GB2196202A

GB2196202A - A monitoring device

Info

Publication number: GB2196202A
Application number: GB08722386A
Authority: GB
Inventors: Patrick Smyth
Original assignee: PANBOURNE Ltd
Current assignee: PANBOURNE Ltd
Priority date: 1987-09-22
Filing date: 1987-09-23
Publication date: 1988-04-20
Also published as: IE860790L; ZA877239B; GB8722386D0

Abstract

A monitoring device (1) for monitoring a parameter of water in a water treatment plant comprises a sealed housing (3) of tubular construction, in which the electronic components of the device (1) are housed. A sensor (6) sealably extending from the housing (3) extends through a plug (7) secured in the housing (3). Signals from the sensor (6) are delivered to an analog to digital converter (20) which in turn delivers the signals to a micro-processor (21). The micro-processor (21) delivers the signals in response to a command from a central control apparatus to an infra-red transmitter (22) for transmission to the apparatus. An infra-red receiver (23) receives a signal from the central control apparatus to activate the device (1). A battery (24) powers the device (1). A clear perspex lens (18) sealably closes the other end of the housing (3). <IMAGE>

Description

SPECIFICATION A monitoring device The present invention relates to a monitoring device for monitoring a parameter of a liquid in a process apparatus and it also relates to process apparatus which comprises a plurality of tanks for storing a liquid or fluid with pipes interconnecting the tanks. The invention further relates to a method for controlling the process apparatus.

In process apparatus which comprises tanks for storing or bottling liquid or fluid which are interconnected by pipes, in general, comprise a plurality of valves in the pipelines for controlling the flow rate and directing the flow from one tank to another. In such process apparatus, the valves are normally remotely controlled by suitable control apparatus. In general, the valves are solenoid operated, or operated by an electric stepping motor, and these are hard wired to the central control apparatus. Further, in such process apparatus a number of monitoring devices are provided on the tanks and/or on the pipelines for monitoring certain parameters of the liquid or fluid in the tanks or pipe.These monitoring devices are, in general, hard wired back to the control apparatus, and the received signals are processed by the control apparatus, and where necessary, corrective action is taken by the control apparatus to change the position of a valve, or switch the valve on or off. This, in many cases, where one is dealing with processes in hazardous environments, can present serious difficulties and problems. The wiring has to be adequately shielded to prevent any danger of fire or explosion in the hazardous environment. Furthermore, where connections are made to the monitoring devices or valves or motors, relatively elaborate shielding has to be provided to avoid any danger of arcing, which could ignite a combustible gas, fluid or liquid. Furthermore, in water treatment plants which are controlled by a central control apparatus, similar monitoring devices and valves are provided.These, in general, where they are electrically controlled are hard wired back to the control apparatus.

This has many disadvantages, particularly where certain parts of the plant may be mounted in inaccessible conditions. Furthermore, in many cases, it may be desirable to mount the control apparatus in a position either adjacent or remote from the treatment plant, and it may also be desirable to be able to readily easily remove the control apparatus from the plant. Where the control apparatus is hard wired into the control apparatus, this can present difficulties.

There is therefore a need for a process apparatus which overcomes these problems.

There is also a need for a monitoring device for the apparatus which similarly overcomes the problems.

The present invention is directed towards providing such a monitoring or control device.

According to the invention there is provided a monitoring device for monitoring parameters of a fluid or liquid, the device comprising a sensor, an infra-red transmitter for transmitting a signal from the sensor to a central monitoring station, an infra-red receiver to receive a signal and means to activate the transmitter in response to a received signal.

Additionally, the invention provides a process plant comprising a plurality of liquid holding tanks, pipelines interconnecting the tanks, valves to control the flow rate and direction of liquids between the tanks, monitoring devices according to the invention in the pipelines and/or the tanks to monitor certain parameters of the liquids flowing through the pipelines and/or in the tanks, control apparatus to control the operation of the process plant, the control apparatus comprising an infra-red transmitter to transmit a signal to the monitoring devices, an infra-red receiver to receive transmitted signals from the monitoring devices, the control apparatus being controlled by a micro-processor. Preferably, the process plant is a water treatment plant.

