Microcomputer system of treatment of chamber stereophotographs using CCD pickups

Computer Physics Communications 50 (1988) 213—215 North-Holland, Amsterdam

213

MICROCOMPUTER SYSTEM OF TREATMENT OF CHAMBER STEREOPHOTOGRAPHS USING CCD PICKUPS S.G. ARZUMANYAN and H.V. NAVASARDYAN Yerevan Physics Institute, Markarian St. 2, Yerevan 375036, Armenia, USSR

A microcomputer system for the treatment of track chamber stereophotographs is described. A CCD 1200 11.111 is used as a scanning pickup (photosensitive cell is 15 ~m wide). The calibration measurement gives an accuracy of the particle track point coordinate pickup of 6 = 3.75 ~m.

In recent years in high energy physics different methods of electronic pickup of experimental information are mainly used but in some cases as before, track chambers with film pickup of expenmental data are used in different hybrid systems. In such systems track chambers are used as vertex detectors. Projectors with different degrees of au tomation are used for measuring track chamber photographs. But in all of them a special marker is manually centered on the point to be measured, when dealing with complicated events. The efficiency of such a system is very low. To provide high efficiency and (in some cases) high accuracy of measurements, application of a CCD scanner [1] is intended. Good photometrical parameters, invariable coupling with the coordinate system, simplicity of digital control and connection to a computer, permit to efficiently use the CCD pickups in chamber film analysis systems of traditional scanning devices. The use of the CCD pickups will allow not only to automate the measurement of particle track coordinates, but also to obtain information about track ionization. A microcomputer system for the treatment of chamber stereophotographs using CCD pickups was designed and constructed in Yerevan Physics Institute. The system compnses measuring projectors with linear CCD scanners. Each of the projec%ors is controlled through a CAMAC bus by microcomputer “Electronika-60” with extended periphery (fig. 1). Depending on the complexity of the photographs, two modes of

measurements are available: automatic track following; automatic overall measurements of the entire

— —

rame. -____________________________________________

OO1O-4655/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

I

L0 P P V U S 5 0 R

D

K

A P

__________________________________ U S

-

C P U

D I S P L A V ELECTRONIICA—60

_______

________

C 0 N TR 0 LL N ~

_____________________________________

I TV CONTROL

I

______ ~

c

II COUNTER

I

A U A C

I

COUNTER

II PROJECTOR DRIVER

II C C D CONTROL

________________________ R

E C 1 0 R

Fig. 1. A block diagram of hardware of the system.

214

S.G. Arzumanyan, H. V. Navasardyan

The microcomputer processes:

/ Stereophotographs using CCD pickups

controls the following

The most important unit of the system is the CCD controller (fig. 2). Its configuration principle [3] permits to control CCDs of different type. The controller functions as follows. The pulse genera-

a) sequence of operator’s actions; b) search for a given frame and automatic measurement of fiducial marks; c) velocity of the measuring stage; d) data gathering and bufferized data transfer to a more powerful computer.

tor recommended by the produces firm. The master controlfrequency table contents is gradually scanned depending on this frequency. The control table is a set of changeable programmed memory units (PMU) with a coded time diagram of CCD control signals. As the cycle is over, it reimtiates beginning from the first address. The PMU outputs are fed through a converter to the CCD. Double correlation selection unit chooses and amplifies videosignals from the CCD. The amplified signal is fed to an ADC and to a discriminator. The ADC converts the signal amplitude, which allows to estimate the ionization of tracks. The discriminator regulates the videosignal level (512 levels) and shapes rectangular pulses for the TTL logics. The appearance of an impulse in the frame interval means that there is a track on the film. Units giving the beginning and the width of the tracks produce signals by which the coordinates and the width of the tracks are fixed and stored as counter codes. For elimination of interferences the interference code is recorded in the noise suppression unit. If the track width is larger than the interference code, the selection logics forms an address for the data buffer.

The process of data gathering includes information filtration, control over the smoothness and quality of the measurement. A section of the image of the photograph measured is projected by means of an optical system on the plane the CCD is situated. The CCD and the marker are placed on the same stage. So, one can supplement the data from manual measurements by automated ones. The CCD is located perpendicular to the direction of the film travel (to the direction of the beam of particles under investigation). In case the track orientation coincides with that of the CCD (it is rather scarce) the measurement should be carried out manually by means of the marker. A further location of one more CCD oriented perpendicular to the existing one, and the use of data from at once two CCDs is supposed. The images of the points of tracks measured are shown on the monitor and the operator can follow the process of measurement and interfere.

I

CONTROL I ~GENERATOR

I

I I

~

CONTROL SIGNAL LEVEL CONVERTER

I

I

I

I

I

I_______ I

r

___

‘MEMORY CONTROL

~M0RY

J

LOGIC

I

NOISE SUPPRESSION

I

I

I

ADDRESS SELECTION

I

DOUBLE

I I

VIDEOSIGNAL

SCORRELATION UNIT ELECTION

I

DISCRIMINATOR (0 A C) I

I

_______

C C 0

II_______

___

I

___

I

I

II

___

I

I

I TRACK

I

BEGINING I G~T0R COORDINATE

A

I 0 A I A

LOGIC

Fig. 2. CCD-controller block diagram.

____

I

I

III II

I B U P P E R

TRACK VALUE GENERATOR

I

I

5G. Arzumanyan, H. V. Navasardyan

Data readout is governed by the computer. A CCD 1200 UJII [2] was used as a scanning pickup (1000 cells; the size of each cell along the photosensitive line is 15 rim). The amplitude of signals from each CCD cell is proportional to the flux of light. Since the track image projection covers several adjacent cells, the centre of the track (signal) is determined better than the size of the cell itself. The position sensitivity of the optical—electric pickup is obtained to be several decimal parts of a cell. But the real accuracy of the coordinate measurement is limited by the so-called “geometrical noise”, which occurs because of spatial fluctuations of dark currents in the CCD cells. As the experimental measurements show, the “high brightness” mode will be used to obtain the maximum signal/noise ratio, which is provided at the maximum output signal obtained at continuous expositions. Since only a motionless “image” is measured, it is possible to measure it for several times and to average the beginning and the width of tracks.

/

Stereophotographs using CCDpickups

215

To estimate the pickup accuracy, the calibration grate was projected on the CCD. The spacings between the grate lines were measured. The rms deviation of distributions of these spacings is a 3.75 p.m. The track coordinate pickup was tested in laboratory conditions on negative photographs from spark and bubble chambers. The spark chambers provided an effective track registration, while in case of bubble chambers (because of different track brightness, width and high-density intervals necessary for highly efficient registration) a thorough light and storage time regulation was required. =

References [1] C. Sequin and M. Tompset, Charge Transfer Devices (Academic Press, New York, 1975). [2] I.D. Kashlakov, V.T. Klyonov and F.V. Kostukov, Linear CCD 1200 WIl, Electronnaya promyshlennost, no. 7(1982) [3] S.G. Arzumanyan, G.Kh. Aslanyan and G.V. Navasardyan, Preprint EPI-916(67)-86, Yerevan (1986).