US3010060A - Input voltage controlled servosystem with one way drive output - Google Patents

Description

Nov.

Filed Feb. 18, 1957 K. P LANNEAU ETAL INPUT VOLTAGE CONTROLLED SERVO-SYSTEM WITH ONE WAY DRIVE OUTPUT 3 Sheets-Sheet 1 I I MAss SPEC ION E- ANALYzER CURRENT 2 SECTION AMPLIFIER r5 (6 STORAGE MAss PEAK UNIT READER FOR PEAK M35 /3 vALUEs sELEcTOR l vOLTAGE 7x SUPPLY ANALOGUE 8\ DIGITAL COMPUTER cONvERTOR l 9 FIGURE I DATA OUTPUT SERVO MOTOR J 9; I INPUT :ga: 4VOLTAGE IO R A .11 sERvO I I N CURRENT AMPLIFIER AMPLIFIER 1 TERMINALS 4b MECHANICAL FIGURE IE ANCHOR Keith Palmer Lanneau Inventors Martin Ottomar Gernand Byl y Attorney UNIDIIKIECTIONAL Nov. 21, 1961 K. P. LANNEAU ETAL 3,010,060

INPUT VOLTAGE CONTROLLED SERVQSYSTEM WITH ONE WAY DRIVE OUTPUT Filed Feb. 18, 1957 3 Sheets-Sheet 2 7 {I6 65 sERvo u f" MOTOR MAGN c ET! 3C 64,54 CLUTCH 1/ 53 i 'I3a- 1 Q1 SERVO I 6 II AMPLIFIER 22 4b 6 IRoN CURRENT AMPLIFIER TERMINALS y 27 %uNI0IREcTIoNAL I (Q LINKAGE 2a 0 MECHANICAL ANCHOR FIGURE-III Keith Palmer LanneaLI Inventors Martin Otfomar Gernand By fl Attorney Nov. 21, 1961 K. P. LANNEAU ETAL 3,010,060

INPUT VOLTAGE CONTROLLED SERVOSYSTEM WITH ONE WAY DRIVE OUTPUT Filed Feb. 18, 1957 3 Sheets-Sheet 3 40 FIGURE 11' T 3 I: 4' "mm" SERVO --I6 .49 MOTOR FIGURE I Keith Palmer Lanneau [Mentors Martin Oflomar Gernand By W Afforr ley INPUT VOLTAGE CONTROLLED .SERVOSYSTEM This invention relates to a data reading and recording device, particularly intended for use with mass spectrometers. The device of this invention is adapted to automatically read and store mass information provided by a mass spectrometer in a form which may directly be used in an automatic computer or can be used in autoniatic data reduction systems. More particularly, this invention provides apparatus for automatically determining the maximum voltage output of a mass spectrometer at the mass peaks detected by the spectrometer. An important feature of the invention is provision for storage of the detected information in a readily useful form for subsequent computation steps which can be carried out to provide the percentage composition of thesample analyzed in the mass spectrometer. g

The invention is set forth herein as a continuation-m part of our co-pending application Serial No. 534,798, filed September 16, 1955, now abandoned.

Mass spectrometers have been used for many years as a basic analytical tool to determine the composition of a wide variety of materials. Basically, the mass spectrometer bombards samples with electrons so as to fragment molecules into ions of various charge-to-mass ratios. The mass spectrometer provides a means for segregating and identifying the relative concentrations of these ions which are indicated by voltage maxima or peak ion currents. By solution of linear simultaneous equations based on this information, it is then possible to compute the original molecular composition of the sample.

In recent years, increasing intereset has developed in use of mass spectrometers for process controlapplications. In this use, a mass spectrometer may be supplied with samples from one or more streams of a process so as to permit more or less continuous determination of the composition of these stream-s during conduct of the particular process. Techniques have been developed for reducing the basic operation of the mass spectrometer to an automatic continuous basis. One of the difficulties in this connection, however, is to provide means for automatically determining the maximum voltages developed by the mass spectrometer at mass peaks indicative of the composition tested. A further difiiculty is the conversion of such detected voltages to a form which can be used to automatically and continuously indicate the actual composition of the sample.

