DE7409448U - ULTRAVIOLET RADIATION SOURCE - Google Patents

Description

• /

20/71 Lü / dh

BBC Aktiengesellschaft Brown, Boveri & Cie., Baden (Switzerland) Ultraviolet radiation source

The invention relates to a device for generating ultraviolet radiation with a high spectral radiance which the radiation in an eiae thermoemissive cathode and A discharge tube with a cylindrical discharge space of diameter D = 4 ... 20mm with a mercury / argon filling through a wall-stabilized direct current gas discharge at a pressure p "of the mercury between 5 * 10 and 5 * 10

Torr and a current density j of the discharge current I between

2 1 and 25A / cm is generated.

Such a device, in short: high-current, low-pressure UV radiation source, is known, for example, from US Pat. No. 3 * 679 * 928. the known radiation source is intended to generate UV radiation

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especially with wavelengths below 2,300 Angstroms (Ä) serve, and used to stimulate photochemical reactions. However, the known radiation source has so far not found entry into the relevant market, probably because they are due to plasma vibrations There is a tendency for instabilities, and because of the power consumption that is too high with regard to the UV yield, it is not economically bearable Lifetimes.

Weak current, low pressure UV radiation sources are well known from fluorescent tube technology. For example, from the US-PS 3 '?. 17'2 ^ 8 a UV radiation source with a mercury gas discharge known at which the mercury vapor pumped from the anode to the cathode during discharge can flow back to the anode through a line connecting the cathode with the anode compartment. A similar source is known from d-.r US-PS 3 '617' 792, in which the return flow line concentrically surrounds the discharge tube.

Finally, there are also many types of high-current, high-pressure mercury and low-pressure burners for Raman spectroscopy known (e.g. Brandtmüller-Moser, Introduction to Raman spectroscopy, Steinkopf-Verlag, 1962, pp. M4-159, 28Η-285, 298-303). However, these burners are designed practically exclusively for longer shaft lengths, namely over 1000 8, and

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are not suitable for generating radiation in the far ultraviolet. Otherwise it concerns with the known Burners also predominantly to laboratory equipment, which for a technical-economical Use out of the question.

The object of the present invention is to create a UV radiation source with a high spectral radiation density, in particular for the wavelength λ - 25 37 η, which is ideally suited for industrial use from a technical and economic point of view.

This object is achieved in that, according to the invention, in a device of the type described at the outset

the discharge tube comprises a pressure equalization space connecting the cathode space to the anode space, the sum of the volumes of the cathode space, the anode space and the pressure equalization space being greater

is than the volume of the discharge space ,

- the pressure p. of argon is between 0.01 and 0.10 Torr , and

- A first control element provided int which the current density j of the discharge current I to a constant

2 value j _n regulates between 1 and 2SA / cm, and

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7 a second control element is provided, which regulates the pressure p "of the mercury to such a value that the yield " O of the line of wavelength 25 37 R, ie the ratio of the spectral radiant power for the wavelength λ = 25 37 % to in the Discharge fed electrical

Performance, at least 80% of the maximum yield rr \

(.max for the set current density j _Q is.

With the device according to the invention it is possible for the first time adapt the radiation power to the material to be irradiated by adjusting the discharge current density j, and yet, by varying the mercury pressure accordingly, always staying in the vicinity of the maximum of the UV yield, what not only for them. Economic efficiency, but also for an optimal service life of the radiation source of the greatest importance is. The special design of the volumes according to the invention the discharge space and the anode, cathode and pressure compensation space prevent plasma oscillations and thus a stable burning process, as well as an even pressure of the discharge medium, which can only be achieved by the coldest Position of the system is determined. The inventive argon pressure has the consequence that the lamp without unacceptably large Effort can be ignited, but igniting from the cathode to the anode through the pressure equalization

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going "is prevented.

Further features and advantages of the invention emerge from the exemplary embodiments explained below with reference to figures. It shows:

Fig. 1 is a discharge tube having M-shaped discharge space, Γ \ i'ig · 2, a discharge tube with coiled discharge space, Fig. 3 shows a discharge tube of U-shaped discharge space

and control elements for setting the discharge current and the mercury pressure,

Fig. 4 shows the cathode, anode and pressure equalization space in the Detail,

Fig. 3 a variant of the anode space, 5 shows a discharge tube with ignition and power supply unit,

6 shows the currents and voltages generated in the power supply unit,

7 shows that for generating the ignition pulses for the power supply unit serving control device,

Fig. 8 measurement curves of operating parameters of a device according to the invention, and

9 shows the relationship between the discharge current density j _Q

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and the mercury pressure determining temperature ^T · He ^{'the for e} ^ - ^nen optimal operation must be taken of the device according to the invention.

