SU570789A1 - Phasometric single beam photometer - Google Patents

Description

(54) PHOTOMOMETRIC UNIFORM PHOTOMETER

one

The invention relates to phase-type single-beam photometers and can be used for automatic monitoring of gas and liquid mixtures, for example, in the chemical industry.

A phase meter photometer is known that contains a radiation source, a cuvette, a shutter unit, a radiation receiver, an amplifier, a reference signal generator, a phase detector, a secondary device.

For the implementation of phase measurements in the photometer, the amplitude of the reference signal is chosen to be less than the amplitude of the total signal at the entrance to the phase detector at least three times. The photometer has a low measurement accuracy due to the dependence of the measured signal on the amplitude of the total signal.

Also known is a phase meter analyzer of a liquid, containing a radiation source, a cell, a photodetector, a total signal amplifier, a phase detector, a reference signal generator, a reference signal amplifier, a secondary device.

In the device for the implementation of phase measurements and compliance with the required measurement accuracy, the initial value of the amplitude of the reference signal at the input to the phase detector is selected less than the total signal several times. The photometer also has a low measurement accuracy due to the effect of changes in the amplitude of the total signal on the measured signal. The prototype of the invention is a phase-meter single-beam photometer containing a radiation source, light filters, a shutter, a measuring cell, a photodetector, such as a photomultiplier tube, a photocell, a reference signal generator, and a reference signal limiter.

The luminous flux of the radiation source passes through two light filters, a shutter, a measuring cuvette, and then enters the photodetector. On the axis of the obturator, rotated by an electric motor, a rotor of the magnetic generator is installed, which creates a reference signal that is synchronous with the rotation frequency of the obturator.

One of the filters separates the part of the spectrum absorbed by the substance to be measured, the other - the comparative part of the spectrum that is not absorbed by this substance. The compared light fluxes are modeled out of phase. Both electrical signals — the total from the photodetector and the reference signal from the generator — through an amplitude limiter — are fed to a phase-sensitive detector. At the output of the circuit is connected to the recording device.

In order to maintain the necessary amplitude ratio of the reference and sum signals at the input to the phase detector, the device uses an AGC system, covering the last stage of the sum signal amplifier.

However, the known photometer has a low measurement accuracy when using a photoelectric multiplier (PMT) as a photodetector and a phase detector with an individual input.

In order to improve the measurement accuracy, a known phase meter photometer containing a radiation source, light filters, a shutter, a measuring cell, a photomultiplier tube, a reference signal generator, a reference signal limiter is proposed to be equipped with a tracking unit consisting of a circuit comparing the amplitudes of the reference and total signals at the input of the phase detector, connected to the input of a phase-sensitive amplifier, the output of which is loaded onto a reversing motor, kinematically connected with the engine of simultaneous matching laziness voltage divider power photomultiplier tube.

The drawing shows a diagram of the proposed photometer.

The luminous flux emitted by the emitter 1 is interrupted by a shutter 2. With the help of optical filters 3 and 4, two luminous fluxes of different spectral composition are distinguished. One light note is a reference, not changing when the analyte is present in the measuring cell 5. The other luminous flux (working) changes as the concentration of the analyte in the measuring cell changes.

The reference and working light fluxes are modulated with the same frequency but phase shifted by the obturator 2. The total light note consisting of the reference and working fluxes is perceived by a photomultiplier tube (PMT) 6, from where the signal goes to the first input of the phase detector 7 The reference signal is generated by a magnetic generator 8, kinematically connected with the motor 9 of the shutter 2.

The signal removed from the geyerator 8 is fed through an amplitude limiter 10 and a second exit of the phase detector 7, from where the measured signal enters the secondary device I. Parallel to the first input of the phase detector 7, a constant voltage divider is connected, which includes diode 12 and resistance 13 and 14. Parallel to the second 15KHOD of the phase detector 7, a divider voltage is connected, made of a diode 15 n of resistance 16 and 17. Resistances 14 and 17 are interconnected by a resistance 18, which is loaded by gxDD th amplifier 19. vyhbDu amplifier connected to a reversible motor 20 kinematically coupled with the engine 21, a variable resistance voltage divider power photomultiplier 6.

DC voltage dividers together with resistance 18 are included in the comparison circuit for amplitudes d of the reference and total

signals.

A change in the internal resistance of the PMT 6 (due to a change in the sensitivity of the photocathode, the intensity of the radiation source, the voltage of the power of the PMT) changes the amplitude and phase of the total signal at the input to the phase detector 7 and changes the ratio of the amplitudes of the reference and total signals, which leads to measurement error.

When the amplitudes of the reference and total signals at the input to the phase detector remain unchanged, there is no signal at the input to the phase-sensitive amplifier 19. When changing the amplitude of the total signal

(the amplitude of the reference signal remains unchanged) a signal of one or another polarity arises at the input to the phase-sensitive amplifier 19. If there is a signal, the reversing motor 9 will begin to rotate in one direction or another the variable resistance slider until the amplitude of the sum signal (internal resistance of the photomultiplier) takes its initial value. Wherein

The measurement error of the photometer is eliminated.

At the same time, the value of the amplitude ratio of the reference and total signals at the input to the phase detector 7, at which the phase-measuring method is implemented, is kept within the desired limits.

Claims (1)

Invention Formula Phase-meter single-beam photometer containing a radiation source, light filters, obturator, measuring cell, photomultiplier tube, reference signal generator, reference signal limiter, characterized in that, in order to improve the measurement accuracy, it is equipped with a tracking unit consisting of a comparison of the amplitudes of the reference and total signals at the input of the phase detector connected to the input of the phase-sensitive amplifier, the output of which is loaded on a reversing motor, kinematically connected to an alternating engine The resistance of the photomultiplier tube voltage divider.