Further, the invention provides a method for a water treatment plant comprising the steps of transmitting an infra-red signal from control apparatus to activate a monitoring device to monitor a parameter of the water, receiving the infra-red signal in the monitoring device, transmitting the monitored parameter from the monitoring device in the form of an infra-red signal in response to the received infra-red signal from the control apparatus, receiving the signal from the monitoring device in the control apparatus, transmitting an infra-red signal from the control apparatus to a control device to activate a valve in response to a monitored parameter rising or falling below a certain predetermined level.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a monitoring device according to the invention, Fig. 2 is an end view of the device of Fig.

1, Fig. 3 is a sectional elevational view of the device of Fig. 1 on the line Ill-Ill of Fig. 2, Fig. 4 is a schematic representation of a water treatment process illustrating the monitoring device of Fig. 1 in use, Fig. 5 is a perspective view of a water treatment plant according to another embodiment of the invention, Fig. 6 is a partly cut-away perspective view of the-water treatment plant of Fig. 5, Fig. 7 is a front elevational view of the water treatment plant of Fig. 5, Fig. 8 is a cross sectional view of the water treatment plant on the line VIll-VIll of Fig. 7, and Fig. 9 is a circuit diagram of control apparatus of the water treatment plant of Fig. 5.

Referring to the drawings and initially to Figs. 1 to 3 there is illustrated a monitoring device according to the invention indicated generally by the reference numeral 1. The device 1 is suitable for remotely monitoring a parameter of a fluid or liquid, in this case the conductivity of water in a water treatment plant. Water treatment plants are described with reference to Figs. 4 to 8 below. Needless to say, by merely changing the probe- or sensor, the device could be used for monitoring any parameter in any process equipment.

The device 1 comprise a cylindrical housing 3 of stainless steel for sealably housing the electronics of the device 1 which are described below. The housing is outwardly flared at one end 4 and inwardly shaped at the other end 5. A sensor 6 for measuring the conductivity of water extends from the housing 3 through a bore 16 of a stainless steel plug 7. The plug 7 is secured in the housing 3 by threads 13 on the plug 7 which engage a threaded inset 9 in the housing 3. The shaped portion 5 of the housing 3 abuts a shoulder 10 on the plug 7 when tightened. A threaded portion 8 of the plug 7 is provided for engaging a pipe or tank in which the conductivity of the water is to be monitored. The thread 8 is a gunbarrel thread. A shield 11 also of stainless steel extends from the plug 7 around the sensor 6.Openings 12 are provided in the shield 11 to allow water to circulate around the sensor 6. The shield 11 acts as the second terminal of the device 1 and thus the current flowing through the water between the sensor 6 and shield 11 is monitored. Electrical continuity is maintained between the shield 11 and plug 7 and in turn with the housing 3. The sensor 6 is secured and sealed in the bore 16 of the plug 7 by an electrical insulating epoxy resin 14. An electrical terminal 15 on the end of the sensor 6 extends into the housing 3.

A lens 18 of clear perspex material is mounted in the flared end 4 of the housing 3 and an O-ring 19 seals the lens 18 in the housing 3.

An analog to digital converter 20 provided by an integrated circuit is mounted in the housing 3 and the analog input of the converter 20 is connected to the.terminal 15 of the sensor 6. A micro-processor 21 connected to the analog to digital converter 20 receives digital signals from the converter 20. An infrb- red transmitter 22 mounted adjacent the lens 18 receives signals from the micro-processor 21 to be transmitted to a remotely mounted control apparatus. An infra-red receiver 23 also mounted adjacent the lens 18 receives infra-red signals from the control apparatus. In general, such signals are provided to activate the micro-processor 21 to transmit data from the sensor 6.

