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I 2 3 4 FLOW RATE, LITERS/MINUTE
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Figure 3. Calibration data for air at three different internal pressures. Rotameter is set up as in Figure 2. Data are for the glass float 0 20 psi 0 30 psi 0 - 40 psi
Mansfield and Winefordner (I) have considered this problem of gas flow measurement and suggest that pressure corrections be applied to the indicated flow rate to convert these to atmospheric pressure. With the system suggested in Figure 2, corrections are not necessary. The rotameter is simply calibrated at the pressure(s) to be used. Flow rates obtained with the wet test meter are essentially at atmospheric pressure. If the rotameter is used at a pressure for which it has been calibrated, the gas flow rate can be controlled by the downstream needle valve without affecting the calibration. Regardless of what occurs downstream, the pressure of the gas in the rotameter is constant and the gas flow rate (atmospheric pressure) can be obtained directly from the calibration curve. These factors must always be considered, no matter what the specific application of these devices. RECEIVED for review December 22, 1969. Accepted January 28, 1970. Research supported by The Petroleum Research Fund administered by the American Chemical Society. (1) J. M. Mansfield and J. D. Winefordner, Anal. Chim.Acta, 40,
357 (1968).
On-Line Computer Interfacing of a Densitometer Film Reader for Measuring the Size of Radioactive Colloid Particles T. R. Barclay, A. C. Morris, Jr., R. L. Hayes, J. E. Carlton, and A. E. MCDOW,Jr. Medical Division, Oak Ridge Associated Universities, Inc., Oak Ridge, Tenn. 37830 SEDIMENTATION-VELOCITY METHODS have been used to measure particle sizes in developmental studies of radionuclide-labeled hydrous ferric oxide preparations ( I , 2). Such colloid preparations should have uniform particle sizes when used as medical scanning agents. Using Kraemer’s method (3) we calculated the particle-size distributions from densitometer traces of ultracentrifuge cell-absorption films. These films are read with a Spinco Model R Analytrol that is fitted with a Beckman Microzone scanning attachment. Calculations made on the densitometric recordings from each film were done by hand, a laborious and time-consuming process. With the purchase of an IBM 1800 on-line computer, we have accelerated these calculations. Recently we interfaced a connection to the computer and are now automatically operating the Analytrol densitometer from a location 400 ft from the computer site. CONSTRUCTION AND PROGRAMMING
The Analytrol instrument was modified to permit remote control of the film-drive circuits. We obtained an analog output voltage proportional to the Analytrol’s pen deflection from a linear precision potentiometer coupled to the servo(1) R. L. Hayes, “Radioactive Pharmaceuticals,” G . A. Andrews, R. M. Kniseley, and H. N. Wagner, Eds., AEC Symposium Series No. 6, CONF-651111, 1966, pp 603-611. (2) R. L. Hayes, J. E. Carlton, B. L. Byrd, and J. J. Rafter, in Research Report 1967, ORAU- 106, Medical Division, Oak Ridge Associated Universities, pp 105-1 11. (3) T. Svedberg and K. 0. Pederson, “The Ultracentrifuge,” Oxford University Press, 1940, pp 325-353.
BECKMAN ANALYTROL INTERFACE
CONTROL MODULE
IBM-1800 COMPUTER
MOTOR O R l V E
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FILM I R I V E MOTOR
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Figure 1. Simplified circuit diagram and control functions for the Analytrol interfacingconnection mechanism drive shaft. A regulated dc power supply excites the potentiometer. Film variations produce a 0-500 millivolt signal that is routed through shielded cables to the computer. Calculations, based on this analog signal, are made in terms of percentage of the total 500-millivolt span. Figure 1 shows the control signals required for operation. To begin sending film-density data, the operator actuates a “start” switch on the control module that completes a process-interrupt-contact (PIC) circuit to the computer (4). When the computer receives the start signal, any lowerpriority program is interrupted and the Analytrol program is (4) IBM 1800 Data Acquisition and Control System Installation Manual-Physical Planning, File Number 1800-15, International Business Machines Corporation, 1966. ANALYTICAL CHEMISTRY, VOL. 42, NO. 6, MAY 1970
685
SAMPLE NO 6 1 A 1 4 0 SAMPLE NAME K EQUAL ~ 2 . 3 4 2 6 E - 1 2 X Z E R O EQUALS + 5 . 8 3 4 4 E+OO
TOSlO
A T 5 0 4 CONCENTRATION
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PARTICLE NO EQUAL + 7 . 6 6 l I
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5 5 2 ON OFF T O CONTINUE
5 5 3 F O R ANALYSIS
Figure 4. Computer printout of header information, computing constants, and initial weight averages
Figure 2. Typical film-density curve as received by the computer
IGG~A HYDROUS F E R R I C O X I D E COLLOID
CURVE
Our computer program detects the film density base line, the inside and outside cell-reference holes, recognizes the cell meniscus, and relates elapsed time to distance from the center of rotation. One use of the outside cell-reference hole is to end data sampling. Using boundary and plateau heights, together with a data-smoothing routine, we determine colloid concentration as a function of the distance from the center of rotation (3). Further analysis of these data provides the particle-size distribution. OPERATION AND RESULTS
1 DISTANCE FROM A X I S OF ROTATION (cm)
072EI
I \ RADIUS
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Figure 3. Computer plots of the sigmoid concentration curve and the particle-weight-sizedistribution loaded into memory and executed (5). The program then generates an electronic-contact-operate (ECO) signal to start the Analytrol’s film-drive motor. Figure 1 shows additional ECO (control) signals from the computer used to indicate a satisfactory data flow and end-of-readout (EOR). Should a higher-priority program interrupt the Analytrol program or if a transmission error is detected, a red “abort” light comes on and the transmission ceases. The “abort” light signals the operator to reposition the same film for another try. As the film moves, the computer samples the analog input signal 50 times per second. When the film is completely read, computer programs turn off the film-drive motor and turn on the EOR light indicating a successful transmission. Computations begin immediately on the stored data determining the particle-size distribution ; the computer printer then tabulates results and an on-line plotter plots the curves. ( 5 ) IBM 1800 Time-sharing Executive System Operating Pro-
cedures, File Number 1800-36, International Business Machines Corporation, 1966.
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ANALYTICAL CHEMISTRY, VOL. 42, NO. 6, MAY 1970
The technician telephones experiment identification, run time, and required calculation constants to the computer operator. The system’s operation is first checked by running a standard film of known results. The technician then begins inserting the experimental films serially into the Microzone scanner, while both he and the computer operator monitor each film’s transmission. Figure 2 shows a typical film-density curve as plotted. Figure 3 shows a sigmoid concentration curve and a size-distribution curve produced by our computer program. Figure 4 illustrates the computer’s tabulation of experiment information, computation constants, weight average, and particle size. A “remote computer terminal” will be installed at the Analytrol site to facilitate printed communication to and from the computer, to avoid the need for a computer operator. Other future plans call for the design and construction of a high-speed film reader that is not dependent on the slowacting servomechanism of the Analytrol instrument. The high-speed reader will increase computer efficiency by reducing the reading time from 11/* minutes to less than 5 seconds. Our present computer operation of the Analytrol, requiring 1 minutes, still represents a considerable improvement over the 5 hours per film required when similar data were laboriously hand calculated. CONCLUSIONS
We find the use of this on-line system greatly speeds the analysis of our ultracentrifuge films. With this system, we also benefit from increased experimental accuracy since we avoid many laborious, error-prone calculations. RECEIVED for review October 27, 1969. Accepted February 9, 1970.
