|Publication number||US2439857 A|
|Publication date||Apr 20, 1948|
|Filing date||Apr 4, 1947|
|Priority date||Apr 4, 1947|
|Publication number||US 2439857 A, US 2439857A, US-A-2439857, US2439857 A, US2439857A|
|Inventors||Millikan Glenn A|
|Original Assignee||Us Sec War|
|Export Citation||BiBTeX, EndNote, RefMan|
|Non-Patent Citations (1), Referenced by (12), Classifications (11)|
|External Links: USPTO, USPTO Assignment, Espacenet|
pril 20, 1948.
G. A. MILLIKAN Filed April 4, 1947 SINGLE KNOB OXIMETER HAVING SELECTIVE CONTROL MEANS FOR MULTIPLE CHANNELS 2 Sheets-Sheet 1 Aprll 20, 1948. G.A.M1LLIKAN 2,439,857
SINGLE KNOB OXIMETER HAVING SELECTIVE CONTROL MEANS FOR MULTIPLE CHANNELS vFiled April 4, 1947 N 2 Sheets-Sheet 2 f/l/W/ll;
Patented Apr. 2o, 194s SINGLE TIVE CHANNELS Glenn A. Mlllikan,
United States of Secretary of War KNOB OXIMETER HAVING SELEC- CONTROL MEANS FOR MULTIPLE Nashville, Tenn., assigner to America as represented by the Application April 4, 1947, Serial No. 739,456
9 Claims. 1
The invention described herein may be manuiactured by or for the United States Government .Y
lor governmental purposes without the payment to me of any royalty thereon.
The present invention relates to a single control compensated circuit oximeter, and also to an electrical control device which distinguishes the present oximeter from those commonly used.
switch forming part of the oximeter control, this view being taken from the rear side of the switch with the rear cover removed; and
Fig. is a cross sectional view of the threeposition switch taken on the line 5-5 of Fig. 4.
Referring to Fig. l, the oximeter, or oxygen l meter, includes four ear units 1a, 1b, 1c, and 1d,
The principal object of the invention is to provide a single knob electrical control means which simplifies the operation of a multi-channel oximetcr and eliminates the chances of incorrect results due to errors in connecting the separate channel switches usually employed in multiple channel oximeters.
In my Patent No. 2,358,992, an oximeter is disclosed in the form of a single unit arrangement capable of handling one personr at a time. As stated in the patent specification, it may be desired to test a number of persons simultaneously,
in which case a multiple type oximeter may be used by mere duplication of the corresponding parts. This would however mean the duplication of switches and rheostats, or the like, and the completed apparatus would present a confusing array of controls which would require careful selection by the operator if uniform and expeditious tests were to be accomplished. Thus one object of the invention is the elimination of complicated controls in a multiple channel oximeter.
A related object of the invention is to provide a combined selector switch and potentiometer control device in which selection of a particular electrical circuit simultaneously eiects accurate registration of a potentiometer control means and control switches which are a part of the circuit selected.
It is a further object of the invention to generally improve the construction and the operation of multiple channel oximeters.
The above and other objects of the invention will become apparent, upon reading the following detailed description and claims in conjunction with the drawings. in which:
Fig. 1 shows a circuit diagram of a four-channel oximeter including the controls of the present invention and also showing a plan view of the selector and control switches;
Fig. 2 is a plan view of the oximeter control panel taken from the front side thereof;
Fig. 3 is a cross sectional view of the panel and associated control devices taken on the line 3-3 of Fig. 2, but omittingrseveral potentiometers;
Fig. 4 is a plan view oi a three-position control each of which may be constructed like the ear unit shown in Fig. 2 of the above-noted Patent Number 2,358,992. These ear units are substantially Ul-shaped in cross section so as to be adapted for fitting over the subjects ear and particularly for embracing the scapha membrane of the ear. Each ear unit includes an electric lamp 8a, 8b, 8c, or 8d, that is connected in parallel to a source of regulated voltage supply through a controlling switch 9. Each ear unit further includes a green-filtered photocell Illa, lllb, IDc, or ld, and a red-filtered photocell lla, lib, llc, or Hd, the green-filtered and red-filtered photocells of each ear unit having their ground terminals connected to a common lead I2a, 12b, I2c, or 12d, all of which in turn are connected to a single ground lead i3. Light from the electric lamp may pass through the ear membrane to energize the corresponding reci and green ltered photocells.