The micro-processor may be programmed to transmit the data simultaneously as it is received from the sensor 6 or to store the data over a period of time for transmission on receipt of a signal by the receiver 23. The micro-processor may also be programmed to compute the conductivity of the water from the received signals prior to transmission.

A battery 24, in this case a lithium chrome oxide battery is mounted in the housing 3 to power the device 1.

Referring now to Fig. 4 there is illustrated process apparatus, in this case a water treatment plant indicated generally by the reference numeral 30. The plant 30 comprises three anion tanks 31 and three cation tanks 32. A hydrochloric acid dosing tank 33 and an NAOH dosing tank 34 are also provided, as is a degassing unit 35. Pipelines 36 connect the various tanks together, and motor controlled valve banks 39 control the mixing of the various components in the plant. An inlet 40 and an outlet 41 are provided to the plant and a pump 42 circulates water throughout the plant.

The operation of such plants will be well known to those skilled in the art.

A plurality of monitoring devices 1 to monitor various parameters of the water in the pipelines 36 are provided. The devices 1 are similar to that described with reference to Figs. 1 to 3 and each monitors a different parameter. The devices 1, as can be seen, are mounted with their lenses 18 directed towards a central control apparatus 44. The central control apparatus 44 controls the operation of the water treatment plant 30 and receives the transmitted monitored parameters from each device 1 as infra-red signals. An infra-red receiver 45 is provided in the control apparatus and is directed towards the monitoring devices 1 to receive signals therefrom.

An infra-red transmitter 46 also provided in the control apparatus 44 delivers infra-red signals from the control apparatus to activate the monitoring devices 1 when it is desired to obtain a reading therefrom. Suitable control circuitry including a micro-processor which is not illustrated is provided in the control apparatus 44 for controlling the apparatus. Such circuitry will be well known to those skilled in the art. Additionally, under the control of the micro-processor 21, each monitoring device 1 transmits a signal through the transmitter 22 for reception by the receiver 45 of the control apparatus 44 in the event that an alarm condition is detected by the sensor 6 of the device 1.

Two control devices indicated generally by the reference numerals 50 are provided in the water treatment plant 30 to control the operation of the valve bank 39 and the pump 42.

Each control device 50 is substantially similar to the monitoring devices 1, in that it comprises a housing with an infra-red receiver (not shown) to receive infra-red signals from the control apparatus 44 to control the pump bank 39 and pump 42. The receiver in each control device 50 receives the signal from the control apparatus transmitter 46 in digital form which is converted into analog form by a digital to analog converter (also not shown) to operate the valve bank 39 and pump 42. The digital to analog converter is connected to suitable control means for actuating the valves or operating the pump which would normally include relays (not shown) and the like. These are also housed within the housing 3. An infra-red transmitter (not shown) is provided in each control device 50 to enable the status of the valves or pump being controlled to be transmitted to the control apparatus 44.A micro-processor (also not shown) mounted in each control device 50 controls the operation of the device. Lenses 18 in each control device 50, as can be seen, are directed towards the transmitter 46 of the control apparatus 44.

Referring now to Figs. 5 to 9 there is illustrated a water treatment plant according to another embodiment of the invention, indicated generally by the reference numeral 60.

In this case, the water treatment plant 60 is housed in a housing 61 mounted on a base 62. The housing 61 is releasable and removable from the base 62. A pair of tanks, namely a cation and anion tank 63 and 64 respectively are mounted on the base 62. A hydrochloric acid tank 65 is also mounted on the base 62. Pipes 66 interconnect the tanks 63, 64 and 65 through motor controlled valves 67. The operation of this plant is similar to other such plants which will be well known to those skilled in the art. The valves 67 are controlled by a central control apparatus 70 illustrated in block representation which is substantially similar to the control apparatus 44 of the water treatment plant 30 of Fig. 4.

