电导率传感器

测量水溶液中电导比率对于水中杂质测量或溶解化学品的浓度测量越来越重要。

什么是电导率?

电导率是测量溶液传递或传输电流的能力。电导率这一术语来自欧姆定律,U = IR;其中,电压(U)是电流(I)和电阻(R)的乘积;电阻值由电压/电流求得。当电压通过导体时,电子流动形成电流,电流值大小取决于导体电阻。  电导率简单地定义为两个电极之间溶液电阻的倒数

详细介绍

测量水溶液中电导比率对于水中杂质测量或溶解化学品的浓度测量越来越重要。

 

什么是电导率?
 

电导率是测量溶液传递或传输电流的能力。电导率这一术语来自欧姆定律,U = IR;其中,电压(U)是电流(I)和电阻(R)的乘积;电阻值由电压/电流求得。当电压通过导体时,电子流动形成电流,电流值大小取决于导体电阻。  电导率简单地定义为两个电极之间溶液电阻的倒数

 

如何测量电导率?
 

测量电导率有两种基本传感器类型:接触式电感式(环形、无电极)
 

使用接触式传感器时,通过向溶液中浸入的传感器电极(共同影响电极常数)施加交流电并测量产生的电压来测量导电性。溶液用作传感器电极之间的导电体。

使用电感式(也称为环形或无电极)传感器,其感应元件(电极口)不会与过程直接接触。这两个匹配(相同线圈)的部件封装在工程塑料 (或特氟龙)中,可保护其免受该过程的不利影响。   


溶液如何导电? 

液体中的离子(NaCaClHOH)是用于负载电流的物质。

 

电导率只是一种定量测量:它对所有离子含量都有反应,并且在存在其他物质的情况下无法区分特定的导电物质。只有可电离的物质才有助于导电;糖类或油类等物质不具有导电性。

 

电导率应用范围广泛,从小于1×10-7 S/cm的纯水到大于1 S/cm的浓缩溶液。这些应用实例有WIFI、软化水、RO水、百分比浓度、锅炉排污和TDS

 

通常,电导率的测量是一种快速且低廉的确定溶液离子浓度的方式。电导率用于测量水的纯度或水中离子化学物质的浓度。这是一种非特异性的技术,不能区分不同类型的离子,而是提供与当前所有离子的组合效应成比例的读数。

 

测量精度受温度变化、接触式电极表面极化效应、电缆电容等的影响很大。

横河电机设计了各种精密传感器和仪器,即使在极端条件下也能应对这些测量。

 

如何选择正确的传感器? 

为应用选择电导率传感器时,需要考虑以下因素:

  • 什么是测量范围?(这决定了需要哪个电极常数)
  • 什么是过程温度?(我们已在Pt1000上标准化)
  • 该过程的化学成分是什么?(这决定了我们提供的结构材料,以确保化学兼容性)

什么是电极常数,为什么我们需要关注它?
 

电极常数是用于确定传感器测量范围的“倍增因子”的数学值。该数学值由电极的几何设计确定。通过将两个测量板之间的距离(长度)除以板的面积进行计算(板的面积由以下方式确定:外部面积 - 内部面积=电极之间的面积)

 

然后将原始电导率值乘以电极常数,这就是我们看到的单位μS(微西门子)/cm

 

横河电机提供四种电极常数:0.010.11.010.0,可提供0-2,000,000 μS整个测量范围的精确度。这些值称为标称电极常数,而传感器上印制的电极常数可能稍有不同(用户将看到0.0198而不是0.02),是该传感器的特定电极常数。 

使用不正确的电极常数时出现的其中一个问题是极化 

correct_cc_selected

第一个例子显示了一种具有正确电极常数的溶液,离子可以自由从一个板移动到另一个板。

wrong_cc_used

第二个例子显示了在高导电溶液中使用的相同电极常数。当电压交替(切换极性)时,由于离子密度太高,离子不能自由移动到另一个板。  这就导致更少的离子接触正确的板,从而导致错误的低读数。

然而,对于ISC40电感式传感器,只有一个电极因数(常数)。它涵盖了几乎整个电导率测量范围0-2,000 S/cm。传感器的准确性只在低端(低于50 µS)受到影响。

参考

概述:

To defray energy costs, many industrial plants have their own boilers to generate steam in order to produce a portion of their energy needs. In addition to generating power, the steam may also be used directly in plant processes or indirectly via heat exchangers or steam jacketed vessels.

概述:

In the past, the boiler feed tank systems in sugar factories had to be checked several times a day to make sure there were no sugar solution leaks. This was a very laborious process and, as continuous monitoring was not possible, monitoring results were not reliable. When a leak occurred, recovery operations were very costly and time-consuming. (AN10D01K01-02E)

行业:
概述:

Caustic soda and hydrochloric acid, produced in electrolyzer plants, are fundamental materials used in varieties of industries; chemicals, pharmaceuticals, petrol-chemicals, pulp and papers, etc. Profit is the result of the effective production with minimized running / maintenance cost. Proper control of the process brings you stabilized quality of products with the vast operational profit.

行业:
概述:

Control of sodium chloride (NaCl) concentration at a salt dissolver where solid salt is dissolved in water, is highly important because of the electrolysis efficiency. A conventional way of measuring the concentration of supersaturated NaCl solution had been performed by using non-contact type sensors (e.g., γ-ray density meter) since NaCl, impurities, and precipitates are in the solution.

概述:

In a semiconductor plant, a variety of chemicals are used in various manufacturing processes. The chemicals used for specific purposes are produced by diluting raw liquid with demineralized water using in diluting equipment, and the control of the concentration at this point is performed by conductivity measurement. 

概述:

In the manufacturing process of Pharmaceutical, Chemical and Food & Beverage industries, the cleaning and sterilization of tanks and piping are done with various cleaning solutions, fresh or hot water and steam after manufacturing products. Clean-In-Place (CIP) is the system designed for automatic cleaning and disinfecting.

概述:

Reverse osmosis (RO) is a separation process that uses pressure to force a solution through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.

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