Ultraviolet detection tube quenching circuitry

Circuitry directed to the rapid de-ionization of ultraviolet detectors by increasing the mobility of the ionized gases within the tubes which will enable the tubes to more effectively operate at low temperatures. The circuitry includes connecting circuitry for shorting the elements of the tube such that they will be at the same potential immediately after firing and also includes circuitry for the shunting of the tube immediately after firing to limit the number of ions generated in the discharge process. The shorting of the elements increases the surface area of negative electrodes for the recapture of the ions and the distance through which the ions must travel is reduced by a factor of one-half.

FIELD OF THE INVENTION 
This invention relates generally to circuitry for the detection of 
ultraviolet radiation, which circuitry includes an ultraviolet detection 
tube and more specifically to the circuitry for the rapid de-ionization of 
such ultraviolet detection tubes. 
BACKGROUND AND OBJECTS OF THE INVENTION 
The use of ultraviolet detection tubes is well known in the prior art. 
Through use of such devices, it has been found that the ability of the 
tube to respond to ultraviolet is definitely affected by the temperature 
to which the tube is exposed. The lowered temperature slows down the rate 
of travel of the ions resulting from tube discharge and for situations 
which require a high number of discharges within a short period of time, 
the presence of these ionized particles has been found to cause false 
discharges. In practice, and that particularly related to fire detection, 
the false operation of such a detector has had adverse effects both from 
the economic and safety standpoints. In such fire detection situations, it 
is important that the apparatus not only properly detect a flame which is 
the source of the ultraviolet, but also that the apparatus not respond to 
ambient conditions to provide false actuations of the fire control system. 
The standard operation of a detector such as the Geiger-Mueller type is 
that when the electrodes of the detector are impressed with a voltage of 
sufficient magnitude, and when ultraviolet radiation strikes the cathode, 
the device will pass a current between the electrodes via the ionized 
gases created in the discharge process. The device will continue to 
conduct until the impressed voltage is reduced below the point that 
supports the ionization process. If, however, the voltage is restored and 
the ultraviolet radiation source is still present, the detector will again 
discharge for as long as the voltage level is sufficiently high. Thus, a 
tube of this type, in order to provide environmental testing for the 
presence of ultraviolet radiation must experience alternate ionization and 
a de-ionization of the gases between the electrodes of the detector. 
Should the de-ionization process not be sufficiently complete, restoration 
of the impressed voltage would result in discharge of the tube without 
ultraviolet initiation. 
In temperatures above approximately 30.degree. F., the de-ionization 
process can normally be accomplished by providing a short duration "off" 
time before restoring voltage across the electrodes. When the temperature 
drops, the mobility of the gases is decreased and the de-ionization 
process takes much longer. 
The primary purpose of this invention is therefore, to decrease the 
de-ionization time by one of several various alternatives. 
It is an object of this invention to decrease the de-ionization time of 
ulraviolet detection devices which devices contain an ionizable gas. 
It is an object of this invention to increase the de-ionization surface of 
an ultraviolet detection tube after discharge thereof such that the 
increased surface area will decrease the time for the de-ionization of the 
gas within the tube. 
It is a further object of this invention to control the number of ions 
generated in the discharge process of an ultraviolet device, which device 
contains an ionizable gas. 
It is a further object of this invention to provide a means for shorting 
the electrodes of an ultraviolet detection tube for the rapid 
de-ionization of gases within the tube after discharge thereof. 
It is yet a further object of this invention to provide a temperature 
responsive control circuitry for an ultraviolet detection device which 
will increase the time during which the electrodes of the device are below 
discharge voltage such that a longer time for de-ionization of the gases 
within the device is provided.