The control apparatus 70 in this case is mounted in the housing 61. A visual display touch screen 73 is provided in the housing 61 to display the status of the apparatus and the monitored parameters and to enable various programmes of the control apparatus 70 to be selected. An infra-red receiver 74 and transmitter 75 on the control apparatus 70 enables the apparatus 70 to communicate with monitoring devices 1 and control devices 72 for controlling the valves 67.

The monitoring devices 1 are similar to those described with reference to Figs. 1 to 3 and are mounted in the pipes 66 to monitor parameters of the water. The control devices 72 control the valves 67 and are mounted on the valves 67. These control devices 72 are similar to the control devices 50 described with reference to the apparatus 30 of Fig. 4.

The control apparatus 70 communicates with the monitoring devices 1 and the control devices 72 through the transmission and reception of infra-red signals. Thus the lenses 18 of the devices 1 and 72 are directed towards the receiver 74 and transmitter 75 of the control apparatus 70.

Referring now to Fig. 9 portion of the circuitry of the control apparatus 7Q is illustrated. In this particular embodiment of the invention to reduce the power consumption of the control apparatus 70, the control apparatus 70 does not poll the various monitoring devices on a regular basis to ascertain their status. Rather, the control apparatus 70 is only activated on an alarm condition being monitored by any of the monitoring devices 1, or when the control apparatus 70 receives an input from the touch screen keyboard 73, or any other input, or once every 32 seconds to update its clock. During the 32 second periods where no alarm condition exists or no inputs are received, the control apparatus remains in a shut down mode.

Fig. 9 illustrates portion of the circuitry of the control apparatus 70. The entire circuitry is not illustrated, nor will it be described, since it is essentially conventional circuitry which will be well known to those skilled in the art. It is only intended to describe that portion of the circuitry which enables the control apparatus 70, and in particular the microprocessor of the control apparatus, to remain in the shut down mode.The control apparatus comprises a micro-processor It 1. A voltage regulator 1C8 activates the micro-processor IC1 when the output pin P2 of the regulator IC8 puts a high on the positive supply pin P9 of the micro-processor IC1. An unregulated positive voltage supply is connected to pin 8 of the voltage regulator IC8. The voltage supply is connected to pin 5 of the regulator IC8 through a resistor R3 of 10 Mohms and holds pin 5 of the regulator IC8 high in the absence of a low on line 91 which will be described below. A high on pin 5 of the regulator IC8 switches off the output at pin 2 of the regulator IC8 and accordingly the micro-processor IC1 is disabled.A low on pin 5 of the regulator IC8 switches on the output of pin 2 of the regulator IC8, which in turn enables the microprocessor.

A crystal oscillator IC2 generates an output signal at 32 KHz. This is fed through binary dividers IC3 and IC4, where it is divided, and an output signal from a NOR gate IC5 connected to the divider IC4 delivers a pulse once every 32 seconds. This is fed to an OR gate IC6 from where it fed through AND gates IC7a to f. Timers provided by resistors RI and R2 and capacitors C1 and C2 hold the signal for twenty milliseconds. The signal from the NOR gate IC5 causes the output from the AND gates IC7 e and f to be low.

Inputs from the infra-red receiver of the control apparatus, the keypad of the ccntrol appa ratus, and other inputs, such as, for example RS323 serial inputs or 12C inputs are delivered on a bus 90 into a NOR gate IC9 and a status register It 10. The outputs from the NOR gate IC9 are connected through a latch IC11, and in turn delivered to the OR gate lC6.

Thus, on a signal appearing on the inputs to the OR gate IC6 from the latch IC11, or from the NOR gate IC5, the outputs of IC7e and IC7f go low.

The output from the AND gate IC7f is connected to a non-maskable interrupt pin P8 of the central processing unit IC1. The low delivered onto this pin updates the clock in the micro- processor unit IC 1 every 32 seconds in the run mode. A low on the output from IC7e is delivered to pin 5 of the voltage regulator IC8, thus enabling the micro-processor IC 1 and activating the micro-processor programme. The programme holds pin 7 of the micro-processor IC 1 low, thereby enabling the run mode of the micro-processor It 1.

