SU1369469A1 - Luxmeter Calibration Device - Google Patents

Abstract

The invention relates to optical measurements and can be used in metrology for calibrating lux meters. The purpose of the invention is to improve the accuracy of verification. The device contains a stabilized light source, optically coupled to the input of a block of replaceable neutral light filters, an amplitude light modulator, a photo-receiver, an amplifier, and a source of reference voltages. I il.

Description

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with

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 with

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The reference relates to optical measurements and can be used in metrology for calibrating lux meters.

The purpose of the invention is to improve the accuracy of calibration of lux meters.

The drawing shows a block diagram of the device.

It contains a stabilized light source 1, a block of 2 interchangeable neutral light filters (attenuator-light flux), an amplitude modulator 3 lights (adjustable attenuator), a photodetector 4, an output 5 of the device, an amplifier 6, a source 7 of reference voltages.

The stabilized light source 1 is optically coupled with a block of 2 replaceable neutral light filters with an optical input of an amplitude modulator of 3 light, the output of which is optically coupled to photo receiver 4 and is also output 5 of the device. Photodetector A is connected to one input of amplifier 6, the second input of which is connected to source 7 of reference voltage, and output of amplifier 6 to electric input of amplitude modulator 3 of light

The device works as follows.

The luminous flux Φ emitted by the stabilized light source 1 passes through a block of 2 interchangeable neutral light filters. By changing the certified neutral light filters installed in block 2, a step change in the illumination of the photocell of a tunable light meter installed on you during the device is achieved.

From the output of block 2, the luminous flux F is fed to the optical input of the amplitude modulator 3 of the light. Luminous flux ff can be mathematically represented as the sum of two light

- F, Fvk,

,; F j, n m + n - 1, constant coefficients, the values of which, when calibrated, change stepwise when changing neutral filters in block 2.

the flux F passes through the modulator 3 of the light and the forchode 5 of the device of the light, which is further received

five

about 5

about

d

35

em on the photocell of the calibrated light meter. The value of f is equal to

F f, t (IR)

where T (s) is the transmittance of the amplitude modulator 3 of the light, depending on the voltage Up at its electrical input. The luminous flux F. passes through the amplitude modulator 3 of the light and forms the luminous flux F., which is fed to the photodetector 4 mounted on one of the inputs of the amplifier 6.

In this case, at this input of the amplifier 6, a voltage U is formed equal to

and lf, and, ,, T (Up),

where f is the photoelectric conversion coefficient of the receiver 4. The voltage U at the output of the amplifier

to "Sy,

mustache

equally

Up - K, C (UO - U)

,, T (ir), where the gain of the amplifier is 6.

Due to the negative feedback from the output of the amplitude modulator of light to its electrical input, an approximate equality is achieved

and,, t (and, h

which is more accurate, the greater the gain coefficient K is thus

T (up)

Uo

;;

f, t (ir)

.

RFW

A constant coefficient rf is introduced, which gives all the losses of light in the device, then

A - J F O / --A

Thus, the magnitude of the input luminous flux Φ is regulated both by installing different neutral filter filters in block 2, since this changes the value of Фр and hence the value of the ratio Ф, / Ф |, (taking into account that Ф Ф, Ф5,) and by changing the magnitude of the reference voltage and.

The change in Φ F is carried out only stepwise by replacing the neutral light filter in block 2. The voltage U, is changed both stepwise and smoothly.

The step change in U is accomplished by changing the neutral light filters in block 2. This is necessary

for calibration of the magnitude of the illumination value formed on the surface of the photocell of the verified luxmeter. Optoelectronic negative feedback provides high stability of the calibrated values of the light intensity generated.

Due to the possibility of smoothly adjusting the magnitude of the reference voltage Uj, smooth control of the illumination on the surface of the photocell is achieved, which is one of the necessary calibration procedures to determine the variation of readings.

The instability of Φ is determined by the expression

LF1 JUe 4F1 4L

  and; Have

Since the light flux f

.I.

 f g x

and f,

1 in are parts of the same

Since the light flux Φ, then their instability is LF UV and tJ are the same, and since they have opposite signs, they are mutually destroyed.

The stability of the values and U is sufficiently high. For example, when using silicon photocell as a photodetector

The diode PD-2AK instability is in the order of 0.001Z.

With a change in temperature, the instability of L ft of silicon photo detectors amounts to 0.2 ± 0.25% / K and can be reduced by thermal stabilization (or thermal compensation) of the photodetector.

Claims (1)

Invention Formula A device for calibrating luxmeters that contains a stabilized light source that is optically (: an attenuator of the luminous flux borrowed from the entrance, is characterized in that, in order to improve the accuracy, an adjustable light attenuator, a photodetector, an amplifier and a reference source are introduced into it voltage, while the light attenuator is optically connected to a series of adjustable attenuator and photo receiver, photo-output output. Connected to the first input of the amplifier, to the second input of which the source is connected to the reference voltage, and an output amplifier connected to the control htsemu optical input | device.