检测技术-of sensors and detection电磁流量计传感器与基础

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电磁流量计1.IntroductionElectromagnetic

flowmeters,

also

known

as

‘Magflows’

or

‘Magmeters’,

have

nowbeen

in

widespread

use

throughout

industry

for

more

than

40

years

and

weretheof

modern

meters

to

exhibit

no

moving

parts

and

zero

pressure

drop.概述法拉第电磁感应定律

3.Construction4.励磁方式非满管安装使用优缺点分析Slide

3信息与控制E

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电磁流量计2.

Basic

Principal—Electromagnetic

Induction—When

an

electrical

conductor

moves

perpendicular

toa

magnetic

field,

a

voltage

is

induced

in

that

conductorperpendicular

to

both

the

magnetic

flux

lines

and

thedirection

of

motion.Slide

4信息与控制Slide

5信息与控制Illustration

of

Faraday’s

Law

ofelectromagnetic

induction.E

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电磁流量计2.

Basic

Principal—Electromagnetic

Inductionif

the

conductor

of

length

(l)

is

moved

through

the

magneticfield

having

a

magnetic

flux

density

(B)

at

a

velocity

(v),

thena

voltage

will

be

induced

where:E=

Bl

vE

-

induced

voltage

(V);B

-

magnetic

flux

density

（Tesla)

(Wb/m2);l-

length

of

conductor

(m);

v

-

velocity

of

conductor

(m/s).2.

Basic

Principal—Electromagnetic

InductionEx

CBDvEx—感应电势；

B—磁感应强度；

D—管道内径；v—垂直于磁力线方向的流速；C—比例系数，即单位换算系数。Q

v

x

D2

D

E

1E4

4

CB

k

xk—仪表常数，取决磁感应强度、管径Ex

kQE

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电磁流量计感应电动势的方向？•右手定则Slide6信息与控制（1）只能测量导电介质电导率限制条件δ≥1～5μS/cm（水>20μS/cm）(低电导率

>

0.05μS/cm

使用

仪表）只要>阈值后，与电导率无关。不能测非导电介质,如气体,油类，如介质含大量气体，测量严重波动（2）必须存在磁场励磁电流流经测量管上下励磁线圈产生磁场。励磁线圈断路，流量计不工作，励磁电流稳定性直接影响仪表测量测量管必须为非导磁材料（采用不锈钢材质），保证磁场穿过导管（3）实际测量值为流体流速速度式流量计测量介质的体积流量熟练流速换算

Q(流量）=π/4DN2V2.

Basic

Principal—Electromagnetic

InductionE

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电磁流量计uS/cm1.00110K50

-500Kerosene

煤油Methyl

Alcohol甲醇Orange

Juice

果汁Tap

Water自来水Beer啤酒1250D.I.Water

除盐水30%H2SO430%硫2

酸1MSea

Water

海水80K90%H2SO490%硫酸Slide7信息与控制E

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电磁流量计LiquidConductivity(μS/cm)Carbon

tetrachloride四氯化碳at

18℃Toluene甲苯Kerosene煤油ine

at

25

℃Soya

bean

oilDistilled

waterAcetone at

25

℃

PhosphorousBenzole

alcohol

at

25

℃Acetic

acid

(1%solution)Acetic

acid

(10%

solution)Latex乳胶

at25

C℃Sodium

silicate（硅酸盐）Sulphuric

acid

(90%

solutionAmmonium

nitrate

(10%solution)Sodium

hydroxide

(10%solution)Hydrochloric

acid

(10%solution)4

x

10–1210-80.0170.0240.040.040.0

x10216

x1025

x

10324

x10310.75

x

10411

x10431

x10463

x104Conductivities

of

some

typical

fluidsIt

should

be

noted

thattheconductivity

of

liquids

can

varywithtemperature导电率随温度变化

and

care

should

be

taken

toensure

the

performance

of

theliquid

in

marginal

conductivityapplications

is

not

affected

by

theoperating

temperatures.Most

liquids

have

a

positivetemperature

coefficient

ofconductivity一般为正温度系数.However

negative

coefficients

arepossible

in

a

few

liquids.Slide8信息与控制Conductivities

of

some

typical

fluidsE

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电磁流量计to

develop

most

of

the

electrode

potential

(e)across

the

input

impedance

(Ri)

of

themeteramplifier,to

minimise

the

effect

of

impedance

variationsdue

to

changes

in

temperature,Ri

needs

to

be

at

least

1000

times

higher

thanthe um

electrode

impedance

Rs.In

older

a.c.

driven

instruments

the

minimumconductivity

of

the

fluid

usually

lay

between

5

-20

μS/cm.

