US2326154A - Thermal relay for fluorescent lamps - Google Patents

Description

Aug. 10, 1943. H. J. M CARTHY THERMAL RELAY FOR FLUORESCENT LAMPS Filed Sept. 12, 1940 J j'l' aa'rlizy INVENTOR.

ATToE/ve Y through the eyelets 4. The resistance Patented Aug. 10, 1943 UNITED STATES PATE NT OFFICE THERMAL RELAY FOR FLUORESCENT LAMPS Henry J. McCarthy, Danvers, Mass, assignor to Sylvania Electric Products of Massachusetts Inc., a corporation Application September 12, 1940, Serial No. 356,566

1 Claim.

lamp to be preheated before the discharge is I started between them.

Another object is to provide a starting switch which will be so timed in its action that no greater interval of time will elapse for the preheating of the cathode than is absolutely necessary.

A further object is to provide a switch which will function under all starting and restarting.

Another object is to provide a switch which will be so mounted as to be capable of withstanding accidental, careless or rough usage without havpossible conditions of ing the precisely adjusted parts thrown out of alignment.

A feature-of this starting apparatus is that it eliminates the unnecessary time lag present in many switches during the starting and restarting period. I

Another feature of this switch isthat it is so mounted that even if it were dropped or otherwise mishandled, the precisely adjusted parts would not be disturbed.

Other objects, advantages and features will be apparent from the following specification taken in conjunction with the accompanying drawing in which:

Figure 1 is a front perspective of the thermal relay assembly with the mounting plate shown dotted for clarity.

Figure 2 is a side elevation detail of the thermal relay.

Figure 3 is a front perspective viewed from below of the thermal relay assembly with the container partly cut away tov show the insulating means.

Figure 4 is a schematic wiring diagram of the thermal relay.

Similar reference characters refer to similar parts in the several views of the drawing and in the specification which follows. The switch in my invention comprises a condenser, a resistance rod supported between and connected to the two lead-in wires, a bimetallic strip bent around the resistance rod, and a high and two low resistance points.

The condenser I is mounted on the mounting plate 2, having its lead-in wires 3 rod 6, supextending ported between and connected to the lead-in wires I and 8, is also mounted on the mounting plate 2 but on the side opposite the condenser I. The lead-in wires 1 and 8 of the resistance rod 6 are joined to the lead-in wires 3 of the condenser at the eyelets 4. The joining of these two sets of lead-in wires at the eyelets 4 may be done by spot-welding, soldering or some similar means.

The lead-in wires 3 of the condenser I are projected through the eyelets 4 in the mounting plate 2. and extend down through the eyelets 9 in the circular base plate III and into the base pins 5 where "they may be soldered. Although eyelets 4 and 9 are used in the mounting plate 2 and the base plate I0, respectively, any other material may be used that will permit a joining and fixing of the lead-in wires at these points. Eyelets, or some similar means are necessary due'to the fact that the base plate and mounting plate are made of Bakelite or some similar insulating material.

The supporting arm II of nickel or some similar material extends inwardly from the lead-in wire I, and attached to the inward end thereof is the bimetallic strip I2 which is bent around the resistance rod 6. Attached to the inner side of the free end of the bimetallic strip I2 is the low resistance contact 25. The resistance rod may have thereon an insulating coating I3 of, for example, alumina and shellac.

I have found that an insulating coating of alumina and shellac is best suited for the particular purpose for which it is herein employed. I apply two coats of a dewaxed shellac and then two coats of an alumina-shellac mixture. Each coat isbaked before another coat is applied. Although I have used two coats of shellac and twocoats of alumina and shellac the number of coats may be varied inasmuch as uniformity of the -coating is the object to be attained. I have just applied two coats of shellac before applying any alumina because with the shellac foundation a higher breakdown voltage is obtained. This coating also prevents the bimetallic strip from cutting through the resistance rod.

wardly therefrom and The supporting arm I4 of nickel'or some similar material extends inwardly from the lead-in wire 8 and attached thereto and projecting upparallel to the bimetallic strip I2 is the strip I5 to which is attached the U-shaped arm I6 of nickel or some similar material. Attached to one end of this U-shaped arm is the high resistance contact II, which maybe of carbon and which is normally closed with the bimetallic strip I2. Attached to the other end of the U-shaped arm is the low resistance contact I8, which may be of silver and which is normally open in respect to the bimetallic strip 12. This low resistance contact acts as an auxiliary starting means for if the filaments of the lamp have not been sufliciently heated to start the discharge across the lamp by the time the bimetallic strip breaks away from the high resistance contact H, the voltage across the resistance rod 6 will continue to heat the bimetallic strip l2 and cause the strip l2 to bend back causing the low resistance contact 25 attached thereto, to touch the low resistance contact l8 thus short-circuiting the resistance rod and starting the preheating of the lamp filaments.

