RF Handbook

98 Pages·2001·1.05 MB·English

AMETEK’

DREXELBROOK

A Practical Guide to
Radio Frequency Level Controls

by
Edward Schuler
About the author...

Edward L, Sctular was Service Deparlment Vanage:, RF Continuous Product Manager,
and Regional Sales Manager “or Drexeltoox Engineering Co. for a7 yeas betore retiring
in 2000. His many years and vast experience wth RF Admittance products mace him an
‘expart in the applicat on, installation and sewvcirg of lave, contral products us'ng this tech-
ology. Ih addition to this referanes kaok, Ed has also authored various arlisles for national
trade oubfcations an the “opie of lave" sensing ane RF Ad-riftance technotogy.

‘The information published in this puh.cation is
oustomars.

Copyright 2001, AMETEK Drexelbro2k.

No reproduction with writes permission from AMETEK Grexelbrook.

ished solely as a serve *o our

42061-591 pg.1
‘TABLE OF CONTENTS:

4. INTRODUCTION

2, THEORY OF OPERATION:
POINT - LCYCL (ON/OFF)

4. SENSING ELEMENTS {PROBES}
4. INSTALLATION OF RF LEVEL INSTRUVENTS
5 CALIBRATION (ONOFF)

6 TROUBLESHOOTING (ON/OFF)

7. THEORY 0" OPERATION:
CONTINUOUS (ANALOG)

8 CALIBRATION OF CONTINUOUS
LEVEL INSTRUMENTS

9 AROUNC THE LOOP
4C. TROUBLESHOOTING {ANALOG}

14, PROPERTIES OF MATERIAL

APPENDIX
A. GLOSSARY OF TERMS
B, GRAPHS TABLES

s20-1-591 092
INDEX

a9

4201-59" pa

SEGTION CONTENTS,

INTRODUCTION
1 Howto Use This Booe
112 One Level Technology for Your Plant
‘THEORY OF OPERATION: POTNT LEVEL
(ONIOFF)
241 Two-Terruna Capsctance Poh Leve! Contro’s
2.2 Three-Terrinal Core-Stield™ Point Level Cortrols
2.3 Thres-Terminal Two-Wre Scte-Stield Point Level Controts
(UCT Laval Consol Teansmitier)
23.1 Capability of Intrinsic Safely
23.2. Remotely Nountse Relay Contact Outputs
23.2 Greater Perscnnel Safety
23 Instument Faure Alarm
23.5 Pushbutton Calibration and Level Veriteation
236 Verty™ System Sunction Valiation Circut
24 Three-Terminel Gote-Shiek Multipoint Level Cortrols
25 FailSate

SENSING ELEMENTS (PROBES)

aa

32

33

Theory (OnlO7)

3414 Two-Terminal Sensing Elements
3.1.2 Tatee-Terrinal Sensing elements
3.1.3. The Vapor Stage

‘Mechanical Gonsirerations (Qnf0rh)

a2t Temperature
222 Pressure

223. Mecherice Suength
324 Gompatiilty of Matedals
325 Mourting

Options and Accassorias
Theory (Continuous)

2.4.1 Measutieg Insulating Materials
34.2 Measuring Conductivs Mataria’s
4a

30

33
36
37

Mecranical Considerations (Cotinuous)
Seal Tyte™ Hermetically Sealed Prabes
Perrv-A-Seai" Injection Molced Port evel Sensing Elemenss

INSTALLATION OF RF LEVEL INSTRUMENTS

Ad

AD

43

4a

Enclosures

4.1... Peoteation of Electronics or Sensing Elernant
4.12, Protection of te Plan:

Mounting Locations

421 Temperaure
422° Vinration

42.3. Carrasive Atmospheres

4.24 Electoniss-i-Head Installations

Intezconnections

43.1 Tecnsica
43.2 Practical

433, Local and Natoral Codes
434° Plant Standards

‘Sensing Element Inetalaion
4.4.1 Mourting Location
44.1.3 Insulating Liguies
4441.2 Conductive Liquids in
Ungrourdied vesse's
4.4.1.3 Mounting in a Vessel
44.1.4 Flenble Sensing Elements

44.2 Open Caannel Flow Probes

‘CALIBRATION (ON/OFF)

Intreduction (Marvally Gal brated
Instruments)

‘Treory of Catocation

Pro: to Calibration

‘Marual Gal bration Procedurae for Singie Paint Controls,

a1 No t-Vsual

342 No.2-Bind
B43 No. 3-Wehout Raising Level

ee

52° pg
544 Calibration For iterfave
54.5 AlMethods of Callranon
548 Highly Conductive Materals
54.7 Foam

