US3817693A

US3817693A - Safety interlock for burners

Info

Publication number: US3817693A
Application number: US00337568A
Authority: US
Inventors: C Sebens; A Russo
Original assignee: Perkin Elmer Corp
Current assignee: Applied Biosystems Inc
Priority date: 1973-03-02
Filing date: 1973-03-02
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18

Abstract

This is a safety interlock in a laboratory burner for insuring that no fuel (or special oxidant) can be supplied to the burner under certain conditions. In particular a plug is attached to a removable burner head and a jack is rigidly attached to the other parts of the burner assembly; fuel flow is inhibited (as by disabling of an electric switch which opens a normally closed solenoid valve in the fuel supply) unless the plug is in the jack, so that no fuel can flow when the head is removed from the burner. Where more than one type of burner head is used with different fuel or oxidants, a second switch (say, controlling the flow of a special oxidant) in the jack is actuated by the special (longer) plug associated with only those burner heads intended to be used with the special oxidant (or fuel), so that such special oxidant can be supplied only when the burner head specifically designed for it is attached to the burner assembly.

Description

United States Patent [191 Sebens et a1.

[ June 18, 1974 SAFETY INTERLOCK FOR BURNERS [73] Assignee: The Perkin-Elmer Corporation,

Norwalk, Conn.

Filed: Mar. 2, 1973 Appl. No.: 337,568

US. Cl. 431/153 Int. Cl. F2311 11/36 Field of Search 431/153, 189, 186

[56] References Cited UNITED STATES PATENTS Primary Examiner--Edward G. Favors Attorney, Agent, or FirmDaniel R. Levinson [57] ABSTRACT This is a safety interlock in a laboratory burner for insuring that no fuel (or special oxidant) can be supplied to the burner under certain conditions. In particular a plug is attached to a removable burner head and a jack is rigidly attached to the other parts of the burner assembly; fuel flow is inhibited (as by disabling of an electric switch which opens a normally closed solenoid valve in the fuel supply) unless the plug is in the jack, so that no fuel can flow when the head is removed from the burner, Where more than one type of burner head is used with different fuel or oxidants, a second switch (say, controlling the flow of a special oxidant) in the jack is actuated by the special (longer) plug associated with only those burner heads intended to be used with the special oxidant (or fuel), so that such special oxidant can be supplied only when the burner head specifically designed for it is attached to the burner assembly.

3 Claims, 3 Drawing Figures Lil/W" l ml. w t

6Q EX? L: a

51mm l J l l nil/Ml WI! SAFETY INTERLOCK FOR BURNERS GENERAL DESCRIPTION This invention relates to a safety interlock for a laboratory burner especially of the type having interchangeable burner heads.

Various types of burners are utilized in laboratories, including, for example, the sample burner of an atomic absorption spectrophometer, which burners have removable portions, for example, the burner head. Removable burner heads allow interchange when the burner is to be used under somewhat different conditions (e.g., different fuel and/or oxidant). In addition making the head removable facilitates cleaning as well as allowing the rest of the instrument to be utilized (by the provision of a second head) while one head is being cleaned. In the typical sample burner for atomic absorption spectroscopy, the fuel, oxidant and a nebulized spray of the liquid (or dissolved or suspended in liquid) sample are premixed in a main chamber of the burner and then all three pass to a burner head where they issue from a slot (or plurality of slots) so as to produce a sample carrying flame, in which the atoms of interest are disassociated. The width and length of the slot are so chosen that the rate of flow of the'combustible mixture is sufficient to avoid flashback of the flame into the other parts of the burner assembly (which are filled with the same highly combustible mixture). Further, when different mixtures are utilized different burner heads, having different length and/or width slots may be necessary to insure that the flow rate of the mixture through the slot at least slightly exceeds the flame propagation rate to avoid such flashback. For example, in atomic absorption spectroscopy an airacetylene flame is commonly used for many metallic compounds to disassociate the metal of interest to neutral atoms. However, more refractory metals may require a hotter flame, such as provided by a mixture of nitrous oxide (N and acetylene. Because of the greater flame propagation rate of this latter mixture a narrower (and typically shorter) slot must be used if the danger of flashback is to be substantially eliminated. Thus a different second burner head must be provided for this (or other similarly different) mixture.

Since an attempt to ignite any combustible mixture without the presence of some burner head (which provides the reduced dimensions of a slot) will typically result in a flashback, and even the use of the wrong burner head (too large a slot in width and/or length) will typically result in similar difficulty, there exists the danger that such ignition may be inadvertently accomplished, resulting in an accident.

