The invention relates to the field of digital valves.

Specifically, the invention is concerned with reducing the energy usage of such a device.

The provision of digital valves on gas cylinders is a recent development in the field. The term digital valve encompasses at least manual valves with electronic sensors,

electrically-actuated valves with or without sensors, and valves comprising locating and communication devices.

Although reference is made to a "cylinder", it will be understood that the invention is applicable broadly to all portable pressurised gas containers whether they are

strictly in the form of a cylinder or not.

Such cylinders are used to supply gas for a range of

applications including welding and cutting hoses and

torches, gas packaging machines and laboratory equipment.

The various types of digital valve have in common the need for the devices (sensors, actuators, locating devices, and/or communication devices) to be powered electrically. The present invention is concerned with digital valves powered by a store of charge on the device, such as a battery or capacitor.

Digital valves on cylinders require small batteries in order to keep the weight of the assembly (valve and cylinder) to a minimum, and the cylinders may be retained for a long time, in some cases in cold environments. There is therefore a technical pressure to conserve the charge of a battery.

Accordingly, there is provided apparatus and a digital valve assembly defined by the appended claims.

For a better understanding of the invention and to show how the same may be put into effect, reference is now made, by way of example only, to the accompanying drawings in which: Figure 1 depicts a schematic representation of a fluid mixing system in accordance with the invention;

Figure 2 depicts a schematic representation of a gas

cylinder for use in the system of Figure 1; and

Figure 3 depicts a preferred digital valve for use in the system of Figure 1.

Figures 1 and 2 depict a first embodiment of apparatus for mixing fluids in accordance with the invention. The apparatus comprises: a plurality of digital valves 110a, 110b, 110c, each mounted on respective cylinders 100a, 100b, 100c; a fluid analysis unit 200; a controller 300; and a mixer 400. The cylinders 100a, 100b, 100c may store, for example, pressurised gases. Each digital valve 110 may be installed on its respective cylinder 100 to thereby control the flow of fluid into and out of the cylinder 100. The term digital valve assembly includes the digital valve 110 and may optionally also be considered to include the cylinder 100 when the digital valve 110 is mounted thereon. The mixer 400 has a plurality of inputs 401, 402, each for receiving a flow of fluid from a plurality of digital valves 100. The mixer 400 is arranged to mix the flow of fluid from each digital valve 100b, 100c connected thereto in order to produce a mixed output flow, provided via output 403. The mixer 400 may comprise a chamber such as a plenum.

The fluid analysis unit 200 is arranged to monitor the composition of a flow of fluid therethrough. For example, the fluid analysis unit 200 may monitor the concentrations of one or more components of the flow. The fluid analysis unit 200 is arranged downstream of the mixer 400 and

receives therefrom a mixed flow of fluid. Optionally, the fluid analysis unit 200 may receive a flow from a digital valve 110a directly, not via a mixer 400.

Optionally, the fluid analysis unit 200 may receive a plurality of separate flows from different sources and monitor these separately.

The fluid analysis unit 200 may be provided with a target concentration and be configured to calculate an error between the actual concentrations and the target

concentrations. Preferably, the fluid analysis unit 200 may wirelessly receive the target concentration. Preferably, the fluid analysis unit 200 may wirelessly transmit a correction signal to one or more of the digital valves 110 when an error is identified between the actual concentration and the target concentration. The correction signal may represent a target value of a parameter of the digital valve 110, or may represent a change of a parameter of the digital valve 110 (either option could be considered a correction signal) . For example, the fluid analysis unit 200 may be provided with a target flow rate and use this to determine whether to increase the provision of one component of a mixture or decrease the provision of another component or both in order to achieve a target flow rate and target concentration.

A controller 300 may be provided to transmit to the fluid analysis unit 200, preferably wirelessly, target data representing the target mixture concentration for the output flow. The controller 300 may be a tablet computer or smart phone. The target data may be entered into the controller 300 by a user via a user interface, or may be selected from one or more options stored on the controller 300, or

accessed from an external data source using the controller 300.

In some embodiments, the controller 300 may be configured to transmit to the digital valves 110, preferably wirelessly, target data representing the target flow rate and/or target pressure for the corresponding cylinder 100 (or correction data representing adjustment of the flow rate and/or

pressure) . However, in more preferred embodiments, the controller 300 only transmits to the fluid analysis unit 200, and it is the fluid analysis unit 200 that instructs the digital valves 110.

