阅读说明：本技术 导电率检测器以及求相位调整值的方法 (Conductivity detector and method for determining phase adjustment value ) 是由 泽田秀人 于 2017-07-07 设计创作，主要内容包括：导电率检测器包括槽、一对电极、电压施加部、放大电路、相位调整值保持部以及信号处理电路。放大电路是以具有多个增益,且使用任一增益将在所述一对电极间流动的电流放大而获得放大信号的方式构成。相位调整值保持部是以保持对各增益预先求出的相位调整值的方式构成,所述相位调整值用于消除使用放大电路的各增益所得的放大信号彼此的相位差。信号处理电路是以使用通过放大电路进行放大所得的放大信号以及与用于获得所述放大信号的增益有关的相位调整值,求出在槽内流动的溶液的导电率的方式构成。(The conductivity detector includes a cell, a pair of electrodes, a voltage applying unit, an amplifying circuit, a phase adjustment value holding unit, and a signal processing circuit. The amplifier circuit has a plurality of gains, and is configured to amplify a current flowing between the pair of electrodes by using any one of the gains to obtain an amplified signal. The phase adjustment value holding unit is configured to hold a phase adjustment value obtained in advance for each gain, the phase adjustment value being used to cancel a phase difference between amplified signals obtained using each gain of the amplifying circuit. The signal processing circuit is configured to determine the conductivity of the solution flowing in the cell by using an amplified signal obtained by amplification by the amplifying circuit and a phase adjustment value related to a gain for obtaining the amplified signal.)

1. A conductivity detector, comprising:

a tank for allowing a sample liquid to flow;

a pair of electrodes immersed in the solution flowing in the tank;

a voltage applying unit configured to apply a predetermined voltage between the pair of electrodes;

an amplifier circuit configured to have a plurality of gains and to amplify a current flowing between the pair of electrodes by using any one of the gains to obtain an amplified signal;

a phase adjustment value holding unit configured to hold a phase adjustment value obtained in advance for each gain, the phase adjustment value being used to cancel a phase difference between amplified signals obtained using the gains of the amplifying circuit; and

and a signal processing circuit configured to determine the conductivity of the solution flowing in the tank by using the amplified signal amplified by the amplifying circuit and the phase adjustment value held in the phase adjustment value holding unit in relation to a gain for obtaining the amplified signal.

2. The conductivity detector of claim 1, said signal processing circuit being configured in the following manner: the phase adjustment value related to the gain for obtaining the amplified signal is used to adjust the phase of the reference signal multiplied by the amplification circuit obtained by the amplification circuit in order to obtain the conductivity.

3. The conductivity detector according to claim 1 or 2, further comprising a gain adjustment unit configured to automatically adjust a gain of the amplification circuit in accordance with a magnitude of the current flowing between the pair of electrodes.

4. A method of finding a phase adjustment value for canceling a phase difference between the amplified signals obtained by gains of the amplifying circuit using a conductivity detector, the conductivity detector comprising at least: a tank for flowing sample water; a pair of electrodes immersed in the sample water flowing through the tank; a voltage applying unit that applies a voltage between the pair of electrodes; an amplification circuit configured to amplify a current flowing between the pair of electrodes by using any one of a plurality of gains to obtain an amplified signal; and a signal processing circuit for obtaining the conductivity of the sample water by using the amplified signal obtained by the amplifying circuit, and the method sequentially comprises the following steps:

conducting the pair of electrodes through a resistance having a resistance value that is negligible in electrostatic capacitance;

acquiring an amplified signal waveform of one cycle of the amplified signal based on a current flowing between the pair of electrodes for each gain of the amplifier circuit; and

and determining a phase difference between each of the amplified signals and the reference signal based on a difference between a time at which the amplified signal waveform of each of the gains reaches a maximum value or a minimum value and a time at which the amplified signal waveform of one cycle of the reference signal reaches a maximum value or a minimum value, and determining the phase difference as a phase adjustment value associated with each of the gains.

Technical Field

The present invention relates to a conductivity detector used for detecting a sample component in an ion chromatograph (ion chromatography), for example, and a method for determining a phase adjustment value for adjusting a phase in the conductivity detector.

Background

A conductivity detector (also referred to as a conductivity meter or a conductivity sensor) immerses a pair of electrodes in a sample liquid flowing in a cell (cell), applies a voltage between the electrodes, and detects a change in magnitude of a current flowing between the electrodes as a change in conductivity of the sample liquid.