The resistance rod should have a high resistance, say 40,000 ohms. For this resistance I have used, for example, a resistance rod, 0.45 inch long and .065 inch in diameter. For my high resistance contact I have used carbon, having a contact resistance of about 15 to 30 ohms. For my low'resistance contacts I have used silver, having a resistance of a fractional part of an ohm. Although I have used these particular materials, my invention does not necessitate the use of these exact same materials. It is suiiicient that a high resistance contact point, low resistance contact points andahigh resistance rod be used. A condenser of .006 microfarad across the contacts has proven to be advantageous for the elimination of radio interference.

The mounting plate 2 is not mounted flush on the base plate [0, but is so out as to be elevated from the base plate at the points where the condenser lead-in wires 3 extend down into the If this were not done it would be cuite difficult to centrally locate the mounting base pins 5.

plate 2 on the base plate l and still have the wires 3 extending down into the base pins in their proper positions. The base pins may be of the type suitable for use in a socket of the type described in the copendingapplication, Serial No. 331,793 filed April 26, 1940.

The manner in which this switch is mounted allows for considerable accidental misuse. Due to the fact that several of the partswhich' are vital to the operation of the switch are very finely proportioned and the slightest change therein would cause ineffective or inefiicient operation, this switch is mounted in a manner as to have those parts which are not finely proportioned and sensitive, absorb the shocks of accidental misuse.

The lead-in Wires 3 of the condenser I are quite flexible. Due to this flexibility of these wires, and the fact that the mounting plate 2 is not flush mounted on the base plate l0, any movement or disturbance of the base plate will not disturb the switch elements because the switch mount as a unit will merely bend forward or backward, the shock'being entirely absorbed by the flexible lead-in wires of the condenser.

The entire switch unit may be inserted in a metal container I9 and may be insulated therefrom by a thin tube of insulating paper 22 around the inner wall of the container l9. and a wafer 21 of insulating material in the top of the container. -Ihis container may have several tangs 20, on the open end which may bendg over the base 'plate l0 after the switch has been inserted in the container. The base plate ID has several notches 2|, therein, over which the tangs 20 are bent. If these tangs 20 ever became loose and permitted the base plate to move, the switch would not be afiected, for the movement of the switch would be absorbed by the flexible wires 3 of the condenser, thereby protecting the more sensitive and vital parts of the switch and preventing them from being thrown out of alignment.

The contour of the mounting plate may take any desired shape. The contour, as shown in Figure 1, has been selected because it facilitates and makes easier the welding operations on the thermal relay. The contour of the sides of the base pins may be fiat or grooved depending on the type of contacts used. If a wire contact is used, I have found that pins with grooved sides provide a firmer contact surface.

What I claim is:

In a thermal relay for electric gaseous discharge lamps: a pair of rigid lead-in wires; a relay means attached to said lead-in wires, said relay means comprising: a resistor, a'contact of material such as carbon having a high contact resistance, a low resistance contact, a bimetallic strip electrically contacting said high resistance contact when said resistor is unenergized and in a position to be distorted by the heat developed in said high resistance contact when the latter passes current, and to open said contact when distorted sumciently, said bimetallic strip also being so positioned as to be distorted by the heat developed in said resistor when the latter passes current and to short circuit said resistor bymaking contact with the low resistance contact, when distorted sufficiently; amounting plate of insulating material on which said relay means is mounted through said lead-in wires, a condenser mounted through semi-flexible lead-in wires on said mounting plate on the side opposite the relay means, a base plate of insulating material to which saidmounting plate issubstantiallyperpendicular, a-pair of contact pins extending fromsaid base plate, said lead-in wires of said condenser extending through said mounting plate and base plate and into said base pins, 2. metal container enclosing said thermal relay and attached to said baseplate and a tube of insulating paper wound around the inner walls of said container to insulate said'container from said thermal relay.

HENRY J. MCCARTHY.

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