SU1377605A1 - Spectrophotometer - Google Patents

Abstract

The invention relates to the field of optical spectral instrumentation. The aim of the invention is to increase accuracy and reliability. The light from the source 1 passes through the cuvette 2 and enters the photoelectric converter 3. The electric signal is amplified and converted to frequency using converter 5, Generator 9 through keys 6 and 7 connected to summing and subtracting inputs of the reversible counter 10, converter 5 through key 8 - to the counter 12 pulses, the information output of which is connected to the first input of the switch 16 reference modes. The output of the switch 16 is connected to the block 13 of the digital readout. After accumulating in the counter 12 the number of pulses 10 from the output of direct transfer of this counter, a signal arrives at the first input of control unit 14, and the outputs of this block receive signals at the control inputs of keys 6, 7 and 8, switch 16 and register 11. Register input 11 is connected to the information output of the counter 10, and the output is connected to the input of the parallel recording of the counter 10.} The 5 output of the counter-transfer conversions 10 is connected to the second input of the block 14. In the spectrophotometer there is a logarithmic converter 15, the control input of which is connected to the sixth vyhodz - block 14. Entrance logarithmic converter 15 connected to the output and the output key 8j - a second input of switch 16. The spectrophotometer is not required to use arithmetic-logic circuits, and the mechanical movable joints, leading to povshekiyu accuracy and reliability. 1 hp f-ly, 1 ill. (ABOUT -4 ssrf

Description

This invention relates to optical spectral instrumentation.

The purpose of the invention is to increase accuracy and reliability.

The drawing shows a block diagram of a spectrophotometer.

The spectrophotometer contains a source of light 1, which is a source of monochromatic light, the wavelength of which can be selected in a certain spectral range, cell 2, photoelectric converter 3, amplifier 4, voltage-frequency converter 5, and electronic-controlled keys (first 6 , second 7 and third 8), 9 clock pulse generator, reversible pulse counter 10, register 11, second pulse counter 12, digital readout block 13, control block 14, digital logarithm converter 15 and switch 16 p presses reference.

The device works as follows.

Before measuring the amount of light absorbed by the sample — its transmittance T—, the sample under study is absent and the spectrophotometer is calibrated, which consists in fixing the reference flux 1 of the light emitted (through the cuvette 2 without a sample or through the cuvette 2 with a reference, reference) , by sample).

The calibration of the spectrophotometer is carried out as follows.

The light from the light source 1 through the cell 2 (without a sample or with a control sample) enters the photoelectric transducer 3. The output of the latter is an electrical signal that, after amplification by amplifier 4 using transducer 5, voltage-frequency conversion - to a frequency f proportional to the intensity of the transmitted light emitting flux lo. In the calibration mode, after the TO command to the control unit 14 is sent, the first and third keys 6 and 8 are simultaneously controlled by the signals received from the first and second outputs of the control unit 4. A simultaneous accumulation of the pulse count begins. The counter 12 accumulates pulses arriving at a frequency fg from the transducer 5 via the third key 8, and the reversible counter 10 accumulates the pulses.

0

j

five

five

0 5 0 5

arriving, with frequency f from the generator 9 clock pulses through the first key 6 to the summing counting input of the reversing counter 10. After the accumulator I2 accumulates numbers

J /

pulses 10, where k is a preselected integer, from the output of direct transfer of counter 12, a signal arrives at the first input of control unit 14. On the first and second outputs of the control unit 14, the turn-off signals of the first and third keys 6 and 8 appear. The pulses entering the counting inputs of counters 10 and 12 stop and the control pulse from the fourth output of the control unit 14 to the control input of the register 11 begins As a result, the contents of the information output of the counter 10 are recorded by means of the register 11 through the input of the parallel recording in the reversing counter 10. Thus, the calibration of the spectrophotometer is completed, as a result of which; Yemeni

t - through the entrance parallel to o

The records in the counter 10 are recorded and stored — the accumulated number of pulses equal to. Thus, using the clock pulse generator 9 and the counter 10, the memory of the time interval t necessary for counting ten pulses (following with the frequency from the output of the converter 5), the number of which is a measure of the calibration of the reference intensity level of the transmitted light emitting light 1, is completed. The spectrophotometer is calibrated and prepared for measuring the transmittance

T of the test sample, where

about . I is the intensity of the radiation flux

light passing through the object (sample).

After calibrating the spectrophotometer in its cell compartment, a cuvette with a measured sample is placed and command 14 is sent to control unit 14. From the first and third outputs of control unit 14, control signals are received, including second and third keys 7 and 8, the output of converter 5 through the third key 8 is connected to the counting input of the counter 12, and the clock generator 9 via the second key 7 is connected to the subtracting counting input of the reversible counter 10.

