CN1946989B - 带有参考电极的磁流量计 - Google Patents

带有参考电极的磁流量计 Download PDF

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CN1946989B
CN1946989B CN2005800123570A CN200580012357A CN1946989B CN 1946989 B CN1946989 B CN 1946989B CN 2005800123570 A CN2005800123570 A CN 2005800123570A CN 200580012357 A CN200580012357 A CN 200580012357A CN 1946989 B CN1946989 B CN 1946989B
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CN1946989A (zh
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罗伯特·K·舒尔茨
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Micro Motion Inc
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Rosemount Inc
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/584Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters constructions of electrodes, accessories therefor
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/60Circuits therefor

Abstract

提供了一种磁流量计(20),其包括参考电极(212),所述参考电极构造成电联接在所述流量计的流管(200)内流动的过程流体。所述参考电极(212)适于测量所述过程流体的电势。限流器(216)构造成限制通过所述参考电极(212)的电流、从而减小所述参考电极(212)的腐蚀。

Description

带有参考电极的磁流量计
技术领域
本发明涉及过程测量及控制工业。更具体地说,本发明涉及磁流量计。
背景技术
磁流量计用来测量通过流管的可导过程流体的流量。该可导流体流经电磁体和电极。根据法拉第电磁感应定律,因施加的磁场而在流体中感应产生电动势(EMF)。该EMF跟流体的流速成比例。电极被设置在流管内,以实现跟流动流体的电接触。这些电极传感在流体内磁感应产生的EMF,所述EMF可随后被用来确定流速。所述EMF通过流量计来测量,该流量计使用跨越电极连接的差分前端放大器。过程流体的电势被用作差分放大器的参照。应注意,该参照不一定是地。
发送器必须以该过程为参照,以提供稳定的读数。该过程连接通过确保流管与该过程之间的电连接而建立。这可以通过利用绑定(strap)到流管的地环、直接连接到流管的地电极、或流管与相邻可导管之间的带来实现。地能够提供低噪声参照,并且,它常常是电安全规程所要求的。然而,地并不是适当操作所必须要求的。一些安装由于过程的电属性或过程流体的腐蚀性而使用塑料或不可导管或在金属管内使用衬里(lining)。在这些情况下,该过程可能处于不同于地的电势。地电极与流管之间通过螺栓或一些其他装置的连接可提供电流到地的路径,这可能导致地环或地电极的腐蚀。
在许多过程安装中,运送过程流体的过程管线是可导的,并跟过程流体是接触的。相应地,简单地从流管到过程管线连接带(strap)将确保可导流体跟流管处于相同的电势。然而,在一些应用中,过程管线本身可能是不可导的,或者,可能具有不可导的内衬里。因而,到过程管线本身的电接触将不会建立到过程流体的参照。在这些情形下,必须采用可选的技术来电联接到过程流体。例如,过程参照可通过使用流量计内或跟流量计相邻的地环或地电极来实现。
根据现有技术,出现在磁流量计中的问题之一是地电极的严重腐蚀。地电极与流管之间通过螺栓或一些其他装置的连接可提供电连接到地的路径,这会导致地环或地电极的腐蚀。在地电极趋于腐蚀的安装中,流管可从地电隔离以去除到地的电路径。一般地,这将防止任何电流流动通过过程流体和地电极到达地。尽管这种方法已经一般地解决了许多问题,但是,它并不能处理所有的情况。
仍然存在一些这样的情况,在这些情况中,由于具体的应用,将流管从地隔离是不可行的。这样的情况的一个例子是用来安装流管的螺栓本身提供了流管与相邻过程管线之间的电路径。另一个例子是使用有金属衬里的管,其阻止流管从相邻管线隔离。然而,这将可能提供到地的某种途径,导致地电极或地环的杂散电流腐蚀。在这样的环境下,可使用接地环。跟地电极相比,接地环提供更大的表面面积,且腐蚀的问题没有那么大。然而,在一些情况下,地环是不实际的。例如,地环的故障会导致过程流体的泄漏。此外,使用惰性金属如铂是昂贵的。因而,提供带有能够耐腐蚀并不像地环那么昂贵的地电极的磁流量计在一些装置中会特别有用。
发明内容
本发明提供了一种磁流量计,包括适于被电联接到过程流体的电路。构造了参考接触件,以接触在流管内流动的过程流体。提供了在参考接触件与电路之间串联的电学部件,以减小通过参考接触件的电流流量。
根据本发明的一方面,提供了一种磁流量计,包括:测量电路;流管;至少第一和第二电极,所述至少第一和第二电极设置在所述流管内,并联接到所述测量电路;至少一个参考电极,所述至少一个参考电极可操作地联接到所述测量电路,并设置成电联接到所述流管内的过程流体;以及限流器,所述限流器联接到所述参考电极,并适于联接到所述测量电路,所述限流器构造成减少所述参考电极的腐蚀,其中所述至少一个参考电极提供了对于流量计的电接地。