For

d.c.

field

instruments

theminimum

conductivity

was

about

1

μS/cm.However

modern

instruments

employ

a

varietyof

technologies,

including

capacitively

coupledmeters

that

can

be

used

on

liquids

withconductivity

levels

down

to

0.05

μS/cm.Modern

high

input

impedanceamplifiers

are

available

in

therange

1013

to

1014

Ω.放大部分输入阻抗应千倍于电极阻抗Slide9信息与控制Conductivities

of

some

typical

fluidsE

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电磁流量计Electrical

conductivity

ofthe

process

liquid

mustmeet

a

certain

minimumvalue,

but

that

is

all.Liquids

withpoorconductivity

presentagreater

electricalin

the

voltage-measuringcircuit

than

liquids

withgood

conductivity,

but

thisis

of

little

consequencebecause

the

inputimpedance

of

thedetection

circuitry

isphenomenally

high.Slide10信息与控制E

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电磁流量计电磁流量计| 传感器系数分析问题引入：某一台电磁流量传感器，B、D为定值时，电极流量信号与被测介质流速成正比不同口径传感器相同流速，无法达到相同的电极流量信号相同口径传感器相同流速，也有不同的电极流量信号原因：是工艺条件限制，B（磁通密度）D（管道内径）不能实现绝对相同Ex

CBDv每台传感器均有自己的特征值，即传感器系数反映某一传感器的流量信号特征（称为传感器常数）Slide11信息与控制Slide12信息与控制E

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电磁流量计12KROHNEROH

EI

C090399600Start,开始计算Stop停止计算测量值0400000参考值脉冲（容量）比如1个脉冲代表1升水0,1%偏差液位开关阀门最大流量:容量:不确定度:30.000

m3/h500m3<0,013%电磁流量计

| 传感器系数分析标定塔电磁流量计标定：非稳压动态水流量标定装置－－－确定传感器系数Slide

13信息与控制3.Construction一体型电磁流量计（C）分体型电磁流量计（F）转换器传感器连接电缆传感器转换器连接电缆磁路— 磁场外壳和接线盒导管—非导磁材料：不锈钢,陶瓷或塑料衬里—金属管道需要衬里一对电极—获取感应电压一对线圈—产生磁场电磁流量传感器E

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电磁流量计学14E

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电磁流量计电磁流量传感器——衬里

•

金属导管内壁的一层耐磨、耐腐蚀、耐高温的绝缘材料防止感应电势被金属测量导管壁短路衬里材料最高温度耐化学腐蚀性耐磨性变形性（温度/压力）（精度下降）口径范围耐真空PTFE四氟≤

180ºC好热碱浓酸取决于设计取决于口径和设计工艺10

–

6003/8”

–

24”取决于口径和设计工艺PFA+钢丝网≤

180ºC好热碱浓酸中等低2,5

–

1501/10”

–

6”很好ETFE≤

120ºC好热碱热酸很好低200

–20008”

–

80”很好PP+钢丝网≤

90

ºC取决于液体类型好低25

–

1501”

–

6”很好硬橡胶≤80

ºC低浓度（耐酸）低低25

–

30001”

–120”中等氯丁橡胶≤

80

ºC低浓度好低25

–

30001”

–120”中等PU聚氨酯≤

65

ºC低浓度优秀低50

–

16002”

–

64”好Ceramic陶瓷≤

180ºC好最耐磨完全不会变形(长期稳定性)2,5

–

2501/10”