In Fig. 1, a discharge tube 1 is shown, which has a cathode compartment 2, an anode compartment 3, one of these two spaces connecting pressure equalization space 4, and an M-shaped discharge space 5 comprises.

FIG. 2 shows a variant of the discharge tube 1 shown in FIG. 1, the discharge space 5 being coiled.

The discharge tube according to Fig. 1 is used for surface irradiation,

.in the goods arranged according to FIG. 2 from the axis of the helix.

As shown in more detail in FIGS. 3, U and la, the The discharge tube 1 has a cathode 9 in the cathode compartment 2 and an anode 10 in the anode compartment 3.

The cathode 9 is thermoemissive or thermionic, i.e. it emits electrons when heated. You can direct or be indirectly heated. It consists, for example, of a coiled nickel mesh strip with a BaO coating. It is from one

7409448 10.1177

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Surrounding pot 24 ', which is open towards the discharge space 5. As a result, the cathode 9 acts in the manner of a hollow cathode. The pot 24 can also be made of nickel. He can end the Cathode 9 be conductively connected.

In FIG. 4 the anode 10 is a graphite body which is used to enlarge the surface in order to improve the cooling Is cup-shaped. Since the anode 10 is subject to high-energy electron bombardment during discharge and becomes very hot as a result, the graphite body is coated with a hard carbon layer, a pyrographite coating 19. This is completely non-porous and prevents the anode from emitting foreign matter or being sputtered when it is heated. The pyro ~ graphite coating 19 is provided with a zirconium coating 20. This not only improves the emissivity of the anode, but also get a very effective getter.

In Fig. 4a, the anode 10 is formed from solid molybdenum in the form of a plate. For the purpose of enlarging the surface and improving the cooling, in particular by radiation, is the Surface with grooves, ribs or the like. Provided. The use of molybdenum as a refractory metal is therefore particularly useful because molybdenum, e.g. in contrast to tungsten, can be processed better. Also the anode 10 off Solid molybdenum can be coated with a zirconium coating 20.

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The 'discharge tube 1 is filled with argon at a pressure between 0.01 and 0 _r l Torr and mercury. While the filling of the gaseous argon does not cause any problems, a mercury dispenser 22 is provided for AaB introduction of liquid mercury at room temperature. This consists of a metal channel 21 with a mercury-aluminum-zirconium compound, which is stable at room temperature. Breaks the connection only by heating to 900 ⁰ C.

Then the mercury is released and condenses on the coldest Point 8 of the discharge tube 1, preferably in the pressure equalization space U, as a mercury drop 23 (Fig. 3). The zirconium-aluminum connection is retained as a getter »

Both the cathode 9 and the anode 10 are surrounded by hollow cylinders 11, 12, for example made of nickel. These hollow cylinders serve as thermal shields. This leads to the associated electrode 9 or 10 does not develop a voltage gradient, which would cause sputtering ("cathode atomization"), are the hollow cylinders 11, 12 suspended electrically insulated, their potential "floats".

The discharge space 5 is cylindrical and has an inside diameter D of 4 ... 20 mm.

The invention is now based to a large extent on the

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that, for optimal operation of the UV radiation source according to the invention, the mercury pressure p _H for certain

Values j. the discharge current density very specific values p " υ ng

must have. In the radiation source according to the invention, this pressure p _H is determined by the temperature T ^ of the coldest point 8 of the system, which is preferably located in the pressure equalization space 4. In the device according to the invention, therefore, in addition to the first control element 6 for regulating the discharge to a specific current density j. A second control element 7 is also provided, in which the actual temperature of the coldest point 8 is entered by a temperature sensor 16, for example a thermistor, and which then regulates the temperature of this point 8 to the setpoint temperature by means of a heater 17. The heater 17 can be a heating resistor, possibly coupled with a Peltier element, but also a fan which blows heated air against the point 8 and the anode space 3.