The conductivity detector obtains the conductivity by using an amplified signal obtained by amplifying a current value flowing between electrodes by an amplifier circuit. When the gain (amplification factor) of the amplifier circuit is large, high sensitivity detection is possible even with a small current change, and therefore the resolution is improved, but on the other hand, the upper limit of the detectable conductivity is lowered, and the detection range is narrowed. Conversely, if the gain of the amplifier circuit is small, the detection sensitivity decreases, but the upper limit of the detectable conductivity also increases, and the detection range becomes wide.

Thus, the detection sensitivity (or resolution) and the detection range are in a trade-off relationship. Therefore, when the range of variation in the conductivity of the sample liquid is large, if the current is amplified by the amplifier circuit using only one gain to detect the conductivity, there are problems such that the conductivity of the sample liquid exceeds the upper limit of the detectable conductivity, and the detection sensitivity is insufficient.

Therefore, when the gain of the amplifier circuit is only one, it is not possible to simultaneously measure the conductivity over a wide range and detect the conductivity with high resolution. In view of such a problem, an operation of changing the gain of the amplifier circuit as necessary has been conventionally performed (for example, see patent document 1).

Disclosure of Invention

Problems to be solved by the invention

When the gain of the amplifier circuit is changed during measurement, the waveform of the conductivity may be disturbed before and after the gain switching and become discontinuous.

The invention aims to suppress waveform disturbance caused by gain switching of an amplifier circuit in a conductivity detector.

Means for solving the problems

The present inventors have obtained the following knowledge about the cause of the disturbance of the conductivity waveform before and after the gain switching of the amplifier circuit: since the delay amounts of the phases generated in the circuits of the gains constituting the amplifier circuit are different from each other, the phase of the current amplified by one gain is shifted from the phase of the current amplified by the other gain. Moreover, the present inventors have arrived at the following ideas: when the delay amount of the phase generated in the circuit of each gain constituting the amplifier circuit is examined in advance, the delay amount can be used to adjust the phases of the currents amplified using each gain so as to be the same with each other. The present invention is based on this idea.

A conductivity detector of the present invention includes a cell, a pair of electrodes, a voltage applying section, an amplifying circuit, a phase adjustment value holding section, and a signal processing circuit. A sample liquid flows through the tank. The pair of electrodes is immersed in a solution flowing in the tank, and a predetermined voltage is applied between the pair of electrodes by a voltage application unit. The amplifier circuit has a plurality of gains, and is configured to amplify a current flowing between the pair of electrodes by using any one of the gains to obtain an amplified signal. The phase adjustment value holding unit is configured to hold a phase adjustment value obtained in advance for each gain, the phase adjustment value being used to cancel a phase difference between amplified signals obtained using each gain of the amplifying circuit. The phase adjustment value is, for example, a delay amount of a phase generated in a circuit including each gain circuit of the amplifier circuit. The phase adjustment value can be studied by the method of the present invention described later. The signal processing circuit is configured to determine the conductivity of the solution flowing in the cell by using an amplified signal obtained by amplification by the amplifying circuit and a phase adjustment value related to a gain for obtaining the amplified signal.

In a preferred embodiment, the signal processing circuit is configured as follows: the phase adjustment value related to the gain for obtaining the amplified signal is used to adjust the phase of the reference signal multiplied by the amplification circuit obtained by the amplification circuit in order to obtain the conductivity.

The conductivity detector according to the present invention preferably further comprises a gain adjustment unit configured to automatically adjust the gain of the amplification circuit in accordance with the magnitude of the current flowing between the pair of electrodes. In this way, the gain of the amplifier circuit is automatically switched according to the magnitude of the current flowing between the pair of electrodes, so that the user can perform detection in a wide range and detection with high resolution without manually adjusting the gain.

The method of the present invention is a method for obtaining a phase adjustment value for canceling a phase difference between the amplified signals obtained by using gains of the amplifying circuit of a conductivity detector, the conductivity detector including at least: a tank for flowing sample water; a pair of electrodes immersed in the sample water flowing through the tank; a voltage applying unit that applies a voltage between the pair of electrodes; an amplification circuit configured to amplify a current flowing between the pair of electrodes by using any one of a plurality of gains to obtain an amplified signal; and a signal processing circuit for obtaining the conductivity of the sample water by using the amplified signal obtained by the amplifying circuit. The method comprises the following steps in sequence:

conducting the pair of electrodes through a resistance having a resistance value that is negligible in electrostatic capacitance;

acquiring an amplified signal waveform of one cycle of the amplified signal based on a current flowing between the pair of electrodes for each gain of the amplifier circuit; and

the phase difference between each of the amplified signals and the reference signal is obtained from the difference between the time at which the amplified signal waveform of each of the gains reaches the maximum value or the minimum value and the time at which the amplified signal waveform of one cycle of the reference signal reaches the maximum value or the minimum value, and the phase difference is obtained as a phase adjustment value relating to each gain.