–

10”完全耐真空Slide

14院E

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电磁流量计Commonly

used

magnetic

flowmeter

liner

materialsMaterialGeneralCorrosionAbrasionTemperaturelimit

(

C)Pressurelimit

(bar)Teflon

PTFEWarm

deformable

resin

withexcellent

ant-stick

properties

and

suitable

for

food

andbeverageExcellentFair18040Teflon

PFAMelt-processable

resin

with

better

shape

accuracy,abrasion and

vacuum

strength

than

PTFEExcellentGood18040PolyurethaneExtreme to

wear

and

erosion

but

not

suitable

forstrong

acids

or

basesWiderangeExcellent50250NeopreneWiderangeGood

toexcellent80100Combines

some

of

theto

chemical

attack

ofPTFE

with

a

good

degree

of

abrasionHard

rubber(Ebonite)Inexpensive

–

finds

its

main

application

in

the

water

andwaste

water

industriesFair

toexcellentFair95250SoftrubberMainly

used

for

slurriesFairExcellent7064ModifiedphenolicDeveloped

for

harsh

environments

containing

H2S/CO2concentrations

and

acidsVery

highGood200Yield

strengthof

pipeFusedaluminium

oxideHighly mended

for

very

abrasive

and/or

corrosiveapplications.ExcellentExcellent180Slide15信息与控制E

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电磁流量计（2）电磁流量传感器——电极The

electrodes,

like

the

liners,

are

in

direct

contact

with

the

process

medium

andagain

the

materials

of

construction

must

be

selected

according

to

the

applicationandtheir to

chemical

corrosion,

abrasion,

pressure

and

teperature.Commonly

used

materials

include:

316

stainless

steel,

platinum/rhodium,Has loy

C,

Monel,

andtantalum电极-从介质中感应电势信号，直接和介质接触，耐介质腐蚀，无电化学反应干扰不锈钢316L,

316Ti哈氏合金B、哈氏合金C钛Ti钽Ta铂Pt铂铱合金安装时要求与衬里Slide16信息与控制电极—三种适应不同的应用场合：普通电极刮刀电极(RE)：可清除电极表面污垢可更换电极(WE)：可在线拆下

污垢E

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电磁流量计Slide17信息与控制E

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电磁流量计If

the

electrode

is

isolated

by

encrustation覆盖物(a)a

60

V

a.c.

voltage

is

appliedacross

the

electrodes

and

electrolyticaction

starts

to

form

microporous

pathsthrough

the

isolating

'barrier'

(b).As

thesepaths eprogressivelylarger,

the

isolating

barrier

starts

to

breakaway

from

the

electrode

(c)

(courtesyTurbo

Messtechnik).覆盖物electrolytic

action

电解方法去除挂料Slide18信息与控制Slide19信息与控制M

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电磁流量计4.励磁方式a

permanent

magnet

恒定磁场—polarization

(electrically

chargedmolecules).to

alternate

the

polarity

极性ofthe

magnetic

field,so

themotional

EMF

polarity

alsoalternates

and

never

gives

thefluid

ions

enough

timetopolarize极化.employ

electromagnet

coils

togenerate

the

magnetic

fluxinstead

of

permanent

magnets.A

photograph

of

a

Foxboro

magnetic

flowtubewith

one

of

the

protective

covers

removed

showsthese

wire

coils

clearly

(in

blue):Slide20信息与控制M

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电磁流量计励磁方式励磁方式种类恒流励磁：用于测量特殊介质，涡流损耗小，交变干扰影响小，但会产生极化现象50Hz正弦波交流励磁：早期电磁产品使用，外界干扰影响大低频恒流（矩形波）励磁：既克服了交流励磁的干扰影响，又消除了极化现象的产生，使流量计

性能增强，仪表稳定性提高KROHNE公司电磁励磁方式为低频恒流励磁不同口径选用不同励磁电流频率，因此性能强DN＜300mm选用（1/4

～1/6）×50Hz励磁频率DN＜1000mm选用（1/16

～1/18）×50Hz励磁频率DN≥1000mm选用（1/32

～1/36）×50Hz励磁频率流量信号的波形与励磁电流波形相一致仪表口径越大，励磁电流频率越低M

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s电磁流量计KROHNE电磁流量计研发史产品介绍和规格开发年代科隆

成立于

1921年,

100%由

Rademacher-Dubbick

拥有在全球10个国家拥有14个生产基地

40

个KROHNE销售公司遍布世界各地年销售额：approx.€448

Mil.全球员工数：超过3092

（中国：>520人）第一台电磁流量计诞生１９５３第一台低频恒流励磁电磁流量计诞生１９７２K300１９７２第一台陶瓷衬里电磁流量计诞生１９７８T900１９７９第一台优化结构电磁流量计诞生１９８２F200１９８２SC100AS１９８５SC150１９９２IFC080１９９３第一台非满管电磁流量计诞生１９９５IFC090１９９５IFC010(IFC020)１９９６IFC110１９９９第一台两线制技术电磁流量计诞生２０００IFC300２００４虚拟基准接地电磁流量计诞生２００６IFC100２００８WATERFLUX3070电池供电电磁流量计２００9Slide21信息与控制M

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电磁流量计5.