(0)

To determine the correct mercury pressure p "or the

associated temperature T ^, it is necessary to know the course of the yield M of the line of wavelength 2537 8 as a function of P _H or T "_. This relationship is shown in Fig. 7c). Accordingly, the maximum yield shifts with a discharge tube of length L = 170 cm (measured from cathode 9 to anode 10 through discharge space 5) and the inner diameter D = 10 mm of discharge space 5, as well as an argon

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Contact pressure p _Ar = 0.05 Torr, from Ί £ ° * ä * 60 ° C for I = 4A, from £ 85 ° C for 1 = 12A. After according to the invention p "so

it is regulated that the yield of at least 30% vonrri

C max must be, thus results from Fig.7c)

- for I _ft = HA on tA ⁰⁾ = 52 69 ° C,

0 ed

- for I ₀ = 8A a T ^ ⁰⁾ = 61 86 ° C, and

- for I ₀ * 12A a Ty ^ = 72 96 ° C.

More specifically, the regulation for the regulation of the mercury temperature T "depending on the selected discharge current density j _Q can be formulated as follows:

(grd) = 2 Λ () j „(A / cm ² ) + HB (grd).

This rule for the second control element 7 is shown by the straight line in FIG. 8 and applies within the following limits:

- p "= 10 ~ ² .,. 4-10 " ¹ Torr, corresponding to T" = 45 ° C ... 100 ° C

Hg Hg

- p _Ar = 2 x 1θ " ² 8 x 1θ" ² Torr

- D = 8 .... 12 mm

- J ₀ = 1 .... 16AZCm ² .

If T "is regulated to the values T" which result from the equation given above, ti is at least very close to its maximum. However, as it is for practical reasons

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The radiation source according to the invention is also permissible Operating at 80% "7 can be derived from the equation

( ITl el X

resulting T "values can be deviated by + 15% without ng -

that this would depart from the scope of this invention.

In Fig. 7a) the arc voltage U is shown as a function of the discharge current I, and in Fig. 7b) as a function of the mercury temperature T _H. It can be seen from this that, in the case of a radiation source with the parameters of the invention, the arc voltage can neither be used as a measurement nor as a control variable.

Although the pressure equalization space 4 is important for stabilizing the discharge, on the other hand it creates the risk that the discharge will ignite directly through the pressure equalization space H. This risk increases with increasing argon pressure P * -, To counter this, according to the invention, essentially three measures can be taken, individually or preferably together:

The geometry of the pressure equalization roughness ' + is chosen so that the voltage for the ignition of an arc through the pressure equalization space 1 is as high as possible. A diameter of the pressure equalization space U that is as small as possible is recommended for this purpose. However, the diameter must be large enough that a pressure equalization between

7409448 iail77

the electrode spaces 2 and 3 can take place. Under these Aspects, a design as shown in FIG A stable connection between the two electrode spaces 2 and 3 is used, the pressure equalization space 4 is a flow tube of diameter d = 2 .... 4 mm. This flow tube can be oval to increase the ignition voltage or otherwise be out of round. (At this point it should also be mentioned that the electrode spaces 2 and 3 as well as the tube of the pressure equalization space t and the tube m serving the mechanical connection are made of normal glass, and only the discharge space 5 enclosing tube must be made of quartz glass for the purpose of transparency for the UV radiation. Such as from 4, the quartz tube is attached to the electrode spaces by means of a so-called horsetail connection 18 connected. In doing so, glass rings are fused together, which have the coefficient of thermal expansion of quartz and normal glass approach each other).

The electrically floating hollow cylinders 11, 12: The generated electric field distribution is influenced by internal measures. It has been shown that the hollow cylinders 11, 12 generate a field which focusses into the pressure equalization space 4. By arranging a

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- Electrically insulated suspended grid 13 on at least one of the inputs into the pressure equalization space H is the Field distribution significantly improved. In addition, the hollow cylinders 11, 12 themselves counteract as obstacles a spark.

The electric field distribution is influenced by external measures. To do this, one has to be preferred ^ negative electrical potential, e.g. -loOV against the

Cathode 9, horizontal conductive coating 15, e.g. made of silver, gold or graphite, proved to be particularly effective on the tube IH. It is important that the topping is over the approach of the tube 14 is pulled up to the electrode spaces 2,3. This will make the focus field almost completely eliminated.

An important idea of the invention also lies in the supply and control device for the discharge current, the “first control element” 6. This must essentially meet the following requirements suffice:

- When the discharge tube 1 is ignited with a cold discharge space (T "is low), the applied arc voltage must be a multiple of the operating arc voltage.

- During operation, the current must be at the specified, constant

7409448 10LH77

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- th value I _Q can be maintained.

- Different values I must be adjustable.

