The present invention relates to an automatic gas detector and more particularly, to a safety circuit for de-energizing a welding machine, upon sensing a dangerous level of combustible gas.
Heretofore in the use of welding machines in environments where combustible gases may be present, such as in and around an oil refinery, conventional audible and/or visual (red light) gas monitor alarm devices have not always been effective in warning a welder of the existence of a dangerous level of combustible gas. The noise from welding machines and surrounding equipment in industries such as at oil refineries, are often so loud as to prevent the welder from safely hearing an audible alarm. Visual lights, if present, are often ineffective because the welder typically faces a different direction during his work and his vision is blocked by his mask as well as by surrounding equipment.
A dangerous situation exists when combustible gases are present with the use of welding machines. Under such circumstances, the arc welding machines can cause a fire, explosion, or detonation which could seriously damage life, limb and property.
The automatic gas monitor of the present invention solves the above problem by providing a gas monitoring apparatus (system) which will automatically de-energize an arc welder when a dangerous level of combustible gas is detected at the site of arc welding.
Detectors for sensing the presence of combustible gas have been known for some time. Examples of some of the previously proposed gas detector systems are disclosed in the following U.S. Pat Nos.:
______________________________________ U.S. PAT. NO. PATENTEE ______________________________________ 2,881,274 Ray 3,471,264 Crozier 3,609,732 Kasahara et al 4,129,030 Dolan ______________________________________
The Ray U.S. Pat. No. 2,881,274 discloses a gas detecting device comprising a pair of bimetal members and means for heating one of the members with the heating means being influenced by the presence of hydrocarbon gases in the surrounding atmosphere for increasing the heating effect when such gases are present. Deflection of the bimetal member will energize a relay which will then energize a circuit for energizing an alarm or a control element.
The Crozier U.S. Pat. No. 3,471,264 discloses a gas detection device including a gas sensing wire which is heated to a temperature in the neighborhood of 850.degree.to 900.degree. F. and which, when exposed to combustible gas, will, as a result of the burning of the gas, increase its temperature to a value as high as 1500.degree. F. This will cause rotation of a drum associated with the wire which will activate a circuit to operate an audible and/or visual alarm.
The Kasahara et al U.S. Pat. No. 3,609,732 discloses a gas responsive switching device for detecting gas concentrations in the air using a heated semiconductor. The gas detector is coupled to two relays, one of which can be used to operate a ventilating fan and the other of which can be used to operate an alarm.
The Dolan U.S. Pat. No. 4,129,030 discloses a sensing apparatus for sensing gases. The sensing apparatus includes a relay which is operated when a certain level of gas is detected. The sensing apparatus includes a bridge circuit and an indicating means for detecting current changes in the bridge circuit. The indicating means can include an alarm to alert people in the area of the presence of a detected gas.
None of the above patents, however, disclose a system which de-energizes a welding machine when a dangerous level of gas is present.