RU2331356C1 - Device for measuring critical frequency of light flashings - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to medical equipment, in particular to devices for measuring critical frequency of light flashings. Claimed device contains generator of linearly changing voltage, mode switch, converter voltage-frequency, RS-trigger, quartz generator, D-trigger, rectifier, counter, scale-of-two circuit, inverse value-computing circuit, source of light impulses, first, second and third univibrators, indication unit, first gate of setting generator in growing voltage generation mode, second gate setting generator in decreasing voltage generation mode, third gate of increasing generator frequency by 0.1 Hz and toggle switch.

EFFECT: reduced of error of measurement of light flashing critical frequency.

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Description

The invention relates to medical equipment, namely to devices for measuring the critical frequency of light flicker.

A device for measuring the critical frequency of light flicker containing the keys "Increase frequency" and "Decrease frequency", toggle switch "KCHSM", display unit, one-shot, valve, counter and series-connected mode switch, a linear voltage generator, voltage-frequency converter, a source of light pulses, and the key outputs are connected to the inputs of the mode switch, the normally-open output of the toggle switch is connected to the input of a single-shot, and normally-closed is connected to the input of zeroing the counter, stroke monostable coupled to a second input gate having a first input coupled to an output voltage-frequency converter, the output - to the counting input of the counter, the counter output is connected to the input of the indication unit (RF Patent №2141253).

The disadvantage of this device is the low accuracy of measuring the critical frequency of light flickering, since it is determined at a continuously changing frequency, and the human eye is more sensitive to the perception of a discretely changing frequency [1].

The closest in technical essence to the present invention is a device for measuring the critical frequency of light flickering, containing a linearly varying voltage generator, a voltage-frequency converter, a light pulse source, a first key to set the generator in the mode of generating rising voltage, a second key to set the generator in the mode of generating incident voltage, the third key to increase the frequency of the generator by 0.1 Hz, mode switch, toggle switch, the first and second one-shot, valve, a readout and an indication unit, the mode switch, a ramp generator, a voltage-frequency converter and a light pulse source connected in series, and the outputs of the first and second keys connected to the inputs of the mode switch, the normally-open output of the toggle switch - with the input of the first one-shot, normal closed - with the counter zeroing input, the output of the first one-shot is connected to the second valve input, the first input of which is connected to the voltage-frequency converter output, the output - with counter input of the counter, the output of the counter is connected to the input of the display unit, the output of the third key is connected to the input of the second one-shot, the output of which is connected to the third input of the mode switch (RF patent №2219821).

The disadvantage of this device is the large error in measuring the critical frequency of light flicker. In the best case, if a crystal oscillator is used instead of the first single vibrator to generate a 1-second pulse, the limit of the permissible absolute error of frequency measurement is Δ _{pre. portions} is equal to [2]:

where δ _kv is the total error of the crystal oscillator (average relative frequency instability of the crystal oscillator); f _ISM - the value of the measured frequency for the time Δt _to ; Δt _to - calibrated time interval.

The average relative frequency instability of the crystal oscillator δ _square according to the technical documentation is ± 1 · 10 ^-6 . The range of presented frequencies of light flicker in the devices for measuring the CSFM is adopted from 20 to 60 Hz. The calibrated time interval Δt in known devices, during which the counting of pulses occurs, is 1 s. Then the limit of permissible absolute error in the measurement of CFCM:

The limit of permissible relative error δ _{before. the} frequency, expressed as a percentage of the measured value, when measuring the frequency is [2]:

where δ _kv is the total error of the crystal oscillator (average relative frequency instability of the crystal oscillator); n is the number of pulses counted during the calibrated time interval.

The number of pulses n, counted during a calibrated time interval of 1 s at the generated initial frequency of 20 Hz, is 20, then the limit of the allowable relative error in the measurement of CFCM:

The inventive device allows to reduce the measurement error of the critical frequency of light flicker.

In the present invention, in a device for measuring the critical frequency of light flickering, containing a linearly varying voltage generator, a mode switch, a voltage-frequency converter, a first and second one-shot, a valve, a counter, a light pulse source, an indication unit, a first key for setting the generator to a rising mode voltage, the second key to set the generator to the incident voltage generation mode, the third key to increase the frequency of the generator by 0.1 Hz and the toggle switch, and the mode switch a mov, a ramp generator, a voltage-frequency converter and a light pulse source are connected in series, the outputs of the first and second keys are connected to the inputs of the mode switch, the normally-open output of the toggle switch is connected to the input of the second one-shot, and normally-closed is connected to the input of resetting the counter, output the third key is connected to the input of the first one-shot, the output of which is connected to the third input of the mode switch, the valve output is connected to the counting input of the counter, R S-flip-flop, D-flip-flop, divider by two, third one-shot, crystal oscillator and reciprocal calculator, with the S-input of the RS-trigger connected to the output of the second one-shot, the output - with the input of the resolution of the divider count by two and with D-input D -trigger, C-input of which is connected to the output of the voltage-frequency converter, output - to the first input of the valve, the second input of which is connected to the output of the crystal oscillator, the counting input of the divider into two is connected to the output of the voltage-frequency converter, the output - to the input of the third one-shot you the course of which is connected to the R-inputs of the RS-flip-flop and the D-flip-flop and to the first input of the reciprocal calculator, the second input of which is connected to the counter output, the output to the input of the display unit.