54.8 Calibration of Multipont Controls

5.5 Digtal Calibration of “~wo-Wite Single Point Controls
88 CrvOff Instrument Options

5.8. Adustable Differential
552 Time Delay

583. Hign Sensiimy
554 Mutipoint

6.0 TROUBLESHOOTING {ON/OFF}

64 Introduatior to Troublesnocting
62 Testing the Elacironics

62.1 Two-Wire, “hree-Teminal OnvON Systems
822 TwooMre Transmite:
623 Iwo-Wire Receiver Syste

63 Testing the Cable

64 Testing the Sensing Element

65 Testing the Relay Cicult

7.0 THEORY OF OPERATION: CONTINUOUS
(ANALOG)

71 Two-Terminal Continuaus Cepactance Irsturent
7.2 Two-Terminal Continuous Cote-Shie Transmitter
73 Three-Terminal Two-W'e Contin sous Cote-Shiela (Aarnttance) Instument
74 Three-Terminal Two-W re Cont nug.is Ramp (Capacitance) Instumert
75 TrueLeval™
7.5.1 Tre Laval Sensing Elements
80 CALIBRATION OF CONTINUOUS LEVEL INSTRUMENTS

BA rtaducton
82 Caioration Contols

821 Analog Transmitters
82.1 Smart Transmitters

BA PrortoCalbration

831 FalSate

420-1-531 pas
a

10.0

8.3.2 Adequate Signal Ftom Probe
83.3 Zero Padding

84 Three Methods cf Catbration

84,7 Precalieated at the Factory
842. Any Two-Paint Calbratior. (Smart Transrittes}
2.43. Galeciated Calitraton

844 Empy & FF

84 4A Long Canle Probes
34.48 Inter‘ace
B44C Proximity
44D Open Channel Flow
Ba4F TmeLevel
8.44F Insulaing Grarular

85

ions Available

85% RFI Protectior
B52 Spark Protection
B53 Time Delay

854 High Sensituty

83° Recalibration

£81. Recalibroticy of Analog Teanemitore
2.6.2. Recalbratien of Smart Trans~nitars

AROUND THE LOOP

84 Introducton

22 Lins of Resistance and Vollage

92 Power Supplies

Qa Sateoret

5 Proportional Setcon (Proportaral
cantrlle">

9.8 Meters and Indicators

97 Infrinsic Safely Barrie's

98 — Singie Channel Receivers

89 Microprocessor Racaivers

‘TROUBLESHOOTING {CONTINUOUS}

10:4 Introduction
19.2 Checkirg the Transmitter

19.3 Checking the -cop

104 Checking the Sensing Element Cable
405 Chackng tie Sensing Elerent

420-1591 py
11.0 PROPERTIES OF MATERIALS

11a Materisl“ypes
47.2 Physica. and Che.cal Properties
123 Electrical Properties

4°.4.1 Dielectric Constant
12.82 Condustinty

11.4 Elects of Materials on Point -eve! RF Controls
5 Effects o* Materials on Continuous Lever RF-Adnittance Controls

APPENDIX A

Glossary of Terms.

APPENDIX B (Graphs and Taoles)

Figure B-1
Figure B-2

Figure B-3
Figure B-4
Figure B.S
Figure 8.6
Figure B-7

INDEX

4204-481 pa?

Unit Carversion Factors

Cireumference, Area, and

Volume Tables

ANS! Steal Flange Dimensions

Sisel Pipe Osta

Temperature Conversion Table
Hazarsous Area Te"minnlogy

‘Sammary of Intrirsic Safety Barrier Codes,
1.9 INTRODUCTION
414 Howto Use This Book

‘This book i intended as a practical, but not-100-
technical guide to understand ard get the most
‘out of your vadio frequecy level measuring
‘cuiprent

“The format permis use as both an ‘rstiuctions
text and a referaroe manual. To use as an
instructional tex, the table of centarrs is orga
nizad to mace learning easiest wner tha books
fead from begirring to end. As areferense
manal, the index in fre back should aid in
Jocafing the desiec informatin.

Infarmation contained hers i not allsnclusive nor
inlerdad 20 replace the epecifcinstraction
manial supalied with the equipment. Practically
all refe-ence ta the application ofthe equipreent
has been let for anetner text

Athough some data is equaiy appltcable to
equipment manufactured by otters, uch irfor-
mations timited to that manu’astured by
Drexelbroak Engineaiing Company, Hersha,
Pennsylvarra, U.S.A. No pertion of this booklet
may be reprocuces in whole arin part withaut the
ceaprays writer carsent of Drexe brook Eg neer-
ing Gompary.

4.2. One Level Technology for Your
Plant

Like temperature, preseura, and flow, LEVEL is
fone of the mast important arocess meastre
ants, To make tre best croice for level instr.
mentation, the spectiar should be familar with
over twenty distnety diferent technologies “at
are commanly used in industy today. Few of us
have the rie or inination to became exses in
al of the technologies. Therefore we tend 10
zero in one one a 7 thal "n0< good’. “his may
Work fone ig fortunate enough %9 ntlaly make
the right choice. Since znesc companies do take #
randam approach to the appieation of netumer
tation, a solution is usually found to meet the
requiremen's of:hat particuta job

420-"-551 wu

Introduction

Tak g an analytical ayproach te the application
of nstrumentation will produce huge larg term
erefis. These henefis include lowered mstalla-
‘ior costs, less mainterarce, “educed personnel
craising and decreased pant downtime. In the
case of evel measurement, theee savings can be
achieved wit 2 sacle, rul-freeted ‘echology.

here ie a univeseal level measuring techrotegy
sahich has proven reliable and is uniquely suited
‘or extremes in process vonditia ns as wll as
ambien: ewiranments,

It provides both POINT LEVEL and CONTINU-
US LEVEL measurement

Itmeasiras all fo.r maternal types" LIQUINS,
GRANDLARS, SLURRIES, and INTERFACES.