根据本发明的一方面,一种用于磁流量计的流管,所述流管包括:具有不可导内表面的可导管;第一和第二电极,所述第一和第二电极设置在内表面上,并适于接触过程流体;参考电极,所述参考电极安装到所述可导管,并从所述可导管电隔离,所述参考电极被设置成电联接到过程流体;以及限流器,所述限流器构造成电联接到所述参考电极,并适于串联联接到测量电路,其中所述参考电极提供了对于磁流量计的电接地。
根据本发明的另一方面,提供了一种减少参考电极的腐蚀的方法,所述参考电极构造成传感磁流量计内的过程流体的电势,所述方法包括步骤:获得限流器;以及将所述限流器跟所述参考电极和流量测量电路一起电串联放置,且所述参考电极提供了对于流量计的电接地。
附图说明
图1是磁流量计的部分剖开视图,本发明的实施例在该磁流量计中特别有用。
图2是磁流量计的图解视图,本发明的实施例在该磁流量计中特别有用。
图3是用在依照本发明实施例的磁流量计中的流管的一部分的简图。
图4是依照本发明实施例的磁流量计的图解视图。
具体实施方式
披露了这样一种磁流量计,对应于在过程中存在的杂散电流,该磁流量计提供了增强的地电极耐腐蚀性。具体地说,本发明的实施例起到了限制或抑制在一些过程装置中存在的杂散电流流动通过地电极到达地的作用。
图1是磁流量计的实施例的部分剖开视图,本发明的实施例在该磁流量计中特别有用。磁流量计20包括带有电绝缘内衬23的流管22,其中,流管22由低磁导率材料形成,电磁体26由线圈、铁磁芯或屏蔽件28、以及电极30、32形成。电磁体26和电极30、32像地电极35一样接线到发送器(transmitter)电路34。在操作过程中,发送器电路34利用电流驱动电磁体26,并且,电磁体26产生由流管22内的箭头所表示的磁场36。过程液体21流动通过流管22内的磁场,并且,所述流在液体21内感应产生了电动势(EMF,电压)。绝缘内衬23防止从液体21到金属流管22的EMF泄漏。电极30、32接触液体21并拾取或传感EMF,根据法拉第定律,所述EMF跟流管22内液体21的流速成比例。
图2是现有技术的磁流量计的电路的图解视图。磁流量计120包括流管124,流管124具有绝缘内衬126,其适于运送流动的液体128,液体128电联接到流管124,并且,流管124一般连接到地130。当过程管线被电联接到过程流体的时候,管线与流管之间的电连接提供了所需的过程流体128到流管的电联接。设置线圈134以响应来自驱动电路152的驱动信号而向过程流体施加磁场。电极138和140分别通过放大器150和148联接到测量电路154。测量电路154根据已知技术提供跟流量相关的输出。
如图2中所示,在磁流量计120内的部件通常联接到共同的参照。例如,放大器148和150以连接到流管的共同参照为参照。这允许发送器参照过程去除每个电极所共有的噪声。
图2中图示出的构造在过程管线本身是金属的并因而能够被直接连接到流管、提供强的到过程流体的电参照的情况下工作得很好。然而,存在一些这样的情况,其中,过程管线并不提供到过程的电参照。具体地说,一些过程装置使用不可导的管线或使用带有不可导内衬里的可导管线。在这些情况下,前端放大器以过程流体的电势为参照仍然是重要的。这是因为,尽管过程流体的电势依赖于杂散电流和/或干扰可能显著地变化,但是跨越电极138、140测得的电势通常在一或多毫伏的量级。在这些情况下,第三接地电极跟磁流量计一起使用。该接地电极被用来电接触过程流体。但是,在一些安装中,接地电极的腐蚀不可接受地迅速发生。本发明包括了这样的认识,在过程流体中存在的杂散电流能够导致地电极的过度腐蚀,其中,所述杂散电流通过电极被分流到地。例如,一些过程要求大的电势或电流施加到过程流体上,其可能通过地电极泄漏。
图3是用在依照本发明实施例的磁流量计中的流管的一部分的简图。流管的部分200包括一对电极138、140,这对电极138、140分别经由不可导的联接器(coupler)204、206延伸通过可导壳202。电极138、140进一步延伸通过不可导衬里208,从而使电极138、140中的每一个电接触在部分200内流动的流体。电极138和140分别通过连接器222和224联接到电路198(在图4中示出)。在图3中,地电极212经由不可导联接器214通过壳202,其中,不可导联接器214优选跟联接器204和206为相似的类型。然而,可以使用以不可导的方式将电可导的电极通过可导壳体202、或与其不同的在将电极212从壳202隔离的同时提供到达壳202内部的电通路的任何方式。地电极212通过限流器(current limiter)216和连接(connection)225联接到电路198(在图4中示出)。在一个实施例中,限流器216简单地是电阻器。然而,能够起到限制或降低通过其中的电流分量的作用的任何装置或电路都能够被用来实践本发明的实施例。优选地,限流器216允许过程流体的电势被联接到测量电路198。相应地,限流器216可包括滤波器或其他电学部件或电路。另外,尽管图3简单地图示出一个地电极212,但是,可使用任意数量或构造的这样的电极,以便将腐蚀在多个这样的电极上扩散。在一些实施例中,地电极212可包括地环。
图4图示出了依照本发明实施例的磁流量计300。跟图2中所示的部件类似的部件以相同方式标记。流管包括地电极212,地电极212通过限流器216被可操作地联接到放大器148、150。相应地,放大器148、150的输出以过程流体的电势为参照。
尽管已经参照优选的实施例描述了本发明,本领域技术人员将认识到,可在不脱离本发明的精髓和范围的情况下作出形式和细节上的修改。典型地,,当采用了电阻器作为限流器时,其阻抗将在10ohm和50kohm之间,然而,可采用任何适当的值,例如100kohm、150kohm或更大。地电极可以由任何适当的材料构成,如铂。例如,通过向地电极加入杂质或将限流器跟地电极一起制作,限流器可以是地电极的整体部件。

