CA1128663A - Multi-channel analyzer - Google Patents

Abstract

ABSTRACT:

In a multi-channel x-ray fluorescence analyzer a multi-channel memory is interconnected between an attri-bute memory bank, a display circuitry and an analog-digital converter. The difficulty to detect associated multiple peaks in the non-contiguous channels are overcome with the circuitry which provides an unlimited flexibility in the detection of these associated multiple peaks. The inven-tion also covers a display circuitry for an on-line tele-vision display.

Description

~Z~ 3 "Multi-channel analyzer"

The present invention relates to a multi-channel analyzer, particularl~ to a multi-channel x-ray fluorescenc~e analyzer.
Such kind of analysing apparatus are described in The Edase editor vol. 8 no.2, page 6-10. In an appa-ratus as described a sample of material is struck by an ~-ray beam in known fashion and the radiation from the sample resulting from x-ray excitation thereof, is col-lected and analyzed. In another application a scanning electron microscope (S~M) is utilized, in which an elec-tron beam strikes a sample and the resulting radiation from the sample is collected and anlyzed. According to the prior art, such analysis of the resulting radiation from the sample, involves feeding the signals or informa-tion from the sample into a pre-amplifier of a known multi-channel analyzer. The signals from the pre-ampli-fier are then f'ed into an analog-to-digital converter from which information is transferred to a comparator, which generally comprises an upper range limit compara-tor cmd a lower range limit comparator. These comparatorsserve to analyze the information received from the con-verter and to de-termine and respond to those items of information or signals whose intensit~ levels, which are indicatlve of elements present in the materials of the -.

~ 3663 16-3-1979 2 P~IA 20 798 sample, falls between the pre-established upper and lower range limits for which the comparators are set. The signals from the anaiog-to-digital converter are also fed into a multi-channel memory, where the various:signals identifying the elemental characteristics of the analyzed sample, are stored.
The output signals from the comparators thus those signals which fall within the pre-established range defined by the comparators are fed into an event detector 10 which can be an "OR-gate" and pulse former and which regis-ters the oc~urrence of the various signals from the compara-tors. Signals or intelligence from the event detector are fed into the output circuitry which in turn can be fed to for example, a scanning electron microscope that constructs 15 an image of the analyzed sample area in accordance with the incoming signals from the event detector.
The apparatus also includes a marker counter, whose function it is to produce indices on the display and locate them appropriately. The attributes can be, for exam-20 ple, the image intensity, or brightness, the display grid,the display range scale, the width of the display window, and, in spectrometry, the K.L. and M marks, as explained below.
Information from the multi-channel memory is 25 fed into display drcuitry of the apparatus, which can be the circuitry for a television display9 on which there can be shown various information indicating the characteristics of the sample, one such characteristic being the intensity, or population, level of signals corresponding to a certain 30 energy or wavelength indicative of a particular chemical element, e.g. iron, the intensi-ty being related to the chemical content of this particular element in the sample.
In this particular type of application, wavelengthjenergy information is stored in a number of sequential memory 35 channels of the multi-channel memory.
-In asmuch as particular energies, and, there-fore, particular channels, relate to specific elements under analysis, it is often desirable to identify these speci~ic -- . ', '' .
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3 PHA 20,798 energy channels, this being done by the prior art, as des-cribed above, by using a comparator or counter-type circuit.
The present invention seeks to provide an improved multi-channel analyzer system and is characterized in that it contains a) an analog-to-digital converter for receiving incoming signals, b) a multi-channel memory connected to the con-verter, c) an attribute memory bank comprising at least one attribute memory and being connected to the multi-channel memory, d) a display circuitry connected to the attri-bute memory bank and to said multi-channel memory, e) a display device connected to the display circuitry, f) an output circuitry connected to ~he output memory band, and g) an output device for receiving and demon-strating the signals from the output circuitry.
According to the invention, the specific energy channels are depositories for signals or information from the apparatus that operates on the specimen by radiation and detection, such signals indicating various characteristics of the specimen, e.g., the relative concentrations of the elements present in the materials of the specimen.
While, as previously stated, the above prior art apparatus employs comparator-or counter-type circuits for identifying specific energy channels, the present invention involves the software-controlled assignment of attributes to discrete hardware memory channels, to allow a synchronous real-time hardware response. The principle of attribute memory involves pre-assigning markers, which signify specific characteristics, or attributes, onto an attribute memory bank that is not in an associated computer, but, instead, is provided by dedicated hardware memory of the multi-channel analyzer. The contents of the attribute memory bank are configured by an associated computer cir-.