Emptypipe

detectionConductivity

probe

for

empty

pipe

detectionIn

the

most

common

system

,aconductivity

probe,

mounted

on

topof

the

pipe,

senses

the

presence

ofthe

conductive

medium.

Ifthemedium

clears

the

sensor,

due

topartial

filling

of

the

pipe,

theconductivity

falls

andarm

isgenerated.Slide22信息与控制M

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电磁流量计6.安装使用：（1）传感器上箭头方向必须与实际流量方向一致（如反向安装，转换器菜单中流动方向一项必须更正）（2）必须保证满管测量状态Slide23信息与控制M

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电磁流量计（3）前后直管段的要求（注意：前后直管段从电极处开始计算！）上游≥5D,下游≥2D避免外界磁场干扰Slide24信息与控制避免剧烈振动法兰面差距小于0.5mmM

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电磁流量计特殊型号（WATERFLUX）无需前后直管段Slide25信息与控制M

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电磁流量计测量范围宽:量程比可达50:1～100:1;口径1～3000mm，精度较高，可达0.5-1.0级；反应速度快，可测脉动流和正、反两向流。

x

4

4

B

D2

D

Eqv

Av

v

优缺点分析优点：无压损（无阻力件）,可测含固体颗粒、悬浮物、液固两相等介质：给排水工程、污水、纸浆、矿浆、强腐蚀液等。在管道直径确定，磁感应强度不变的条件积流量与电磁感应电势有一一对应的线性关系，而不受介质的流体密度、粘度、温度、压力和电导率（>阈值）等物理性质的影响；Slide26信息与控制M

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电磁流量计缺点：仅适用于导电液体(>阈值)。不能测量电导率很低的液体，如石油制品和 等。不能测量气体、蒸汽和含有较多较大气泡的液体。由于与磁场强度B有关，易受外界电磁场干扰影响，必须有良好的措施，不能安装于强磁场附近。测量平均速度，需要直管段，前5D，后2D。由于衬里材料和电气绝缘材料的限制，不能用于测量较高温度的液体。Slide27信息与控制M

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电磁流量计1、电磁流量计的精度是多少?一般电磁流量计的测量精度可以达到0.5%相对测量误差。一些经过特别校验或者特别制造的电磁流量计的精度可以更高。2、电磁流量计是否有测量限制?一般来说,我们有以下因素必须在测量前考虑:1)流体是否导电,或者说所测的液体必须具有一定的的电导率。诸如:油、纯水、碳氢化合物液体不能测量。

2)液体中含铁磁性物质不能测量。3、压力校验台如何判定液体的电导率?如在现场可以用电导率仪来检验。通常经过自来水厂处理过的自来水的电导率为200m

s/cm~300m

s/cm其他液体可查阅液体的电导率表格。4、能否测量含有气泡的液体?在气泡含量较少的情况下可以测量。但是此时流量计所显示的是包含气泡在内的总流量,sgaic所推荐的含气量为小于5%的体积比,且要求气泡均匀。5、是否能测量含固体颗粒的液体或浆料?

可以。但要注意:

固体颗粒:颗粒量的含量

过总体积的5%,固体颗粒直径不宜大于3mm.

浆料:其含量要比固体颗粒的含量要大,但考虑衬里和电极的磨损,

物位开关要注意材质的选定。另外考虑到减缓对衬里和电极的

磨损程度,流速不宜过高。Slide28信息与控制M

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电磁流量计6、能否测量粘度高的液体?能。因为电磁流量计不受粘度的影响。测量诸如果浆的液体或易粘结的污水都没有问题。但要注意粘度高时,流速变慢。选型时要注意提高流速。7、

衬里的作用是什么?为了不让传感器产生的感应电动势信号损失,传感器

必须用衬里来绝缘。8、衬里的种类有哪些?根据流体的特性,一般分为五种9、在安装时有何要求如安装方向等是否会对测量有影响?前后必须有直管段,以保证进入测量管的流体的流态充分发展。10、现场安装的前后直管要求是多少?建议最低的要求是前直管5d后直管段3d。Slide29信息与控制M

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