Neon circuit malfunction detector

A neon sign circuit is disclosed having a neon tube forming the lighted portion of the sign, a source of electrical power, and a high voltage transformer between the electrical power source and the neon tube. The circuit also includes a neon sign circuit malfunction detector circuit. This circuit includes a ground fault detector connected in the circuit between the source of power and the transformer, to ground, and to the neutral load side of the primary windings of the transformer. A pair of adjustable spark gaps are each connected to one of the secondary windings of the transformer between the transformer and the neon tube. A light source is connected between each spark gap and ground and light sensitive resistors are positioned adjacent to each light source. The resistors are connected between the ground connection of the ground fault detector and the neutral load connection between the transformer and the ground fault detector so that when a malfunction in the neon sign circuit occurs,a spark will jump one of the spark gaps to energize the light source, increase the resistance of the light sensitive resistor and cause the ground fault detector to cut off power to the transformer, as if it was sensing a ground fault.

This invention relates to a circuit for detecting a malfunction in a neon 
sign circuit generally, and in particular to such a circuit that will cut 
off power to the neon sign circuit when such a malfunction occurs. 
A neon sign circuit normally includes a neon tube forming the lighted 
portion of a sign, etc., a source of electrical power, and a high voltage 
transformer between the electrical power source and the neon power tube. 
Should the neon tube break, or a wire connecting the power source to the 
neon tube come loose, or if this loose wire falls to a grounded article, a 
potentially dangerous condition will exist. 
For example, if the neon tube breaks, but no short circuit occurs, the 
transformer is overheated because of a neutral (no) load condition and can 
cause a fire if the high heat melts down the transformer insulation. The 
same condition exists when a wire comes loose but no short occurs. When a 
wire comes loose from the neon tube's electrode and connects the 
transformer's output secondary to ground, the high voltage will cause a 
high voltage arc and very likely start a fire. 
It is an object of this invention to provide a neon sign circuit 
malfunction detector circuit that will sense when anyone or any 
combination of the three things described above occur and cut off power to 
the neon tube, by disconnecting the transformer's primary from input 
power. 
It is a further object and advantage of this invention to provide such a 
malfunction detector for a neon sign circuit that can be adjusted for the 
particular load of the neon sign circuit with which it is associated. The 
load varies with the size of the transformer, the number of neon tubes, 
the length of the tubes and the diameter of the tubes. 
It is a further object and advantage of this invention to provide a neon 
sign circuit malfunction detector circuit that includes a ground fault 
detector connected in the circuit between the source of power and the 
transformer that will be actuated to cut off power to the neon sign 
circuit when anyone or any combination of the three events described above 
occur. 
It is a further object of this invention to provide such a malfunction 
detector circuit that includes a ground fault interrupter circuit and an 
adjustable spark gap on the secondary side of the transformer that is 
adjusted so that no spark occurs during normal operation of the neon sign 
circuit but that will cause a spark to jump the gap when anyone or any 
combination of the three events described above occur, at which time the 
voltage jumping produced by the spark gap will light a neon glow lamp that 
is in direct proximity to a photo resistor thereby changing the resistance 
from low resistance to high resistance causing the ground fault 
interrupter circuit to cut off power to the neon sign circuit because the 
ground fault interrupter circuit interprets this as a ground fault.

In the usual neon tube circuit, power is supplied to the neon tube through 
a high voltage transformer, the neon tube being connected across the 
secondary of the transformer. This is true of the circuit shown in FIG. 1 
where neon tube 10 is connected across secondary winding 12 of high 
voltage transformer 14. Primary winding 16 of the transformer is connected 
to power source 18 through ground fault interrupter circuit 20. Ground 
fault interrupter circuits are well-known and so the circuit is indicated 
diagrammatically. Power from the power source is provided to primary 
windings of the transformer through conductor 22 connected to the power 
output terminal of the ground fault interrupter circuit. The other side of 
primary 16 is connected to the neutral load terminal of the ground fault 
interrupting circuit through conductor 24. The ground fault circuit is 
connected to ground through conductor 26. 
In accordance with this invention, each side of the secondary winding is 
connected to an adjustable spark gap. Specifically, conductor 28 is 
connected to one side of spark gap 30 and conductor 32 is connected to one 
side of spark gap 34. The other side of spark gap 30 is connected to neon 
light emitting source 36. Spark gap 34 is connected to similar neon light 
admitting source 38. Each light emitting source is located in a housing, 
such as housings 40 and 42 along with photosensitive resistors 44 and 46. 
Housings 40 and 42 enclose the neon light and photosensitive resistors so 
that no light from outside can enter the housing to make sure that they 
are affected only when light is produced by the neon light emitting source 
located in the housing with them. The photo sensitive resistors are 
connected to ground 26 through conductor 48. Each photo sensitive resistor 
is also connected to the neutral side of primary coil 16. 
Adjustable spark gap assembly 30 is shown in FIGS. 2 and 3. Adjustable 
spark gap assembly 34 is of the same construction. The assembly includes 
copper strip 52 having one end shaped to be held in the housing 50 against 
longitudinal movement by posts 54 that are attached to the bottom of the 
housing. Strip 52 extends out of the housing to be connected electrically 
to the secondary of the transformer. Neon light 36 is located in housing 
40. Also located in housing 40 is photosensitive resistor 44. Conductors 
56 connect the neon light and the resistor into the circuit as shown in 
FIG. 1. 
Conductor 58 connects the neon light to one end of strip 60 of electrically 
conducting material, such as copper. Strip 60 is held in the housing in 
the same manner as strip 52 by posts 62. End 60a of the strip is bent 
toward strip 52. The spark gap is the space between the end of strip 60. 
This can be adjusted by rotating screw 64 mounted in the wall of housing 
50. 
In operation, with power being supplied to the neon tube, the adjustable 
spark gap assemblies 30 and 34 are adjusted until a spark jumps across the 
gap. The gap is then widened a preselected amount so that during normal 
operations the voltage across the spark gaps will not produce a spark. 
Should a short or similar malfunction occur in the neon tube circuit 
causing an increase in voltage, a spark will jump across one or the other 
or both of the spark gaps causing one or the other or both of the light 
emitting devices 36 and 38 to emit sufficient light to cause the 
resistance of photo sensitive resistors 44 and 46 to increase. This sends 
a signal to the ground fault interrupter circuit that there has been a 
ground change in the circuit similar to a fault and the ground fault 
interrupter circuit will cut off power to the transformer. 
The spark gap assemblies should be on opposite sides of the balanced 
resistance loop. As shown in FIG. 4, four neon tubes 70, 72, 74, and 76 
make up the circuit. With spark gap assemblies 30 and 34 located on 
opposite sides of the load and balanced point B, at least one will 
function. For example, a short at A will cause spark gap assembly 34 to 
trip, but spark gap assembly 30 may not. So, preferably, two spark gap 
assemblies are used with each assembly located on opposite sides of the 
balance point in the circuit. In the event of an open circuit, such as 
when a tube breaks or when one of the leads is disconnected but no short 
occurs, both spark gap assemblies will trip simultaneously. 
From the foregoing it will be seen that this invention is one well adapted 
to attain all of the ends and objects hereinabove set forth, together with 
other advantages which are obvious and which are inherent to the apparatus 
and structure. 
It will be understood that certain features and subcombinations are of 
utility and may be employed without reference to other features and 
subcombinations. This is contemplated by and is within the scope of the 
claims. 
Because many possible embodiments may be made of the invention without 
departing from the scope thereof, it is to be understood that all matter 
herein set forth or shown in the accompanying drawings is to be 
interpreted as illustrative and not in a limiting sense.