SU871132A1 - Device for automatic determination of exposure - Google Patents

Description

one

The invention relates to the field of photographic equipment, in particular for the automatic determination of exposure during photo printing, and can also be used to control the shutter of a camera.

A device for automatically determining exposure is known, using a change in photodiode resistance, depending on the illumination, to control the charging current, the time of the reference capacitance, which makes it possible to adjust the exposure time of the charge center

 The disadvantage of this device is that the low input impedance of the bipolar transistor does not allow to obtain high accuracy of exposure.

The closest in technical essence is a device containing a bridge circuit in which a photodetector is connected in series with a capacitance time and makes up two shoulders of a bridge circuit, in the other two arms of which variable resistors are included, a high-resistance matching circuit, a comparison circuit zheniy amplifier

(electronic key) and the actuator (relay) Gz.

A disadvantage of this device is that, due to the inertia of the semiconductor photodetector, the charging current time of the reference capacitance is not established instantaneously, but for a certain period of time, which leads to inaccurate determination

10 exposure ..

The aim of the invention is to improve the accuracy of exposure determination by reducing the effect of the inertia of a semiconductor photodetector.

The goal is achieved by the fact that the time of the driving capacitor is connected in series with the resistor determining the charging current of this capacitor, and with it the two arms of the bridge

20 schemes / a photodetector is included in the third, adjacent to this capacity, cxeNU bridge shoulder.

FIG. 1 shows a device diagram / in FIG. 2 is a graph of voltage measurements for the time of the capacitance and photodetector.

Claims (2)

The proposed device consists of a bridge circuit 1, -containing the time specifying the capacitance 2, connected successively with the resistor 3 and composing with it two arms of the bridge circuit, a photodetector 4, included in the third, adjacent to this capacitance, the bridge of the bridge circuit, circuit matching 5, circuit. Comparison of the electronic key 7, the actuator (relay) 8 and the starting contact 9. The device operates as follows. When the contact 9 is short-circuited, the relay 8 is turned on, which with one pair of its contacts switches on the load (not shown), the second pair of contacts blocks contact 9, and the third pair of contacts disconnects from the capacitor 2 the discharge resistor 3 and starts charging the capacity with a current, the value of which depends on the size of the resistor 3. At this time, the semiconductor photodetector 4 under the influence of the light flux changes its resistance to a fixed value. At the same time, a photovoltage KG 4 sets the voltage of a certain value (see Fig. 2), which through the matching circuit 5 is applied to one input of the comparison circuit b, the second input of which is also applied through the matching circuit 5 capacitance 2. When comparing voltages (point bsr. in FIG. 2), the comparison circuit gives a command to stop the exposure. Thus, during the charging time of the capacitance 2, the resistance of the photodetector 4 reaches a steady-state value. This improves the accuracy of exposure. FIG. Figure 2 shows the change in the voltage of the SRI (axis). In time (axis X) on the capacitance and photodetector, at the point ic.p. exposure stops. The described technical solution makes it possible to reduce the effect of the inertia of the photodetector on the accuracy of exposure as a function of the type of photodetector and the range of illumination by two to five times. Due to this, the consumption of photosensitive material is reduced, and labor productivity is increased. Apparatus for automatically determining exposure, comprising a series-connected bridge circuit consisting of a semiconductor photodetector, a capacitance time and resistors, a matching and comparison circuit, an electronic switch and an actuator, characterized in that, in order to improve the accuracy of exposure determination by decreasing the inertia effect of the photodetector, the time specifying the capacitance is connected in series with the resistor determining the charge current of this capacitance, and is them two arms of the bridge circuit, and is included in the third photodetector adjacent to this container, the shoulder of the bridge circuit. Sources of information taken into account in the examination 1. US patent number 3947855, cl. 354-50, published. 1976. 2. USSR author's certificate number 567099, cl. G 03 B 7/08, 1974 (prototype). LRM aLg schaag MMMUYA Rga ..