GB2479520A - Remote sensor data transmission - Google Patents

Abstract

A remote sensing system comprises a sensor unit 12 including sensor means 14, a memory 18, a timer 20 and a transmitter 16, and a monitoring unit 10 including a receiver, the sensor unit 12 being operable, at intervals determined by the timer 20, to transmit data to the monitoring unit 10. The memory 18 is operable to store at least one previously transmitted sensor reading, and the data transmitted to the monitoring unit 10 comprises both new, previously untransmitted data and data representative of the previously transmitted sensor reading from the memory 18. The transmitted data may comprise new data and the previous three or more sensor readings. Error detection may be further enhanced by check-sum digit encoding and receive antenna selection diversity 22. Transmissions from different sensors may be at randomly selected points around the sample period.

Description

Remote Sensing This invention relates to remote sensing, for example to the remote sensing of environmental or other parameters in one or more locations to be wirelessly transmitted to another remote location where the measured parameters may be monitored.

A number of remote sensing systems are known. For example, systems are known in which a sensor periodically senses an environmental or other parameter and transmits data indicative of the sensed parameter to a monitoring station. The sensed parameter may take a range of forms. For example, it may relate to the temperature and/or humidity at a location. Alternatively, it may relate to an operating state of a piece of equipment or machinery, or the output of another form of sensor. Typically, several remote sensors will be arranged to transmit data to a single monitoring station.

Systems of the above described type can suffer from the disadvantage that data can be lost. For example, interference in the transmitted data may result in the monitoring station being unable to decode or make use of the data. Clearly, this is undesirable as it leads to incomplete monitoring of the relevant parameters. This could lead to, for example, a fault going undetected. Depending upon the application in which the system is being used, this could result in, for example, a quantity of perishable stock having to be disposed of as the system may be unable to confirm the conditions under which it has been stored.

In order to enhance system integrity, systems have been developed in which the monitoring unit periodically polls the sensors associated therewith to obtain sensor information therefrom, rather than having the sensors arranged to output the information automatically. As, in such arrangements, the monitoring unit can poll for additional information in the event that transmitted data is corrupt or unusable, the risks associated with missing data are reduced. However, systems of this type are significantly more complex and expensive, requiring both the sensors and the monitoring unit to be able to both receive and transmit signals. In addition it will be appreciated that the power consumption of the sensors is significantly increased as the receiver thereof must be powered permanently in order that it can monitor for the transmission of a polling signal. Where the sensors are battery powered, this increase in power consumption may not be acceptable and results in installation being more complex.

It is an object of the invention to provide an arrangement whereby a parameter can be sensed at a remote location and monitored reliably by or from a monitoring unit.

According to the present invention there is provided a remote sensing system comprising a sensor unit including sensor means, a memory, a timer and a transmitter, and a monitoring unit including a receiver, the sensor unit being operable, at intervals determined by the timer, to transmit data to the monitoring unit, wherein the memory is operable to store at least one previously transmitted sensor reading, and the data transmitted to the monitoring unit comprises both new, previously untransmitted data and data representative of the previously transmitted sensor reading from the memory.

Such an arrangement is of relatively simple form. As the sensor unit does not transmit a signal as a result of the reception of a polling signal, there is no need for it to include a receiver means, and as a result power consumption savings can be made.

As the transmitted signal includes both new data and previously transmitted data, there is an opportunity for the monitoring unit to check, correct and/or complete data that may have been lost or corrupted during data transmission.

By way of example, the transmitted data may comprise data representative of the most recent or current sensor reading together with data representative of the previous, say, three sensor readings from the memory. In such an arrangement, four consecutive data transmissions would have to be lost or corrupted before any data is permanently lost.

Conveniently, several sensor units are arranged to transmit data to the monitoring unit. With such an arrangement, if all of the sensor units are arranged to transmit data at the same interval then there is a risk that, if two signals are transmitted simultaneously by two of the sensor units, then the subsequent signals will also be transmitted simultaneously with the result that there is an increased risk of data loss.

In order to counter this, the intervals at which data is transmitted are conveniently selected at random or have a random element. For example, where the sample period is approximately 10 minutes, the transmissions may take place at a randomly selected point up to 0.9 seconds before or after the end of the 10 minute sample period. In this manner, the likelihood of the consecutive transmissions from the aforementioned sensor units being simultaneous is much reduced, and so the risk of data loss as a result of consecutive transmissions colliding with one another is low.

In order to further enhance the integrity of data transmission between the sensor unit and the monitoring unit, the monitoring unit preferably has two or more antennas associated therewith and means whereby the strongest received signal at any given time is used by the monitoring unit. The provision of such an arrangement can overcome or avoid transmission problems arising from the location and/or orientation of the receiving antenna, simplifying installation, and can also increase the operating range of the system.

Each transmission is conveniently encoded using a Manchester encoding technique. The encoding technique may incorporate a check-sum digit determined by an appropriate algorithm to permit error detection and, in some cases, correction.