The inventive device due to the introduction of RS-flip-flop, D-flip-flop, a divider into two, a third one-shot, a crystal oscillator and a reciprocal calculator can reduce the measurement error of the critical frequency of light flicker.

Thus, the claimed device differs from the known new property, which determines the receipt of a positive effect.

Figure 1 presents a structural diagram of the inventive device, figure 2 is a timing diagram of a change in the frequency of light flickering, figure 3 is a timing diagram of a device.

The inventive device comprises a linearly varying voltage generator 5, a mode switch 6, a voltage-frequency converter 8, an RS-trigger 10, a crystal oscillator 11, a D-trigger 12, a valve 13, a counter 14, a double divider 15, an inverse calculator 16, a source 17 light pulses, the first, second and third one-shots 7, 9 and 18, display unit 19, the first key 1 to set the generator 5 in the mode of generating rising voltage, the second key 2 to set the generator 5 in the mode of generating the incident voltage, the third key 3 to increase the frequency of the gene Rathore 5 0.1 Hz and tumbler 4.

As the generator 5 of a linearly varying voltage, a standard integrator is used on the operational amplifier with input resistors switched by a switch 6 to obtain a different rate of voltage rise at the output of the generator 5, and by changing the polarity of the input voltage, change the direction of integration (rise or fall of the output voltage).

The crystal oscillator 11 is designed to generate a frequency of 10 KHz and can be performed according to the known scheme.

The inverse calculator 11 can be performed by a.s. 1173412 [3].

Keys 1-3 are manual switches to two positions for closing and opening electrical control circuits and are made in the form of control buttons.

The device operates as follows. In the initial state, the toggle switch 4 is in the "Measurement" position, as shown in figure 1. When the power is turned on, the RS-flip-flop 10, the D-flip-flop 12, the divider by two 15 and the output register of the calculator 16 are reset (circuits not shown). The generator 5 provides a constant voltage to the converter 8, corresponding to the initial frequency F1 = 20 Hz of light flicker. The Converter 8 converts this voltage to a frequency that controls the source 17 (figure 2, the time interval 0-T1).

The test subject closes the key 1 (figure 2, the time T1) and through the switch 6 sets the generator 5 in the mode of generating a ramp voltage corresponding to the rate of change of the frequency of light flicker of the order of 20 Hz / s. Converter 8 converts this voltage into a proportionally changing frequency, which source 17 is converted into light pulses presented to the subject (figure 2, the time interval T1-T2).

On the time interval T1-T2, the test subject, holding the key 1 in the closed state, determines the moment of fusion of light flickers, in which the key 1 opens (Fig. 2, time point T2, frequency F2). In this case, the generator 5 maintains a constant voltage at the output corresponding to the frequency F2.

Then the subject closes the key 2 (figure 2, time T3) and through the switch 6 sets the generator 5 in the mode of generating a linearly incident voltage corresponding to the rate of change of the frequency of light flicker of the order of 1 Hz / s. Converter 8 converts this voltage into a proportionally changing frequency, which source 17 is converted into light pulses presented to the subject (figure 2, the time interval T3-T4).

On the time interval T3-T4, the test subject, holding the key 2 in the closed state, determines the moment of distinguishing light flicker, which opens the key 2 (figure 2, time T4, frequency F3). In this case, the generator 5 stores a constant voltage at the output corresponding to the frequency F3.

Next, the test person by sequentially closing the key 3 determines the actual value F of the critical frequency of light flicker (figure 2, the time interval T4-T5). With each closure of the key 3, the first 7 one-shot generates a pulse, the duration of which corresponds to an increase in the frequency at the output of the converter 8 by 0.1 Hz. After the time T5, the generator 5 stores a constant voltage corresponding to the frequency F at the output. The converter 8 converts this voltage to a frequency that is converted by the source 17 into light pulses presented to the test person (figa).

At the end of the measurements, the test subject switches the toggle switch 4 to the “Read” position, the second 9 single-vibrator generates a short pulse (Fig.3b), which sets the RS-trigger 10 to one (Fig.3c), which is input to the resolution enable of the divider 15 and to D- D-trigger input 12. On the front of the next pulse from the output of the converter 8 (Fig. 3a), a unit (Fig. 3d) is opened in the D-flip-flop 12, opening the valve 13. On the front of the next pulse from the output of the converter 8 (Fig. 3a), the output the divider 15 is set to a single state, on its front starts a third th single-vibrator 18, generating a short pulse (Fig.3d), which resets the RS-trigger 10 (Fig.3c) and D-trigger 12 (Fig.3d) to zero, the signal from the input of the resolution of the account of the divider 15 is removed, the valve 13 is closed .

