Protection circuit against electric shocks during welding
First Claim
1. A circuit for controlling the power supply to a shielded electrode of the type used in a shielded metal arc welding process (SMAW) whereby to protect a user from electric shocks, said circuit comprising a measuring circuit for determining the dynamic impedance value between said electrode and a workpiece to be welded;
- and a power feeding device connected in series with said power supply and said electrode, the power feeding device being controlled by said impedance measuring devie so as to render conductive said power feeding device when the dynamic impedance value detected by said measuring device reaches a level value lower than a predetermined threshold impedance value for delivering power to said electrode, said predetermined threshold impedance value being set at about 500 ohms whereby a wet human body will not be subjected to an electrical shock when the body contacts the electrode and the workpiece simultaneously.
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Accused Products
Abstract
A circuit for controlling the power supply to an electrode of the shielded type, such as that used in a shielded metal arc welding process (SMAW) whereby to protect a user from electric shocks. The control circuit is a protection circuit which serves to protect welders against electric shocks by decreasing the circuit voltage between the electrode tip and the workpiece to be welded. An AC or DC power supply may be used to feed the electrode. The control circuit is comprised of a high impedance voltage source applied to the electrode, a detection circuit for determining the level value of the impedance appearing between the electrode and the workpiece. The detection circuit compares the impedance thus detected with a threshold impedance and generates a control signal when the detected impedance is lower than the threshold impedance. The control signal operates a driver circuit which energizes a power feed device serially connected between the electrode power supply and the electrode itself. The predetermined threshold impedance value is set at about 500 ohms whereby a wet human body will not be subjected to an electric shock by contacting the electrode and the workpiece simultaneously.
16 Citations
16 Claims
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1. A circuit for controlling the power supply to a shielded electrode of the type used in a shielded metal arc welding process (SMAW) whereby to protect a user from electric shocks, said circuit comprising a measuring circuit for determining the dynamic impedance value between said electrode and a workpiece to be welded;
- and a power feeding device connected in series with said power supply and said electrode, the power feeding device being controlled by said impedance measuring devie so as to render conductive said power feeding device when the dynamic impedance value detected by said measuring device reaches a level value lower than a predetermined threshold impedance value for delivering power to said electrode, said predetermined threshold impedance value being set at about 500 ohms whereby a wet human body will not be subjected to an electrical shock when the body contacts the electrode and the workpiece simultaneously.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A circuit for controlling the power supplied to a shielded electrode of the type as used in shielded metal arc welding process (SMAW) whereby to protect a user from electric shocks, said circuit comprising a high impedance voltage source applied to said electrode;
- a detection circuit for determining the dynamic impedance value existing between said electrode and a workpiece for comparing said impedance to a predetermined threshold impedance value and for generating a control signal when the detected impedance is lower than said threshold impedance;
a driver circuit operative upon receiving said control signal, a power feeding device including at least one thyristor and mounted in series between said power supply and said electrode, said thyristor being fired by said driver circuit when the latter is energized, said predetermined threshold impedance value being set at about 500 ohms whereby a wet human body will not be subjected to an electrical shock by contacting the electrode and the workpiece simultaneously. - View Dependent Claims (15, 16)
- a detection circuit for determining the dynamic impedance value existing between said electrode and a workpiece for comparing said impedance to a predetermined threshold impedance value and for generating a control signal when the detected impedance is lower than said threshold impedance;
Specification