The present invention solves the problem involved in satisfying these objectives by providing apparatus which can automatically read the output of a mass spectrometer so as to detect voltage maxima contributed by detected mass peaks. In addition, the device incorporates means to essentially store the voltage determinations in a form directly useable in automatic analogue computers which can be used With this invention, or to provide peak height data in printed or punched-card form for use in conventional digital computers.

In accordance with this invention, voltages are applied to the analyzer section of a conventional mass spectrometer so as to scan one or more mass peaks in a given analysis. It will be appreciated that in the case of radio frequency mass spectrometers, varying frequency, rather than voltage, may be used to scan the mass peaks. This or other alternate means for scanning mass spectra" do not aifect the application of this invention with respect United States Patent 2 to peak detection and storage. For the purpose of describing this invention, the operation of conventional mass spectrometers only will be considered. The ior current derived from the amplifier of the mass spectrometer as a direct result of the scanning operation is then used as the input signal to the device of this invention. The mass peak reader of this invention employs a servo motor so as to compare ion current from the mass spectrometer with a variable source of reference voltage. To accomplish this, the servo motor, driven by the ion current signal input, is mechanically linked to a variable resistance connected in series with a standard voltage source. The mechanical coupling referred to is a particular feature of this invention. This coupling utilizes a slip clutch arrangement and a unidirectional rotary linkage so that the variable resistance referred to can be driven to balance the maximum voltage detected for any one mass peak, atwhich point the variable res-istancewill retain its position even though the signal voltage then drops below its maximum value as the peak is scanned. In accordance with this invention, different provisions are then made for utilizing this positioning of the variable resistance for subsequent data computation. A magnetic clutch is included as an integral part of the mechanical coupling arrangement, serving to permit subsequent return of the variable resistance to an initial position for sequential use of the system.

The nature of this invention will be described with reference to the accompanying drawings which diagrammatically illustrate the basic principles of the invention. In these drawings: v

FIGURE I illustrates in a block diagram form the essential components of the invention in its operative entirety;

FIGURE II diagrammatically illustrates the manner in which the servo system is used to position a variable resistor in a circuit providing a voltage equal to the maximum voltage of a mass peakdetected by the mass spectrometer;

FIGURE III diagrammatically illustrates a modification of the arrangement of FIGURE II permitting storing or, the detected information;

FIGURE IV is a plan view of a preferred mechanical arrangement of the servo system employed and is related to;

FIGURE V which shows the corresponding elevational arrangement of this mechanism.

Referring first to FIGURE I of the drawings, an under standing of the basic operation of the present invention can be obtained. A sample to be analyzed is supplied to mass spectrometer analyzer 1 through line 2. The sample will be ionized and the charged ions will be segregated by mass number in the analyzer, section 1 of the mass spectrometer in accordance with accelerating voltages derived from voltage supply 3. In the practive of this invention, voltage supply 3 is of a nature to focus ions of particular mass-to-charge ratio to exhibit the peak response of the mass spectrometer forthe particular ions. For example, a continuously increasing accelerating voltage or continuously decreasing accelerating voltage maybe supplied by voltage supply 3. In this case, ion currents detected in the analyzer section of the mass spectrometer will periodically increase to a maximum value and then decrease as ions of different specific mass number are detected. i

