SU1387980A1 - Apparatus for measuring specific electric resistance of biological liquid - Google Patents

Abstract

A device for measuring the electrical resistivity of a biological fluid contains a generator 1, a cell 2 with a pair of current 3.4 and a pair of potential 5.6 electrodes, a differential amplifier 7 and a synchronous detector 12. In order to improve accuracy, current-voltage converter 8 is introduced into it unit 9, temperature compensation, a second synchronous detector 10, an analog-digital converter 13 and a measuring unit 17. Cell 2 is made in the form of a glass tube 14, inside which are current and potential electrodes 3, 4, 5, 6 and thermistor 15; on the one hand, the tube ends with a rubber bulb 16. I Cp f-ly, 2il. with (L

Description

CO 00 CO

00

ffjuai

The invention relates to medical technology and can be used in urology, nephrology, in particular, to determine renal failure.

The purpose of the invention is to improve the measurement accuracy.

Figure 1 shows the structural electrical circuit of the device; in fig, 2 is a cell.

The device contains a voltage generator (g) 1, a cell 2 having a pair of current 3 and 4 and potential 5 and 6 electrodes, a differential amplifier (RC) 7, whose inputs are connected to the terminals of cell 2, a current-voltage converter 8 (PTN) whose input is connected to the electrode 4 of cell 2, and the output to block 9 of temperature compensation (VTK), the output of which, in turn, is connected to the inputs of the second synchronous detector (SD) 10 and the amplifier-limiter (VO

11, the first synchronous detector (SD)

12, the input of which is connected to the output of the remote control unit 7, analog-to-digital converter (ADC) 13, the inputs of which are connected to the corresponding outputs of CD10 and 12, and their control inputs are connected to the output of the EO 11, and the current output of the 3 cells is connected to the output of the generator.

The appearance of the cell is shown in Fig. 2, This is a glass tube 14, inside of which there are current and potential electrodes 3-6 and a thermistor 15 located in the VTC. On one side, the tube 14 ends with a rubber bulb 16, which is necessary for sampling the fluid. It has a measuring unit 17.

The device works as follows.

The voltage of the operating frequency from the output of the generator 1 is fed to the cell 2, which in this case has a new function: it serves to sample biological fluid (urine)

and keep it at the time of measurement, as well as for fixing in it a thermistor 15 intended for fixing the temperature of the sample. Under the action of the applied voltage in the cell, a current Iq flows, which creates a voltage drop U. between the electrodes 5 and 6:

Ux I, RX,

five

0

five

about

five

0

where Ry is the resistance of the measured

plot of the object.

Further, this voltage is removed with the help of the remote control and is fed to the input of the LED 12. If the transfer coefficient of the CTN 8 is equal to RJ ,, then the cell current 2, the pass through the PTN 8, is converted to the voltage

and IgRo.

This voltage is fed to the input of the VTK 9, the transmission coefficient of which is K. Thus, the voltage U, “loRo K,” will act at the input of the LED 10. The same voltage in UO 11 is converted into a square wave, which goes to the control inputs SD 10 and 12, and representing the keys that perform the function of a full-wave top, with a low-pass filter at its output. Straightened by means of LEDs 10 and 12, the voltage and and Uj,: go to the corresponding inputs of the ADC 13, on the code of which the code N Ujf / Uo appears, which later goes to the information output device:

  -k; g-

Urine can be represented as an electrolyte of low concentration. Obviously, its resistance R depends on temperature. In the first approximation, this relationship is linear:

R x RO (I -ott).

In order for the code N to be temperature invariant, BTC 9 is entered. Its transmission coefficient

R t + RI,

.

The easiest way to compensate is if

R t R (l + fi t),

where of and p are temperature coefficients;

R is the resistance of thermistor 15-,

then code N does not depend on temperature, provided that

S-tP-l-Rl- - R. R,

TO

Rt.

to

R,

P of Otherwise, if the temperature dependence of the thermistor 15 is nonlinear, it is necessary to calibrate in

different points of the temperature range using a resistor R.

Claims (2)

1. A device for measuring specific electrical current, biologic resistance, containing a voltage generator connected to one of the current electrodes, a cell with a pair of current and a pair of potential electrodes, a differential amplifier whose inputs are connected to potential electrodes, and the output - to the first synchronous detector, measuring unit, which is different from the fact that, in order to increase accuracy, it is equipped with serially connected transducer /four current-voltage, temperature compensation unit, second synchronous detector and analog-digital converter, as well as an amplifier-limiter, whose input is connected to the first input of the second synchronous detector, and the output - to the second inputs of the first and second synchronous detectors, the output of the first of which connected to the second input of the analog-digital converter, to the output of which the measuring unit is connected. 2. The device according to claim 1, wherein the cell is made in the form of a glass tube, inside which four electrodes and a thermistor are fixed, terminating on one side with a rubber bulb. phage. g sixteen