The photocells are arranged for connection to a sensitive galvanometer i4 by means of a selector switch l5 and a mechanically related control switch i6. It may be noted also that the selector vswitch I5 is equipped for making connection to six ear units even though the circuit as shown includes only four units. The selector switch I5 includes sir: upper contacts lla to lli, an upper arcuate shaped contact bar iS, six lower contacts I9a to l9f, a lower arcuate shaped contact bar 2B, and an insulating brush bar 2l carrying wiper brushes 2id and 2lb on opposite ends thereof. The insulating brush bar 2l is adapted to be rotated to allow the wiper brushes Zia or 2lb to bridge the contacts lla to i'lf and the upper arcuate contact bar i8, or the contacts i911 to lilf and the lower arcuate contact bar 2B. Each of the upper contacts llc to I'ld is connected to one of the red-filtered photocells lia to iid, respectively, through one of the potentiometers 22a to 22d, respectively; While each of the lower contacts l9a to l9d is connected to one of the greenfiltered photocells lila, to ld, respectively, through one of the potentiometers 23a to 23d, respectively, one terminal of each potentiometer being connected to the common photocell ground. The contacts lla to Ilf, contacts lila to I Sf, and. arcuate contact bars I8 and 20 are understanding of 3 all mounted in a switch body of insulating material and may have connecting ears for soldering conductors thereto, as is well known in the art. The insulating brush bar2l is non-rotatably secured to a shaft 24 for operating the selector switch as will be later described.
Referring to Figs. 1, 4, and 5, the three-position control switch 6 is shown having upper contacts 3|, 32, and 33, an upper arcuate contact bar 94, lower contacts 35, 36, and 31, a lower arcuate contact bar 38. and an insulating brush bar 39 carrying spring contact brushes 40 and 4| on opposite ends thereof. The spring contact brushes 49 and 4|, and the contacts 3| to 33 and 35 to 31 have interfitting portions to provide an impositive detent means. 'I'he insulating bar 39 is xed to a shaft 42 that is rotatably mounted in an insulating switch case 43 that supports the contacts 3| to 33, contacts 35 to 31, contact bar 34, and contact bar 38. 'I'he contacts and contact bars have connectors for making soldered connections extending to the exterior of the switch case 43. The outer end of the shaft 42 has a bifurcated member 44 attached thereto for the purpose of actuating the control switch i6 to the position shown in Fig. 1 when the brush contact 2|a of the selective switch |5 is operating across the upper larcuate contact bar I 8, of actuating the insulating bar 39 to a vertical position when the selector switch brush contact 2|a is between contacts 11a and |9f, and of actuating the control switch insulating bar 39 to a position diametrically in line with the contacts 33, 31 when the selector switch insulating bar 2| is rotated such that contact brush 2|a is cooperating with the lower arcuate contact bar 2'6 in a manner later to be described. The spring contact brush 4U cooperates with contacts 3| to 33 inclusive for separately connecting one of these contacts with the upper arcuate contact bar 34; while the spring contact brush 4| cooperates with the lower arcuate contact bar 38 for electrically connecting the contact bar 38 with one of the contacts 35, 36, or 31.
'I'he contacts 32 and 36 are connected together through a damping resistance 4'6 by a conductor 41. Contact 3| is connected to the upper arcuate contact bar I8 of the selector switch I5 by a conductor v48, and contact 35 is connected to the lower arcuate contact bar 20 of the selector switch by the conductor 49. The contact 35 also connects the contact 33 through the resistance 50 by a conductor 5| and connects terminal I4a of the galvanometer I4 through an adjustable resistance 52 by a conductor 53. Contact 31 is con'- nected to the common ground lead I3 of the photocells. The upper arcuate contact bar 34 is connected by the lead 54 to the terminal |4b of the galvanometer while the lower arcuate contact bar 38 is connected by the lead 55 to the galvanometer terminal 4a.
The galvanometer I4 has a single translucent scale 56 over which a spot of light is reiected from a deflection mirror receiving light from a light source as is well known in the galvanometer art. Connections for the light source of the galvanometer have not been shown since such a disclosure is not believed to be necessary for a clear the invention but this light source may be connected to the regulated voltage supply through switch 9 for convenience, if desirable.