The current must not go through zero as the radiation source otherwise it would expire.

The control element should be inexpensive and reliable.

That shown in Fig. 5 and forming part of the invention Control element 6 fulfills these requirements.

The control element 6 has a power unit 25 which comprises two anti-parallel connected thyristors 30 and a bridge rectifier 31. The power unit 25 is connected, for example, to phases R and T of the three-phase network. The ignition angles oC of the two thyristors are controlled by the control unit 26 explained below with reference to FIG. At oC = 180, each passage of current is blocked by the two thyristors 30. At «* - = 0 ° the two phase voltages are fully let through.

The input of the control unit. 26 is from a curable NTC resistor, the NTC unit 29, controlled, which is heated by the voltage across the shunt 32. This creates a sluggish current regulation achieved what in terms of

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The tendency of the system to vibrate (negative characteristic of the gas discharge) is particularly advantageous.

Another advantage of this technology is that the NTC unit 29 is connected to an auxiliary voltage before ignition can be preheated so that only a small current flows when igniting. With the ignition, this auxiliary voltage is then switched off and the NTC resistor cools down accordingly the discharge current increases slowly up to the stabilized target value. This causes the current to overshoot when Ignition prevented.

To ignite the discharge, the outside of the cathode is 2 an auxiliary electrode 33 is provided, to which a high-voltage pulse is fed from an ignition unit 34. Instead of the auxiliary electrode 33, an ignition pin can also be attached to the discharge tube 1 be provided.

The ignition voltage U in the amount of 500 ... 700V is provided by the DC voltage source 27, which has a bridge gliding device; comprises a reactor and a capacitor. The DC voltage source 27 is connected in parallel to the power unit 25 via the high-resistance series resistor 28 (R s "1 .." 5 kfl). This ensures that when the value of the output

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Current * i of the power unit 25 is zero, a small holding torque i via the current-limiting series resistor 28

ρ now

continues to flow through the discharge tube 1, which prevents the discharge from going out.

In Fig. 6, the currents and voltages of the power unit 25 are shown.

The "white" impulses in the u / t diagram control the one who dark hatched the other thyristors 30.

The pulses I correspond to an ignition angle oC = 180.-As can be seen, the current i * and accordingly also the Current i to zero.

The pulses II correspond to an ignition angle <Λ «» 60 ^ο . The result is the bold curve for the current i *, and behind the bridge rectifier 31 the pulsating direct current i and i. The pulsating direct current i includes the pulsating direct voltage u, which fluctuates between the ignition voltage U and the arc voltage at maximum current. The pulsating direct current i or the pulsating direct voltage u are damped in a choke 35 before they are fed into the discharge tube 1.

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The ~ control is set in normal operation so that the direct current component of the current i together with the holding current i. just gives the necessary DC discharge current I _Q corresponding to a discharge current density j.

The control unit 28 shown in FIG. 7 functions in the essential as follows:

The NTC resistor of the NTC unit 29 is part of a bridge circuit that also has resistors 36, 37 and 38 includes. 36 is a NTC resistor identical to the aforementioned NTC resistor. 37 is a fixed resistor. At 38 the setpoint I of the discharge current I is set * ucr nüxxZwcig uc7 jj £ ^: uCjC £ nsCiiciLii

Tr 1, Tr 2 and Tr 3 formed. Transistor Tr 3 blocks as long as the bridge circuit is balanced. As the imbalance grows, Tr 3 opens more and more and induces one growing current in the tranbistor Tr M-.

The light emitting one emits proportional to the current through Tr 4 The diode of the optocoupler OK increases the light intensity, which in turn further opens the transistor of the optocoupler OK.

/the Current flowing through the transistor of the optocoupler OK

a charging capacitor UO is charged, its voltage then

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a unijunction transistor UJ opens when its threshold voltage is reached.

The "· Ti'äiiSi» toi · the OptükOppIex'-S OK and the frame of the transformer T connected downstream of the unijunction transistor UJ are fed by a pulsating DC voltage, which is generated by full-wave rectification in the bridge rectifier Ul and cutting to the Zener voltage of the Zener diode Z An alternating voltage is applied to the bridge rectifier 41, which runs synchronously with the voltage feeding the antiparallel thyristors 30. As can be seen, pulses are generated in the transformer T on the secondary side whenever the unijunction transistor UJ has been opened by the capacitor HO. These impulses then control the thyristors 30. The impulses will come earlier the further the transistor of the optocoupler OK is opened Discharge direct current I _Q results. An imbalance in the bridge reduces or increases the value of oc.

