digit between 1 and 1 5. The total time period for the transmission of each digit includes an extra space time approximately equal to half the maximum digit time. This enables differentiation between successive digits.Each number comprising between 1 and 1 5 pulses would occupy a time period of 6.86 microseconds and the extra space time would be 3.43 microseconds. With this half number interval, each digital number would occupy a total time period of 10.29 microseconds as shown in Fig. 1 b which is a waveform diagram showing one complete word (i.e a number from 1 to 15) together with part of the next word. The first 6.86 microseconds would have between 1 and 1 5 pulses and this would be followed by the space of 3.43 microseconds before commencement of the next word representing a following digit.

A sequence of digits comprising 1 6 separate digits can be transmitted therefore in 1 64 microseconds as shown in Fig. Ic where each pulse shown represents a complete word.

The complete code, that is to say the 1 6 words, is repeated at a time interval typically between 1 and 10 seconds as shown in Fig.

1 d where each pulse represents a code giving 1 6 words, that is to say representing 1 6 digits.

It will be seen that in the above example the transmitter is coded utilising 1 6 predetermined numbers each of which may be any figure between 1 and 1 5. This gives 1 516 different code variations.

A transmitter for transmitting such a coded signal is illustrated in the block diagram of Fig. 2. A radio frequency oscillator 10, which would be operative at 35 Mhz in the example above, is gated in the lO-cycle burst by means of a zero crossing detector gate 11 which is controlled in a manner to be described later. The output from the gate is fed to a power amplifier 1 2 and thence to a radiating antenna 1 3. Signals from the oscillator 10 are fed to a bit and space generator 14 which generates the signals of 10 cycles duration with 5 cycles intervals. The bit signals are fed to a counter 16, the output of which is compared in a digital comparator 1 7 with a code stored in a programmable readonly memory 18.The output of the digital comparator 1 7 controls a word (number) and space generator 1 9 which applies signals from the bit and space detector 14 to the gate 11.

The word and space generator 1 9 also, by means of a word and space counter 20, controls the programmable read-only memory 18 to provide the successive different words.

The complete code sequence, as explained with reference to Fig. 1 d, is repeated at time intervals typically between 1 and 10 seconds, which time intervals are determined by a timer and code spacing gate 21 which resets the word and space generator at the end of each complete coded message. The timer 21 is inhibited by a condition monitor such as an intruder detector 23 so that, if any abnormal condition is to be signalled, transmission of coded signals is inhibited. It will thus be apparent that any tampering with the equipment which inhibits transmission will be signalled as an abnormal condition.

The condition sensor may take any of a wide variety of forms depending on the requirements which are to be monitored. For use as an intruder detector, it may be a doppler, sonic or radar unit or any other sensor including even a simple break switch.

It will be noted that the transmitter has a low duty cycle in that the time during which radiation takes place is only a small fraction of the total time interval. It is thus possible to use high peak power and, even if inefficient aerials are employed, an adequate range of transmissions can readily be obtained.

The receiver is shown in Fig. 3. This is tuned to the transmitter and is preferably crystal controlled to ensure stability. A simple tuned radio frequency receiver unit 30 coupled to a receiving antenna 31 is employed, the receiving unit feeding a crystal detector in a bit detector and shaper stage 32. The output of this bit detector 32 is fed in the first place to a word interval timer 33 for controlling a word counter 34. The individual bits from the bit detector and shaper 32 are fed to a bit counter 35 and the counted output therefrom is compared in a digital comparator 36 with the predetermined code from a programmable read-only memory 37. This readonly memory contains the complete code and is addressed by the word counter 34 so that the successive words (digital numbers) are utilised by the digital comparator 36.The word interval timer 33 generates a strobe pulse which is combined with the correct result from the digital comparator in a word length verifier 38 to operate the word counter 34. The strobe pulse from the word interval timer 33 also resets the bit counter 35 to await the next stream of digit bits. Any missing bit in the digit stream compared with the code in the read-only memory 37 would be detected by the word length verifier 38 and may be utilised to operate an alarm 40. The output from the word counter 35 is also checked in a code length verifier 41 and any missing word is detected and utilised by a missing pulse detector 42 to operate the aforementioned alarm 40. It will thus be seen that the receiver checks on the individual digits and also on the total number of digits and operates the alarm in the event of any failure to receive a pulse or a digit.

Provision may be made so that, if an error is detected in the counts either by the word counter 34 or the bit counter 35, then both these counters are reset and a further check is made to see if the correct code is received on the transmission of the next sequence of groups of pulses.

It will be noted that the actual period of transmission from a transmitter is very short compared with the intervals between the transmissions.

Claims

1. A radio link for a condition monitor comprising a transmitter arranged to radiate regular repetitive sequences of radio frequency pulses, each sequence comprising a predetermined number of groups of pulses, which groups of pulses are followed by an interval of predetermined duration, each group of pulses comprising one or more radio frequency pulses followed by an interval such that the total time of the pulses and subsequent interval in each group is the same for each of the groups, and means controlled by a condition monitor operative to suppress radiation of pulses when a condition change is to be notified and, at a distant point, a receiver for receiving said repetitive sequences of groups of pulses, means checking the number of pulses in each group and the number of groups of pulses and operative to give an output indication or signal if the predetermined groups are not received.

2. A radio link as claimed in claim 1 wherein the transmitted pulses have a pulse duration which is very short compared with the overall time between successive sequences.

3. A radio link as claimed in either claim 1 or claim 2 wherein each pulse is a few cycles duration at the radio frequency of the transmitter.

4. A radio link as claimed in any of the preceding claims wherein the transmitter comprises a read-only memory controlling the code constituted by the number of pulses in each group of pulses in the transmission from the transmitter.

5. A radio link as claimed in claim 4 wherein the transmitter includes logic means comparing the output of counting means counting pulses from a pulse bit and space generator with a code programme in the readonly memory, the comparator controlling gating means gating the signals from a radio frequency oscillator to be transmitted.

6. A radio link as claimed in any of the preceding claims wherein the transmitter may incorporate a timer for controlling the repetitive transmission of the coded signals.

7. A radio link as claimed in claim 6 wherein the condition monitor is arranged to inhibit the timer output controlling the transmitter so as thereby to prevent transmissions.

8. A radio link as claimed in any of the preceding claims wherein the receiver is a tuned radio frequency receiver with a crystal detector.

9. A radio link as claimed in any of the preceding claims wherein the receiver includes a bit counter, a digital comparator and a memory and wherein the detected pulses are fed to said bit counter to give an output compared in said digital comparator with information stored in said memory.

10. A radio link as claimed in claim 9 wherein the memory in the receiver is a programmable read-only memory.

11. A radio link as claimed in any of the preceding claims wherein the receiver comprises a missing pulse detector arranged to operate an alarm.

1 2. A radio link for a condition monitor substantially as hereinbefore described with reference to the accompanying drawings.

13. A transmitter for a condition monitor radio link substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

14. A receiver for a condition monitor radio link substantially as hereinbefore described with reference to Figs. 1 and 3 of the accompanying drawings.