CN103048546A - Input circuit for measuring liquid electricity conductivity - Google Patents

Abstract

The invention discloses an input circuit for measuring liquid conductance. The input circuit includes an operational amplifier. The non-inverting input terminal of the operational amplifier is connected with a sine wave oscillator, the inverting input terminal is connected with a conductance measuring electrode, and the resistance is connected across the operational amplifier. output and inverting input. The beneficial effects of adopting the present invention are: the circuit is not only simple, cheap, and easy to implement, but also the output voltage signal of the circuit has a linear relationship with the conductance value to be measured, and the output voltage signal of the circuit is sent to subsequent rectification, filtering, amplification, A/D, single-chip microcomputer circuit, can accurately and reliably measure the conductance value.

Description

An input circuit for measuring liquid conductance

technical field

The invention relates to an input circuit for measuring liquid conductance, which belongs to the technical field of measuring instruments.

Background technique

Liquid conductance is an important electrochemical analysis parameter, and its measurement has been widely used in chemical industry, metallurgy, biology, medicine, food, water conservancy, environmental protection, energy and other fields. However, the current input circuit of the conductivity meter is designed using the principle of a balanced bridge, but the balanced bridge circuit has disadvantages such as complex structure and non-linear error, and the conductivity meter made from this has disadvantages such as low accuracy and inconvenient use.

Contents of the invention

The technical problem solved by the invention is to provide a linear, simple, accurate and reliable input circuit for measuring liquid conductance.

The invention provides an input circuit for measuring liquid conductance, which is characterized in that the input circuit includes an operational amplifier, the non-inverting input terminal of the operational amplifier is connected to a sine wave oscillator, the inverting input terminal is connected to a conductance measuring electrode, and the resistance is connected across the Between the output terminal of the op amp and the inverting input terminal.

The sine wave oscillator is an RC bridge sine wave oscillator.

The beneficial effects of adopting the present invention are: the circuit is not only simple, cheap, and easy to implement, but also the output voltage signal of the circuit has a linear relationship with the conductance value to be measured, and the output voltage signal of the circuit is sent to subsequent rectification, filtering, amplification, A/D, single-chip microcomputer circuit, can accurately and reliably measure the conductance value.

Description of drawings

Fig. 1 is an input circuit diagram for measuring liquid conductance according to the present invention.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention is specifically introduced as follows:

An input circuit for measuring liquid conductance described in the present invention includes an operational amplifier U1, and the non-inverting input terminal (+) of the operational amplifier U1 is connected to the RC oscillator, the inverting input terminal (-) is connected to the conductance measurement electrode, and the resistance It is connected between the output terminal Uo of the operational amplifier and the inverting input terminal (-), that is, the operational amplifier forms a proportional amplification circuit of the same phase.

That is, the non-inverting terminal (+) of the operational amplifier is connected to the RC oscillator, that is, the sine wave signal ui is connected, and the inverting input terminal (-) is connected to the conductance measurement electrode, that is, the resistance to be measured is connected to Rx, and its reciprocal is the conductance to be measured Gx, the feedback resistor is Rf, then

$\mathrm{<span\; class="notranslate">\; uo</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; ui</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; ui</span>}$

Because ui is a stable signal, that is, a constant. According to the above formula, it can be concluded that Uo has a linear relationship with Gx, and the output voltage signal of this circuit is sent to the subsequent rectification, filtering, amplification, A/D, and single-chip circuit, and the conductance value can be measured accurately and reliably.

The present invention has been disclosed above with preferred embodiments, but it is not intended to limit the present invention. All technical solutions obtained in the form of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims (2)

1. An input circuit for measuring liquid conductance, characterized in that the input circuit comprises an operational amplifier, the non-inverting input terminal of the operational amplifier is connected to a sine wave oscillator, the inverting input terminal is connected to a conductance measuring electrode, and the resistance is connected across the operating put between the output terminal and the inverting input terminal. 2. An input circuit for measuring liquid conductance according to claim 1, characterized in that the sine wave oscillator is an RC bridge sine wave oscillator.

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