JPS6318258A - Polarization curve measuring apparatus - Google Patents

Abstract

PURPOSE:To enable accurate measurement of a polarization curve, by providing a voltage follower circuit to keep an energizing current constant even when a resistance for measuring current is changed during the measuring operation. CONSTITUTION:A D/A converter 9 outputs a potential Va corresponding to a set signal (a) from a control section and an amplifier 6 outputs a potential Vb corresponding to a deviation between the potential Va and an output Ve of an amplifier 7. Then, amplifiers 6 and 10 are arranged in a two-stage construction with an view to the control of a current I for polarization to energize a counter electrode 4 and the counter electrode 4 is energized through a resistance R1 or R2 from an amplifier 10 while a potential Vc of the counter electrode 4 is fed back to an input of one side of the amplifier 10 to form a voltage follower circuit 11. With such an arrangement, the current I can be kept constant without being affected by a electrostatic capacitance between a reference electrode 3 and a test piece 2 free from switching between the resistances R1 and R2 to eliminate changes in the polarization state. This enables the implementing of accurate measurement in a wide range by changing a current measuring range as desired during the measurement of a polarization curve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a polarization curve measuring device for nondestructively evaluating corrosion resistance, etc. of metal materials.

(Prior art) In order to non-destructively evaluate the corrosion resistance of metal materials, the metal material to be evaluated is cut out as a test piece, a potential is applied to it in a solution such as 3% saline, and the potential and current are Methods of measuring the relationship or polarization curve are widely used.

In this method, as shown in FIG. 2, the above-mentioned test piece 2, reference electrode 3, and counter electrode 4 are placed in an electrolytic solution in an electrolytic bath 1, and a polarization curve measurement device 5 is used to conduct a test from the counter electrode 4. A current (2) is passed through the piece 1 and the potential Vd generated at the reference electrode 3 is measured. Then, this potential Vd is varied within a predetermined range, a polarization curve is obtained in relation to the current flowing at that time, and the test piece 2 is evaluated based on this.

Therefore, the polarization curve measuring operation 5 operates as follows.

That is, the potential Va is input to the amplifier c (AMP) 6 as a setting signal by a circuit (not shown) inside this device. The selected one of the range selector switches Gl and G2 is on, and the amplifier 6 outputs a current proportional to the difference between the potentials Va and Ve, and this current I flows to the counter electrode 4, h. The amplifier (AMP) 7 amplifies the potential Vd of the reference layer 3 generated as described above and outputs the potential Ve. This potential Ve is
It is fed back to amplifier 6.

Here, it is assumed that the gain of the amplifier 6 is sufficiently large and that the gain of the amplifier 7 is K. Now, assuming that the potential Va>Ve, the amplifier 6 amplifies this deviation and increases the current {circle around (2)}. Since this electric current flows from the counter electrode 4 to the test piece 2, the potential Vd of the reference electrode 3 also rises. Also,
When the potential reaches '/a (Ve), contrary to the above, the current flow decreases, lowering the potential Vd.

However, since the amplifier 7 amplifies the Vd and feeds back the output as the potential Ve to the input of the amplifier 6, the above operation adjusts the current V so that the potential Va=Ve. At this time, the potential Ve
depends on the potential νd of the reference electrode 3 and the gain of the amplifier 6, Ve=K・νd (1
), and from the above Va = Ve, Va= -Vd - (2), that is, Vd = - Va (3)
becomes. Therefore, since the potential Vd can be arbitrarily set by changing the potential Va using the setting signal, by measuring the current I at each potential, the relationship between the potential Vd and the current (2), that is, the polarization curve can be obtained. In addition, the electric current at this time is resistor R1
, R2, a constant current corresponding to the potential Vd flows.

Therefore, in order to measure this current 1, resistor R1 or R
The voltage Vf generated across the terminal 2 is detected by a differential amplifier, and the current is calculated from the detected voltage and the resistance value. At this time, the range selector switch selects the resistor R1 or R2 depending on the magnitude of the current so that a voltage within a predetermined range is applied to the differential amplifier 8.

Now, when the range selector switch G1 is closed and a current is applied to the resistor R1, and the above measurement is performed, if the output voltage of the amplifier 6 is vb and the potential of the counter electrode 4 is Vc, then the input voltage is input to the differential amplifier 8. The applied voltage Vf is.

vf=vc-vd=I-R1 (4). When this voltage Vf approaches the allowable input voltage of the differential amplifier 8, the range selector switch G1 is opened and the range changeover switch 62 is closed, and the resistor R2 is switched to, for example, R2=R1/10.

At that moment, the load resistance of the amplifier 6 decreases, and the current flowing through the resistor R2 tends to increase.

