MONITORING OF THE CONTINUOUS ADDITION OF A LIQUID AGENT TO WATER The invention relates to monitoring, and in particular to the monitoring of the addition of one liquid to another. The invention is seen to good effect in the monitoring of the continuous addition of a liquid agent to water to be used for domestic, industrial or commercial purposes, and so will be described in that context, but the scope of the invention is not to be limited to that use.

It is known to add a donor of chlorine, e. g. sodium hypochlorite, to a water supply.

Typically, the agent is drawn from a tank, via a pump, and is then added to the water supply.

It has been realised that things can go wrong and for this reason it is known to associate a chlorine monitoring device with the final pumped water supply to detect when too little (or too much) chlorine is present in the water. We have now realised that this monitoring technique is not good enough, because water which has no chlorine or too much chlorine must be dumped. The invention is based on the realisation that by continuously monitoring the addition of the agent any shortfall can be acted upon before unacceptable variances are observed by the chlorine monitor.

According to the invention in one aspect there is provided a water supply system including a main pump for continuously pumping a fast flow of a liquid dosing agent to a body of water, the system including monitoring apparatus for monitoring the continuity of the fast flow of the agent, the monitoring apparatus comprising means for forming the liquid into discrete moving drops, detecting means arranged to detect the passage of individual liquid drops and to generate corresponding output signals, and means responsive to the output signals from the detecting means, the monitoring apparatus being connected to a standby pump and arranged to activate the standby circuit when the main pump fails whereby the continuous supply of the liquid agent is maintained.

Preferably the monitoring apparatus is located on the dosing pump delivery pipework so that a disruption in the flow may be detected quickly whereby the standby supply can be activated as quickly as possible. In yet another aspect the invention provides a method of maintaining a substantially constant addition of a liquid dosing agent to a main volume of liquid, the method comprising passing a stream of drops of the liquid dosing agent through a light beam to generate a varying electrical signal and activating an auxiliary standby supply of the liquid agent in response to a cessation or slowing of the variation in the electrical signal.

Preferably the detecting means comprises a fibre optic arranged to detect the interruption or modification of a light beam directed across the path of the liquid drops.

The light beam need not be visible but could be, e. g. IR or of any other suitable electromagnetic radiation.

In yet another aspect the invention provides a pump system comprising a pump unit connected to a supply of a dosing agent and in circuit with monitoring apparatus as defined.

In order that the invention may be well understood it will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a block diagram showing the dosing system in accordance with the invention; Figure 2 is a vertical section through the form of monitoring apparatus of the invention; and Figure 3 is a plan view, partly in section of the monitor & PLC interface.

The apparatus comprises a system for dosing liquid chemical e. g. hypochlorite, to add a source of chlorine disinfectant to a supply of water for domestic, industrial or commercial use.

The system of Figure 1 comprises a main supply pipe 1 to introduce water to a reservoir (not shown) the system being arranged to dose the water with a liquid agent to chlorinate the water. The agent is sodium hypochlorite held as a concentrated liquid in tank 2. The agent is pumped by a peristaltic pump 3 via a pipeline 4 to a device M. That pipeline contains water drawn from a tank 5 (which in turn is supplied by a pipeline 6 from the main line 1). The diluted agent is supplied via an eductor 7 along a pipe and then to the main pipe 1 via pipe 8. In this way the hypochlorite is diluted and supplied at a low concentration to the main pipeline. A monitor unit 9 further downstream measures the level of chlorine and, if necessary, sounds an alarm, or actuates water pumping station pumps.

As shown best in Figure 2, the device M comprises a vertically mounted light transparent tube 11 e. g. of plastics such as polycarbonate or of glass. At the top end of the tube is a stopper 12 having a small diameter throughbore 13. The tube 11 is mounted in a frame which contains a pipe 15 leading to the dosing agent supply line. A length of optical fibre cable 16A, 16B is mounted on each side of the passageway 11 and arranged so that a light beam B extends across the tube and in the path of liquid 17 dripping from the stopper. The cables 16A, 16B are connected to a fibre-optic amplifier, not shown, arranged to generate a signal when the light beam is interrupted. A flow of the dosing liquid is passed via the device M so that a stream of drops falls from the stopper continuously. Each time a drip interrupts the beam a signal is amplified and sent to a PLC 10, (shown in Figure 3), which registers the flow. If, after a preset interval, the beam is not interrupted, (which interval can be set manually or by the PLC), a switch is triggered to connect a standby pump to the supply pipeline. In this way the monitoring device M can ensure that the supply of dosing liquid is substantially constant.

As shown in Figure 3, the cables 16A, 16B of the monitor device M are connected to a unit 30 comprising the cable terminations and a self teach amplifier. This provides a transistorised input to the PLC 10, which is connected to another unit 31 and monitor device Ms, connected to the stand by pump, not shown. The monitor device Ms is the same as device M and has the same beam system Bs. The amplifier is self-teaching, i. e. it learns to detect and register when the beam is interrupted and it activates the standby dosing circuit when the beam is not interrupted after a predetermined time interval. The PLC 10 may be arranged to activate the stand by pump in any convenient way. Preferably the PLC 10 records the signals from the transistorised input as digital pulses and if one is not generated in a specific time interval, e. g. 10 seconds, the PLC is programmed to activate the stand by pump and/or generate an alarm signal.

In use, dosing liquid is drawn by the pump from the main tank into the pipeline. Water is also drawn from the tank to enter the same pipeline and to dilute the agent. Because the detection is so rapid there is no risk of overdosing or supplying water free of dosing agent, either of which can cause problems.