The control unit described has two notable ideas in particular:

- So that when the discharge tube 1 is started, it is not immediately subjected to full current, which becomes unbearable

Would lead to stability problems, the heating resistor of the NTC unit 29 is initially set to the start resistor 39 switched and the NTC resistor preheated. After ignition of the gas discharge is then on the shunt 32 switched over, so that the NTC resistor, as only a small discharge current for the time being flows, cools. This causes the ignition pulses at the output of the transformer T to change from the initial block position at «c <=> 180 only slowly to the later operational situation pushed over.

So that the base voltage of the transistor connected upstream of the charging capacitor 10 does not change constantly changing emitter potential is disturbed, the galvanically separated control is via the optocoupler OK provided.

A final, very essential part of the invention resides in the use of a device as described above for dry short-term cold sterilization in situ, especially of packaging material for food that does not penetrate Heat can be sterilized in a packaged state, e.g. dairy products, or liquids with sufficient UV transparency (e.g. water), or for surface sterilization of bulk and powder.

Claims (1)

- 20 - 20/74 3. c h u t ζ a η s ρ r Ü c h e 1. Device for generating ultraviolet radiation with high spectral radiance, in which the radiation in one a thermoemissive cathode and a cylindrical discharge space of diameter \ D = 4 .... 20 mm having a discharge tube with a * mercury / argon filling by means of a wall-stabilized synchronous current gas discharge at a pressure p "of mercury between 3u 5.10 ~ ^ and 5.10 Torr and a current density j of the 2 charge current I between 1 and 25 A / cm is generated, the pressure p. of the argon is between 0.01 and 0.10 Torr and a first control element (6) is provided, which the current density j of the discharge current, I on. regulates a constant value j _Q between 1 and 25 A / cm, and "a second regulating element (7) is provided which _{regulates the pressure P H of} the mercury to such a value that the yield Vj of the line of wavelength 2538 S, ie the ratio of the spectral radiant power for the wavelength Λ = 2537 Å to the electrical power fed into the discharge, at least 80 % of the maximum yield η for the set current density j _Q is _| 7409448 11/10/77 21 - 20/74 characterized in that the discharge tube (1) connects the cathode compartment (2) to the anode compartment (3) Comprises pressure equalization space (4), the sum of the volumes of the cathode space (2), the anode space (3) and the Pressure equalization space (4) is larger than the volume of the discharge spaces (5). 2. Device according to claim 1, characterized in that the geometric design of the pressure equalization space (4) is such that its flow resistance is at most is the same as that of the discharge space (5), but its ignition voltage for a through-ignition between the electrode spaces (2, 3) under operating conditions is greater than fü " the discharge space (5). 3. Device according to claim 1, characterized in that the cathode (9) and the anode (10) each of a metallic . Conductive, electrically insulated suspended hollow cylinder (11, 12) are surrounded. 4. Device according to claim I _9, characterized in that at least one of the two inputs into the pressure compensation space (4) is closed by a metallically conductive, electrically insulated suspended grid (13). 7409448 10.1177 G 74 09 448.7 March 4th, 1976 Lü / Approx 20/74 5. Device according to claim 1, wherein the pressure equalization space (4) in a tube (14) between the ends of the Legs of the discharge space (5) provided electrode spaces (2, 3), characterized in that the the pipe (14) containing the pressure compensation space (4) has a metallically conductive coating (15) on the outside which extends over the approach of the tube (14) to the electrode spaces (2, 3) is pulled out. 6. Device according to claim 1, characterized in that the anode (10) is used for the purpose of enlarging the surface cup-shaped graphite body coated with a pyrographite coating (19). 7. Device according to claim 1, characterized in that the anode (10) with a purpose to enlarge the surface Grooves, ribs or the like provided solid metal body made of molybdenum. 8. Device according to claim 6 or 7, characterized in that on the pyrographite coating (19) or on the surface of the solid metal body, a zirconium coating (20) is provided. c r ■ t - 23 - 9. Device according to claim 1, characterized in that a mercury dispenser (22) is provided in the anode compartment (3). 10. Device according to claim 1, characterized in that at the coldest point (8) of the discharge tube (1), preferably in the pressure compensation chamber (4), a temperature sensor (16), preferably a thermistor, is arranged, and a heating (17) acting on the coldest point (8) of the discharge tube (1) is provided. 7409448 iail77