GB836313A - Improvements in or relating to time switches embodying discharge tubes - Google Patents

Abstract

836,313. Control systems for resistance welding. PHILIPS ELECTRICAL INDUSTRIES Ltd. May 7, 1958 [May 8, 1957], No. 14615/58. Class 38 (4). [Also in Group XL (c)] A timing system comprises a gas tube fed via a resistor from a D.C. supply, a resistor connected between the cathode and the positive supply terminal, a mechanical or electronic switch between the cathode and the negative supply terminal, the control electrode being connected to a tapping across the supply; the timing being controlled by the discharge of a capacitor connected between the control electrode and cathode. In Fig. 1 the capacitor 4 is first charged via resistor 6 and part of the potentiometer 9. The timed period is initiated by closing a switch 7 which holds the tube 1 cut off until. capacitor 4 has discharged at a rate determined by the setting of the potentiometer 9. Tube 1 now conducts, providing a rapid fall of voltage between the output leads 14, 21. A discharge resistor may be connected at points 23, 24 and may be shunted by a diode to speed up the charging. In Fig. 4 (not shown), switch 7 is replaced by a further timer of the type shown in Fig. 1, so that two separate periods may be controlled by three output leads. Fig. 6 shows a part circuit of a combination of three such timers to provide control over three timed periods by leads 14, 21. A flip-flop formed by valves 30, 31 replaces the switch (equivalent to 7 of Fig. 1) of the last timer 1<SP>11</SP> and also provides re-setting of the system. Tube 30 is cut off when tube 31 is made conductive by an ignition pulse at 36. When the tube 30 is fired by a pulse at 37, tube 31 is cut off and timer 1<SP>11</SP> is started. Subsequently timers 1<SP>1</SP> and later 1 are started. When the last tube 1 fires, a pulse from the grid fires tube 31 and resets the system. If a repetitive operation is required, a time delay 41 is included so that the sequence may be restarted a certain time after the firing of tube 1. It is stated that the system may be coupled directly or via further tubes to control alternating current by means of a main pair of gas tubes connected in parallel opposition. Power frequency pulses from a saturated transformer may be injected into the system to provide synchronized operation. Resistance welding control.-The above-described system shown in Fig. 6 provides control of the duration of electrode pressure, welding current, and after pressure.