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6~3 4 PHA 20,798 cuit but the attribute memory bank operates independentlyand asynchronously of the computer.
A multi-channel memory having, e.y., 1000 chan-nels with 4 assignable attributes would provide a 1000 word by 4 bit attribute memory bank.
In the present invention, a memory channel is identified as a member of a small group of channels repre-senting a specific elemental energy peak width, wherein one or more of the channels of the group are located in the multi-channel memory of the computer (i.e., a first multi-channel memory) and others of the channels of the group are located in one or more further multi-channel memories that are, as stated above, located not in an associated computer, -but, instead, are in a separate attribute memory bank, with the operation of the memory or memories of the attribute memory bank being configured by the associated computer cir~
cuit and operating independently and asynchronously of the ~;
computer. The difficulty to detect associated multiple peaks in the non-contiguous channels are overcome with the apparatus according to the present invention.
An advantage of the present invention is that its employment of a multi-channel analyzer attribute memory provides unlimited flexibility in detecting associated multiple peaks in the non-contiguous channels. The present 25 invention is also usable as a single channel analyzer. In ~
a preferred embodiment of the invention the display cir- ~;
cuitry of the analyzer apparatus comprises a) means for producing a maximum si~nal value (Nmax) to be fit to a signal truncator, b) a frequency ratioer connected to the trun-cator and to a system frequency clock, c) a first gate connected to the frequency ~-ratioer for receiving a display synchronizing signal F, d) a counter connected to the first gate, said counter receiving signals (Nchannel)to be monitored, e) a zero detector connected to the counter, and f) a second gate connected to the zero de-.

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16-3-1979 5 PHA 20 7g8 tector and to the first gate for receiving a television synchronizing signal TF from the first ga-te the second gate providing an output signal z modulating the display device.
Brief description of the drawings.
Fig. 1 is a schematic block diagram of a cir-cuit in the prior art for processing spectral data, using a comparator-type circuit as described.
Fig. 2 is a schematic block diagram of an apparatus according to the present invention, employing a lO multi-channel memory and an attribute memory bank providing - non-contiguous memory channels.
~igure 3 is a schematic representation of digi-tal means of the display circuitry according to a preferred embodiment of the present invention.
Figure 4 is a schematic depiction of a vertical television raster representing scan timing data.
Figure 5 is a schematic representation of analog means for achieving a vertical television raster output spectrum.
Flgure 6 is a schematic representation of digital neans for achieving horizontal television raster output spectrum.
Figure 7 is a schematic representation-of analog means according to another embodiment of the present 25 invention, for achieving horizontal television raster~
In fig. 1 an x-ray detector 11, a pre--amplifier 12, an analog-digital converter 14, an upper limit compara-tor 16, a lower limit comparator 18, a multi-channel memory 20, an evcnt detcctor 22, an output circuitry 24, a scan-30 ning electron microscope 25, a marker counter 26 a displaycircuitry 28 and a display 29 are listed and interconnected as described above in accordance with prior art.
The preferred embodimen-t of fig. 2 is related to an x-ray spectameter but can be used in other types of 35 a~alysator appara~us as well. Signals generated by an x-ray detector 52 in response to radiation emanating from an ~-ray impinged sample, not shown but previously de~scribed, the signal populatlon and makeup thus, the energy of the ' , ....... .. . ......... ... . . ...... . . .
.