Alternatively, voltage supply source 3 may be used to provide preselected voltages to step from one mass number to another. In this case, each of the preselected voltages will be varied enough at each mass number so as to traverse the mass peak band width and thus scan the ion current over the range contributed by ions of a particular mass number. To accomplish this, voltage Patented Nov. 21, 1961 supply source 3 may comprise a voltage divider network having suitable voltage taps. Selected voltages obtained from these taps focus ions of a particular mass-to-charge ratio at a point on either side of the peak response of the mass spectrometer for a particular ion; that is, the instrument is focused at the base of either side of a peak. After the instrument is focused at such a point, the total voltage across the mass selector voltage supply divider network is varied by a small fixed percentage in the proper direction. This causes a scan or sweep across the mass peak. This incremental voltage variation is, for example, of the order of 1% in a case where the resolution of the mass spectrometer is 1 part in 100. The voltage variation is a percentage value of the total voltage and therefore for a conventional mass spectrometer will be of the proper magnitude for any mass selected in the operating range of the mass spectrometer. Sequential operation of the mass selector voltage supply for each selected mass may be controlled manually or may be controlled by a timing device. A given time interval for the scan and reading of a single mass peak is selected so as to permit a complete scan of the peak and retransmission of the peak value from the peak reader as will be described.

As described then, the mass spectrometer analyzer section 1 is controlled by voltage supply 3 so as to provide an output current at the ion current amplifier 4 embracing the peak voltage response at selected mass numbers. This detected voltage response will ordinarily be of a sharply peaked character and element 5 of FIGURE I is employed to determine the maximum voltage of each of these peaks.

This is accomplished by impressing the detected ion currents on the mass peak reader to be described, identified by number 5 in FIGURE 1.

As will be described, mass peak reader 5 is of a nature to position a variable resistance in a standard voltage comparison circuit so as to equal the maximum voltage provided by any one mass peak detected by the mass spectrometer. Positioning of the variable resistor referred to in order to accomplish this objective may be mechanically used to position an electrical component such as a potentiometer in the storage unit 6. Storage potentiometers set in this manner may subsequently be employed in an analogue computer 7. Such an analogue computer can be of the nature described in Serial No. 357,694, filed May 27, 1953, in the names of Keith P. Lanneau and Lindsay I. Griflin, Jr., now Patent No. 2,911,146. In this case, the output of analogue computer 7 may be supplied to a digital converter 8 so that the data recorded by data reducer 9 represents the actual percentage composition of the sample analyzed. Alternatively, the positioning of the variable resistor of the mass peak reader 5 for each mass peak may be mechanically transmitted to a digital converter 8 so that data obtained from element 9 will be in a form useable for computation. These and other methods of utilizing the output of the mass peak reader 5 will be more fully understood from the description which follows. I

Referring now to FIGURE II, the heart of this inven tion is diagrammatically illustrated. In the system illustrated by FIG. II, the numerals 4a and 4b designate the signal output terminals of an ion current amplifier of a mass spectrometer such as is indicated by the numeral 4 in FIG. 1. The signal developed by the amplifier 4 of FIG. I is impressed across the terminals 4a and 4b in characteristic fashion for transmission by a circuit component 10, connected at one end to the terminal 4a, and at the other end to one input terminal 11, of two input terminals provided for a servo amplifier 13. The component 10, as shown includes a switch 14. The other input terminal provided for amplifier 13 is designated in the diagram by the numeral 12. In the circuit diagram provided by FIG. II, the output terminal 4b is connected to ground as at the indicated point 15. This signal transmitted to the input terminal 11 will constitute a variable voltage corresponding to the output of the mass spectrometer in scanning the peak provided by ions of a particular mass number. The voltage of the input signal to terminal 11 will therefore vary from a minimum or baseline value to a maximum or peak value, and then will decrease to the baseline value as the peak is scanned. For the purpose of this invention, it is preferred that the scanning rate be such that the peak of a particular mass number is covered in about 1 to 10 seconds. Signal voltage during this period will vary from about 0 to 10 volts. The circuit of FIGURE II serves to determine the peak or maximum value of this voltage variation.

Further, as shown by FIG. II, a servo system is employed to obtain a measurement of the output voltage signal from the ion current amplifier 4. The measurement is obtained by opposing to the output voltage of amplifier 4 a voltage, from a standard voltage source, and impressed on the input terminal 12, which will produce a zero output from the servo amplifier 13. The servo system also includes a servo motor 16 activated by the output of servo amplifier 13 through connections 17 between the amplifier output terminals 13:: and motor input terminals 160.