The present invention provides a safety interlock by which no fuel will be supplied to the burner assembly unless a burner head is in place. More specifically where the fuel (and oxidant) is controlled by at least one electromagnetic (solenoid) valve, a switch in series with the electrical path through the solenoid may be added to the burner assembly and this switch (electrically) closed by a mechanical element physically connected to the burner head, so that no fuel can be supplied unless the burner head (and in particular such mechanical element) is in place. Further where two or more types of burner heads (having different size slots) are used with the same burner assembly, the mechanical element associated with each burner head may also be specifically different in size or shape so that the desired mixture for one such burner head can be supplied only when that head (or more particularly its associated mechanical element) is in place. For example, the particular burner head used for a nitrous oxide and acetylene mixture may have attached a larger (e.g., longer) mechanical element, the end of which closes a switch in series with a solenoid valve controlling the nitrous oxide supply, so that nitrous oxide can only be supplied when this particular burner head (and its associated longer mechanical element) is in place. The mechanical element associated with both heads would of course still have a portion for contacting and closing the switch in series with the fuel-controlling solenoid valve. In this way, fuel can be supplied only when some burner head is attached to the burner assembly, and nitrous oxide can be supplied only when the special burner head with its special (e.g., longer) mechanical element is in place.

An object of the present invention is thus the provision of a safety interlock for a burner of the type having a removable burner head which allows ignition only when some burner head is present.

A somewhat more specific object is the provision of a safety interlock for a burner of the above type which allows fuel flow only when some burner head is connected to the burner assembly.

Another object of the invention is the provision of a safety interlock for a burner of the type with which two different types of burner heads may be used, which interlock allows the use of a special oxidant only with the particular. burner head intended to be used with such special oxidant.

Other objects, features and advantages of the invention will become obvious to those skilled in the art from the following specification, in conjunction with the accompanying drawing, in which:

FIG. 1 is an elevation with some parts broken away of an otherwise conventional laboratory instrument burner showing the addition of some of the parts of the safety lock in accordance with the invention;

FIG. 2 is a fragmentary side view taken along the lines IIIII in FIG. 1; and

FIG. 3 is a'schematic diagram of the entire safety interlock showing how it is utilized in the system for controlling the fuel and oxidant to the burner assembly of FIG. 1.

DETAILED DESCRIPTION In FIG. 1 is shown a known type of burner assembly for introducing the sample, fuel and oxidant mixture to a flame 10. Such a burner assembly comprises a mixing chamber 12 into which the sample nebulizer (not shown) aspirates a sample vapor (from the sample liquid supplied by tube 13) and is powered by compressed gas (e.g., air) fed to the nebulizer by tube 14. A gaseous fuel (e.g., acetylene) and an additional or auxiliary supply of oxidant are supplied to the mixing chamber as by

tubes

16 and 18, respectively. After mixing the contents of the mixing chamber 12 fill vertical hollow column 20 of the burner assembly, through the top of which they reach a removable (as at 22) interchange able burner head 24. The top 26 of this burner head is provided with at least one relatively narrow, long slot through which the mixture of sample droplets, fuel and oxidant reach the combustion zone so as to support flame 10. The lower part of the column 20 is rigidly attached to a burner assembly base 28, rigidly attached to a mount 30, which in turn is attached to, say, an atomic absorption spectrophotometer or other mechanically stable structure. To insure that the burner head 24 is not blown away from the burner assembly area upon flashback, tie-

down cables

32, 34 are provided. One end of each of the cables is attached as by

screws

36, 38 respectively to the burner head, and the other end is releasably attached to a non-removable part of the burner assembly. For example, this other or lower end of the cables may be provided with a loop 40 which may be slipped between the legs of an almost U- shaped spring clip 42 which in turn is fastened as at 44 near the joining of the mixing chamber 12 with the vertical column 20, as may be seen in FIG. 2. The parts thus far described are those of a prior atomic absorption sample burner, in particular the one supplied with the Model 403 atomic absorption spectrophotometer manufactured by The Perkin-Elmer Corporation of Norwalk, Connecticut. The remaining parts of FIG. 1 show the safety interlock added to this burner assembly in accordance with the invention.

According to the exemplary version of the invention shown in FIG. 1, a plug 50 is attached as by intermediary loop 52 formed in cable 32 (which is therefore initially made longer than unmodified cable 34) to the burner head 24. Plug 50 has a long body or pin portion 54 and a larger diameter portion 56 defining a flangelike lower shoulder 58. Plug 50 fits through a jack 60 seated in an opening in the top of a switch box or housing 62; shoulder 58 defines the extent that plug 50 can penetrate into the switch box 62. Inside the box are two

switches

64, 66, each of which includes a

switchactuating button

68, 70, respectively and an actuating arm 72, 74' of a springy (e.g., metallic) material. The switches and actuating arms therefor are so positioned that a relatively short plug (as shown) will press actuating arm 74 against button 70 so as to actuate or close switch 66 (hereinafter sometimes referred to as the fuel switch), but it requires a longer plug or pin to reach the actuating part of arm 72 of switch 64, so that switch 64 (hereinafter sometimes referred to as the special oxidant or nitrous oxide switch) is only closed when a longer plug is inserted through jack 60. Such a longer plug will be connected of course to a burner head (having smaller slot dimensions) intended to be used with the special oxidant, such a longer pin being shown in dotted lines in FIG. 1.