On commencement of the programme, the micro-processor IC1 monitors the status register It 10 to ascertain if the signal received has been as a result of an input on the data bus 90, or as a result of a pulse from the NOR gate IC5. If the status register shows that all the input lines in the bus 90 are inactive, then the micro-processor updates its clock and switches off.

Prior to switching off pin 7 of the microprocessor IC1 is configured as an input port by the micro-processor programme, and the voltage supply through the resistor R3 holds pin 5 of the voltage regulator IC8 high, thereby retaining the microprocessor in the shut- down mode which removes a supply from pin 9 of IC1.

On activation of the micro-processor IC 1 as a result of an input on the data bus 90 the central processing unit IC1 runs through its software. It polls each of the monitoring devices 1 to ascertain the status of the water being monitored by each device, and appropriate corrective action is taken, should this be necessary. This is achieved by sending an infra-red signal from the transmitter 75 of the control apparatus 70 to the appropriate control device 72 to activate a valve.

Once the appropriate action has been taken, and the alarm condition no longer exists, the micro-processor shuts down until it is reactivated to update its time clock by the next thirty-two second pulse from the NOR gate 5, or alternatively as a result of another input on the data bus 90. Where the input on the data bus 90 is as a result of an input from the touch screen 73, the micro-processor IC1 undertakes the appropriate operation commanded by the touch screen 73. Similarly, in the case of any other inputs, the micro-processor operates according to the inputted instruction.

Referring now to Fig. 8 one of the tanks 63 which is similar to the anion tank 64 is illustrated in more detail. The tank 63 comprises an outer shell 80 comprising a cylindrical portion 81 closed by convex end caps 82. A pair of internal end caps 83 at each end form a cavity 84 with the end caps 82. Water inlets 85 and water outlets 86 are provided into the tank 63. A plurality of jets 87 deliver water from the cavity 84 into the interior 89 of the tank 63. Accordingly, a relatively even distribution of water into the tanks is achievable.

The advantages of the invention are many.

However, one particular advantage is that by virtue of the fact that the monitored data and commands from the control apparatus is transmitted by means of infra-red signals between the devices and the central control apparatus wiring can be eliminated. Since each monitoring device and control device is powered by its own battery, wiring to the probes is not required. Thus the control apparatus and monitoring devices and control devices can be mounted in a hazardous environment and the infra-red signals beamed into the area.

Thus, the monitoring and control can be achieved without any danger of fire or explosion.

Further, by virtue of the fact that wiring between the control apparatus and the monitoring control devices is not required, the control apparatus can readily easily be removed without the need for disconnecting wires or the like. In particular, in the case of the embodiment of the invention illustrated with reference to Figs. 5 to 9 where the control apparatus is mounted in the housing, the housing can readily easily be removed.

A further advantage of the invention is that by virtue of the fact that the micro-processor can operate in a shut down mode for a considerable period of time, in fact, until an alarm condition exists or until activated by an input on the data bus 90, the power consumption of the micro-processor and control apparatus is relatively low. Thus, the control apparatus can be operated perfectly adequately for considerably long periods on a battery. The power requirement to update the micro-processor clock every thirty-two seconds is minimal.

It will be appreciated that while a particular construction of housing and of the monitoring and control devices has been described, any other suitable housing arrangement could be used. It will also, of course, be appreciated while particular circuitry has been described in respect of the monitoring device, any other suitable circuitry could be used. In fact, it will of- course, be appreciated that while a monitoring device has been described for monitoring conductivity, it could be used for monitoring any parameter in any process whether it be a water treatment processing plant or indeed any other process, whether chemical or otherwise.

