US2625584A

US2625584A - Oxygen detection and measurement

Info

Publication number: US2625584A
Application number: US104576A
Authority: US
Inventors: Edward L Kells; Delmar H Larsen
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-07-13
Filing date: 1949-07-13
Publication date: 1953-01-13
Anticipated expiration: 1970-01-13

Description

Jar'l- 3, 53 E. 1.. KELLS ETAL 2,62

OXYGEN DETECTION AND MEASUREMENT Filed July 15, 1949 INVENTOR S "pLxmu.

Patented Jan.

West Hollywood Calif.

nitration-11y '13, 1949, Serial No. 104516 from combustion process es' ,,gives an indication of the efiiciency of the combustion; many chemieal pr se n o in -i'sas ous reactions n e pend for proper control upon the oxygencontent. of the feed or output, gases; where air isused o s pport l e ndh abil yofho sy en depl tion is present the necessity of knowing the oxygen concentration is QbY DuSM. .p v. c 4 all c a plieatie s it s ighl vadva ta ous, d, enera y .abs ut yc e essary, to have t e a a ic l .r suitsimmedia y a ai ab e. While oxy e conc n ati ns. b det rmi e y nd hem ea me h ds. of as. analysis,v the delay introduced thereby generally renders the analysis useless asitisthen'too late to make y nd at ha es.,.in,.-Qpe in condition Accordingly,- many devices have been developed which s r ,.o ..'by oneme nsor ot n: a ap d an si iof.a.sas forr xy en. and ally provide e esu tn n nehiorm t at it can be continuously recorded; ,Unfoitl natelymost such devices are mechanically complex; depending as they do upon characteristics of oxygen notjreadily adaptable to simple and foolproof; measure ment, and thus notonly are expensive but require expert attention. v p. v ,I

At the same timejitis not onlynecessary; to w W a t e xygen c c ntr ions t environments m nti ned. as. ex mplesic t it; i also hi ad anta eous; inim id .v mea se ticularly adapted to simple mechanical embo'di- Another object of the invention is to provide new and novel means. 0 controlling oxyeenconcentrations" and processes dependent upon the latter.

r; chins. 1.17am) 2 Another object of the invention is to providea means of/ determining oxygen concentrations instantaneously. s

, Other .objectsof the invention will appear as the descriptionthereofproceeds so vBroadly stated; according to the present inven-, tion thei'oxygen content ofa; gas isfound (and if desired, controlled); by determining; directly or by a: function thereof,- the magnetic susceptibility ofthe gas in, question andrelating the value, so found,v to the. oxygen contenthIt is possible to do .,this1'b'e'cause; ,of all the :.gas,es commonly occurringiin the fieldsof applicationof this. invention' oxygen isthe only one possessing paramagnetism; ,a1l,other.commonly ,occurring gases, such as, nitrogen carbon dioxide; carbon monoxide, sulfur, dioxide, sulfur v.trioxide;,.hy1.irogen and gaseous hydrocarbons, ,are diamagnetia. (More- 1 over; the absolutevalue. of the volume magnetic susceptibility of oxygen-;,.that is, susceptibility per unitvolume), is morethan times vthat of. most othercommon gases, and inufactis about ZSQHti'mes that of ,the non -foxygen, portion of ordinary flue gases. The following values are c e-f nm e w. ciii i'bein 'ri i' an diamagnetic g chane'i'n direct propore iaihe P e i nxys n chan substantially myerseiy' w the absolute tern} pasture; and that of the diafn'agneticgass is substantiallydnvariable with temperature, volunies maintained c assiest As the susceptibility of mmes'g s substannauy additive "respastic; the part 'i-iiolijihi'es'pisntg it is easy in ter'fio'calculate' the susceptibility of a example flue gas'o'ntainin'g 10%" oxygen, atanyd 'ir'ed prs'sure and temperature froniithe'fla tions ju'si'i'stated-f i s n Thus, according td'ith'ej invention, the suscep, tibility of the gas sample-is determined, and the value obtainedis' suitably corrected for te'mpei'a= ture and pressure as indicated above, and the value so obtained is compared with the figures given in table above. The comparison is facilitated by plotting the values on a graph, as the relationship between oxygen content and susceptibility is linear for the ordinary gases comprised in the fields of application of this invention.

Not only will we proceed to show how the process of the invention may be carried out, but also it will be shown how the operation described above can be done as completely mechanically as desired, so that corrections for temperature and also for pressure are automatically made and final readings obtained directly in terms of oxygen content, either as a partial pressure or a volume percentage. Also we will show how control of oxygen concentration can be automatically achieved.