The invention will further be described, by way of example, with reference to the accompanying drawing, Figure 1, which is a diagrammatic illustration of a remote sensing system in accordance with one embodiment of the invention.

The remote sensing arrangement illustrated in Figure 1 is intended for use in monitoring environmental parameters or conditions in a number of locations within a building or site. The arrangement comprises a central monitoring unit 10 arranged to receive data from a plurality of sensor units 12 located in appropriate positions within the building or site, the data being transmitted from the sensor units 12 to the monitoring unit 10 via a one-way radio communications link, ie the sensor units 12 are able to transmit data to the monitoring unit 10, but there is no provision to allow data or control signals to be transmitted from the monitoring unit 10 to the sensor units 12.

Each sensor unit 12 comprises a sensor 14 operable to measure an environmental parameter of the location in which the sensor unit 12 is positioned. The environmental parameter could take a range of forms. For example, it may comprise a measurement of the air temperature at the location or the humidity at the location.

Other parameters that could be sensed include, for example, vibrations, sounds levels, voltage and/or current levels in associated circuits, door/window position sensors, etc. Further more, each sensor unit 12 may include sensors sensitive to two or more of these parameters, if desired. In the description hereinafter, references are made to temperature sensing, but it will be appreciated that the invention is not restricted in this regard.

Each sensor unit 1 2 further includes a transmitter 1 6 operable to transmit a data signal to the monitoring unit 10, a memory 18 and a timer 20. The sensor unit 12 is operable such that at predetermined intervals determined by the timer 20, a measurement of the temperature is made by the sensor 14. Data representative of the measured temperature reading is stored within the memory 18 along with data representative of at least one previous temperature reading. The capacity of the memory 18 is chosen such that, for example, four temperature readings can be held therein. As shown, the memory 18 is arranged to store the current or most recent temperature measurement and the three preceding measurements, and each time a new temperature reading is measured, the oldest stored measurement is lost and the remaining stored measurements are updated to reflect that a new reading has been made. In the arrangement illustrated this is achieved by associating an age flag 18a with each piece of data stored therein. Thus, each time a new temperature reading is taken, the age flags 18a of each stored piece of data are incremented, and the oldest piece of data, ie the one with the highest age flag, is lost by being overwritten with the current reading and the age flag 1 8a associated therewith is reset to one to reflect the fact that the stored data is the most recent. Although this is one technique by which the data may be stored, it will be appreciated that many other techniques could be used and the invention is not restricted in this regard.

At a time controlled by the timer 20, the data stored within the memory 18 is transmitted by the transmitter 1 6 to the monitoring unit 1 0. The transmitted signal thus includes data representative of the previously untransmitted, current or most recent temperature reading together with data representative of the previously transmitted temperature data stored, at that time, in the memory 18. Typically, the timer 20 will trigger the transmission of data to the monitoring unit 1 0 simultaneously or very shortly after each temperature reading is taken. It will be appreciated that, with such an arrangement, each temperature reading will be transmitted a total of four times before that temperature reading is lost from the memory 18.

Conveniently, the data transmitted by the sensor unit 12 is encoded, for example using a Manchester encoding technique. The encoding technique preferably involves adding a checksum digit to the encoded data to allow the monitoring unit 10 to verify the integrity of the transmitted data. If the checksum digit shows the data to have been corrupted then, depending upon the algorithm used and the nature of the corruption, the monitoring unit 10 may be able to automatically correct the data.

Alternatively, it may simply flag that the received data may not be reliable.

In order to increase the reliability of the remote sensing arrangement, the monitoring unit 10 conveniently includes a plurality of antennas 22 spaced apart from one another and orientated differently to one another. The signals received by the antennas 22 are compared with one another and, at any given time, the strongest received signal is used by the monitoring unit 10, weaker signals either being disregarded or used for verification purposes. As a result, the risk of data being lost due to transmissions being missed is reduced. Further, depending upon the positions of the antennas 12, the operating range of the remote sensing arrangement may be enhanced.

Where several sensor units 12 are each arranged to transmit data to the same monitoring unit 10 at the same time intervals, then there is a risk that, if two or more of the sensor units 1 2 make data transmissions simultaneously, the next subsequent data transmissions by those sensor units 12 will also be simultaneous. As the monitoring unit 10 is only able to receive and use a single signal at a time, such simultaneous data transmissions can result in a loss of data. Furthermore, if several subsequent data transmissions also collide in this manner, then data may be lost permanently. In order to reduce the risk of this, each sensor unit 12 is preferably arranged to modify the transmission timing, slightly, by a random amount. Consequently, if the transmissions from two sensor units 12 collide, the random element of the timing at which each sensor unit 12 will make its next subsequent transmission results in the risk of a subsequent collision occurring being far reduced.

