GAS MONITORING SYSTEM

Field of the Invention

The invention relates to systems to monitor the use of a gas in a factory or laboratory gas distribution system, to detect leaks, system malfunctions, and inappropriate system settings. The invention has particular application in monitoring the use of inert gases in m u lti -station welding systems.

Background

Many industries use gaseous feedstocks as part of a manufacturing or production process. Historically these were provided by means of individual gas cylinders located at each point of consumption within the factory or production system. As factories have become more streamlined, it is now more common to provide a central gas storage location and to transport the gas around the factory to the various points of use by means of a pipework distribution system. Whilst such a distribution system has clear advantages in servicing the gas requirements of the factory, it becomes increasingly difficult to detect leaks within the distribution system or to audit the use the gaseous components at each individual point of use. The present invention seeks to overcome many of these difficulties and is presented with particular reference to the use of inert shielding gases in a multi-station electric arc welding facility.

Summary of the Invention

Accordingly, the invention provides:

In a first aspect: apparatus to monitor the use of gas in a gas distribution system having one. or more individual gas consuming units within the system, said apparatus comprising: an inlet gas consumption monitor; and a controller configured to: receive information on the expected gas consumption in the system; receive a measure of gas consumption from said inlet gas consumption monitor; calculate the difference between said expected and measured gas consumption over a given monitored period; and raise an alarm if said difference is outside predetermined limits.

In a second aspect: apparatus according to the first aspect wherein said information comprises the operating periods of the welding system in which said expected gas consumption is essentially zero and said monitored period is within one or more of said operating periods.

In a third aspect: apparatus according to the second aspect, further comprising shut-off valves within the gas distribution system, said valves being controllable by a signal from said controller; and wherein said controller is further configured, on detection of gas consumption from said gas consumption monitor during a period of expected non- consumption of gas, to sequentially shut off said valves and thereby isolate or determine the location of any gas leakage. By isolating sections of the pipework and re-measuring the gas consumption, the location of a leak may be determined, and the leak isolated by control of one or more such shut-off valves.

In a fourth aspect: apparatus according to any preceding aspect further comprising gas flow meters at individual gas consuming units and wherein said controller is further configured to: receive a measure of gas consumption at the or each gas consuming unit; receive information on the expected gas consumption at the or each gas consuming unit; calculate the difference between said measured and expected gas consumption at the or each gas consuming unit; and raise an alarm if said difference is outside predetermined limits.

In a fifth aspect: apparatus according to the fourth aspect wherein said gas distribution system comprises a multi-station welding system, and said gas consuming units comprise welding stations, said apparatus further comprising means to measure a parameter at a welding station bearing a known relationship to gas consumption, and wherein said controller is further configured to calculate the expected gas consumption at the or each welding station from said parameter.

In a sixth aspect: apparatus according to the fifth aspect wherein said parameter comprises the rate of welding wire consumption.

In a seventh aspect: apparatus according to aspect 5 wherein said parameter comprises the duty time of an arc welding station.

In an eight aspect: apparatus according to aspect 5 wherein said parameter comprises a measure of gas concentration within or surrounding the system or monitored unit thereof.

The scope of the invention also includes apparatus substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings.

The scope of the invention also includes a gas monitoring method in which predicted gas consumption within a factory gas distribution system, drawn from known or demanded performance of one or more individual gas consuming units within a gas distribution system, is logged and in which actual gas consumed from a gas supply inlet is subsequently measured; and the difference between the two - if any - dictates whether the gas consumption over a given monitored period is to be regarded as normal or as abnormal.

The scope of the invention also includes: A gas monitoring system or method in which predicted gas consumption, drawn from know or demanded performance of one or more individual gas consuming units within the system, is logged and in which actual gas consumed from a gas supply inlet is subsequently measured; and the difference between the two - if any - dictates whether the gas consumption over a given monitored period is to be regarded as normal or as abnormal.

Preferably, the performance of the gas consuming units in the system is monitored as those units operate and is fed to a controlling means which co-ordinates the resultant information.

More preferably, the controlling means compares its information, obtained from the expected and/or demanded and/or operationally logged performance information with that which the controller is simultaneously or substantially simultaneously measuring by way of gas actually consumed; and raises an alarm if the compared difference between the two fails to satisfy acceptable parameters.

More preferably also, the controlling means monitors in real-time the performance of an individual unit within the system - for example a welding unit - and determines whether or not gas - for example shielding gas - is flowing adequately or at all and compares that observation with information stored and/or with gas being supplied to the unit; and decides whether or not an alarm is to be raised.

More preferably also, the controlling means makes its decision on the basis of a comparison of gas being consumed or expected to be consumed, and another parameter whose rate of consumption bears a known relationship to gas consumption.

More preferably also, the other parameter comprises the rate of welding wire consumption. More preferably also, the rate of welding wire consumption is determined by measuring the change in weight of the drum of wire as it is consumed.

More preferably also, the other parameter is a measure of atmospheric conditions within or surrounding the system or any monitored unit thereof.

The scope of the invention also includes a gas monitoring system substantially as described herein with reference to and/or as illustrated in any appropriate combination of the accompanying text and/or drawings.

The scope of the invention also includes a method substantially as described herein.

Brief description of the drawings

Figure 1 is a schematic diagram illustrating an embodiment of the invention and showing a range of sensors, control elements and input-output devices.

Description of the preferred embodiments

Figure 1 is a schematic diagram of a multi-station welding facility, generally indicated by 1. In arc welding processes, shielding gases are used to protect the piece to be welded from the action of atmospheric gases such as nitrogen and oxygen. Various inert gases may be ^' used such as argon and helium (for non-ferrous welding). Inert gas mixtures may also be used, such as argon-helium. For any particular welding operation, there is a particularly desirable rate of gas flow depending primarily on the weld, the type of shielding gas employed as well as the operational parameters of the welding operation itself such as electric current and the overall speed of the welding operation. As well as ensuring that shielding gas is not wasted, it is clearly important that the shielding gas is used at an optimal rate to ensure good quality welds.