Reference is now made to the drawings accompanying this specification; therein:

Figure 1 shows a form of apparatus which is suitable;

Figure 2 shows a variation of detail in the apparatus of Figure l.

In Figure 1 an electromagnet i is excited by an alternating current coil H. The pole pieces in this instance are shaped to give maximum field strength in a relatively small space between them; gradient of field strength is of no particular importance. There are inserted into the field between the pole pieces two rods, I2 and 13, which almost touch in the strongest part of the field. These rods maintain a substantially constant cross-sectional area until the limits of the strong portion of the magnetic field are reached, whereupon they taper out and terminate at the needles" of two ordinary pickups, I5 and 18, such as are used for phonograph record reproduction. The rods are positioned by supports I! and I8, which may be rubber collars or the like. The two pickups are connected to an amplifier, at least the first stage of which is a push-pull stage, and the basic parts of which are schematically indicated in Figure 1. The pickups are connected with respect to polarity so that when both rods are mutually repelled or mutually attracted, the two grids of the first stage are given opposite polarities so that an impulse results in the secondary of the transformer [9.

Conversely, with such an arrangement, movement of the two rods in the same direction, with unchanged mutual separation, will result in changes in primary currents in the transformer [9, which cancel each other and give no impulse. Potentiometer 25 can be adjusted to balance out inequalities between the two outputs. An alternating current output meter is placed across the output of the amplifier, which may. of course, contain more stages of amplification than shown if necessary. The output meter 29 is calibrated in units of oxygen partial pressure. An enclosure 2! is placed around the electromagnet and is fitted with

tubulations

22 and 23 whereby the enclosure can readily be filled with the gas to be tested.

The rods 12 and [3 are constructed of a hard, durable substance having a susceptibility which for best results is approximately within the range of that of the gases to be tested. A suitable material is an aluminum-zinc alloy containing about 45% zinc, or a platinum tube containing a close fitting antimony rod, of suitable mutual proportions. Glass or plastic rod, containing a core of a sufficient proportion of paramagnetic material such as platinum, aluminum, tourmaline, ebonite and the like may be used. of these, those which do not conduct electricity throughout the mass are preferable because damping by eddy currents is thereby avoided. Here generally it is preferable to have the volumar susceptibility of the rod or rods within the approximate limits of l0 l0- to +l 10- volumar C. G. S. units.

The mode of operation of the apparatus of Figure 1 is as follows: When a gas which is more paramagnetic than the rods 12 and i3, surrounds the latter, the rods will tend to move out of the magnetic field, which of course occurs when the magnet is excited by current during a portion of the alternating-current cycle. When the magnetic field is zero, as occurs approximately at the time when the alternating current is changing direction, the tendency to move out of the field will cease, and the rods will spring back into place. When the current is reversed during the second half of the cycle, the magnetic field will again rise to a maximum and the rods will be repelled. Thus, if the current energizing the magnet has a frequency of cycles per second, the rods will vibrate cycles per second. If the gas is less paramagnetic than the rods, the latter will tend to move into the field during the period when the magnetic field is present.

Now the force attracting or repelling the rods is, other variables being unchanged, directly proportional to the algebraic difference of the volumar susceptibilities of the gas and the rod, and therefore a direct function of the oxygen content of the gas. Since the E. M. F. developed by the pickups is a function of that force, and can be suitably amplified and transformed into a meter reading, the ability of this device to read oxygen directly is at once apparent. The meter may be of the indicating type, as shown in Figure 1 or it may be a recording meter. For the general case, an alternating current milliammeter is used, although a rectifying device such as a tube or copper oxide disc-pile can be placed in the output circuit so that a direct current meter may be used. It is advantageous to have the meter scale calibrated directlyin units of oxygen concentration; also, the output of the amplifier can be connected to a control mechanism, as de-- scribed more fully hereinbelow.

A method of automatic temperature compensation incorporable into the apparatus of Figure 1 will now be described. Since the mass susceptibility of oxygen varies inversely as the first power of the absolute temperature, and since the isobaric volume of oxygen also varies inversely with the first power of the absolute temperature, the isobaric volume susceptibility evidently varies inversely as the square of the absolute temperature. Now for the region of ordinary room temperatures, this amounts to a change of approximately 0.67% per degree centigrade. Accordingly, if a resistance 26 having a temperature coeificient of that amount is placed in the gas to be measured, and also is simultaneously placed in the electrical circuit by means of

leads

21 and 28 so that it will change the output of the amplifier by that amount,then the amplifier gain will be automatically compensated for changes in temperature.