The single control device for controlling the multi-circuit oximeter is shown more particularly in Figs. 2 and 3. In these gures there is shown 4 the oximeter control panel 6| having rotatably mounted thereon a control dial 62. 'I'he dial is secured on the outer end of the selector switch shaft 24. the switch itself being mounted on the panel 6I by nuts threaded on a central bushing which serves as a bearing for shaft 24. 'I'he shaft 24 includes a shoulder portion 24' against winch the dial 62 is held by means of a cap nut 63. Thus rotation of the dial 62 by means of a knob 64 thereon effects movement of the insulating brush arm 2| of the selector switch I5 previously mentioned and a dial indicia 62' may be set opposite the channel or station Nos. 1 to 6 to select the corresponding contacts of the selector switch |5. The panel 6| carries besides the channel numbers the legends Set filter and Saturation to indicate which groups of contacts of the selector switch I5 are being selected in moving the dial. 'Ihe Off position between the legends indicates that the wiper brush 2|a is between contacts Ila and I9f, since the knob 64 is arranged in radial alignment with the brush contact 2|a, and also indicates that the control switch I6 is turned Oi" in which the insulating brush arm 39 is diametrically in alignment with contacts 32' and 36.
The control panel carries upper and lower groups of potentiometers 22a to 22d, and 23a to 23d, corresponding to the potentiometers shown in Fig, 1, but including additional potentiometers for upper and lower stations or channels 5 and Y y 6. Considering the potentiometer 22h in Fig. 3, it will be seen that the potentiometer bushing carries mounting nuts, and the bushing provides a bearing for a shaft 65 having a clutch disc 66 xed on its outer end. I'he disc 66 is adapted to register with a disc 61 xed on a knob shaft |58,
lwhich carries the single control knob 64. The clutch disc may be radially grooved for better driving action when engaged and it is also noted that a conical projection in the center of disc 66 is adapted to t into a similar recess in disc 61 for more accurate registration of the discs. A coilV spring 69 on the knob shaft '68 between the dial 62 and the knob 64 normally holds the disc 61 out of driving engagement with the potentiometer disc 65. The other potentiometers are each mounted on the panel in the manner shown in Fig. 2 and driven by the knob 64 in exactly the same manner as described above for the potentiometer 22b. It should be noted that locating the knob 64 and the dial indicia 62' at any one station or channel seeks a photocell section to the galvanometer and at the same time positions the knob 64 directly over the only potentiometer in the circuit that would require adjustment in such location.
The dial 62 also carries a control switch actuating pin 10 projecting within the space between the dial 62 and panel 6|. The control switch I6 is mountedon the panel 6| with the bifurcated member 44 extending such that it is adapted to be engaged by the pin 10 to transmit rotary motion to the control switch insulating brush bar 39. As shown in Fig. 2 the dial 62 may be rotated to any one of the Saturation stations with the pin '10 disengaged from the blfurcated member 44 of the control switch I6 leaving the control switch in what `will be later referred to as its Saturation position in which contacts 3|, 34 and contacts 35, 38 are connected, but upon turning the dial 62 counterclockwise to the O i position the pin 10 will engage the bifurcatedmember 44 and rotate it clockwise about its shaft 4.2 until the shaft 42, member 44, pin 10, and
shaft 2G are in alignment in which contacts 32. Il and 36, 3B are connected placing the damping resistance 46 across, the galvanometer terminals. Further counterclockwise rotation of the dial B2 to any one of the Set filter stations will rotate the insulating brush bar 39 of the control switch ,approximately 45 degrees to what may be referred to as the control switch Set illter position in which it may be seen in Figs. l. and 4 that the insulating brush bar 39 will be in diametrical alignment with the contacts 33 and 81. The impositive detent construction of the control switch i8 retains this switch in any one of its three preselected positions until rotary motion is transmittedto it by the pin 1U.
The operation of the selector switch, control switch, and potentiometers will now be described in greater detail in their relation to the ear units and galvanometer. The oximeter as shown diagrammatically in Fig. l is based on a colorimeter type of oxygen meter as disclosed quite fully in my patent previously identied. The patent is relied on ior a discussion of the theory of the oximeter and its use in determining the percent of oxygen concentration in the blood, or a relative amount of o'xyhemoglobin.