~Z8663 signal which is dictated by the energy and wavelength of the emanated radiation, indicate various characteristics of the sample, e.g. the identities of the elements present in the sample material and their relative concentrations. These signals are transferred, preferably, to a pre-amplifier 54, whose output is then fed into an analog-to-digital converter 56.
The digital data from the a.d. converter 56 are fed into a multi-channel memory 64 and further into an lO attribute memory bank 58, which can comprise one or more attribute memory components 60, 62, etc. The output of the multi-channel analyzer is fed into a display circuitly 66, to which a television display 67 maintained to equal or ex-ceed somewhat the value of the highest peak of the informa-15 tion being collected. The means comprises apparatus toachieve a display of line G on the television display screen the contents of a particular channel, N, are placed in a count-down counter whose content is rnonitored. At time t2 the counter is counted down by a clock F and simultaneously 20 the Z mode of the tube is brightened. When the contents of the counter are zero (at t3) the brightness modulation is switched off. To ensure the correct operation, the follow-ing parameters are employed:
f~ Nmax ~ T histogram g N max g a - N channel f T histogram = T scan x k Where f is the clock frequency, N max is the vertical scale maximum value, T historgrarn is the time to display a line of maximum amplitude, T scan is the sweep or scan time of display (e.g.
ty-t1 ), T bright is the bright time (e.g. t3-t2), N channel is the content of the particular channel ,, "' ' ' ..

-- -~2~3663 that is displayed, and k is the proportion o~ the t~tal vertical sweep used for full vertical scale.~
In accordance with the present invention, when S a certain threshold value is exceeded by any channel of the display, the maximum full scale Nmax, is constantly varied to ~ollow the level or contents of the highest level chan-nel. In this situation, logic memory. Further, the attribute memory bank can be such as to provide reserve bits to which 10 other attributes can be assigned, thus permitting the as-signment of such attributes being done by software changes instead of hardware changes. In prior art mode of analysing commonly re~erred to as the fixed vertical scaling mode, the vertical amplitude of the signals is established at some 15 predetermined level and the ~ata are collected and fed into the display apparatus, it sometimes occurring that certain respective pea~s of various components of the spectrum ex-ceed this pre-established level and are not registered in the visual display.
More specifically, if the upper limit of the vertical scale is set at a given value A, and analytical x-ray fluorescence of a sample is carried out in a fashion familiar to the art, as the analysis is continued, informa tion is continuously fed into the display device (e.g. a 25 television display) as a result of which? at a certain time, the measure of the intensity of a constituent material of the sample is at a level C and at a subsequent time, such intensity is at a level B, with the intensity level there- -after reaching, and subsequently exceeding, level A. Con-30 sequently, the peak portion of a first sample component (which can be the intensity of, e.g. iron in the sample) endsup off the display while a second sample component (which can represent the intensity of e.g. nickel in the sample) remains fully within the display viewing field, this ob-35 viously being an undesirable result due to the inabilit~to gauage the pea~ of the ~irst sample component.
According to the present invention the upper limit of the range of the vertica] scale is initially set :~ .............. . .. .

~Z~G63 . ..
at pre-set fixed value and when this value is reached by the highest data point, the upper limit of the ~ertical scale range is then continuously maintaine~ at a level that is at least equal to and preferably exceeds somewhat, the 5 highest peak value of the data, such that there is a dynamic adjustment of the upper limit of the vertical scale, there-by énsuring tha-t all of the data are displayed and permit-ting the relatively low values on the vertical range to be maintained for a period of time and thus enabling reading 10 and comparison of these lower values for a larger projcction of the examination time than is available wi-th the previously described prior art techniques. Specifically, as the inten-sity, i.e. the vertical scale reading of the highest peak of the data displayed (i.e. the peak for display component 15 corresponding to the first sample component increases dur-ing the eæamination of the samp~e, the extent of the ver-tical range increases commensurately. As mentioned above, the visual display can be achieved with a television dis-play, using either a vert~ical television raster in which 20 historgram lines are provided by the television scan line, i.e. the display comprises one or more vertical bars or lines or a horizontal television raster.
In fig. 3, where the display is produced by a vertical television raster, two successivellines G and H
25 are shown with t1 designating the beginning of the scan for line G, t2 designating the starting time of the histo=gram being produced, t3 designating the stopping time of the histogram, and t4 the start of the flyback. At t6 the histo-gram H is begun to be written with such writing stopping 30 at t7 and t8 designating the start of the flyback. The starting times of the histogram, t29 t6~ t1o are alway9 the same and the respective finishing times of the his~ograms t3, t7, t11 being determined by the contents of the com-ponents or channels being displayed at those particular tim-35 es.
~ eferring to figure 4, there is describeddigital means for modulating the vertical televisio~ raster according to the present invention, where the upper range .

