SU1415217A1 - Device for measuring the error of still-life cameras - Google Patents

Abstract

The invention makes it possible to increase the accuracy of controlling the exposure parameters by using the capacity of the integrator together with a resistor connected in parallel to it through a key, as an RC circuit (key is closed) and as an integrating capacitor (key is open). The presence of the same capacitance in the integrator and in the RC circuit allows the use of a double integration method for measuring the exposure error, in which the meter readings do not depend on the integrator capacitance. The meter contains sequentially installed reference light source 1, the test camera 2, a photodetector 3 connected via a switch 4 between the inputs of the integrator 5, parallel to the integrating capacitor of which a switch 6 is connected via a switch 6, which together with the integrating capacitance forms a CS circuit, comparator 8, trigger 9, a key 10 connected to a generator 11 and a reversible counter 12, as well as a photodetector 17, a zero level detector 16, a control circuit 15, a trigger 14 characters, an indicator 13 .. When the camera shutter 2 is triggered, the light The flow of light source 1, converted by a photodetector 17 and a zero level detector 16 to an electrical pulse, the duration of which corresponds to a full shutter speed, controls the operation of integrator 5 (switch 4 is closed and switch 6 is open) through control circuit 15 charged by the current of the photodetector 3. On the falling edge of the pulse of the control circuit 15 (switch 4 is closed, and clocks 6 is closed), the discharge of the integrating capacitor through the resistor 7 follows the logarithmic law and simultaneously Key 10 runs (L

Description

one

The invention relates to instrumentation, namely, devices for monitoring parameters of cameras, and can be used to measure the exposure error of cameras of any type.

The aim of the invention is to improve the accuracy of measurements of the exposure error.

The drawing shows a block diagram of the meter.

The meter contains sequentially installed reference source 1 of light, the test camera 2, a photodetector 3 connected via a switch 4 between the inputs of the integrator 5, parallel to the integrating capacitor of which, via KLouch 6, a resistor 7 is connected which, together with the integrating capacitance, forms an RC circuit, comparator 8, to the second the input of which is connected to the source of the reference voltage Up, and the output of which is connected to the trigger 9 connected to the key 10 connected between the generator 11 and the reversible pulse counter 12, which is connected to and the indicator 13, the trigger 14 characters connected to the indicator 13, and with the control circuit 15 connected to the trigger 9, keys 4 and 6 and through the zero-level detector 16 to the second photodetector 17,

To describe the feature of the device, the following mathematical apparatus is introduced.

For exposure error:

ulgH log.

And idm

 n

(one)

- Exposure error ,.

steps; measured exposure

lk with; - nominal exposure,

lk- with.

For a logarithmic meter:

and,

T, Tin

(2)

ten

15

where T is the RC time constant; TX is the capacitor discharge time; and - capacitor charge voltage;

and - threshold voltage, In the proposed capacitor charge voltage meter

Д. Ur, 1 / j Vt

(3)

Where

T

- photodetector current, corresponding to the light curve;

tgjj, .- full shutter speed; C is the capacity of the integrator, and corresponds to H, and UQ corresponds to HQ,

Then the formula (2) takes the form

.ig-30

With

 1 / k; T, log, jj

.

Since the permissible exposure errors of the cameras can be positive and negative and do not exceed two steps, an artificial method is used in the meter, according to which the voltage is assumed to be equal to the value corresponding to minus two steps of the nominal exposure LD. The value 200 is entered into the counter and the number -2.00 is displayed on the indicator,

The use of a second photodetector, a zero-level detector in conjunction with a control circuit, determines the phases of charge and times3 4

p yes capacitor, i.e. the start and end of the pulse of light when the shutter is triggered by pressing the Shutter button.

The device works as follows.

In the initial state, key A is open, and key 6 is closed.

When the shutter of the camera 2 is triggered, the light flux of the photodetector 1 and the zero-level detector 16 is converted into an electrical pulse whose duration corresponds to full shutter speed.

On the leading edge of this pulse, control circuit 15 closes key 4, opens key 6, zeroes counter 12, and generates a short pulse, on the trailing edge of which the number 200 records the number 200 and the character trigger 1A sets counter 12 to the Subtraction mode. At the same time on the indicator 13 the number -2.00 is indicated (the comma is indicated permanently).

At the moment when the key 4 is closed and the key 6 is opened, the integration process begins, in which the capacitor 5's capacity is charged by the current of the photodetector 3. At the moment when the voltage of the integrator 5 exceeds the voltage Ud, the output voltage of the comparator 8 appears does not change the initial state of trigger 9. The integration process continues during the pulse. On the trailing edge of the pulse (the end of integration), control circuit 15 opens key 4, closes key 6 and opens trigger key 10 through trigger 9, which changes its state, 10. The process of discharge of integrator 5 begins and the counter 12 starts counting the number of pulses arriving at it from the generator 11 through the public key 10. The pulses of the generator 11 are subtracted from the pulses recorded in the counter 12 until they pass through O.

At the time of transition through O, the counter 12 changes the state of the trigger

7

14 ppakl, which placed the counter 12 in the Addition mode and on the indicator 13 is displayed +.

In the process of discharging the capacity of the integrator 5 to the resistor 7 output. the voltage of the integrator 5 is compared by the comparator 8 with the voltage U, At the moment of equality of these voltages on

The output of the comparator 8 is a negative pulse differential, which returns the trigger 9 to its initial state. In this case, the key 10 is closed and the flow of reiieper 11 pulses to the counter 12 is stopped. The indicator 13 indicates the value of the camera exposure error in the steps with the corresponding m sign.

20

Claims (1)

Invention Formula Exposure error meter for cameras containing: a consistently connected reference light source, photodetector, first key, integrator, comparator, trigger, key circuit, reversible pulse counter and indicator, second key, connected to the integrator output, a generator connected to the cxeNibi key information input and control circuit connected to the first output with the control inputs of the first and second keys, and the second output with a reversible pulse counter, characterized in that, in order to improve the measurement accuracy, A resistor, an additional photodetector, a sign trigger and a zero-level detector are inserted into the meter, the resistor being connected via the second switch to the integrator output, an additional photodetector connected to the detector input the left level, the output of which is connected to the control circuit input, the trigger by the second input is connected to the third output of the control circuit, the input trigger is connected to the indicator output, and the output is connected to the second input of the reversible pulse counter, the second input of the comparator is connected to the reference voltage source. extra Order 3874/45 Circulation 442 Prod, -polygr. pr-tie, Uzhgorod, st. Project, 4 Subscription