In use, each sensor 14 is triggered, periodically, by the timer 20 associated therewith, to take a new temperature reading. The age flags 18a of the data stored within the memory 18 are incremented as outlined hereinbefore, and the data representative of the new temperature reading is stored in the memory 18 as the most recent temperature reading. All of the data from the memory 18, ie both the new, previously untransmitted reading and the older, previous transmitted readings, are encoded using the aforementioned Manchester encoding technique and the encoded data is transmitted by the transmitter 16 for reception by the antennas 22 of the monitoring unit 10.

The monitoring unit 10, upon receipt of the transmitted signal, decodes it and uses the checksum digit of the signal to verify the integrity of the signal. The monitoring unit 10 can then update a database holding data representative of the output the sensor 14 of that sensor unit 12. As the received data signal includes both previously untransmitted data and previously transmitted data, the monitoring unit 10 is able to compare the data previously stored in the database with the incoming data to verify that no data has been lost, check the accuracy of any data corrected relying upon the checksum algorithm, and to complete any holes or missing data.

Conveniently, the monitoring unit 10 is arranged so that the database can be accessed remotely, for example via the internet, to allow a remote user to monitor the environmental conditions being sensed. In the event that the received data shows that the temperature at the location of the sensor unit 12 falls outside of a predetermined range, or has changed by an unacceptable amount, then appropriate alarms can be raised, for example by activating audible or visible warning devices, by sending email or textlsms alerts, by making an automated telephone call to an appropriate person or by any other suitable means.

It will be appreciated that each reading is transmitted several times before being deleted or lost from the memory 18, thus the risk of it being permanently lost is very low. The techniques described hereinbefore further reduce the risk of data loss, for example, by enhancing the system integrity, by avoiding repeated data collisions, and by allowing the system to verify and correct received data. The system is thus suitable for use in a wide range of applications in which it is important to ensure that complete, accurate data records are held. For example it may be used in locations in which food or pharmaceuticals are stored and it is important to ensure that the storage conditions fall within predetermined temperature and/or humidity ranges or the like.

As the arrangement uses wireless communications techniques, installation is relatively simple. The sensor units 12 can be battery powered rather than requiring mains power to be connected thereto which, again, simplified installation. As the sensor units 12 are arranged to transmit data, but not to receive incoming data or control signals, there is no need for the transmitter to be energised permanently.

Rather, it may be energised only when data is to be transmitted. As a result, significant power savings can be made, significantly increasing battery life. The multiple transmission of each sensor reading ensures that the enhancements in battery life and simplicity of the system, compared to arrangements in which the sensor unit transmits sensor readings in response to the reception of a polling signal, is not at the cost of loss of data or data integrity.

It is envisaged that up to 16 sensor units 12 may communicate with a single monitoring unit 10, with each sensor 12 having up to three sensors 14 or sensor inputs.

Depending upon the application in which the remote sensing arrangement is used, the timer 20 may be arranged to trigger the capturing of data and the transmission of data to the monitoring unit 10 at intervals of approximately 10 minutes, with the memory 18 being configured to store the most recent 4 data readings. Where a transmission interval of 10 minutes is used, then conveniently this is modified by a random value of up to 0.9s either ahead of or after the end of the 10 minute interval to reduce the risk of data collisions. However, it will be appreciated that these parameters are merely examples and that, depending upon the application in which the invention is used, they may be changed or modified. For example, the most recent 5 data readings could be stored and transmitted, or more or fewer readings may be stored. The random value used to determine when transmissions should take place may be varied, for example it could be in the range of 0 to 5s either ahead of or after the end of the said interval.

A wide range of modifications and alterations may be made to the arrangement described hereinbefore without departing from the scope of the invention.

Claims (8)

1. CLAIMS: 1. A remote sensing system comprising a sensor unit including sensor means, a memory, a timer and a transmitter, and a monitoring unit including a receiver, the sensor unit being operable, at intervals determined by the timer, to transmit data to the monitoring unit, wherein the memory is operable to store data representative of at least one sensor reading that has previously been transmitted, and the data transmitted to the monitoring unit comprises both new, previously untransmitted data and data representative of the previously transmitted sensor reading from the memory.
2. 2. A system according to Claim 1, wherein the transmitted data comprises data representative of the most recent or current sensor reading together with data representative of the previous three or more sensor readings from the memory.
3. 3. A system according to Claim 1 or Claim 2, wherein several sensor units are arranged to transmit data to the monitoring unit.
4. 4. A system according to Claim 3, wherein the intervals at which data is transmitted by the sensor units are selected at random or have a random element.
5. 5. A system according to Claim 4, wherein the sample period is approximately 10 minutes, and the transmissions take place at a randomly selected point up to between 0.9 and 5 seconds before or after the end of the 10 minute sample period.
6. 6. A system according to any of the preceding claims, wherein the monitoring unit has two or more antennas associated therewith and means whereby the strongest received signal at any given time is used by the monitoring unit.
7. 7. A system according to any of the preceding claims, wherein each transmission is encoded using a Manchester encoding technique.
8. 8. A system according to any of the preceding claims, wherein the encoding technique incorporates a check-sum digit determined by an appropriate algorithm to permit error detection.