Itpertorns these tasks under pracess conditions
ranging fram vacuum to 10,000 PSI, and tan
peratures of <300°F to +1000°F

Itmekes ne measurement independent of vase
fiowsin DENSITY, CHEMICAL COMPOSITION,
ard ELECTRICAL PROPERTIES.

Itie sate, proven, easy to epecify, and cost
sernpetitve. THIS TECHNOLOGY 1S
RADIO FREQUENCY ADMITTANCE

Itis imporant nat o confuse RADIO FRE:
QUENCY ADANTTANCE with its iook alike”
CAPACITANCE level measurement, which is
sirilar to comparing caleu'stors 7o PCs. Bota
Ceacu ator and a PC wil do the easy jobs, but only
the FC, propery programmed, wilt provide a
efficient solution fo a complex problem. Similarly
‘only RT ADMITTANCE wl cefeviate the reat level
rmeasungmait inthe presence of widefined and
Lncont‘ofied varlables. Despke coating buidups,
ar changes in density, arelectrcal properties, the
RF level neasuremert will net be affectec, even
if are acting at tha sametime.
Introduction

WHAT MAKES A LEVEL TECHNOLOGY
UNIVERSAL?

To quality as 4 un'versal eve" tachnology, there:
are a number of :mportant cnter'a which mus: be
ret. The first test :s the abilly to measure both

paint level (an/of) and continucus level fanaing,
‘ypioaly 4-20 mA).

POINT LEVEL measurements, as the name sug-
gests, ae hove which ‘ndicate whettwr tha mate
fia level nas risen or faler to some aredeter-
rmined point in the vessel. Same typical ex-
amples of thesa measuremants are ‘over-fl"
protectian, pump: cavitation pfotec:ion, pump start
and stop contral. and “pugged shute" detector.
Historically, she output ode of a acintlevel
‘ontrol haz baen ane ar more pairs of DPOT dry
relay contacts. However, the trend is cortirually
roving in the direction of a switched change
Detsteen high and low current in the 4-20 mA
range. Ihis currsnt change is en transmitted to
a receiver in the control roam which may bea
process controler, PLC, of other simifar

device. The receiver then converts the current
signal ten alarm ar control acon. A universal
Point level cevice should be able to provide ettuer
utputmede.

CONTINUGUS LEVEL measurerrmnts a1 ne
ther hard, provide a cantinuaus reading of the
actual natetial [evel in a vessel. The cutput
rode of a continuous level measurements
typically a 4-20 ev signal that is proportional io
the level. Because users frequentiv want the
information in their ures of choice, the continuous
lave! signal should indicate how many ‘est of

lave. of galons (va.ume} oF pounds fweight) are
Present. Obviously, a successful leve' technology
wll be able to provide (he ariswers in the miost
Useful form, Whe a 4-20 ma elgnalts stl the
rast comman format for this clags cf nstrumen-
talion, other forms such as the digtal formats of
3-232 and 422 and the not yet fnaizad
Fieldbus, ara gaining acceptance as w= move
toward increased automation

MATERIAL TYPES

Tre second test of univarsalty isthe abilty of the
technolagy to measure all fou types of materials
{ound ir industry ‘oday. The four fypes of mater
als areas, granulas, sluries, and hiterface

PROCESS CONDITIONS

“Thos third suet of univerwabty isthe ability so rmaa-
sure level under tha wide ranga of pracass condl-
tions commenly found im industry. The conditions
‘of mast concern are: temperature. pressure, agi-
tation, carrosior (chemical compatbity), foam=
ing, explosien hazards, and potentialy lethal
materials

PHYSICAL AND CHEMICAL PROPERTIES

‘Tre fount testof urivarsalty ls makrig a mea
surement independent at changas in material
densty, shernical compasition, buid-up, viscosity.
of elect’cal propertias. Certain technologies
depend on some af these specife properties te
make their measurements and are, therefore,
‘seneitive to changes in ham.

WHAT IS RF ADMITTANCE? WHY IS ITA
UNIVERSAL TECHNOLOGY?

RF ADMITTANCE is @ universal technology
bbeeatiee when maasuing level tis measuring
‘something comman to everything in the universe.
Allthings, even a vacuum, have an alactcal
property called DIELECTRIC CONSTANT (k).
‘The other electrical propery is conductivity (a)
\Which is the nemesis of CAPAC TANCE tevel
measuremant

RADIO FREQUENCY ADMITTANCE is a tech
nology that takes both properies into account
‘when computing the level. The measurement :s
mada at a predetermined radio frequency rate.
‘That feaquancy ie usually betwaen 15 Khz and
400 Khe. Hace the narie RADIO FREQUENCY
ADMITTANCE.

For information on how more materials affect the
rmeasurerient, see the section cn “Properties of
Materials

420-1-891 39.