It will also, of course, be appreciated that while the device is responsive to a signal from a central control apparatus, this is not necessary, the micro-processor in each device could be programmed to transmit signals to the central control station at predetermined or indeed at any random intervals as desired. Further, it will be appreciated that while the device has been described as transmitting signals in the event of an alarm condition, this is not necessary.

Additionally, while the housing for the electronic circuitry has been described as being a sealable housing, while this is preferable, it is not necessary. Indeed, in many cases, it is envisaged that the lens may be dispensed with altogether.

It is also envisaged that instead of powering the monitoring or control means with a battery, it could be powered by a low-leakage capacitor. In which case, it is envisaged that the low leakage capacitor could be powered by a photovoltiac cell mounted in the control or monitoring apparatus. The photovoltiac cell could be powered by daylight, or alternatively, could be directed to the central control apparatus and could be powered by a light beam directed from the control apparatus. Needless to say, in certain cases, it is envisaged that batteries other than lithium batteries could be used.

Additionally, it will be appreciated that the central control apparatus may be powered either by a battery or a mains supply, or any other suitable powering means. In fact, where it is powered by a battery, it is envisaged that it will be powered by a long-life lithium battery.

Further, it will be appreciated that while the process apparatus has been described as being a water treatment plant in the case of the embodiments of the invention described with reference to Figs. 4 to 9, the process plant could be any other suitable process plant besides water treatment. Indeed, while specific water treatment plants have been described, any other suitable construction of water treatment plant could be used without departing from the scope of the invention. It is also envisaged that the water treatment plant described with reference to Figs. 5 to 9 could be used for other treatments of water besides water softening. For example, it could be used for water purification and the like. In which case, the cation and anion tanks would be used instead for filtering the water.It is envisaged that the hydrochloric acid tank would be used for storing and regenerating the filter medium. Indeed, it will be appreciated that the water treatment plant 60 of Figs. 5 to 9 could be used for any of the following water treatment operations, water treatment chemical dosing and control, boiler feed water, cooling water and effluent treatment. Filters used could be screen filters, depth filters, sand filters, iron filters, carbon filters, micro filters ultra filters or reverse osmosis. Deionisation could be provided by base exchange softening, organic trap, dealkalisation, two bed exchange, (cation-anion) mixed bed exchange (cation-anion).

Further, it will be appreciated that while the monitoring devices have been described as comprising infra-red receivers, the receivers, if desired, could be dispensed with, and additionally in the case of the control devices, the infra-red transmitters could be dispensed with.

Claims

1. A monitoring device for monitoring parameters of a fluid or liquid, the device comprising a sensor, an infra-red transmitter for transmitting a signal from the sensor to a central monitoring station, an infra-red receiver to receive a signal and means to activate the transmitter in response to a received signal.

2. A monitoring device as claimed in Claim 1 in which an analog to digital converter is provided to convert the sensor signal to digital form for transmitting by the transmitter.

3. A monitoring device as claimed in Claim 2 in which the means to activate the transmitter is a micro-processor which controls the operation of the monitoring device, the microprocessor being connected to the analog to digital converter to receive a digital signal from the converter.

4. A monitoring device as claimed in any preceding claim in which a battery is provided in the device to power the device.

5. A monitoring device as claimed in any preceding claim in which the device comprises an elongated tubular housing sealably closed for housing the transmitter and receiver and other associated electronic components.

6. A monitoring device as claimed in Claim 5 in which the sensor extends from an opening in the housing, the sensor being sealably mounted in the opening.

7. A monitoring device as claimed in Claim 6 in which the housing is adapted for sealable engagement with a pipe or vessel with the probe extending into the pipe or vessel.

8. A monitoring device as claimed in any of Claims 5 to 7 in which a lens is sealably mounted in the housing for transmission and reception of an infra-red signal therethrough.

9. A monitoring device substantially as described herein with reference to and as illustrated in the accompanying darwings.