Therefore, the potential Vc of the counter electrode 4 tends to rise, and the potential Vd of the reference electrode 3 also tends to rise. However, since the amplifier 7 amplifies the potential Vd and feeds it back to the input of the amplifier 6 as the potential Ve, the amplifier 6 operates to reduce the current ■, and as a result, the current ■ and the potential Vc become The state before switching the above resistance is maintained. As a result, the voltage Vf input to the differential amplifier 8 is reduced to 1/10, and the current T can be measured in a tenfold range.

(Problems to be Solved by the Invention) However, normally, a large electrostatic capacitance C of several hundred μF to several F is generated between the reference electrode 3 and the test piece 2 arranged in the electrolytic cell 1. . For this reason, when switching to the resistor R2 as described above, the potential Vd does not rise immediately in response to the increase in current flow.

The potential follows the increase in current after a certain time delay.

Therefore, the feedback of the increase in the potential Vd as described above is delayed, and an excessive current flows through the resistor R2 for a certain period of time.

If such an excessive amount of current flows during polarization curve measurement, the polarization state within the electrolytic cell 1 will change, resulting in a problem that accurate measurement results cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a polarization curve measuring device that can change the current measurement range during measurement and perform accurate measurements over a wide range.

[Configuration of the Invention (Means for Solving Problems) Therefore, the present invention includes a deviation amplifier that calculates the deviation between a set potential for a reference electrode and its detected potential, and a deviation amplifier that calculates the deviation between a set potential for a reference electrode and its detected potential, and a current to be applied to a counter electrode based on the deviation. the output signal of the deviation amplifier is input to the + side input terminal of the current control amplifier, and the output signal of the deviation amplifier is connected to the opposite electrode via a current detection resistor from the output of the current control amplifier. While energizing, the potential of the opposite electrode is fed back to one input terminal of the current control amplifier to form a voltage follower circuit.

(Function) With the voltage follower circuit, even if the current measurement resistor is switched during the measurement operation, the current applied is kept constant, making it possible to accurately measure the one-polarization curve.

(Example) Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 1 is a circuit diagram of a polarization curve measuring device according to an embodiment of the present invention. In FIG. 5, the same reference numerals as in FIG. 2 indicate the same parts. The electrolytic cell 1 contains an electrolytic solution such as, for example, 3% saline.

It contains a test piece 2 taken out from the material whose corrosion resistance etc. are to be evaluated, a reference electrode 3 that serves as a standard for measuring the electrode potential of the test piece 2, and a reference electrode 3 for polarizing the electrode potential of the test piece 2 to a predetermined value. A counter electrode 4 through which a current flows is arranged.

The polarization curve measuring device 5 is a device that measures the potential difference between the reference type [i3 and the test piece 2 and the current flowing to the counter electrode 4, and plots them on a graph to obtain a polarization curve.

A digital-to-analog converter (D/A) 9 receives a setting signal a from a control section (not shown) inside the polarization curve measuring device rH5 and outputs a corresponding potential Va.

The amplifier (AMP) 6 is an operational amplifier, and the potential Va
It outputs a potential vb according to the deviation between the potential Vb and the potential Ve.

Resistors R1 and R2 are used to measure the current value by the voltage drop that occurs when the current flows through the counter electrode 4.
One of the resistors is selected by the range selector switches Gl and G2. Amplifier (AMP) 10 is an operational amplifier capable of outputting a large current, and outputs the above-mentioned current I.

Further, the potential Vc on the opposite electrode 4 side of the resistors R1 and R2 is
It is fed back to the input terminal of 0.

A voltage follower circuit 11 is configured. amplifier(
AMP) 7 is an amplifier with a constant gain K, which amplifies the potential Vd of the reference electrode 3 and outputs the potential Ve.

The differential amplifier 8 is an amplifier with a constant gain, and is used to input and amplify the voltage Vf generated by the voltage drop across the resistor R1 or R2. Sample hold circuit (S
/H) 12 holds the amplified voltage Vf, and the analog-to-digital conversion circuit 13 converts the held voltage into a digital signal and outputs a detection signal.

The polarization curve measuring device 5 of this embodiment has the above configuration and operates as follows. In other words, one side of the range selector switch 1
For example, when G1 is turned on, a setting signal a is sent from a control section (not shown).
When input, the digital-to-analog converter 9 outputs a potential Va corresponding to the setting signal a.

Now, assuming that the potential Va>Ve, the potential vb of the output of the amplifier 6 increases. As a result, the potential of the + side input of the amplifier 10 increases, and the current I, which is its output current, also increases. This electric current flows from the counter electrode 4 to the test piece 2,
With this increase in current flow, the first position Vc of the counter electrode 4 and the potential Vd of the reference electrode 3 rise. Also.

If the potential Va<Ve, then, contrary to the above, the current ■
decreases, and both potentials Vc and Vd begin to decrease.

However, since the potential Vd is amplified by the amplifier 7 and fed back to one side input of the amplifier 6 as the potential Ve, the potential Va and the potential Ve are
The electric current is adjusted so that a=Ve. At this time, the potential of the reference electrode 3 is set to Vd, and the amplifier 7
Let K be the gain of , and Ve be the potential of its output.

