SU1597843A1 - Device for automatic exposure control - Google Patents

Abstract

The invention relates to photographic equipment and, in particular, can be used to build highly accurate automatic exposure control systems in photographic equipment. The purpose of the invention is to improve the accuracy and thermal stability of the device by eliminating the non-identity error of logarithmizing the signals of the sensors of the exposure parameters and eliminating the influence of the temperature dependence of the logarithm and adder on the overall temperature error. The goal is achieved by the fact that the signals of the sensors 8 of the exposure parameters and the output signal of the photoconverter 7 through the analog switch 1 are alternately fed to one common logarithm 2, the output of which with a sign corresponding to the sensor of the exposure parameter or photoconverter connected to the logarithmizer are successively summed in the accumulator 3 , and at the end of the conversion cycle, the result of summing the signals of all the sensors is recorded in the 4-storage circuit 4 and then fed to cx it is 5 comparisons with a threshold signal, the output of which is controlled by the drive 6, affecting one of the exposure parameters in the direction of eliminating the inequality of the compared signals. 1 il.

Description

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The invention relates to photographic equipment, in particular, can be used to build highly accurate systems of automatic exposure control in photographic equipment.

The aim of the invention is to improve the accuracy of automatic exposure control by increasing thermal stability and reducing errors in the conversion of signals of exposure parameters.

The drawing shows the block diagram of the device.

The device contains serially connected analog switch 1, logarithmic analog-to-digital converter (ADC) 2, digital accumulating adder 3, digital sampling-storage circuit 4, digital comparison circuit 5, drive 6, with analog inputs a, b, c, d of analog switch 1 is connected to the output of the photovoltaic converter 7 and the terminals of-. sensors from exposure sensors (Ri, film sensitivity (), diaphragm (.), digital address inputs of analog switch 1 and address inputs f of digital accumulating adder 3 are connected to output bits h of pulse counter 9, whose overflow output G is connected A reset input k of accumulating adder 3 and a record / sample 4 storage / storage input, and an input of pulse counter 9 and a clock input of a digital accumulating adder 3 are connected to the output of pulse generator 10. Regulation eq position is performed by controlling the diaphragm 11 of the camera lens 12, the movement mechanism of which is driven by a drive unit 6. The engine potentiometric sensor diaphragm 8 is kinematically connected to the diaphragm actuator 11 June.

The device operates cyclically under the action of the pulse generator 10, the pulses of which successively change the state of the pulse counter 9 from zero to maximum (equal to the number of analog inputs of analog switch 1). The output code of the pulse counter 9 is fed to the address inputs of the switch 1 and the digital accumulating adder 3. Depending on the counter code 9, through the analog switch 1, the corresponding potentiometric sensor or phototransducer is connected to the input of the logarithmic ADC 2. From the output of the ADC 2, the signal enters the accumulating adder 3, where it accumulates with the accumulated measurement result of the signals of the previous sensors with the sign "4- or" - depending on the signal sensor connected to the ADC 2, i.e., depending on the code, I enter on the adder 3 from the counter 9 pulses.

After the state of the counter becomes maximum, i.e., the conversion and sequential summation of all input sensors is performed, the output signal G of the pulse counter 9 is set to an overflow signal, according to which the final result of the accumulation in this measurement cycle is remembered : The next clock pulse generator 10 pulses counter 9 pulses

is set to zero, the overflow signal is turned on, on the falling edge of which the accumulator 3 is reset to zero, and the device performs the next measurement cycle.

The result of the summation stored in the sampling-storage scheme 4 until the end of the next cycle is fed to the digital comparison circuit 9, which is a zero-authority.

If the result is not equal to zero, the outputs of the comparison circuit are generated

the signals "and" control the operation of the actuator 6, which changes the aperture value and, therefore, the signal value of the potentiometric aperture sensor in the direction of eliminating inequality.

Similarly, it is possible to control the exposure time parameter by connecting the actuator 6 to an exposure working mechanism (not shown). Thus, automatic exposure control is accomplished by solving the main exposure equation.

t-E-S K.

; i)

where /

exposure time (exposure);

E - illumination created by the subject in the plane of the photographic material; S is the photosensitivity of the material; / С - lens aperture value, in accordance with its transformed view:

logat- iOgaE + lOgaS - / Oga / C 0,

(2)

Since the signals of all sensors of the exposure parameters and the signal of the photovoltaic converter pass through one logarithmizer, the full identity of the logarithmic process is observed. In this case, the drift of the logarithm observed under the temperature is expressed in the change of the scientific research institute of the base of the logarithm (2), but since the logarithm is common to all input signals, then all members of equation (2) change the base of the logarithms a in the same way, which is not leads to a violation of the equality of equation (2). 55 In addition, the use of a logarithmic ADC, a digital accumulator, a sampling-storage circuit, and a comparison circuit eliminates the error of summation.

due to thermal drift analog adder.

Claims (1)

Invention Formula An automatic exposure control device containing a photo-converter, a block of potentiometric sensors of exposure parameters, a block of individual indicators, kinematically associated with the mechanism of movement of the diaphragm and the engine of the potentiometer sensor of the diaphragm, characterized in that, in order to increase the accuracy and thermal stability, it is possible to increase the accuracy and thermal stability. analog switch, logarithmic analog-to-digital converter. digital accumulator, digital sampling-storage scheme, digital comparison circuit whose output is connected to the execution and indication unit, the analog inputs of the switch are connected to the output of the photoconverter and the outputs of potential sensors of exposure parameters, and the digital address inputs of the analog switch and digital accumulator connected to the output bits of the pulse counter, the overflow output of which is connected to the reset input of the accumulating adder and the circuit recording input sampling-storage, and the input of the pulse counter and the clock input of the accumulating adder are connected to the clock pulse generator.