US3187221A

US3187221A - Control apparatus

Info

Publication number: US3187221A
Application number: US272164A
Authority: US
Inventors: Philip J Walsh
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-04-10
Filing date: 1963-04-10
Publication date: 1965-06-01
Anticipated expiration: 1982-06-01

Description

June 1, 1965 P. J. WALSH 3,187,221

CONTROL APPARATUS Filed April 10, 1963 INVENTOR United States Patent 3,187,221 CONTROL APPARATUS Philip J. Walsh, 239 Phelan Ave., San Francisco, Calif. Filed Apr. 10, 1963, Ser. No. 272,164 2 Claims. (Cl. 315-182) This invention relates to apparatus for operating gas discharge tubes, as for example, fluorescent lamps and sign tubing.

Fluorescent tubes are characterized by the fact that the greater the current through them, the lower the voltage they require. If supplied by a constant voltage source, the current through them will increase to a value that destroys the tube. To prevent this in conventional types, a ballast impedance is included in circuit with the tube, which drops the voltage across it as the current increases, the impedance usually being built into the transformer as leakage reactance. Accordingly the transformer must be built to supply a much higher voltage on open circuit than is required across the tube in normal operation. Furthermore, a different voltage transformer is required for each different length of tube. Tubes cannot be operated in parallel, for if they were, one would carry all of the current and be destroyed. Conventional transformers are bulky in comparison to their power output and correspondingly expensive. They operate at a low power factor i.e., the power company must supply a large current in relation to the power supplied, and therefore the rate charged for the power used is relatively high.

Among the objects of the present invention are to provide automatic control apparatus for the operation of gas discharge tubes of the same length and diameter, or of dilierent lengths and diameters in parallel and supplied by a common source such as a transformer. Further it is an object to provide means to control the switching action of the parallel gas discharge tubes and their series condensers so as to produce stable operation and good waveform of the current flowing through the tubes for maximum light output.

Referring to the drawing:

The single figure is a system diagram depicting one form of my invention.

In the drawing, I show a source of alternating current power 1 connected through the switch 3 to the primary winding 5 of the transformer 7 having the secondary winding 9. This transformer is preferably of the low reactance type described and claimed in my patent, Number 2,875,378. The two gas discharge tubes 11 and 13 can be of any length up to the limit determined by the value of the voltage supplied by the secondary 9. Many tests of the invention were made using two tubes of the same length and diameter, two tubes of diflferent lengths, and two tubes of different diameters. Satisfactory operation of the tubes occurred in all of the tests. The waveform of the tube current, and switching action of the tubes can be changed by adjustment of the rheostat 15 to produce maximum light output from the tubes.

When the arm 17 of the rheostat 15 is moved to the point 21, the resistor is short circuited, the

condensers

23 and 25 are connected in parallel and all of the current flows through only one of the tubes. That is, only the tube that is electrically shorter than the other tube will light up.

When the arm 17 is moved to the point 19, the resistor is disconnected and the switching action of the tubes is such as to produce many current pulses through each tube for each half cycle of the fundamental frequency of the source 1. The tubes switch on and off, one at a time, one is on while the other is off. The action can best be described by starting With a charge of the same polarity in each condenser. That is, when switch 3 is opened, it will Patented June 1, 1965 be found that if the right hand terminal of condenser 23 is plus, the right hand terminal of condenser 25 will also be plus as shown by the plus and minus signs in the drawmg.