Claims (19)

1.一种磁流量计,包括:
测量电路;
流管;
至少第一和第二电极,所述至少第一和第二电极设置在所述流管内,并联接到所述测量电路;
至少一个参考电极,所述至少一个参考电极可操作地联接到所述测量电路,并设置成电联接到所述流管内的过程流体;以及
限流器,所述限流器联接到所述参考电极,并联接到所述测量电路,所述限流器构造成减少所述参考电极的腐蚀,其中所述至少一个参考电极提供了对于流量计的电接地。
2.如权利要求1所述的流量计,其中,所述参考电极包括铂。
3.如权利要求1所述的流量计,且进一步包括另一个参考电极,所述另一个参考电极可操作地联接到所述测量电路,并设置成接触过程流体。
4.如权利要求1所述的流量计,其中,所述限流器包括电阻器。
5.如权利要求4所述的流量计,其中,所述电阻器具有在10ohm和150kohm之间的阻抗。
6.如权利要求1所述的流量计,且进一步包括可导的流量计壳,所述可导的流量计壳包含发送器电路,并被联接到所述流管,其中,所述限流器被联接到所述壳,且所述壳被联接到地。
7.如权利要求1所述的流量计,其中,所述参考电极经由不可导的联接器被联接到所述流管,以将所述参考电极从所述管电隔离。
8.如权利要求1所述的流量计,其中,所述测量电路包括联接到所述第一电极的放大器,并且,其中,所述放大器通过所述参考电极和限流器以所述过程流体的电势为参照。
9.如权利要求1所述的流量计,其中,所述参考电极包括地环。
10.一种用于磁流量计的流管,所述流管包括:
具有不可导内表面的可导管;
第一和第二电极,所述第一和第二电极设置在内表面上,并适于接触过程流体;
参考电极,所述参考电极安装到所述可导管,并从所述可导管电隔离,所述参考电极被设置成电联接到过程流体;以及
限流器,所述限流器构造成电联接到所述参考电极,并串联联接到测量电路,其中所述参考电极提供了对于磁流量计的电接地。
11.如权利要求10所述的流管,其中,所述限流器为电阻器。
12.如权利要求11所述的流管,其中,所述电阻器具有在10ohm和150kohm之间的阻抗。
13.如权利要求10所述的流管,其中,所述参考电极包括铂。
14.如权利要求10所述的流管,其中,所述参考电极经由不可导的联接器安装到所述流管。
15.如权利要求10所述的流管,其中,所述参考电极包括地环。
16.一种减少参考电极的腐蚀的方法,所述参考电极构造成传感磁流量计内的过程流体的电势,所述方法包括步骤:
获得限流器;以及
将所述限流器跟所述参考电极和流量测量电路一起电串联放置,且所述参考电极提供了对于流量计的电接地。
17.如权利要求16所述的方法,其中,所述限流器包括电阻器。
18.如权利要求17所述的方法,其中,所述电阻器具有在10ohm和150kohm之间的阻抗。
19.如权利要求16所述的方法,其中,所述参考电极包括地环。
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