Each digital valve 110 is arranged to receive a correction signal, preferably wirelessly, from the fluid analysis unit 200. Each digital valve 110 comprises an actuator 120 for

adjusting the pressure and/or rate of flow of fluid from a cylinder 100 storing fluid. The actuator 120 may be an electromagnetic actuator such as a solenoid or motor.

The actuators 120 of the digital valves 110 preferably comprise an adjustable regulator for adjusting the pressure of the fluid leaving the cylinder 100. Alternatively, or additionally, the actuators 120 of the digital valves 110 preferably comprise a flow controller for adjusting the flow rate.

For example, the flow controller may allow the mass flow of the fluid through the digital valve 110. The flow controller may for example comprise a mass flow sensor.

Figure 3 shows an example of a suitable digital valve 110, which preferably comprises: a flow channel 116 from an inlet 112 to an outlet 113; a processor 111; a store of charge 115 (for example, a battery or capacitor) ; means for attachment to an external power supply; and an actuator 120.

In the example of Figure 3, the actuator 120 is used to adjust the pressure regulation function of a regulator 117. Specifically, in this example, the actuator 120 comprises a motor that can drive a linear gear that increases or

decreases the compression of a spring against a membrane to vary the pressure of a fluid flowing along the flow channel 116. Alternatively, or additionally, the actuator 120 may also comprise a flow controller (for example, a mass flow controller) for controlling the rate of flow of fluid along flow path 116.

In a digital valve assembly, the digital valve 110 is mounted on a cylinder 100 such that the inlet 112 is in communication with the cylinder 100.

The outlet 113 may be attached to external piping or tubing. Each digital valve 110 is arranged to adjust the flow therethrough using the actuator 120 based on the received correction signal. For example, when the actuator 120 comprises a regulator, the digital valve 110 is arranged to adjust the pressure of the flow therethrough using the actuator 120 based on the received correction signal and when the actuator comprises a flow controller, the digital valve 110 is arranged to adjust the rate of the flow

therethrough using the actuator 120 based on the received correction signal.

In preferred embodiments, the digital valve 110 periodically determines whether it is required to provide a command to control the actuator 120 to adjust the flow (irrespective of whether the actuator 120 is configured to adjust the rate and/or pressure of the flow) . Of course, the adjustment of the actuator 120 comes at a cost in terms of the depletion of stored charge. It is therefore preferable, when the digital valve is powered by its store of charge, for the digital valve 110 to limit the use of the actuator 120 to provide a flow adjustment not more frequently than a maximum adjustment frequency (this corresponds to imposing a minimum period between subsequent uses of the actuator 120) . For example, the correction signal from the fluid analysis unit 200 could demand flow changes at a greater frequency than the maximum adjustment frequency of the digital valve 110. In which case, the digital valve will use the actuator 120 to adjust the flow at the maximum adjustment frequency.

In another example, the correction signal from the fluid analysis unit 200 could demand flow changes at a lesser frequency than the maximum adjustment frequency of the digital valve 110. In which case, the digital valve will use the actuator 120 to adjust the flow at the lesser frequency.

In preferred embodiments, the digital valve 110 may be connectable to an external power supply 122. In which case, there is no longer a benefit in enforcing a maximum

adjustment frequency. Such a digital valve 110 may therefore be programmed to operate in a self-powered mode or an externally-powered mode.

Such a digital valve 110 will operate in the self-powered mode when powered by its store of charge, and will operate in the externally-powered mode when powered by an external power supply 122.

In the manner set out above, in the self-powered mode, the digital valve 110 will limit the use of the actuator 120 to provide a flow adjustment not more frequently than a maximum adjustment frequency.

In externally-powered mode, the digital valve 110 will not limit the frequency of use of the actuator 120. The maximum frequency of use of the actuator 120 will therefore be set as the maximum achievable by the electronics (e.g., the clock speed of the digital valve 110) . Preferably, the digital valve 110 is arranged to sense whether it is attached to an external power supply 122 and to thereby automatically select the self-powered mode or the externally-powered mode.