In the welding facility illustrated in figure 1, elements of each of the welding stations are enclosed within the indicated box 2. In this instance, the welding station 2 comprises a supply of welding wire 3 and shielding gas flow meter 4, a manually-operable flow control valve 5, a welding arc detector 6 and an environmental gas monitor 7.

The welding gas is fed from a central storage location through a total gas flow meter 8 and distributed to a number of welding stations via a pipework system. Each welding station, or group of welding stations, may be isolated from the system by means of a welding station shut-off valve 9.

At the heart of the gas monitoring system is a controller 10. The controller 10 may be conveniently implemented in software using e.g. an industrial microcomputer, or may be conveniently implemented using programmable logic controllers. Information 11 concerning the shielding gas requirements in relation to the welding operation, details of the times of operation of the welding station and other key matters is loaded onto the controller 10.

The various elements of the welding facility send or receive information to or from the controller by means of appropriate transducers and control signals. For example, the main shielding gas flow meter 8 may have the form of a mass flow meter to transmit output reading 28 to the controller 10. Similarly the flow meter 4 at each welding station may transmit its measured flow rate 24 to the controller 10. The periodic use of welding wire may readily be monitored by e.g. weighing the drum of welding wire 3 at intervals to determine wire usage 23 which may then be transmitted to the controller 10. In order to determine the active periods of arc welding, a welding current or spark detector 6 maybe employed to determine the intervals of welding operations; alternatively a direct measure of the welding current may be made. In either case the signal quantifying the welding duty time 26 may be readily transmitted to the controller 10.

In its basic form, the gas monitoring system acts by logging the daily gas consumption by the factory. This gas consumption can be compared to the information 11 stored in the controller 10 and the two figures compared to determine whether the gas consumption is normal or abnormal.

With this configuration, the system is also capable of carrying out simple gas leak detection. The operating periods of the welding facility are programmed into the controller 10. This information could comprise e.g. the operating hours and shut down breaks of the welding operators. For example, if the welding facility operates two shifts per day then the information 11 provided to the controller 10 might indicate that the factory will be shut down between the hours of 10.00pm and 6.00am. During this time period, the controller can log the gas flow through the main flow meter 8 by means of its transmitted signal 8; if any gas flow should occur during this time the controller can raise an alarm condition to indicate a gas leak in the system.

In other circumstances, e.g. if the factory is in operation for 24 hours per day, then the information 11 provided to the controller 10 might detail the rest or meal breaks in operation in the factory so that the controller 10 can carry out the leak detection during those periods.

In a more sophisticated embodiment of the gas monitoring system, one or more solenoid shut-off valves 9 may be installed at pre-set places within the gas pipework system. The

valve, or valves, 9 may be controlled by a signal 29 from the controller 10. With this facility, should a gas flow be detected from the main gas flow meter 8 during a period when the factory is not operating, then a sequence of commands within the controller 10 may sequentially isolate sections of the gas distribution pipework by means of the shut-off valve, or valves, 9 in order to isolate and/or determine the location of any gas leakage. In factories using explosive fuel gases (rather than shielding gases in the welding example) the safety benefits of such a system would be extremely useful.

In a yet more sophisticated embodiment of the gas monitoring system, welding stations 2 are provided with a flow meter 4 to measure the flow of shielding gas at the station, and to transmit a signal 24 indicative of the flow rate to the controller 10. Information 11 is supplied to the controller to indicate a desired upper and lower limit to the gas flow rate at each welding station. Should the welding gas flow rate deviate from the desired bounds (e.g. because an operator has manually set the flow rate incorrectly, or as a result of a fault on the system) the controller 10 can be programmed to indicate an alarm condition.

As a further feature, welding stations 2 are provided with a welding arc detector set that transmits a signal 26 to the controller 10, the signal being indicative of whether a welding operation is in process. For example, start or stop signals from the controller might be sent when a welding arc is struck and when the welding current ceases respectively.

Alternatively, the signal 26 might comprise a measure of the welding current being employed. In this way, the controller 10 may readily monitor the welding set to determine whether shielding gas is flowing when there is no welding arc and so detect gas leaks between the outlet and the welding torch. Again, an alarm condition can be raised by the controller 10 if such a condition arises.

In a yet further sophisticated embodiment of the gas monitoring system, the consumption of welding wire 3 may be measured at the welding station 2. This may be conveniently effected by e.g. measuring the change in weight of the drum containing the welding wire 3 and the measurement 23 transmitted to the controller 10. The ratio of welding wire consumption to shielding gas consumption will be a known parameter of the welding process, as will the range over which this ratio may vary, and this information 11 can be loaded into the controller 10. By this means, the controller may be readily programmed to

determine whether the gas usage falls out of the desired parameter range, and again trigger an alarm condition should this be the case.

In a further embodiment of the system, an environmental gas detector 7 is also provided. In the case of systems using inert gases which might cause an asphyxiation hazard, especially where used in confined areas, such as in welding operations, the gas monitor 7 may comprise an oxygen monitor atmospheric oxygen concentrations does not fall significantly below around 21%. A measured reading below this would be indicative of a leak of inert shielding gas, and the controller 10 can readily be programmed to detect this and to either raise an alarm, or shut off the gas supply to that particular welding station 2 by means of the solenoid shut-off valve 9. In situations where fuel gas is being used (e.g. oxy-acetylene cutting), the gas detector 7 might comprise an acetylene monitor, again to directly detect a gas leakage..