The manner in which the invention operates is best seen from the schematic illustration of FIG. 3. Again the conventional parts of the complete (though simplified) burner system will first be described. The main parts of the burner assembly itself (already described) are shown in FIG. 3 by use of the same reference numerals. Thus, the burner mixing chamber 12, vertical column portion 20, burner head 24 and base 28 are schematically shown again, as are the fuel line 16, oxidant line 18 and cable 32. Also schematically shown are the plug 50, jack 60 and

switches

64, 66 forming parts of the invention. The other conventional parts of the whole burner system include a source of fuel 80, connected by fuel line 16' to the burner fuel line 16; a normally closed solenoid valve 82 for opening and closing line 16'; a solenoid driver 84 for fuel solenoid valve 82; and a control system 86 (e.g., manually operable switches including one for actuating the solenoid driver 84) connected by leads 88 to driver 84. Similarly the normal oxidant (assumed to be compressed air) is supplied by a source of compressed air 90 (e.g., a compressor of ambient air) connected through a normally closed solenoid valve 92 in line 94 to branch line 18" which in turn is connected to the line 19 supplying oxidant to (both the nebulizer line 14 and the auxiliary line 18 of) the burner assembly. Solenoid valve 92 is controlled by a solenoid driver 96, which in turn is controlled by the control system 86 by leads 98. Finally a source of special oxidant (e.g., nitrous oxide) is obtained from a source 100, through line 102 controlled by normally closed solenoid valve 104, which in turn is opened by driver 106 controlled by electrical leads 108 from the control system 86. A pressure regulator valve (an attendant pressure gauge) and a flow-adjustment needle valve (all not shown) would normally be present in both the fuel line (anywhere in line 16) and in the oxidant line 18. Preferably the pressure regulator would be in the common part 19 of the oxidant line and the flow-adjustment valve 21 only in the auxiliary oxidant line 18, since the nebulizer should receive a constant pressure source of gas. It should be noted that the shut-off solenoid valves 92 and in particular 104 shut off the supply of oxidant to both the nebulizer line 14 and the auxiliary oxidant line 18.

Thus the operator normally turns on the fuel, and either the normal oxidant (air) or the special oxidant (say, nitrous oxide) by manual switches of the control system. However, the previously described

switches

64 and 66 are placed in

electrical lines

88 and 108, respec tively, so that

solenoid valves

82 and 104 cannot be opened unless these switches are closed. Thus only if some plug (of either the long or short type) is in jack (compare FIG. 1) so that switch 66 is closed, can the fuel solenoid valve 82 be opened and fuel actually supplied to the burner assembly through lines 16' and 16. Similarly only if the long plug associated with the special oxidant head (having smaller slot dimensions) is in jack 60 can the special oxidant (e.g., nitrous oxide) be turned on by opening of solenoid valve 104 since only then will switch 64 be closed. Since each of these plugs is physically attached to the respective burner heads, it is substantially impossible to ignite the burner when no burner head 24 is on the vertical column 20'of the burner assembly since no fuel will then be supplied to the burner assembly; similarly, unless the special oxidant (nitrous oxide) burner head is the one being utilized, the special oxidant cannot be supplied to the burner assembly.

The particular arrangement described is of course merely exemplary of the various ways in which the invention may be utilized. Thus the stopping of the fuel (when no head is in place) is considered the most desirable way of assuring that ignition cannot occur, but it is at least possible to control the nonnal" oxidant instead, or of course both the fuel and normal oxidant by, respectively, placing switch 66 in either line 98 or in both of

lines

88 and 98. Similarly the concept of providing a second switch which renders operable a special source only when a special plug is inserted in the jack can be utilized to disable a special fuel instead of or in addition to disabling a source of special oxidant. Further by providing additional switches and providing more types of plugs than two which may differ from each other not only in size but also in shape) various combinations of sources of fuels or oxidants can be disabled. Additionally it is obvious that the relatively simple technique of using a plug and jack type of connection is only exemplary of different types of mechanical parts that may be used to insure that switches closed only when it is safe to do so. Further, although the particular movable mechanical part (the plug 50) actuating the switches is shown as attached to the tie-down cable, it may be attached in other ways to the burner. The use of the tie-down cable as the plug-carrying element has the advantage of encouraging the operator to actually attach the cable 32 to spring clip 42. It should be noted that the arrangement (see FIG. 1) in the exemplary embodiment is such that if the burner head is blown off the column because of operator error (as by improper adjustment of the fuel and/or the oxidant) the plug will be pulled out of they jack (whether or not the cable 32 is attached to the spring clip 42), thus discontinuing the flow of fuel (and the special oxidant if this is in use), so as to provide an additional safety feature. Thus in the specific exemplary embodiment shown the operator is protected against the following operator errors: (l) igniting the burner with no burner head in place (or more specifically no plug 50 in the jack 60); (2) igniting a special oxidant (e.g., nitrous oxide) and fuel (e.g., acetylene) mixture when the wrong burner head is in place. Secondary safety features include: the encouraging of the operators use of the tiedown cable (32), and the cutting off of fuel (and special oxidant if in use) should a flashback occur during operation of the burner.