ADVANTAGEOUS EFFECTS OF INVENTION

The conductivity detector of the present invention is constituted as follows: since the conductivity of the sample liquid is determined by using the phase adjustment value obtained in advance for each gain, which is used to eliminate the phase difference between the amplified signals obtained by using each gain of the amplification circuit, together with the amplified signal obtained by amplifying the amplified signal by the amplification circuit, it is possible to suppress the disturbance of the conductivity waveform due to the gain switching of the amplification circuit, and to obtain a continuous conductivity waveform.

According to the method of the present invention, a phase adjustment value used in the conductivity detector can be obtained.

Drawings

FIG. 1 is a schematic view showing the configuration of an embodiment of a conductivity detector.

FIG. 2 is a schematic diagram for explaining the principle of conductivity measurement according to the embodiment.

Fig. 3 is a schematic diagram for examining the configuration of the phase difference adjustment value used in the conductivity detector of the above-described embodiment.

Fig. 4 is a flowchart showing an example of a method for obtaining a phase difference adjustment value for each gain.

Fig. 5A is a diagram showing an example of a conductivity waveform when the phase of the reference signal is not adjusted.

Fig. 5B is a diagram showing an example of a conductivity waveform when the phase of the reference signal is adjusted.

Detailed Description

Hereinafter, an embodiment of the conductivity detector and the method for obtaining the phase adjustment value used for the conductivity detector according to the present invention will be described with reference to the drawings.

First, a configuration of an embodiment of the conductivity detector will be described with reference to fig. 1.

The conductivity detector includes a tank 2, a pair of electrodes 4a and 4b, a voltage applying unit 6, an amplifying circuit 8, a gain adjusting unit 10, a signal processing circuit 12, and a phase adjustment value holding unit 14.

The sample liquid flows in the tank 2, and the pair of electrodes 4a and 4b are immersed in the sample liquid flowing in the tank 2. The voltage applying unit 6 is configured to apply a predetermined voltage between the electrodes 4a and 4 b. The amplifier circuit 8 is configured to amplify a current flowing between the electrodes 4a and 4b when a predetermined voltage is applied by the voltage application unit 6, and generate an amplified signal. The amplifier circuit 8 has a plurality of gains, and amplifies the current flowing between the electrodes 4a and 4b with any one of the gains.

The gain adjustment unit 10 is configured as follows: the level of the current flowing between the electrodes 4a and 4b is previously made to correspond to a gain for amplifying the current, the magnitude of the current flowing between the electrodes 4a and 4b is read, and the gain corresponding to the magnitude is selected. Thus, when the conductivity of the sample liquid flowing in the cell 2 exceeds a certain value, the gain of the amplifier circuit 8 is automatically switched, and the current amplification factor is reduced. The gain adjustment unit 10 is a function realized in the form of hardware (hardware) or software (software).

The amplified signal generated by the amplifier circuit 8 is taken into the signal processing circuit 12. The signal processing circuit 12 is configured to obtain the conductivity of the sample water flowing in the cell 2 by using the amplified signal from the amplifying circuit 8. The signal processing circuit 12 is configured as follows: when the conductivity is obtained using the amplified signal, the influence of the phase delay specific to the gain is removed using the phase adjustment value relating to the gain used to generate the amplified signal. The phase adjustment value of each gain is held in the phase adjustment value holding unit 14. The phase adjustment value holding unit 14 is implemented by a partial area of the storage device.

The measurement principle of the conductivity detector will be described with reference to fig. 2. In the following description, for convenience, a voltage (input voltage) V applied between the electrodes 4a and 4b is applied_inThe notation sin θ.

As shown, the groove 2 can approximate the electrostatic capacitance C between the electrodes 4a and 4b_cellAnd resistance value R_cellThe parallel circuit of (1). Capacitance C between the electrodes 4a and 4b_cellAnd resistance value R_cellIs a variable whose value varies depending on the conductivity of the sample liquid.