Now let us assume that both condensers are charged so that both right hand terminals are plus and that the half cycle of the voltage across coil 9 is'building up from zero value and making its left hand terminal plus, and that the tube 11 is electrically shorter than the tube 13. When the voltage across coil 9 in series with the voltage across condenser, 23 is high enough to strike an arc in tube 11, tube 11 switches on and condenser 23 discharges through tube 11. This causes a reduction in the value of the voltage across secondary 9 and the voltage across condenser 23 falls to a low value. Thus the voltage across tube 11 falls to a value too small to maintain the are through tube 11, so the tube switches olf. The half cycle of voltage across coil 9 continues to rise and when the voltage value across tube 13 reaches its striking value, tube 13 switches on and condenser 25 discharges through tube 13. At this point both condensers are discharged and no current flows through the tubes. But the value of the voltage across coil 9 is still rising and when it reaches the striking value of the tube 11, tube 11 switches on and condenser 23 is charged in the opposite direction, as illustrated by the plus and minus signs in circles. The voltage built up across condenser 23 bucks the voltage across coil 9 and tube 11 switches off leaving a charge in condenser 23 of the polarity illustrated by the plus and minus signs in the circles. When the value of the voltage across coil 9 reaches the striking value of tube 13, tube 13 switches on and condenser 25 takes a charge and of the polarity shown by the plus and minus signs in the circles. At this point, with both condensers charged and both tubes switched ofr', the voltage across coil 9 suddenly drops from its peak value to zero. When the next half cycle of voltage builds up across coil 9, making its terminals plus and minus as illustrated by the plus and minus signs in the circles, the actions just described repeat.

With the arm 17 set on point 19 the system requires careful adjustment of the voltage of the source 1 and tube lengths to avoid flicker and to obtain stable operation.

By means of the rheostat 15, stable operation is ob- 'tained, the timing of the switching action controlled and tube current waveforms for best light output obtained. The setting of the rheostat 15 is not critical. The rheostat 15 can be adjusted to a value of resistance that causes both tubes to switch on and off together and the current through the tubes can be made to approach sine wave form.

In one of the tests of this invention, tube 13 was made up of several lengths of 15 millimeter mercury sign tubing connected in series, to make a total length of 45 feet. Tube 11 was made up of the same kind of tubing connected in series, to make a total length of 40 feet. Each of the condensers had a value of .025 microfarad. The

value of the current through each tube, as measured by a thermal milliammeter, was 50 milliamperes. The noload voltage across coil 9 was 4300 volts R.M.S. The input power was 325 watts and the power factor was 91%. Rheostat 15 had a value of about 60,000 ohms. The loss in resistor 15 was about 6 watts. The total length of tubing lighted up by this small low voltage light weight control unit was feet. The potted cased unit weighed about 20 pounds.

According to the tube footage chart, published by the manufacturers of conventional luminous tube transformers, to light 85 feet of 15 millimeter mercury tubing, would require two 9,000 volt, 60 milliampere transformers. 42.5 feet of tubing connected across each trans- 7 The test circuit described is only one of the many pos-- sible ones'and it is not intended as limiting the scope of the invention as defined in' the claims that -follow.

I claim: 7 1. In a gas-discharge tube lighting circuit, a pair of gas discharge tubes adapted for connection to a source of alternating current power, a single reactor comprising a condenser connected in series with each tube, and variable impedance means connected from one condenser to the other condenser, whereby the timing of the switching action of said tubes and the waveform of the current in said tubes can be changed by adjustment of said variable impedance.

2. The combination as defined in claim 1 wherein said variable impedance, means comprises a variable resistor.

No references cited.

10 DAVID J. GALVIN, Primary Examiner.

Claims

1. IN A GAS-DISCHARGE TUBE LIGHTING CIRCUIT, A PAIR OF GAS DISCHARGE TUBES ADAPTED FOR CONNECTION TO A SOURCE OF ALTERNATING CURRENT POWER, A SINGLE REACTOR COMPRISING A CONDENSER CONNECTED IN SERIES WITH EACH TUBE, AND VARIABLE IMPEDANCE MEANS CONNECTED FROM ONE CONDENSER TO THE OTHER CONDENSER, WHEREBY THE TIMING OF THE SWITCHING ACTION OF SAID TUBES AND THE WAVEFORM OF THE CURRENT IN SAID TUBES CAN BE CHANGED BY ADJUSTMENT OF SAID VARIABLE IMPEDANCE.