In accordance with the accompanying drawings, the principle of rapid 
de-ionization of the ionized gas within ultraviolet tubes is accomplished 
with various control circuitry. 
The preferred form of the invention and the circuitry therefore is 
illustrated in FIG. 1. This Figure includes a variation within itself and 
will be so described. In FIG. 1 as in all of the other views, the 
ultraviolet detection tube containing the ionizable gas is designated 10. 
The basic circuitry of FIG. 1 includes a source of power 11 connected in 
series to a first resistance 12 and thereafter connected to a parallel 
circuit. The parallel circuit has, in one leg thereof, a capacitor 13, and 
in the other leg thereof, a resistance 14 connected in series to a second 
parallel circuit which second parallel circuit provides, in one leg 
thereof a switching member 15 and in the other leg thereof, the detector 
10. As illustrated, the second parallel circuit is reconnected to a series 
resistance arrangement which includes a pair of resistances 16, 17. As 
also illustrated, the capacitor leg 13 and the switching-tube leg of the 
primary curcuit provide the outlet for the circuitry which will provide 
signal pulses. 
The operation of this basic circuitry is as follows: The detector tube 10 
is normally non-conductive. In this state, there is an impressed voltage 
across the electrodes. When an ultraviolet photon strikes the cathode of 
the tube 10, the gas therein becomes ionized and this ionization supports 
current flow through resistances 14, 16 and 17 as well as tube 10. When 
the voltage across 16 exceeds a predetermined value, the switching member 
15 turns on, thus shorting the electrodes of the tube 10, bringing them to 
a common potential, thereby increasing the surface area for the attraction 
of the ions of gas for the deionization of the same. It should also be 
noted, that bringing these electrodes to the same potential will also 
reduce, again by a factor of two, the distance that an ionized particle 
must travel to reach a surface for deionization thereof. With the values 
selected, the turn on time for switching element 15 is approximately 0.5 
milli-seconds and therefore the tube 10 is energized for only this short 
period of time, but without this additional switching circuitry the 
conducting time has been found to be approximately 10 milli-seconds. 
Therefore the conduction time is reduced by a factor of 20. 
The switching element 15 will remain in the on or shorting position until 
the capacitor 13 is discharged through resistances 14 and 17 as determined 
by their respective values. When the current flow decreases to less than 
approximately 1 microamp, element 15 will switch to the off position and 
capacitor 13 will recharge through resistance 12 until the voltage 
thereacross reaches the voltage required for ionization if there is still 
ultraviolet present or to the total value of the impressed voltage if 
there is no ultraviolet present. The tube 10 is ready to discharge 
immediately after the voltage across capacitor 13 exceeds the ionization 
potential. 
A modified form of the invention is also illustrated in FIG. 1. This 
modified form includes an additional parallel circuitry interposed, in 
series with the first resistance 12 and prior to the main parallel 
circuit. In the form shown, this added element includes a temperature 
responsive resistance 20 arranged in parallel with an additional 
resistance 21. Resistance 20 is commonly referred to as a thermistor and 
such a unit will increase in resistive value as the temperature decreases. 
With this inclusion, the time allowed for the tube 10 to de-ionize is 
increased due to the slower recharging of the capacitor 13. The operation 
of the circuit with this modification is varied only with the slower 
recharging effect. At normal temperatures or what may be termed elevated 
temperatures, this thermistor-resistance combination will not affect the 
total operation of the circuit as the mobility of ions is primarily 
affected by lower temperatures. 
The circuitry illustrated in FIG. 2 is a solid state version of the relay 
circuit illustrated in FIG. 4. In this schematic view, the tube is again 
designated 10 and a plurality of switching members 25, 26, 27 and 28 are 
provided. It should be obvious from this drawing that the switching 
element 26 will bring the electrodes of the tube to a common potential 
when the same is energized or switched to its on position. Elements 29, 30 
and 31 are control and analyzing gates. The output from each of these 
elements is determined by the input thereto. As illustrated, the 
recharging capacitor for the recharging of the tube 10 is designated 32 
and an additional capacitor 33 is provided in series between gates 30, 31. 
The primary difference obtained with this circuit and the relay circuit of 
FIG. 4 as compared to the circuit of FIG. 1 is the means for switching 
power from the tube 10 immediately upon the receipt of a signal therefrom. 
This arrangement will limit the ionization of gases within tube 10 and, 
obviously, such a limitation will insure more rapid deionization of the 
gases in tube 10. 
In its condition to detect ultraviolet but what may be termed a quiescent 
state, tube 10 is in a non-transmitting condition, elements 26, 27 and 28 
are in a non-transmitting or off condition and 25 is in a conducting 
condition. In this state, the outputs of 29 and 31 are low and the output 
of 30 is high. Capacitor 32 is also charged to the limit of the input 
power supply. 
When ultraviolet is present at the cathode of the tube 10, the tube 
transmits and switching element 27, receiving such transmission is turned 
on and a pulse is generated by 29, 30, 31, through capacitor 33 and 
resistance 34. The pulse width of the signal received by the switching 
element 27 is determined by the values of capacitor 33 and resitance 34. 
This pulse turns on switching transistors 26, 28 and when switch 28 turns 
on, switch 25 will turn off, thereby opening the circuit through the tube 
10 and capacitor 32. The closing of switch 26 shorts or brings the 
electrodes of the tube 10 to a common potential. Immediately following the 
generated pulse, the circuit returns to its quiescent state and following 
charging of the capacitor 32 the circuitry is in condition to respond to 
ultraviolet exposure. This circuitry then is a limiting circuit as well as 
being a circuit which will provide for the rapid de-ionization of the 
gases within the tube 10. 
The circuitry of FIG. 3 is a simple representation of a unit which will 
short the electrodes of the tube 10 after a signal is received from the 
tube. This signal is generated by the ultraviolet exposure of the tube and 
the shorting of the electrodes is provided by the switching element 39. 
The circuitry of FIG. 4 is the mechanical-electrical equivalent of the 
circuitry of FIG. 2. In this illustration, a two position switching 
element 40 is provided and this element is controlled and actuated by a 
solenoid device 41. As illustrated, the switching element 40 is arranged 
to control energy flow to the tube 10 through one 40a switch element 
thereof and the shifting thereof will bring the other switch element 40b 
into closed position thereby shorting the electrodes of the tube 10. This 
switching is accomplished upon a signal being generated through tube 10 by 
the impingement of ultraviolet upon the same and immediately upon such 
generation, voltage to the tube 10 is terminated to again limit the number 
of ions which are created by such impingement. After the tube 10 has 
pulsed, the switching is accomplished and a hold time for the solenoid may 
be provided to insure that voltage is terminated for a predetermined 
period of time. Whether such timing device is included, the inherent 
actuation and deactuation of such a mechanical device will insure a 
sufficient time for gas de-ionization of the tube 10. Upon de-energization 
of the solenoid 41, the switches 40a, 40b will be returned to their 
conductive and nonconductive positions, and the tube will be in condition 
to respond to ultraviolet exposure. 
With any of the forms shown and discussed herein, the purpose of the 
invention should be obvious. As stated, the primary consideration of the 
invention is to insure and speed the de-ionization of gases within the 
tube 10. This is obtained by increasing the deionization area of the tube, 
by limiting the number of ions or the extent of ionization of the tube or 
by a combination of both conditions. 
It should be obvious that this invention provides a means for insuring the 
responsiveness of an ultraviolet detection tube, particularly when the 
same is exposed to conditions which would adversely effect normal 
de-ionization of the gases within the tube.