SU1497462A1 - Logarithmic photometer - Google Patents

Abstract

The invention relates to an analytical technique, in particular, to photometric analyzers of the composition of liquid and gaseous media, can be used for measurements in many areas of the industry, chemical, oil refining, in medicine, etc. The purpose of the invention is to expand the field of application and improve the accuracy of measurements. The photometer contains a dual-beam optical unit 1 with outputs of a comparative and measuring channels, a series-connected logarithm 12, a subtractive amplifier 14 feedback-fed through a differential amplifier 18, and three devices 15–17 for sampling and storage, to the outputs of which are a separating device 19, output which is connected to the recorder 20, the synchronization device 13, the corresponding outputs of which are connected to the control input of the sampling and storage devices. The photometer also contains a resistive divider 8 and three keys 9-11. The measurement cycle consists of 3 cycles. In the first cycle, a signal proportional to the logarithm of the voltage of the photodetector of the comparative channel is entered into the sample and storage device 15. In the second cycle, a signal proportional to the logarithm of the signal ratio from the voltage divider 8 and the non-divided voltage of the photoreceiver of the comparative channel is entered into the sample and storage device 16. In the third cycle, a signal proportional to the ratio of the voltages of the photodetectors of the measuring and comparative channels is entered into the device 17 for sampling and storage. As a result, the signal at the output of the dividing device 19 is proportional to the logarithm of the ratio of the voltages of the measuring and comparative photodetectors and does not depend on the temperature coefficient of the logarithm. 1 il.

Description

The invention relates to analytical technique, in particular to photometric analyzers of the composition of liquid and gaseous media, and can be used for measurements in many industries: chemical, oil refining, medicine, etc.

The purpose of the invention is the expansion of the field of application and increase the accuracy of measurements.

The drawing shows a diagram of a logarithmic photometer.

The photometer consists of a two-beam optical unit 1, containing a radiation source 2, an optical system 3, cuvettes 4 and 5, and photodetectors 6 and 7 of the comparative and measuring channels, respectively, a resistive divider 8, first 9, second 10, third 11 keys, logarithm 12, a synchronization device 13, a subtracting amplifier 14, a first 15, a second 16, a third 17 sampling and storage devices, a differential amplifier 18, a dividing device 19, a recorder 20.

In the course of the radiation of the radiation source 2 of the optical unit 1, the optical system 3, cuvettes 4 and 5, and photodetector devices 6 and 7 of the comparative and measuring channels are arranged in series. The output of the comparative channel is connected to the resistive divider 8. Between the input of the logarithm 12 and the output of the reference channel, the output of the resistive divider 8 and the output of the measuring channel, the first 9, second 10, and third 11 keys are included. To the output of the logarithm 12, a subtracting amplifier 14, a second 16 and a third 17 sampling and storage devices, a dividing device 19, a recorder 20 are connected in series. The subtracting amplifier 14 is feedback-coupled through the differential amplifier 18 and the first sampling and storage device 15. The corresponding outputs of the synchronization device 13 are connected to the control inputs of the first 9, second 10, third 11 keys and the first 15, second 16, third 17 sampling and storage devices.

The device operates as follows.

The light of the radiation source 2 is formed by the optical system 3, passes through the cells 4 and 5 and enters the photodetector devices 6 and 7 of the comparative and measuring channels, respectively.

The signals at the outputs of these channels are U _cp and U c _ЗМ , and at the output of the resistive divider ^U ep is “gG where η is the division coefficient of the divider.

At the first moment of time, according to the signal of the synchronization device, the first key 9 is opened and the first key 9 and the sampling and storage device goes into the sampling mode.

The second and third keys are closed, and the second and third sampling and storage devices 20 operate in storage mode. The subtracting amplifier 14 is covered by feedback through the first sampling and storage device 15 and the differential amplifier 18, which seeks to set the voltage difference between its inputs to zero. The voltage at the output of the subtracting amplifier is equal to _{& L1CH} = K (Α (Τ) · Ίηυ _sr - and _A ), where A (T) is the temperature coefficient of the logarithm;

K is the gain of the subtracting amplifier;

U ₁ is the voltage at the output of the first sampling and storage device.

K (A (T) lnUcp - U- |) = 0 '/ whence ₄₀ U ₁ = A (T) IntJ _cf.

Then, the synchronization device 12 opens the second key and closes the first, at the same time putting the first sampling and storage device into storage mode, and the second into sampling mode.

The voltage U ₇ ad = K (A (T) ln (U cp / n) - A (T) lnU _cp ) ad = ka (t) 1n --- is remembered by the second device for sampling and storage.

η

At the next instant of time, the third key is opened and the third sampling and storage device goes into the sampling mode, the second key is closed and the second sampling and storage device goes into the storage mode5. Voltage remembered by the third sampling and storage device:

U ₃ = K (A (T) InU _IEM - A (T) lnU _cp )

Sham

U ₃ = KA (T) 1n ------.

^wed 10

The durable device divides the signal U ₃ by the signal U ₂ , the result of which

recorded by the registrar 20, the measurement result does not depend on the temperature coefficient of the logarithmic- ^{z z} and changes in the transfer coefficient of the subtracting amplifier.

During cyclic operation of the device at the recorder input, there is 25 steady-state value of the measurement result, based on which the concentration of the substance in the measuring cell is determined.

Claims (1)

Claims gg A logarithmic photometer comprising a light source, optically coupled to the measuring and comparative _(Tel'nykh channels, each of which is formed by the cuvette, and a photodetector sequentially included logarifmator, the subtracting amplifier swept through feedback differential amplifier and a first sample and hold device and the second and a third sampling and storage device, the outputs of which are connected to a dividing device, the output of which is connected to the recorder, a synchronization device, the corresponding outputs which is connected to the control inputs of the first, second and third sampling and storage devices, characterized in that, in order to expand the scope and improve measurement accuracy, a resistive divider, first, second and third keys are additionally introduced into it, and the output of the photodetector of the comparative channel is connected with the input of the resistive divider, the first, second and third keys are connected between the input of the logarithm and the outputs of the photodetector of the comparative channel of the resistive divider and the photodetector of the measuring channel ootvetstvenno and K of the control inputs of respective outputs connected device synchronization.