10. A process plant comprising a plurality of liquid holding tanks, pipelines interconnecting the tanks, valves to control the flow rate and direction of liquids between the tanks, monitoring devices as claimed in any of Claims 1 to 9 in the pipelines and/or the tanks to monitor certain parameters of the liquids flowing through the pipelines and/or in the tanks, control apparatus to control the op eration of the process plant, the control apparatus comprising an infra-red transmitter to transmit a signal to the monitoring devices, an infra-red receiver to receive transmitted signals from the monitoring devices, the control apparatus being controlled by a micro-processor.

11. A process plant as claimed in Claim 10 in which the control apparatus is mounted remotely of the monitoring devices.

12. A process plant as claimed in Claims 10 or 11 in which a housing is provided to house the tanks, pipelines and valves and monitoring means, and the control apparatus is mounted integrally with the housing.

13. A process plant as claimed in any of Claims 10 to 12 in which a display means is provided to display the monitored parameters, the display means being connected to the control apparatus.

14. A process plant as claimed in any of Claims 10 to 13 in which control devices are provided to control the valves, each control device being mounted adjacent to the valve which it controls, comprising an infra-red transmitter and receiver to receive and transmit a signal to and from the control apparatus, and a control means to activate the valve or pump means.

15. A process plant as claimed in Claim 14 in which the control means is provided by a relay.

16. A process plant as claimed in Claims 14 or 15 in which a digital to analog converter is connected between the infra-red receiver and the control means to convert a received digital signal into an analog signal.

17. A process plant as claimed in any of Claims 14 to 16 in which a micro-processor is provided in each control device to control the control device.

18. A process plant as claimed in any of Claims 10 to 17 in which the control apparatus comprises a voltage control regulator connected to the micro-processor, a clock signal generating means to deliver a pulse output at predetermined intervals to the voltage control regulator to activate the voltage regulator to in turn activate the micro-processor to update the clock of the micro-processor.

19. A process plant as claimed in Claim 18 in which a timer is provided to hold the clock signal output pulse for a predetermined period of time.

20. A process plant as claimed in Claim 19 in which the timer holds the clock signal pulse for twenty milliseconds, and the clock signal generating means generates a pulse every thirty-two seconds.

21. A process plant as claimed in any of Claims 18 to 20 in which the clock signal pulse from the clock signal generating means is delivered to one input of an NOR gate, the other input of the OR gate being connected to any one of a series of inputs to the control apparatus, the OR gate delivering the signal to the timer and in turn to the voltage regulator.

22. A process plant as claimed in Claim 21 in which the signal from the OR gate is fed through a series of AND gates.

23. A process plant as claimed in any of Claims 10 to 17 in which the plant is a water treatment plant.

24. A process plant substantially as described herein with reference to and as illustrated in Fig. 4 of the accompanying drawings.

25. A process plant substantially as described herein with reference to and as illustrated in Figs. 5 to 9 of the accompanying drawings.

26. A method for controlling a water treatment plant comprising the steps of: transmitting an infra-red signal from control apparatus to activate a monitoring device to monitor a parameter of the water, receiving the infra-red signal in the monitor ing device, transmitting the monitored parameter from the monitoring device in the form of an infrared signal in response to the received infra-red signal from the control apparatus, receiving the signal from the monitoring device in the control apparatus, transmitting an infra-red signal from the control apparatus to a control device to activate a valve in response to a monitored parameter rising or falling below a certain predetermined level.

27. A method as claimed in Claim 26 in which the method includes the step of transmitting an infra-red signal from the control apparatus to the control device to activate a valve after a predetermined time.

28. A method as claimed in Claim 26 or 27 in which the method further includes the step of transmitting a signal from the control device to the control apparatus to indicate the status of the valve under the control of the control device.

29. A method as claimed in any preceding claim in which the signals are transmitted in digital form.

30. A method for controlling a water treatment plant substantially as described herein with reference to and as illustrated in the accompanying drawings.