We claim:

1. A safety interlock for a burner system of the type including a burner assembly having a removable burner head, a source of fuel, at least one source of oxidant, and means operatively connecting each of said sources to said burner assembly, further comprising:

a first normally closed valve in said means connecting said source of fuel to said burner assembly;

first means for causing opening of said normally closed valve;

one part of said first opening means being physically connected to said burner assembly; another part of said first opening means being physically attached to said removable burner head;

said first opening means being of such construction that it is operative only when said one part and said other part are in physical contact,

a second normally closed valve in said means connecting said one source of oxidant to said burner assembly;

a second means for causing opening of said normally closed valve;

one part of said second opening means being physically connected to said burner assembly;

another part of said opening means being physically attached to said removable burner head;

said second opening means being of such construction that it is operative only when said one part and said other part are in physical conduct,

whereby fuel and oxidant from said one source of oxidant can be supplied to said burner assembly only when said burner head is in close physical proximity thereto.

2. A safety lock according to claim 1, in which:

said burner assembly comprises two different removable and interchangeable burner heads, only one of which is intended to be utilized with said oxidant from said one source;

each of said different'burner heads having attached thereto said other part of said first opening means, but only said one of said different burner heads intended to be used with said oxidant from said one source having attached thereto said other part of said second opening means,

whereby oxidant from said one source can be supplied to said burner assembly only when said one burner head intended to be used with said oxidant from said one source is in close physical proximity to the rest of said burner assembly.

3. A safety lock according to claim 2, in which: I

said one part of said first opening means comprises a first switch having an actuator;

said one part of said second opening means comprises a second switch having an actuator which is displaced along a line relative to the position of said actuator of said first switch;

said other part of said first opening means comprises a plug of sufficient length as to physically contact at least said actuator of said one part of said first opening means;

said other part of said second opening means comprises an extended length of said plug so that said plug is of sufficient length to physically contact said actuator of said second opening means,

whereby the length of said plug allows said oxidant to be supplied only to said one burner head intended to be used therewith.

Claims

1. A safety interlock for a burner system of the type including a burner assembly having a removable burner head, a source of fuel, at least one source of oxidant, and means operatively connecting each of said sources to said burner assembly, further comprising: a first normally closed valve in said means connecting said source of fuel to said burner assembly; first means for causing opening of said normally closed valve; one part of said first opening means being physically connected to said burner assembly; another part of said first opening means being physically attached to said removable burner head; said first opening means being of such construction that it is operative only when said one part and said other part are in physical contact, a second normally closed valve in said means connecting said one source of oxidant to said burner assembly; a second means for causing opening of said normally closed valve; one part of said second opening means being physically connected to said burner assembly; another part of said opening means being physically attached to said removable burner head; said second opening means being of such construction that it is operative only when said one part and said other part are in physical conduct, whereby fuel and oxidant from said one source of oxidant can be supplied to said burner assembly only when said burner head is in close physical proximity thereto.

2. A safety lock according to claim 1, in which: said burner assembly comprises two different removable and interchangeable burner heads, only one of which is intended to be utilized with said oxidant from said one source; each of said different burner heads having attached thereto said other part of said first opening means, but only said one of said different burner heads intended to be used with said oxidant from said one source having attached thereto said other part of said second opening means, whereby oxidant from said one source can be supplied to said burner assembly only when said one burner head intended to be used with said oxidant from said one source is in close physical proximity to the rest of said burner assembly.

3. A safety lock according to claim 2, in which: said one part of said first opening means comprises a first switch having an actuator; said one part of said second opening means comprises a second switch having an actuator which is displaced along a line relative to the position of said actuator of said first switch; said other part of said first opening means comprises a plug of sufficient length as to physically contact at least said actuator of said one part of said first opening means; said other part of said second opening means comprises an extended length of said plug so that said plug is of sufficient length to physically contact said actuator of said second opening means, whereby the length of said plug allows said oxidant to be supplied only to said one burner head intended to be used therewith.