The standard voltage source may be a battery 18 connected in parallel with a resistor 19, through connections 20, 21 and 22, to ground at the indicated point 15. The resistor 19 is in effect a potentiometer or voltage divider with a variable tap 23. The variable tap 23 is coupled in turn by means of connection 24, to the second input terminal 12 of servo amplifier 13.

As represented by the dashed line 25, the servo motor 16 is mechanically connected with the variable tap 23 through a slip clutch 26. The connection also includes a magnetic clutch 27 and a unidirectional linkage arrangement and anchor, 28 and 29 respectively. A more specific illustration of this mechanical connection and related parts is provided by FIGS. IV and V. The slip clutch, magnetic clutch and unidirectional linkage may be of a conventional character and these elements are commercially available. The slip clutch 26, for example, can constitute the type marketed by Industrial Associated Electronics. The unidirectional linkage 28 may be of the character supplied by Miniclutch Company, and the magnetic clutch 27 may be of the type manufactured by the Reeves Instrument Corporation.

In using the arrangement of FIGURE II, it will be assumed that tap 23 is pre-positioned at the lower portion of resistor 19 to impress a zero voltage or a minimum voltage on amplifier 13. When the variable mass spectrometer signal output is then impressed on terminal 11, during increasing values of this voltage, the servo system will act through the unidirectional linkage 28, with the magnetic clutch 27 engaged, so as to position variable tap 23 to develop an increasing and equal voltage. This drive will continue as long as a signal of increasing magnitude is impressed on terminal 11. However, when the peak voltage value has been reached in the operation of this arrangement, unidirectional drive 28 will operate to lock the potentiometer tap 23 so as to prevent its moving in the opposite direction. to balance against decreasing voltages impressed on terminal 11. In this condition, although the servo motor 16 will continue to operate, due to a voltage dilfcrence between terminals 11 and 12, by virtue of the slip clutch 26, the potentiometer tap 23 will remain unaffected because of the locking action of the uni-directional linkage.

As described therefore, the arrangement of FIGURE II serves to drive variable tap 23 so that the voltage drop along the resistor from the point of contact to ground will equal the .peak or maximum voltage impressed on terminal 11. In this arrangement, the ultimate result is to position the tap 23 in a position proportional to the peak voltage of the mass spectrometer signal. In a sense,

55 this is equivalent to a mechanical detecting andmemorizing system for peak voltages. Positioning of the potentiometer tap 23 in this way may be calibrated so as to exhibit the peak voltage value for visual determination.

Alternatively, tap 23 may be ganged to taps of other similar potentiometers in a re-transmitting system. After position of tap 23 is retransmitted or otherwise recorded, magnetic clutch 27 can be released to perrnitreturn of tap 23 to its base line position. Then the magnetic clutch 27 is re-cngaged and the system is ready to read another maximum peak value. The basic arrangement of FIGURE 11 may be used in these or other ways, although the preferred system is illustrated in FIGURE III.

Referring now to FIG. III, it will be seen that the basic circuits and mechanical elements are those as shown by FIG. II. The system has been modified, however, by the addition of a storage circuit for the peak values derived by operation of the system according to FIG. II. Only one storage circuit has been illustrated, but additional similar circuits may be employed as required to provide storage of peak values derived from a series analysis performed by means of the mass spectrometer. The added circuitry and mechanical connections may be substantially identified with the storage unit designated in 3 FIG. I by the numeral 6.

The added storage circuit and operating means include a resistor element, designated by the numeral 59, connected in parallel with the battery 18 through connections 60, 61, and 62, connection 62, for simplicity, forming part of the connection from terminal 4b to ground, at point 15. The resistor is shown and intended as a counterpart of the resistor 19, described with reference to FIG. II, including a variable tap 63. The tap 63, like tap 23, is coupled to the servo amplifier 13. The couple is accomplished, to the terminal 11, by means of a connection 64 including a switch 54. I

A mechanical connection, similar to that between tap 23 and servo motor 16,'is provided between'the servo motor and tap 63, and this mechanical connection is represented in FIG. III by the dashed line 65. This connection is made through a magnetic clutch 67. The basic system, as shown by FIG. II, is also modified as shown in FIG. III by the addition of a second magnetic clutch 77 in the mechanical connection between tap 23 and servo motor 16, and by a cross connection 70 between the line 24 and the line 62, including a switch 74. This cross connection and switch is provided to short one input terminal, 12, to ground in order to facilitate zeroing of the tap 63 on resistor 59.