The amplifier circuit 8 changes the gain by changing the resistance value of an operational amplifier (operational amplifier). Here, the amplifying circuit 8 is illustrated as having a resistance value R passing through two_gainH、R_gainMTwo gains (high and medium) are achieved, but the amplification circuit 8 may also have more than three gains. An amplified signal S obtained by amplifying a current flowing between the electrodes 4a and 4b by using the respective gains_gainHAmplifying the signal S_gainMAre represented by the following formulae (1) and (2), respectively. Alpha of formula (1) or (2)_H、α_Mω is an angular frequency which is a delay amount of a phase generated in a circuit including each gain.

The signal processing circuit 12 includes a circuit for amplifying the signal S_gainHAmplifying the signal S_gainMA multiplier for multiplying the reference signal and a filter for accumulating the multiplied value for one period. The reference signal is the same sin θ as the input signal. The conductivity detector of the embodiment is configured to adjust the phase of the reference signal using the phase adjustment value held in the phase adjustment value holding unit 14, and the description will be continued with the reference signal being sin θ.

Will amplify the signal S_gainHAmplifying the signal S_gainMMultiplies the reference signal sin theta by the reference signal sin theta, accumulates the multiplied reference signal sin theta for one period, and divides the accumulated value by the resistance value R_gainHResistance value R_gainMThe obtained compound is represented by the following formulae (3) and (4).

When the above formulas (3) and (4) are divided by π, respectively, the electric conductivity G is obtained_HConductivity G_M. I.e. G_H、G_MAre represented by the following formulae (5) and (6), respectively.

From the above-mentioned formulas (5) and (6), the conductivity G obtained by calculation_HConductivity G_MNot only dependent on R_cellAnd C_cellAnd also depends on the delay amount alpha of the phase generated in each circuit_HRetardation amount alpha_MSaid R is_cellAnd C_cellDepending on the actual conductivity of the sample water. Retardation amount alpha_HRetardation amount alpha_MIs a value peculiar to a circuit including each gain, so α_H≠α_M. Thus G_H≠G_MAs shown in fig. 5A, the waveform of the conductivity is discontinuous before and after the gain switching.

Here, α_H、α_MAmplifying the signal S for AND_gainHAmplifying the signal S_gainMThe phase difference of the multiplied reference signals, so that if the signal S is to be amplified_gainHAmplifying the signal S_gainMThe phase difference with the reference signal multiplied by it is set to 0, i.e. the signal S is amplified by the sum_gainHAmplifying the signal S_gainMThe multiplied reference signals are respectively set to sin (theta-alpha)_H)、sin(θ-α_M) Then alpha of the formula (5) or the formula (6)_H、α_MRespectively become 0 to become

Thus, as shown in fig. 5B, the waveform of the conductivity is amplified by the amplifier circuit 8The gain of (2) is switched continuously before and after. The phase adjustment value holding unit 14 (see fig. 1) holds a delay amount α of a phase generated in a circuit including each gain of the amplifier circuit 8_HRetardation amount alpha_MAs a phase adjustment value.

Obtaining the phase adjustment value α using the schematic diagram of fig. 3 and the flowchart of fig. 4_HPhase adjustment value alpha_MThe method of (1) is explained.

In obtaining the phase adjustment value alpha_HPhase adjustment value alpha_MThen, as shown in fig. 3, a resistor (resistance value R) having a capacitance that is negligibly small is interposed between the electrodes 4a and 4b instead of the groove 2 (step S1). In this state, any gain of the amplifier circuit 8 is selected (step S2), and the amplified signal obtained by amplifying the current flowing through the resistor by applying the voltage sin θ between the electrodes 4a and 4b using the gain and the reference signal sin θ are read out for one cycle by the arithmetic Processing Unit 16 implemented by, for example, a Central Processing Unit (CPU) (step S3).

An amplification circuit 8 amplifies a current flowing between the electrodes 4a and 4b by using gains to obtain an amplified signal S_gainHAmplifying the signal S_gainMAs follows.

The arithmetic processing unit 16 calculates the times at which the amplified signal and the reference signal sin θ reach the maximum value (or the minimum value), and calculates the phase difference α between the amplified signal and the reference signal from the difference between the times_HPhase difference alpha_M(step S4). Then, the obtained phase difference is stored as a phase adjustment value in the phase adjustment value holding unit 14 (step S5). The operation is performed for all the gains set in the amplification circuit 8, whereby the phase adjustment value relating to each gain can be found.

Description of the symbols

2: trough

4a, 4 b: electrode for electrochemical cell

6: voltage applying part

8: amplifying circuit

10: gain adjustment unit

12: signal processing circuit

14: phase adjustment value holding unit