SU1385051A1 - Device for measuring concentration of ions in electrolytic solution - Google Patents

Abstract

The invention relates to a measurement technique, and more specifically to measuring the concentration of ions in electrolyte solutions, and can most effectively be used in analytical systems with a small volume of samples under study. The aim of the invention is to increase the measurement accuracy — achieved by compensating for errors caused by the temperature sensitivity of field-effect transistors, an auxiliary electrode, and a potential jump at the electrolyte-dielectric interface. To achieve this goal, the device additionally introduces the first, second and third adders, the third and fourth voltage sources, the first, the second and third large-scale blocks, the analog voltage divider, the first and second switches, the first, second and third keys, while A thick layer is formed over the sensitive area of the first field effect transistor, and a thin dielectric layer is formed above the sensitive area of the second field effect transistor. Measurement accuracy is also enhanced by the fact that the results are not affected by the successive resistances of the diffusion regions of the transistors, errors due to the imperfection of the special polymer membrane are eliminated, low-frequency noise is reduced, and the identity and reproducibility of characteristics are improved. 2 Il. "(L with 00 ate

Description

The invention relates to a measurement technique, is intended for the operational control of the concentration of ions in electrolyte solutions and can be used in the chemical and other sectors of the industry.

The aim of the invention is. increase of measurement accuracy due to temperature, compensation of the operating mode of the sensitive element.

Fig, 1 shows the functionality of the proposed device; in fig. 2 - technological section of the first and second field-effect transistors.

A device for measuring the concentration of ions in an electrolyte solution contains the first 1 and second 2 field-effect transistors and the auxiliary electrode 3 placed in a controlled solution of the electrolyte 4 in the tank 5, the current source 6, is adjustable. The switchable resistor 7, the first 8, the second 9j, the third 10 and the fourth 11 voltage sources, the first 12 and second 13 voltage followers, the differential amplifier 14, the first 15, the second 16 and the third 17 adders, the analog voltage divider 18, the recorder 19 , which is used as a voltmeter, first 20, second 21 and third 22 scale units, first 23 and second 24 switches, first 25, second 26 and third 27 keys.

The first 1 n second 2 field ranzors are located in the same semiconductor substrate 28 covered with a dielectric layer 29, moreover, a dielectric layer (d, 1 μm) is formed above the sensitive area 30 of the first field-effect transistor 1) field-effect transistor - dielectric layer (20 them d 200 nm). The source pins of the transistors (total area 32) are connected to the common head of the device. The output of the substrate is connected to the output of the drain 33 of the first field-effect transistor. The device operates as follows.

Before measurements, the device is configured. Field-effect transistors 1 .and 2 are removed from the solution. Switches 23 and 24 are set to position I, and keys 25, 26 and 27 are opened. Transistors 1 and 2

0

five

0

five

0

five

They work in the bipolar mode. This mode is possible if the diffusion length of minority carriers in the substrate exceeds the distance between regions 32-33 and 32-34. Since the topological sizes of transistors I and 2 are the same, their configuration is a current mirror. Transistor 1 operates in a diode connection, therefore, the voltage at point A will be linearly dependent on temperature.

 By adjusting the resistance of the resistor 7, a zero voltage is obtained at the output of the differential amplifier 14, which is controlled by a voltmeter 19. After that, the switch 23 is switched to position II, the switch 26 is closed, and the transistors 1 and 2 together with the auxiliary electrode 3 are lowered into a solution with a known concentration at a known temperature. Regulating the output voltage of the voltage source 10, a zero voltage is set at the output of the adder 16 at a given temperature, as judged by a voltmeter 19. Thereafter, the voltage at the output of the adder I6 is directly proportional to the temperature change.

After that, open the key 26, the switch 24 is switched to position II. In this case, the output of the differential amplifier 14, which has a large gain (K, more than 10), will have a voltage

14

0

five

0

five

and

14

uS

kt,

+ I / + --- Ina r -f- Е ° nq 1

back -

(ABOUT

P

- °

 YSP

q where id is the voltage at point A; - standard potential;

I K constant Boltzmann; T {, - absolute temperature; valence of the potential-determining ion; electron charge; the activity of potential-dissociation of the Haz ion; potential of auxiliary electrode relative to solution at temperature

, t „.