In operation of the modified system according to FIG- URE III, let it be assumed that the system has been operated, in the manner first described with reference to FIG. II, so that tap 23 has been driven to a position to balance the voltage peak of a mass spectrometer signal. When this has been accomplished, switch 14 may be opened and switch 54 may be closed so that the second variable resistor 59 connected across battery 18 will be connected in a circuit with the input terminal 11 of servo amplifier 13. Also when this is accomplished, the magnetic clutch 77 which previously had been engaged, to permit positioning of the tap 23 in the first instance, is now activated for disengagement, leaving the tap 23 in the position attained by the initial operation. Then, with clutch 77 disengaged, switch 14 open and switch 54 closed, a voltage is derived from the resistor 59 and tap 63 which is opposed through the servo amplifier 13 to the fixed voltage derived through the resistor 19 and tap 23 at its previously attained position. Any voltage difference between the terminal connections 11 and 12, thus serves to produce a voltage output at terminals 13a such as to activate the servo motor 16. Through the mechanical connection 65 and the clutch 67 the tap 63 then will be moved to a position where the voltage drop along the resistor 59 from the contact point of tap 63 to ground potential will equal that along the resistor 19 from the contact point of tap 23 to ground potential. This circuit therefore serves to position the tap 63 of resistor 59 so as to reproduce and store the voltage and positionalinformation of resistor 19. The arrangement of FIGURE III isgenerally useful to permit utilization of a single resistor 19 as shown in FIG- URE II for determination of a series of mass peaks with subsequent transfer of the detected information, as shown in FIGURE III to a plurality of storage resistors such as 59 which may correspond in number to the number of mass peaks of interest. The arrangement of FIGURE III is particularly valuable for utilization in an analogue computer of the type described in Serial No. 357,694, re-

ferred to formerly.

While a variety of mechanical arrangements may be employed to embody the essential features of the arrange ments illustrated in FIGURE II, one mechanical arrangement of these elements is illustrated in FIGURES IV and V. As shown in these figures, servo motor 16, pctentiometer 19, and the coupling arrangement between the servo motor and the potentiometer may be supported on a common mounting plate 40. A gear 41 may be fixed to the shaft of servo motor so as to rotate freely on the shaft except for braking friction applied by spring 42. Thus, spring 4-2 will act as a slip clutch, such as element 26 in FIGURE II, to provide a small but positive rotary coupling between servo motor 16 and gear 41, controlled by the tension between spring 42 and gear 41. Rotation of gear 41 is imparted to potentiometer tap 23 through mating gear 45. Spring 42 will be adjusted so that with reg-ardto the elements described, rotation of servo motor 16 will cause rotation of the tap 23 through gears 41 and 45. In order to secure the desired unidirectional relation in driving tap 23, a unidis rectional linkage 28 of the type describe-d may beconnected to gear 48 directly coupled with gear 45. 'This arrangement will therefore permit gear 45 of potentiometer 19 to rotate in a single direction while preventing rotation in the opposite direction. In this arrangement, magnetic clutch 27 is employed to disengage the unidirectionai linkage 28 when it is desired to return the potentiometer 19 to a zero base line value. Thus, after operation of the arrangement of FIGURE II to determine a given mass peak, actuation of magnetic clutch 27 will permit the servo motor to drive tap 23 to a position of minimum voltage output in the circuit arrangement of FIGURE II.