While nearly any frequency of alternating current may be used to energize the magnet, ordinary 50 or 60 cycle current is particularly convenient in actual application. Whatever frequency is used, care should be taken to adjust the resonant frequency of the mechanical vibrating system to such a value as will assure smooth response to the energizing force, in accordance with well-known laws of mechanically resonant systems.

It is desirable to make the system independent of externally imposed shocks, vibrations, accelerations and rotations so that installations where severe operating conditions prevail, such as in warships, are feasible. This can be done in several ways, as now discussed in detail. First the arrangement of the armature rods I2 and I3, in Figure l, with the pickup output connected in push-pull as described hereinabove, largely avoids such troubles. Moreover, both armature rods can be L shaped and can be pivoted and so designed as to be in both dynamic and static balance; in fact such a design of the armature is particularly advantageous where only one armature rod is used. The general design of such a pivoted armature is shown in Figure 2, where 30 and 3| are the pole pieces of the magnet, 32 is the pivoted armature with at least the portion 33 which projects into the strong part of the field being of material of suitable susceptibility, and 34 is the pivot, rotation about which point allows the end of the armature 33 to move in and out of the magnetic field. 35 is a single pickup, the leads of which, 36, are connected to an amplifier, not shown.

Freedom of instrument reading from vibration can also be achieved for instruments working on the general type of Figure 1 by causing the amplifier to be selective for the driving frequency of the electromagnet. For example, a sharply peaked band pass filter may be incorporated into the amplifier circuit, which will pass only the frequency generated by the magnetic field, and will not pass the frequency vibrating armature which as explained hereinabove will in general be different from the former.

Again, some of the alternating current from the source which energizes the electromagnet can be passed through a phase shifting circuit, then rectified, and, without filtering, used to supply grid or plate voltage for some convenient tube in the amplifying circuit, so that that tube amplifies only those impulses which are of a frequency and phase derivable from the action of the pulsating magnetic field on the armature assembly. Of course, the exact manner of application of these various amplifying current refinements will be evident to an electronic engineer, and need not be detailed herein.

In most cases where oxygen concentrations are of interest it is desirable to control the processes or conditions giving rise to the particular concentrations encountered. Usually an oxygen concentration within certain fixed limits indicates optimum operation; when those limits are exceeded, it is desirable to change operating conditions to bring the concentration back to normal. Thus, in a gas-fired boiler flue, less than about 1% oxygen indicates the necessity of increasing the air-gas input ratio if efiicient combustion is to be maintained. If the flue gas rises above about 3 oxygen, then the air-gas ratio should be reduced. Again, in supercharged airplane cabins. submarine interiors, or the like, the oxygen concentration must be controlled within certain limits.

The devices embodying the present invention can be readily adapted to such an automatic control, by causing the oxygen content indicator to operate relays or the like which are in turn connected to the primary variable mechanisms, such as oil, gas, air and oxygen inlet valves, dampers, coal stokers, and the like.

It will be understood that while several devices have been described in detail hereinabove, multitudinous modifications can be made therein within the broad scope of the invention. Also, while as many separate embodiments as conveniently desirable within the proper limits of conciseness have been disclosed, it will be understood that the invention broadly embraces many other modifications, and is not necessarily limited to the particular devices shown herein.

We claim:

1. An apparatus for the determination of the oxygen content of a mixed gas containing oxygen, comprising, an alternating current magnet, providing an alternating magnetic field, an object capable of being surrounded by said gas, and positioned in said alternating magnetic field, so that one portion is in a relatively strong part of the field and another portion is in a relatively weak part, restraining means to substantially inhibit translational motion of the object while permitting it to vibrate, and a vibration receptor operatively connected with said object, and oxygen indicating means operatively connected to said vibration receptor.

2. An apparatus of the type of claim 1, in which the object has a volume magnetic susceptibility approximately within the range of 10 10- to 10- C. G. S. units.

3. An apparatus of the type of claim 1, in which the object is statically and dynamically balanced.

4. Apparatus for measuring the oxygen content of a gas, comprising means forming a chamber for holding the gas, a magnet having a gap disposed within said chamber, means for energizing said magnet with alternating current, armatures movably mounted within said gap, a pickup connected with said armature, a voltage amplifier connected to said pickup, and an indicating member connected with said voltage amplifier.

5. Apparatus of the type of claim 4, in which the armature material has volume magnetic susceptibility approximately within the range of 10 10- to 150 10* C. G. S. units.

EDWARD L. KELLS. DELMAR H. LARSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,416,344 Pauling Feb. 25, 1947 2,467,211 Hornfeck Apr. 12, 1949