in the operation of the above described oximeter it is necessary for initially conditioning the device for use to properly adjust the variable resistor 52. The conductorsi and d3 including the resistances d and 52 constitute an attenuat- 'ing circuit for use in the standardization of the electrical and optical system in accordance with some selected standard filter in one of the ear units. The attenuating circuit may take the form of a single control potentiometer, if more desirable. In order to initially standardize this device for use let it be assumed that a standard .5A iilter is used. With the main switch 9 in the "Oif position rotate the dial d2 to both No. 2 stations and adjust potentiometers 22h and 23h to the left stop in which case these potentiometers are short circuited. Snap on the main switch 9 and adjust the galvanometer spot by the regular galvanometer zero adjusting means until the spot rests at 891/2. Place the .5A lter in the ear unit 1b and allow a few minutes for the ear unit to reach thermal equilibrium. Turn the dial 62 until the knob 64 comes to the Set lter" No. 2 station and manually turn the control switch bifurcated member it back to its Saturation" postion, which is the position shown of this control switch in Fig. 2. Push .the knob 54 in and rotate the 'potentiometer 23h until the galvanometer spot rests at 50 on the scale 56. This connects the green-filtered photocell lllb to the terminal ila of the galvanometer i4 through the selector switch i5 and the control switch i6, the ground lead i'2a being connected to the terminals Mb through the potentiometer 22h. Since the red-filtered photocell is short circuited" any opposing voltage by the red-filtered photocell is eliminated. Further, the potentiometers for-the green-nitered photocells are of much higher resistance than the corresponding red-filtered photocells such that complete control of photoeleetric current furnished by any one of the greenfiltered photocells is realized by the corresponding potentiometer 23. Manually turn the bifurcated member M to its Set filter" position,7 wherein it will be in a position for engagement by the pin 10 upon the dial 62 being rotated to "O or Saturation positions. This connects only the green-filtered photocell Nb to the galvanometer il through the attenuating network 50, 5I 52, and 5l, the red-nlteredphotocell being short circuited and its circuit to the galvanometer Il being broken at contact 3l. Adjust variable resistance 52 (which may be positioned behind the panel at any place though a bit inconvenient since this adjustment need-be made only once unless future checks are desirable) until the galvanometer spot rests at 100. A standard resistance may be used in place of the variable resistance 52 if properly calibrated for the particular standard filters being used but use of a variable resistance is preferable for accurate adjustment. After the potentiometer 23h and the variable resistance 52 are adjusted as described above the dial should be rotated to the O position and the galvanometer spot adjusted to rest at 50 on the scale 56 by the galvanometer scale zero adjusting means not shown herein since such adjusting means are comnon in galvanometer units. The purpose of the above described adjustments is to standardize the electrical and optical system such that the attenuating circuit has the bias ratio to give a deflection of the galvanometer spot to the left when the control switch i5 is in a Saturation position which is 2% times the deflection of the spot to the right on the scale 5S when the control switch it is on Set iilter position. This bias ratio should loe d 'if an A filter is used. The attenuating circuit described above is merely for the purpose of standardization of the device by 'using the single scale E56 within the limits of 50 to lill) whereas in the absence of the attenuating circuit the scale would have to extend 2i/2 or 5 times to the left of 50 to arrive at such standardization. Since the above procedure of standardization need be made only once such conditioning of the device is not burdensome. The above operation may be made using any one of the ear units.
With the above adjustments made and the standard filter still in place rotate the dial B2 in the Set filter direction until the indicia 62' rests at the station No. 2. This connects the green photocell lllb through the potentiometer 23h, contact ISE), brush 21a, bar 20, conductor 49, conductor 5|, resistance 50, contact 33, brush 40, bar 34, andv conductor 5d to the terminal Mb of the galvanometer. The other terminal Ma of the galvanometer is also connected through conductor 49, resistance 52, and conductor 53 to the green photocell Nb. The ground of the green photocell illb is connected through the conductors l2b, and I3 to the contact 31, brush di, bar
G38, and conductor 55 to the galvanometer terminal Ita, the circuit through the resistance 52 being parallel to the circuit through the galvanometer Id. The circuit from the red-filtered photocell lib is broken at the Contact 3| of the control switch I6. The knob Se is then depressed and the potentiometer 23h adjusted until the galvanometer spot rests at on the scale 56. This provides full scale deflection of the galvanometer but with the proper ratio between the resistances 5B and 52 as formerly standardized. The dial B2 is then returned to the Off position and the standard filter replaced by the subject's ear. Where more than one subject is being tested the above procedure should be carried out for each ear unit. Using ear unit lb for the purpose of illustration the dial E2 is again returned to the Set filter. position ior station No. 2. The ear should be allowed to warm up with the dial in this position. When the galvanometer spot stops moving to the left, the ear is fully flushed and an ear reading may be taken as a useful reference, if desirable.
