SEMI-AUTOMATIC SETUP FOR PROCESSING PHYSICAL EXPERIMENT DATA

G. A. Zheltovskii, K. F. Berkovskaya, P. I. Goskov,
V. B. Zhanauskas, S. G. Li, V. I. Mantorov

(Presented by the scientific-technical seminar of the Department of Electrical Equipment, AEMF)

This article presents the results of a study of a new semiconductor photosensitive sensor of the “scanistor” type [1] as applied to the problem of automating the processing of experimental data using a digital computer.

In the works of other authors, the influence on the resolving power of the scanistor of the form of the current–voltage characteristic, the longitudinal conductivity of the base, and the load resistance has been considered.

Of practical interest in creating semi-automatic and automatic devices for processing graphical information is taking into account also the influence of illumination on the time parameters of the signals obtained from the scanistor when graphical information is projected onto it.

The differential equation describing a scanistor cell has the form:

\[ \frac{a\sigma}{j_s}\frac{d^2 U_{\mathrm{b}}}{dx^2} = l^{-\alpha U_{\mathrm{bk}}} \left[ \exp\left( -\alpha\left[ U_t - Ex - j_k\frac{a}{\sigma} \right] \right) +1 \right] -2-\frac{\beta Q}{j_s}, \tag{1} \]

where \(j_s\) is the density of the junction dark current; \(U\) is the voltage across the junction; the subscripts “kb,” “eb” denote the corresponding junction; \(\alpha = q/AKT\) is a coefficient characterizing the deviation from an ideal junction; \(\beta\) is the junction separation coefficient; \(Q\) is the density of the luminous flux incident on the scanistor; \(U_{\mathrm{b}}\) is the base potential; \(l\) is the length of the scanistor; \(x\) is the current coordinate along the scanistor; \(\sigma\) is the specific conductivity of the base; \(U_t\) is the collector potential; \(E\) is the field strength in the emitter; \(j_k\) is the collector current density; \(a\) is the base thickness.

The results of solving equation (1) on a computer are presented in Fig. 1.

As follows from the above and from [2], the error in processing graphical information by means of such a sensor is a function:

\[ \Delta = F(f_{\mathrm{p}}, \Delta f_{\mathrm{p}}, \Delta U_{\mathrm{p}}, N, P, L_{\mathrm{sk}}, \Phi, R), \tag{2} \]

where \(f_{\mathrm{p}}\) is the frequency of the sawtooth-voltage generator; \(\Delta f_{\mathrm{p}}\) is the instability of the sawtooth-voltage frequency; \(\Delta U_{\mathrm{p}}\) is the instability

sawtooth voltage; \(N\) is the nonlinearity of the sawtooth voltage; \(P\) is the nonlinearity of the scanistor; \(L_{\text{sc}}\) is the length of the scanistor; \(\Phi\) is the light flux incident on the scanistor; \(R\) is the location of the information on the scanistor. To compensate for errors due to \(f_{\text{p}}\), \(\Delta f_{\text{p}}\), \(\Delta U_{\text{p}}\), \(N\), \(P\), and \(L_{\text{sc}}\), in the semiautomatic device developed and manufactured for the Research Institute of Nuclear Physics, Electronics, and Automation, a circuit is used (the fill-pulse formation unit) in which the compensating element is a discrete scanistor.

Fig. 1.—In Fig. 1, \(a\)—curves of the distribution of \(e^{\alpha U_{\text{bk}}}\) over \(l\) at \(U_t = 0.5\ \text{V}\), \(a = 50\ \mu\text{m}\), \(\rho = 10^5\ \Omega\cdot\text{cm}\), as a function of \(M\), where \(M = 2 + \beta Q/j_s\). The switching line of the scanistor cells passes at \(e^{\alpha U_{\text{bk}}} = 1\) (the switching point of a scanistor cell is delayed the more, the higher its illumination). In Fig. 1, \(b\)—the dependence of \(l^{\alpha U_{\text{bk}}}\) for \(a = 20\ \mu\text{m}\), \(\rho = 10^5\ \Omega\cdot\text{cm}\). Curves 1 and 2 are for \(M=2\), and curves \(1'\) and \(2'\) for \(M=8\), with and without allowance for the transverse resistance of the base region. (An increase in the transverse resistance of the base region entails an expansion of the cell-switching zone.)

The semiautomatic device makes it possible to measure track angles \(\varepsilon\) in the range from “0” to \(\pm 30^\circ\) from film of size \(24 \times 36\ \text{mm}\). The measurement error does not exceed \(0.012\ \text{rad}\). The measurement result is recorded on paper by means of a digital printing machine. The gap number, determined visually by the operator, is also recorded on the paper by the digital printing machine. The time for processing a single event and recording it on paper does not exceed \(10\ \text{s}\). The semiautomatic device is powered from a \(220\ \text{V}\), \(50\ \text{Hz}\) AC mains supply.

Fig. 2. Block diagram of the setup

The block diagram of the setup is shown in Fig. 2. The scanistor and film-transport mechanism unit serves to project onto the table an enlarged image of the track projection and to read it by means of

of the scanistor to the track inclination angle. The scanistor is interrogated by a sawtooth voltage supplied from the sawtooth-voltage generator unit (hereinafter denoted S.V.G.). The signal from the scanistor, containing information on the magnitude of the angle, enters the unit for extracting the signal from the scanistor and circuit “I,” where the signal is shaped into a rectangular pulse whose duration is proportional to the magnitude of the track angle. Simultaneously, the voltage from the S.V.G. enters the fill-pulse forming unit, which consists of 51 cells of a discrete scanistor and produces 51 rectangular pulses, and then enters the signal gates unit. The pulses from the fill-pulse forming unit enter the unit for forming the signal from the scanistor and circuit “I.” Circuit “I” is prepared to issue to the input of the “SSS” rack a burst of pulses whose number is proportional to the magnitude of the track angle. The burst of pulses is sent to the input of the “SSS” rack only after the operator presses the “start” button of the PS-1 counter on the “SSS” rack. The pulse arriving from the counter at the signal gates prepares them to receive pulses from the S.V.G.

With the first pulse from the S.V.G., after the signal gates have been prepared, the electronic circuit of the signal gates is started and selects a rectangular pulse with a duration equal to the period of the sawtooth voltage from the S.V.G.; this pulse passes the burst of pulses from circuit “I,” characterizing the track angle, to the PS-1 counter of the SSS rack. After 1 sec the result is automatically recorded on paper by means of a digital printer.

The unit for forming pulses marking the stopping of the spark serves to form a number of pulses equal to the number of the gap in which the spark stopped. The burst of pulses from it enters the counter of the SSS rack and is then recorded on paper by means of the digital printer.

The sign of the track angle is recorded on the paper of the digital printer by means of the “+” or “−” buttons.

References

1. K. F. Berkovskaya. A vacuumless television image converter—a scanistor. Semiconductor Devices, No. 20, 3, 1968.

2. G. A. Zheltovskii, P. I. Goskov. Measurement of the coordinates of elementary-particle tracks by means of a linear scanistor. PTE, 3, 1970.