The pulses from the output of the converter 5, the frequency f of which is now proportional to the value of T, are accumulated by the counter 12. At the same time, the clock pulses from the generator 9 clock pulses with the frequency f are fed to the subtractive counting input of the reversing counter 10. At a time interval t after a reverse counter is subtracted by N pulses, a control signal appears at its reverse transfer output, post-output to the second input of control unit 14. The latter, through the first and third control inputs, turns off the second and third keys 7 and 8, thereby stopping the flow of pulses to the counting inputs of counters 10 and 12. The content Ny of the counter 12 from its information output goes through the switch 16 to the digital reference unit 13. At the last, a figure appears that represents the absorbance value of the sample.

T

N.

ten

By selecting the value of 1/10 by selecting the conversion factor of the counter 12 ,. The required accuracy and resolution (number of significant bits) of a digital reading of the measured light absorption value can be easily established. Thus, the spectrophotometer, by automatically selecting the measurement time t, depending on the predetermined accuracy (selection of the coefficient k), ensures high accuracy of calibration and measurement at various levels of the intensity of the reference radiation Ijj. The basis of degree 10 for the exponent — the coefficient k — was chosen to simplify the display by the digital reading unit 13 both absolute and percentage values of T, which in this case is achieved by the corresponding simple arrangement of decimal

numbers - the measurement result. Thus, for example, with N 10 and N, (5000, the absolute value of T is equal to 0.500; the percentage, respectively, 50.0%. Consequently, the practical implementation of block 13 of the digital readout is simplified, since it does not require the use of arithmetic-logic or other schemes that implement

5 f5 20 25

30 5 do s

0

five

a function to determine the ratios of two consecutively incoming numbers. To achieve the possibility of direct reading on the digital readout block of the optical density (extinction) value of sample D

lg control unit 14 is given a command D, after which the control signal from the sixth output of control unit 14 is fed to the charging input of the digital logarithmic converter 15. The converter 15 connected to the output of the third key 8 converts the number N of pulses proportional to the value of T (input 1X from the output of the converter 5), implement the function lg- ()

lg p D. After this conversion

the digital value of optical density through the switch 16 reference modes is supplied to the block 13 of the digital reference. The converter 15 contains a binary counter — an address counter and a persistent storage device, the address input of the latter being connected to the information output of an address counter. In order to measure the optical absorption values of the sample, the pulses from the output of the third key 8 during the measurement time t are accumulated by the counter in the form of a number N. The contents of this counter are used to address a permanent storage device, in which for each address that is determined number N, the corresponding value of D is written according to the relation

 1 -Ig,.

Thus, connecting the information output of the digital logarithmic converter 15 through the switch 16 of the reference modes to the digital reading unit 13 can accurately and reliably display the measured amount of light absorption - the optical density D of the sample under study.

The absence of inertia in the spectrometer, which has a very limited accuracy of mechanical moving joints (due to unavoidable backlashes and friction in them), leads to an increase in the calibration accuracy — fixing the reference level of the optical transmission of the optical measurement channel and, consequently, on the whole, to a sharp the accuracy of the spectrophotometer measurement of light absorption values.

Claims (2)

1. A spectrophotometer containing: an optically coupled light source to a sample cuvette and a photoelectric converter, as well as a voltage-frequency converter, through an amplifier connected to a photoelectric converter, a control unit and a digital readout unit, differing from The goal is to improve accuracy and reliability / it additionally contains a clock pulse generator, the first second and third keys, each of which is equipped with a control input, information input and output, a reversible counter, a counter and pulses, register to the switch of reference modes, with the output of the voltage converter — the frequency is connected to the information input of the third key, the output of which is connected to the counting input of the pulse counter, the information output of the pulse counter is connected to the first input of the counting switch, five the output of the counting mode switch is connected to the digital digital clock unit, the output of the clock pulse generator is connected to the information inputs of the first and second keys, the output of the first key is connected to the summing input of a reversible counter, the output of the second key is connected to the subtracting input of a reversible counter connected to the input of the parallel recording of information of this counter, the output of the direct transfer of the pulse counter is connected to the first input of the control unit, the output of the reverse first transfer nose-down counter coupled to the second input of the control unit, the first, second, third, fourth and fifth 0 n th outputs of the control unit are respectively connected with the control inputs of the third key, the first key, second key register and the reference switch modes. 2. The spectrophotometer according to claim 1, which means that it is additionally equipped with a logarithmic converter, the input of which is connected to the output of the third key, the output to the second input of the counting mode switch, and the control input with the sixth output of the control unit. five 0