_,. _.. _.. __.. ._ .. ... _ . ~ _ .... ... ,. . . ~. . :. _ .. ._ . .... ..... ~ . . ... _.. _.. ~.. .. ... , . , _ .. ... ._.. _ , ~, 16-3-1979 g P~ 20 798 limit of the display is continuously.
The output of a first attribute memory 60 of the bank 5~ is fed into the display circuitry 66 (it being possible to feed into the display circuitry 66 the output o~
more than one attribute memory bank). The output of the first attribute memory 60 can provide one or more indices to the display circuitry, such as, for example~ the brightness of a portion of interest of the display, energy range markers, peak centroid identifiers, or ~-axis modulation bits for lO windo~ annunciation. Where other attribute memories address the disp]ay circuitry 66, other indices can be provided by them to the display device, such indices appearing on the display screen and being usable for reference purposes or for other purposes.
The output of a second attribute memory 62 is fed into the output circuitry 68 which can drive a scanning electron microscope (S.~.M.) display 69 to enhance an image of the inspected sample. This is a single-channel analysis, in principle.
By employing the present apparatus, the attri-butes or indices, that are desired for the output and dis-play devices can be provided to them by simultaneous opera-tion with the provision thereto of the information from the multi-channel memory instead of the prior art technique of 25 employing separate processing steps for providing the attri-butes or indices to the output and display devices. The present invention provides a simpler and less expensive apparatus by virtue of the possibility of omitting the comparator (16, 18 of Fig. 1) and the necessary there still 30 applies the equatlon f Nmax T histogram and, since T histogram is a constant, the frequency f is directly proportional to Nma~.
In the operation of the digital means as sho~n in fig. 4 for vertical television raster, the value Nmax of the highest level information channel is fed into a p~ogrammable frequency ratioing device 72 via a truncator .

:; ` - -74, which frequency ratioing device can be a digital diffe-rential analyzer, binary rate multiplier, or any other digi-tal device available in the art. Device 72 ensures to pro-duce a frequency propor-tional to Nmax and inversely propor-tional to T histogram. While it is preferred that the valueof N be truncated to reduce high frequency problems, this is not essenti~
The~'threshold value for the count (vertical axis) is preset into a data register 76. In the case of 10 spectrum coliection (i.e. dynamic data coilection), each time an event occurs in any channel (horizontal axis) the count magnitude is fed into a further data register 78, this data then being compared with the threshold value stored in the past data register 76 by means of a digital comparator 15 80. A logic circuitry element 82 then will cause the con-tents of data register 78 to be shifted into the first data register 76, when the data value in the further data regis-ter 78 exceeds the value of the first data register 75. Thus when the threshold value is exceeded, the last data value 20 stored in the first data register 76 is the Nmax value.
Generally, the value of NmaX at the end of the last -tele-vision frame is fed into frequency ratioer 72 via truncator 74 and this value will be used to scale the following tele-vision frame. ~n the case of a spectrum which had been pre-25 viously collected and stored, N x is generated using thecircuitry as shown in fig. l~ 5 but then the channel data values are compared only once, that being when the memory is loaded from the storage.
A s~stem clock frequency, Fs is also fed into 30 the frequency ratioer 72. The output frequency f, from the frequency ratioer is then proportional to Nmax, such output frequency being fed into a gate 86, to which a television synchronizing signal is fed. The output of gate 86 is used to count down the contents of counter 88, into which the ver-35 tical scale value, Nchannel has been preset. The contents ofcounter are fed into detect zero means 90, whose output is fed into another gate 92. The -television synchronizing sig~
nal is also fed into gate 92, the output of which pro~ides . .