The frequency from the output of the crystal oscillator 11 passes through an open valve 13, at the output of which a packet of pulses is formed (Fig. 3f), the number of pulses in the packet is equal to the pulse duration at the output of the D-trigger 12, that is, the period of the critical frequency of light flicker with an accuracy of 0.1 ms (figa). The burst of pulses arrives at the counting input of the counter 14, the counting result is recorded by the pulse from the output of the third one-shot 18 to the calculator 16, the calculation result equal to the critical frequency of light flickers with an accuracy of 0.1 Hz is sent to the display unit 19.

The limit of permissible absolute error when measuring time intervals Δ _{pre. BP} is [2]:

- погрешность преобразования (среднеквадратическая относительная погрешность запуска); h - отношение сигнал/помеха; Т_сч - период следования счетных импульсов.where δ _kv is the total error of the crystal oscillator (average relative frequency instability of the crystal oscillator); Δt is the measured time interval;

- conversion error (root mean square relative start error); h is the signal-to-noise ratio; T _sc - the period of the counting pulses.

The average relative frequency instability of the crystal oscillator δ _square according to the technical documentation is ± 1 · 10 ^-6 . The range of measured time intervals Δt when measuring the CSFM in the range from 20 to 60 Hz, equal to one period of the CFPSM, is from 17 to 50 ms, the period of the counting pulses T _cf at a crystal oscillator frequency of 10 KHz is 0.1 ms.

We take the signal-to-noise ratio of 40 dB, since the invisibility of interference in the visual image is ensured with a signal-to-noise ratio of about 41.5 dB [4], then h = 100, the mean square relative error of the start:

limit of permissible absolute error in estimating the recovery time:

The limit of permissible relative error in the measurement of time intervals δ _{before. BP} , expressed as a percentage of the measured time interval Δt, is [2]:

- погрешность преобразования (среднеквадратическая относительная погрешность запуска); h - отношение сигнал/помеха; m - число счетных импульсов, заполняющих измеряемый интервал времени Δt.where δ _kv is the total error of the crystal oscillator (average relative frequency instability of the crystal oscillator);

- conversion error (root mean square relative start error); h is the signal-to-noise ratio; m is the number of counting pulses filling the measured time interval Δt.

Since the range of measured time intervals Δt in the time estimation is from 17 to 50 ms, the period of counting pulses T _cf is 0.1 ms, the number of counting pulses m filling the measured time interval Δt is from 170 to 500. Then the limit of the allowable relative time estimation errors:

Thus, the proposed device can reduce the measurement error of the critical frequency of light flicker.

Information sources

1. A.S. 1346136 USSR, MKI А61В 5/16. A device for studying the critical frequency of flicker fusion / V.A. Maksimovich, V.I. Prokopets (USSR). - 4 p.

2. Handbook of electronic devices. In 2 t. T. 2. / Ed. D.P. Linde. - M .: Energy, 1978. - 328 p.

3. A.S. 1173412 USSR, MKI G06F 7/52. A device for calculating the reciprocal of 48-bit numbers / A.E. Boyarsky, Yu.V. Zakharov, Yu.I. Mitropolsky et al. (USSR). - Publ. 08/15/1985, Bull. No. 30.

4. Krasilnikov NN Generalized functional model of vision and its application in image processing and transmission systems // Avtometriya. - 1990. - No. 6. - S.7-14.

Claims (1)

A device for measuring the critical frequency of light flickering, containing a linearly varying voltage generator, a mode switch, a voltage-frequency converter, a first and second single vibrator, a valve, a counter, a light pulse source, an indication unit, a first key for setting the generator to an increasing voltage generation mode, a second key setting the generator to the incident voltage generation mode, the third key is to increase the generator frequency by 0.1 Hz and the toggle switch, and the mode switch, the generator is linearly changed voltage converter, the voltage-frequency converter and the light pulse source are connected in series, the outputs of the first generator set switch to the rising mode generation and the second generator set switch to the falling voltage generation mode are connected to the inputs of the mode switch, the normally-open output of the toggle switch is connected to the input of the second one-shot, normally closed - with the input of zeroing the counter, the output of the third key to increase the frequency of the generator by 0.1 Hz is connected to the input of the first one-shot, the output is connected to the third input of the mode switch, the output of the valve is connected to the counter input of the counter, characterized in that it additionally introduces an RS-flip-flop, D-flip-flop, a divider into two, a third one-shot, a crystal oscillator and a reciprocal calculator, and the S-input The RS-flip-flop is connected to the output of the second one-shot, the output - with the input of the resolution of the divider by two and with the D-input of the D-flip-flop, the C-input of which is connected to the output of the voltage-frequency converter, the output - with the first input of the valve, the second input of which is connected from to by a quartz oscillator, the counting input of the divider into two is connected to the output of the voltage-frequency converter, the output is connected to the input of the third one-shot, the output of which is connected to the R-inputs of the RS-trigger and D-trigger and to the first input of the reciprocal calculator, the second input of which is connected with the output of the counter, the output - with the input of the display unit.

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