In the operation of the invention described, a' firs-t step in the procedure of anaylzing a given sample is to' apply a voltage to the mass spectrometer analyzer section so as to scan a given mass peak. The detected ion current, varying from the zero or base line to the maximum or peak value and back to the base line value will be impressed on the circuit of FIGURE II so as to drive tap 23 to a position determined by the peak voltage value. This may then be re-transrnitted for storage by utilization of the circuit of FIGURE III, with return of this system to a base line value for sequential use for other mass peaks, by utilization of the magnetic clutch as described. While the invention has been described with respect to the basic arrangements used and with reference to sequential and manual operation of switches to secure the desired transition between the different arrangement-s used, it is apparent that preferably automatic and sequential switching systems are to be employed. This and other design refinements are employed in the practice of the invention.

What is claimed is:

1. A peak reading device for determining the maximum voltage output of a mass spectrometer during scanning of a given mass peak including in combination: a servo amplifier having a first input terminal and a second input terminal and having voltage output terminals, said servo amplifier being adapted to developan output voltage proportional to a pair of input voltages impressed on said respective input terminals, a source of reference voltage,

a resistance having a variable voltage tap connected to said reference voltage, electrical circuit means connecting said mass spectrometer voltage output to one of said servo amplifier input terminals, electrical circuit means connecting said variable voltage tap to the other of said servo amplifier input terminals, a servo motor connected to the output of said servo amplifier, said motor being characterized by 'an output shaft, and mechanical means coupling said variable voltage tap and the output shaft of said motor, said mechanical means including a slip clutch and a unidirectional linkage whereby motion in one-direction only may be imparted to said tap by said motor and said voltage tap be driven to a limiting position during scanning of said mass peak.

2. In a mass spectrometer peak reading device, the improvement which comprises a servo amplifier having a first input terminal and a second input terminal and having voltage output terminals, a servo motor characterized by an output shaft, electrical connections between said motor and said amplifier through the output terminals, means to apply a variable voltage to the first input terminal, means including a variable resistor having an adjustable voltage tap to apply :a second voltage to the second input terminal, and mechanical means coupling said variable voltage tap and the output shaft of said motor, said mechanical means including a slip clutch and a unidirectional linkage whereby motion in one direction only may be imparted to said tap by said motor.

3. A peak reading device for determining the maximum voltage output of a mass spectrometer during scanning of a given mass peak including in combination: a servo amplifier having a first input terminal and a second input terminal and having voltage output terminals, said servo amplifier being adapted to develop an output voltage proportional to a pair of input voltages impressed on said respective input terminals, a source of reference voltage,

8 V a first resistance having a variable voltage tap connected to said reference voltage, electrical circuit means connecting said mass spectrometer voltage output to one of said servo amplifier input terminals, electrical circuit means connecting said variable voltage tap to the other of said servo amplifier input terminals, a servo motor connected to the output of said servo amplifier, said motor being characterized by an output shaft, mechanical means coupling said variable voltage tap and the output shaft of said motor whereby motion in one direction only may be imparted to said tap by said motor and said voltage tap be driven to a limiting position during scanning of said mass peak, a second resistance having a variable voltage tap connected to said reference volt-age, electrical circuit means for disconnecting said mass spectrometer voltage output from said servo amplifier, circuit means for connecting the voltage tap of said second resistance to said servo amplifier, means to mechanical-1y uncouple said finst resistance tap from the output shaft of said servo motor, and means to mechanically couple the output shaft of said servo motor to the voltage tap of said second resistance whereby the voltage tap of said second resistance may be positioned in accordance with said limiting position of the voltage tap of said first resistance.

References Cited in the file of this patent UNITED STATES PATENTS 2,425,733 Gille et al Aug. '19, 1947 2,489,365 Bronsouse Nov. 29, 1949 2,512,902 Rossire June 27, 1950 2,790,945 Chope Apr. 30, 1957 2,791,738 Pringle May 7, 1957 2,799,461 Anderson July 16, 1957 2,847,633 Finkel Aug. 12, 1958 2,913,654 Clark Nov. 17, 1959

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