When a electrolyte – dielectric section is placed in the solution at the boundary, a potential jump arises, creating an electric field that can be used as a dielectric through a thin dielectric.

for example, SijN, TajOj, TiO, etc.) of the second transistor affects the near-surface region of the semiconductor, the transmission coefficient of the second transistor 2 changes. At the same time, the transmission coefficient of the first transistor 1 practically does not change, since due to the thick dielectric the electric field is significantly weakened . Thus, the current through the transistor .1 remains the same, and through the transistor 2 changes, which leads to a change in potential at point B. Due to the negative feedback loop through the differential amplifier 14 and the auxiliary electrode 3, the voltage at the output of the differential the amplifier is changed in such a way that the potentials at points A and B will be almost the same (since the differential amplifier has a large gain). Regulating the output voltage of the voltage source 9 via a voltmeter 19 sets a zero voltage at the output of the first adder 15. After that, the switch 24 is switched to the position I and the switch 27 is turned on. The output voltage, the voltage of the voltage source 1I, is set at the output of the third adder living

.zsht .. ",

Open the key 27, close the key 25. This completes the device setting.

Transistors 1 and 2 and auxiliary electrode 3 are removed from the test solution and immersed in the test solution. In this case, the output of the differential amplifier 14 occurs voltage

,,,,one-

, .- EZ „and, h - (/, 2, ZOZKTo 9 2, ZOZK (That + lT).

-. - - dpajng 1 ng

-2- ffiV; -H -... T. (3)

where pa ° -lga%

Lra pa.-pa, o (- temperature

odds

a high-voltage electrode (for an Ag / AgCl electrode d — 0.66 mV / C).

Adder 15 compensates for all the terms on the right-hand side of expression (3), with the exception of the fourth term, which carries useful information about the concentration of the test solution. In this case, the first term is compensated for by adding different signs with voltage applied to the third input of the first adder 15. The seventh item is compensated for by adding different characters with voltage to the fourth input of the adder 15 from the output of the first scale unit 20, d / f transfer coefficient, where f is the temperature coefficient of voltage at the output of the adder 15. The fifth term is compensated for by adding with different signs with voltage applied to the fifth input of the adder 15 from the third output scaling unit 22 having a coefficient peredachi.ra °, the input of which receives the voltage output from the second scaling block 21 having a transfer coefficient 2,303K / ngy. The second, third and sixth terms are compensated by the voltage applied to the second input of the adder 15 from the output of the voltage source 9.

Thus, at the output of the first adder 15 there will be a voltage

2 303К That + LT

dpa, (4)

At the output of the third adder 17, a voltage is formed:

- 2j., “T)

and "..".

 ng

(five)

Accordingly, at the output of the analog voltage divider, we will have

Ua a

ytra ..

(6)

™

.

55

where A is a given coefficient.

For example, if A is 1B, then a tenfold decrease in concentration (dpa.l) corresponds to a change in output voltage by 1 V.

Claims (1)

Invention Formula  A device for measuring the concentration of ions in an electrolyte solution containing the first and second field five transistors and auxiliary electrode placed in tanks with a controlled electrolyte solution, current source, first and second voltage sources, adjustable resistor, first and second repeaters. The differential amplifier and the recorder, while the source terminals of the transistors are interconnected, the drain terminal of the first transistor is connected to the current source and the input of the first voltage follower, the output of which is connected to the first input of the differential amplifier, the drain terminal of the second transistor is connected to to the input of the second voltage follower and through an adjustable resistor to the first voltage source, and the output of the second voltage follower is connected to the second input of the differential amplifier, which is so that, in order to improve the accuracy of measuring the temperature com- pound of the operating mode of the sensitive element, the device is additionally equipped with first, second and third adders, third and fourth voltage sources, first, second and third {1I scale block, analog divider voltage, the first and second switches, the first, second and third keys, while over the sensitive area of the first field-effect transistor forming a dielectric layer with a thickness of more than / 1 micron, and above the sensitive area v cerned FET - a dielectric layer thickness of 20 to 200 nm output substrate of the first and second transistors connected to terminal hundred The first field-effect transistor, -a / source terminals of the field-effect transistors are connected to the common bus of the device, the output of the differential amplifier is connected to the first input of the first sum of the mat and the common output of the first nepet switch, the first contact terminal of which is connected to the auxiliary electrode, and the first contact terminal of the second switch, the second contact terminal of which is connected to the first input of the analog voltage divider, and the common terminal to the output of the first Totalizer, to the second input of which A second voltage source is connected to it, the first input of the second adder is connected to the output of the first repeater 12 voltage and the third input of the first adder, the third voltage source is connected to the second input of the second adder, the output of which is connected to the inputs of the first and second scale units and through the second key with the recorder, the output of the first scale unit is connected to the fourth input of the first adder, the output of the second scale unit - to the first input of the third adder and the input of the third scale unit, the output of which th is coupled to a fifth input of the first adder, a fourth voltage source connected to the second input of the third adder, the output of which is connected to a second input of analog divider voltage and via the third switch - with the registrar, which through the first switch connected to the output of the analog voltage divider. FIG L 33 30 32 31 3