Ve = K-Vd -- (5) ie.

Vd=-Ve...
・(6)K becomes. Also, from the above, Va = Ve.

Vd=-・Va (7
). That is, by inputting a predetermined potential Va using the setting signal a, the potential Vd of the reference electrode 3 can be arbitrarily set.

At various potentials Vd set in this way, the resistance R1
The voltage Vf generated by the differential amplifier 8 is detected and amplified by the differential amplifier 8. The amplified voltage is sent to the sample and hold circuit 1.
A control section (not shown) detects the value of the voltage Vf based on this measurement signal, converts it into a digital signal in the analog-to-digital conversion circuit 13, and outputs the measurement signal. Calculate the value of current (■) from the magnitude of R1 and create a graph of the polarization curve.

Incidentally, in the above, the voltage follower circuit 11 operates as follows. That is, since the potential Vc of the counter electrode 4 is fed back to one side input of the amplifier 10,
The amplifier 10 has the potential Vc and the potential vb such that Vc =
While maintaining the condition of Vb, by changing the output potential vg, -ff1l*Vd becomes l/d=Va/
Adjust the electric current so that the

Now, in the measurement operation of one polarization curve, when the value of voltage Vf approaches the allowable input voltage of differential amplifier 8, range selector switch G1 is opened and G2 is closed, so that, for example, R2=R
Switch to a resistor R2 of 1/10.

At this time, since the resistance serving as the load of the amplification rilO becomes smaller, the current {circle around (2)} tends to increase. However, when the current ■ increases, the potential Vc rises, and the amplifier 10 lowers its output potential Vg so that the potential Vb = V
This results in a behavior that preserves c.

Current I is held constant. Therefore, when switching the resistors R1 and R2 as in the past, due to the capacitance generated between the reference electrode 3 and the test piece 2, the feedback operation to keep the current constant is delayed, causing an overcurrent. will no longer flow for a certain period of time.

In this way, in this embodiment, in order to control the current flow for polarization that supplies current to the counter electrode 4, a two-stage configuration of amplifiers 6 and 10 is provided, and the current flow is detected from the output of the amplifier 1o. While energizing the opposite electrode through the resistor R1 or R2,
A voltage follower circuit 11 is formed by feeding back the potential Vc of the counter electrode 4 to one side input of the amplifier 1o.

Thereby, even if the resistors R1 and R2 are switched, the current flow can be kept constant without being affected by the capacitance between the reference electrode 3 and the test piece 2, and the polarization state will not change.

Therefore, during the measurement of one polarization curve, the current measurement range can be changed arbitrarily, and the above-mentioned measurement can be performed accurately over a wide range.

In this embodiment, the range switching is a two-stage switch and is arbitrarily selected, but a multi-stage configuration may be used so that the control section automatically switches the range according to the magnitude of the measured current.

[Effects of the Invention] As described above, according to the present invention, a two-stage amplifier is provided to control the current flowing to the opposite electrode, and the output of the second stage is connected to the opposite electrode via a current detection resistor. While energizing, the potential of the counter electrode is fed back to one side input of the second stage amplifier to form a voltage follower circuit, so even if the resistance value is changed, the current can be held constant.
By arbitrarily switching the current measurement range over a wide range during polarization curve measurement, highly accurate measurements can be performed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a polarization curve measuring device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional polarization curve measuring device. 1... Electrolytic cell, 2... Test piece, 3... Reference electrode,
4... Counter electrode, 5... Polarization curve measuring device, 6, 7, 1
0...Amplifier, 8...Differential amplifier, 9...Digital-to-analog conversion circuit, 11...Voltage follower circuit. 12... Sample hold circuit, 19... Analog-to-digital conversion circuit, R1, R2... Resistor, Gl, G2
...Range selection switch. ■−; −−1

Claims (1)

[Claims] A test piece for evaluating corrosion resistance, a reference electrode for potential detection, and a counter electrode for energizing the test piece are arranged in an electrolytic solution, and a first amplifier for controlling the current to be applied to the counter electrode; It includes a resistor for passing a current and detecting the amount of current based on the voltage drop thereof, and a second amplifier that detects the potential of the reference electrode and feeds back a signal corresponding to the potential to the first amplifier. In the polarization curve measuring device,
A third amplifier for controlling the energizing current, a plurality of the resistors, and a switching circuit for switching the resistors are provided;
inputting the output signal of the first amplifier to one input terminal of the amplifier, and supplying current to the counter electrode from the output of the third amplifier via the switching circuit and the resistor;
feedback the potential of the counter electrode to the other input terminal of the third amplifier to form a voltage follower circuit;
A polarization curve measuring device characterized in that when switching the resistor, no change occurs in the conduction current.