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36~3 Z modulation.
In the operation of the apparatus~ the counter 88 is preset'with a Nchannel value at time t1? t5, tg~ etc.
(Figure 4) or at least some time between t3 and t6, t7 and tlo etc. Then, at time t2, t6, t10 gate 86 is opened by the television synchronizing pulse, causing -the frequency f (fi-gure 4), to start counting down counter 88. Simultaneously, the television synchronizing pulse opens gate 92, allowing the output of the zero detection means to provide a Z modu-10 lation. When counter 88 is at zero value, this occurring att3, t7, t11, etc., then Z modulation will then automatically disappear since this is produced only when the zero detec-tion means output does no-t represent zero. Thus, in bullding each TV frame, frequency ratioer 72 is loaded once per 15 frame at the ~eginning of the rrame and counter 88 is preset once per line.
To achieve vertical television ras-ter modula tion in the analog mode, according to the present invention (Figure 5), the value Nmax is truncated by truncator 100 20 (where truncation is desired, same being preferred but not required) and is converted by digital-to analog converter 102 into a D.C. voltage which is used as an initial condi-tion in an analog integration circuit 104 whose input is a voltage corrresponding to Nchannel, a television synchroni-25 zing signal being fed into the analog integratlon circuit104. The ou-tput of the integrator 104 is logically clamped to produce a Z modulation signal.
The integrator run down is started at t2, t6, t10 etc., by the television synchronizing pulse and reaches 30 zero level at t3, t7, t11, etc. This circuit is the analog equivalent of the circuit in figure 4.
To achieve horizontal television raster accor-ding to the present invention, where this is desired to be achieved by digital means, information is transferred from 35 a multi-channel analyzer memory 110 (figure 6) to a display memory 112, the contents of each channel being divided by kN by digital means 114, thus normalizing the value of each channel to a rnaximum vertical scale value of N
max - , .

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~Z8~63 16-3-1979 12 PHA 20 7g8 .
Such digital means can comprise a computer, microprocessor or hardwire digital arithmetic circuitry.
'Such horizontal television raster can be achie~
ved by analog means according to a further embodiment of this invention, with a multi-channel analyzer 120 (figure 7), from which information is transferred to a digital-to-analog converter 122, from which converter information is fed into a voltage divider 124 to which VN is fed, the max lO output of which voltage divider is then transferred to the analog shift register array 126 with the output therefrom being fed to a display devlce~

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Claims (2)

PHA 20,798 THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for dynamically scaling displayed information on a two-dimensional dynamic display with analog means to modulate the vertical scale comprising:
means to preset an upper limit of the range of the scale of said display in the vertical axis; said means presetting a maximum vertical signal value Nmax;
means to store inputed data to be displayed on the ver-tical axis of said display;
means to compare the maximum vertical signal value Nmax, said stored data, with the preset limit of said dis-play scale, said preset limit serving as a threshold value;
logic means to reset said upper limit of said scale value when said stored data exceeds said maximum sig-nal value threshold;
means for producing a new maximum signal value Nmax to reset said upper limit;
a signal truncating means;
means to provide said updated maximum signal value to said signal truncating means;
a system clock means;
a digital-to-analog converter to convert the output of said truncator into a DC voltage;
an analog integration circuit having as inputs a voltage corresponding to the signal N channel and a display synchronizing signal; and means to logically clamp the output of said integrator to produce a Z modulation signal fox said display.

2. An apparatus for dynamically sealing displayed information on a two-dimensional dynamic display with dig-ital means to modulate the vertical scale comprising:
means to preset an upper limit of the range of the scale of said display in the vertical axis; said means pre-setting a maximum vertical signal value Nmax;

PHA 20,798 means to store inputed data to be displayed on the ver-tical axis of said display;
means to compare the maximum vertical signal value Nmax, said stored data, with the preset limit of said dis-play scale, said preset limit serving as a threshold value;
logic means to reset said upper limit of said scale value when said stored data exceeds said maximum sig-nal value threshold;
means for producing a new maximum signal value Nmax to reset said upper limit;
a signal truncating means;
means to provide said updated maximum signal value to said signal truncating means;
a system clock means;
a frequency divider receiving Nmax signals from said truncator and receiving a signal Fs from said system clock;
said frequency divider providing an output proportional to Nmax and inversely proportional to the sweep time of the display multiplied by the proportion of total vertical sweep time;
first gate means receiving a display synchronizing sig-nal f from said frequency divider;
counter means for receiving said signal F from said fre-quency first gate means;
a television synchronizing signal supplied to said first gate means;
zero detect means for detecting when said counter counts down to zero;
and second gate means for receiving signals from said zero detect means, said gate means also receiving said display synchronizing signal, said second gate means providing an output signal modulating the Z modulation of said display device of said apparatus until said zero detect means detects a zero in said counter.