The dial 62 may then be rotated in a clockwise direction to the Saturation position, station No. 2. Both red and green-ltered photocells lb and IIb are now connected to the galvanometer I4 in opposition. The green-ltered photocell Ib is now connected to the terminal I 4a of the galvanometer through the potentiometer 23h, contact I9b, brush 2 Ib, bar 20, conductor 49, contact 35, brush 4I, bar 38, and conductor 55; while the red-filtered photocell II b is connected to the terminal I4b ofthe galvanometer I4 through the potentiometer 22h, contact IIb, brush 2Ia, bar I8, conductor 48, contact 3|, brush 40, bar 34 and conductor 54. The knob 64 should be depressed and the potentiometer 22h adjusted to bring the galvanometer spot to 100 at any altitude below 30,000 feet if the subject is breathing pure oxygen (or 95 if the subject is breathing air at or near sea level). This is the physiological setting and any subsequent reading taken from the galvanometer I 4 will indicate the per cent saturation of oxygen in the blood.
In the event the blood thickness of the subjects ear changes the dierence in the photoelectric current from the green-filtered photocell I0b, compensates automatically for this change in blood thickness, in the manner in which manual adjustment was used in the aforementioned patent, to allow accuratesatux-ation readings at all times.
As may be seen from the foregoing description any one of the lsix stations may be connected I fortesting per cent saturation of any one of six subjects merely by grasping the knob 64 and rotating the dial 62 to the desired station or channel. Any of the potentiometers 22a to 22d, and 23a to 23d, all inclusive, may be adjusted by simply depressing the knob 64 to bring the clutch discs 66 and 61 into engagement. The proper relation of the selector switch I5, control switch I6, and potentiometers is provided by operation of this single knob 64 which greatly simplies an otherwise confusing operation. More than six subjects could be tested by such an oximeter device if additional contacts were constructed in the selector switch, and additional potentiometers and ear units added.
The embodiments of the invention herein shown and described are to be regarded as illustrations only and it is to be understood that the invention is susceptible to variations, modications, and changes Within the spirit and scope of the appended claims.
1. A single control multiple channel oximeter comprising, a, plurality of vphotocell units each including a photocell means and a light source and being adapted to receive a living membrane between the photocell means and the light source, each photocell means including a separate control potentiometer, a galvanometer adapted to be connected to each photocell unit to indicate the per cent of oxyhemoglobin in the blood of said living membrane, a selector switch for connecting only a single photocell unit to said galvanometer at a time, adjusting means connected to said selector switch and adapted to engage only one of said potentiometers at a time according to the position of the selector switch, and the electrical connections between the selector switch and photocell units including the connection of the potentiometers and the photocell means being such that selection of a particular photocell unit by 8 the selector switch thereby positions said adjusting means for engagement with the potentiometer connected to the photocell means included in said last mentioned photocell unit.
2. A single control multiple channel oximeter comprising a plurality of photocell units each including a green-nitered photocell, a red-filtered photocell, and a light source and being adapted to receive the living membrane ofv a subject between the photocells and the light source, each photocell being connected to a separate circuit each including a separate control potentiometer, a galvanometer adapted to be connected to each photocell unit through said separate circuits to indicate for the green-nltered photocell the sub-V jects ear type and for the red and green filtered photocells the subjects oxyhemoglobin percentage, a selector switch for connecting only a single photocell unit to said galvanometer at a time, adjusting means connected to said selector switch and adapted to engage only one of said potentiometers at a time for operation thereof according to the position of said selector switch, and the electrical connections between said selector switch and photocell units including the potentiometers and the respective red and green ltered photocells being such that positioning of said selector switch to obtain ear type indication or oxyhemoglobin percentage indication thereby positions said adjusting means for engagement with the potentiometer connected to the green-filtered or the red-iiltered photocell respectively, included in the selected photocell.-4
3, An oximeter as recited in claim 2 including, a control switch adapted for actuation by said selector switch and providing means to automatically connect any one of said green-filtered photocells to said galvanometer through an attenuating circuit through the respective separate circuit when said selector switch is actuated such that the adjusting means is in position to adjust the potentiometer of said one of said green-illtered photocells, and to automatically connect both red and green ltered photocells of any one of said photocell units to said galvanometer through the respective separate circuits when said selector switch is actuated such that -said adjusting means is positioned to adjust the potentiometer of said red-ltered photocells of said any one of said photocell units.
4. A control device for a multiple channel oximeter comprising, a channel selector dial mounted for rotation about a central axis, a selector switch actuated by rotationof said selector dial and including a .plurality of pairs of switch contacts arranged arcuately about said central axis, each contact pair being adapted to connect corresponding red and green filtered photocells ofa separate oximeter channel to an indicating instrument, a plurality of potentiometers arranged arcuately about said central axis, one each being in the connection of the red and green filtered photocells and being relatively stationary with respect to said selector dial, potentiometer control member mounted for rotation on said dial eccentrically thereof, said control member being adapted to register with actuating means on the respective potentiometers as said dial is rotated to select the respective pair of switch contacts for therespective red and green photocells, and the selection of a particular pair of red and green iltered photocells by said selector switch simultaneously bringing said control member into registration with the actuating means of a potentiometer which is adapted to control the photoelectric current of the selected photocell of the pair.
5. A` control device for a multiple channel oximeter comprising, a channel selector dial mounted for rotation about a central axis, a selector switch actuated by rotation of said selector dial and including a plurality of pairs of switch contacts arranged arcuately about said central axis, a plurality of pairs of potentiometers arranged arcuately about said central axis, each pair corresponding to a lpair of switch contacts and being relatively stationary with respect to said selector dial, a potentiometer control and drive means eccentrically mounted on said dial, said control and drive means being adapted to register with actuating means on the respective potentiometer as said dial is rotated to select the respective pair of switch contacts, each pair of coni tacts providing selection of a separate oximeter channel and at the same time bringing said co'ntrol and drive means into registration with the actuating means of one of the pair of potentiometers connected in the circuit of said separate oximeter channel.
6. A control device for multiple electrical circuits comprising, a circuit selector dial mounted for rotation about a central axis, a selector switch actuated by rotation of said selector dial and including a plurality oi .pairs of switch contacts arranged arcuately about said central axis, a plurality of pairs of potentiometers arranged arcuately about said central axis, each pair corresponding to a pair oi switch contacts and being relatively stationary with respect to said selector dial, a potentiometer control and drive means eccentrically mounted on said dial, said control and drive means being adapted to register with actuating means on the respective potentiometers as said dial is rotated to select the respective pair of switch contacts, each pair oi contacts providing selection of aseparate electrical circuit and at the same time bringing said control and drive means into registration with the actuating means of one of the pair o! potentiometers connected into said pair of separate electrical circuits.
'7, An electrical control device comprising a selector member lmounted for movement and adapted to assume a plurality of separate positions, a selector switch controlled by the selector member and having a pair of contacts corresponding to each of said positions, a plurality of potentiometers which are relatively stationary with respect to said selector member, there being one potentiometer corresponding to each of said positions, a potentiometer control means mounted on said selector member and adapted for operative connection yto the respective potentiometer one at a time as said selector member is moved to select the respective pair of switch contacts one at a time.
8. An electrical control -device comprising a selector dial mounted for rotation about a central axis, a selector switch actuated by rotation of said selector dial and including a plurality of pairs of switch contacts arranged arcuately about said central axis, a plurality of pairs of potentiometers corresponding to said pairs of switch contacts arranged arcuately about said central axis and being relatively stationary with respect to said selector dial, a potentiometer control and drive means eccentrically mounted on said dial, and said control and drive means being adapted to make driving connection with the respective potentiometer one at a time as the dial is rotated to select the respective pair of switch contacts one at a time.
9. An electrical control device as recited in claim 8 wherein said rpairs of switch contacts are arranged in two series together forming a circular array about said central axis, and including a control switch adapted for actuation by said selector switch and providing means to automat- 4ically connect a source of electric current through one circuit including one oi said potentiometers when said selector switch is connected to a pair `0i' contacts of one series and to automatically connect two sources of electric current of two separate circuits through both of the pair of said v corresponding potentiometers when said selector switch is connected to a pair oi contacts of the other series.
GLENN A. MILLIKAN.
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|US2706927 *||Aug 4, 1949||Apr 26, 1955||Research Corp||Apparatus for determining percentage oxygen-saturation of blood|
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|U.S. Classification||356/41, 200/5.00R, 307/112, 338/128, 338/215, 338/188, 324/140.00R, 250/210|