Fluke FPG8601 User Manual
FPG8601™/VLPC™
Operation and Maintenance Manual
© 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
High pressure liquids and gases are potentially hazardous. Energy stored in these liquids and gases
can be released unexpectedly and with extreme force. High pressure systems should be assembled and
operated only by personnel who have been instructed in proper safety practices.
© 2007 DH Instruments, a Fluke Company All rights reserved.
Information in this document is subject to change without notice. No part of this document may be reproduced or transmitted in any
form or by any means, electronic or mechanical, for any purpose, without the express written permission of DH Instruments, a
Fluke Company 4765 East Beautiful Lane Phoenix Arizona 85044-5318 USA.
DH Instruments makes sincere efforts to ensure the accuracy and quality of its’ published materials; however, no warranty,
expressed or implied, is provided. DH Instruments disclaims any responsibility or liability for any direct or indirect damages
resulting from the use of the information in this manual or products described in it. Mention of any product or brand does not
constitute an endorsement by DH Instruments of that product or brand. This manual was originally composed in English and was
subsequently translated into other languages. The fidelity of the translation cannot be guaranteed. In case of conflict between the
English version and other language versions, the English version predominates.
DH Instruments, DH, DHI, PG7000 and CalTool are trademarks, registered and otherwise, of DH Instruments, a Fluke Company.
Swagelok is a registered trademark of the Swagelok Company
Krytox is a trademark of the Dupont de Nemours Company
Document No. 550122e
060105
Printed in the USA
© 2007 DH Instruments, a Fluke Company
TABLES AND FIGURES
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TABLE OF CONTENTS .............................................................III
TABLES................................................................................VII
FIGURES..............................................................................VIII
ABOUT THIS MANUAL.............................................................XI
1. INTRODUCTION
1.1 OVERVIEW..............................................................................................................................................1
1.2 REQUIREMENTS.....................................................................................................................................2
1.3 SPECIFICATIONS....................................................................................................................................2
1.3.1 GENERAL SPECIFICATIONS.......................................................................................................................2
1.3.1.1 FPG8601 GENERAL SPECIFICATIONS...................................................................................................2
1.3.1.2 AMBIENT AND INSTRUMENT CONDITION MEASUREMENTS..............................................................3
1.3.1.3 PISTON-CYLINDER...................................................................................................................................3
1.3.1.4 PRESSURE MEASUREMENT...................................................................................................................3
1.3.2 VLPC GENERAL SPECIFICATIONS............................................................................................................4
1.4 FPG PLATFORM FRONT AND REAR PANELS AND VLPC FRONT AND REAR PANELS.................5
1.4.1 TERMINAL FRONT AND REAR PANELS....................................................................................................5
1.4.1.1 FPG TERMINAL FRONT PANEL...............................................................................................................5
1.4.1.2 FPG TERMINAL REAR PANEL .................................................................................................................6
1.4.2 FPG PLATFORM FRONT VIEW ...................................................................................................................7
1.4.3 FPG PLATFORM BACK VIEW .....................................................................................................................8
1.4.3.1 VLPC REAR PANEL ASSEMBLY..............................................................................................................9
................................................................. 1
2. FPG THEORY OF OPERATION ........................................... 11
2.1 OVERVIEW............................................................................................................................................ 11
2.2 PISTON-CYLINDER...............................................................................................................................11
2.3 LOAD CELL...........................................................................................................................................13
2.4 LUBRICATION PRESSURE..................................................................................................................14
2.5 VACUUM REFERENCE PRESSURE....................................................................................................14
2.6 SIMPLIFIED FORMULA FOR CALCULATING DIFFERENTIAL PRESSURE......................................15
2.6.1 REFERENCE LEVEL...................................................................................................................................16
2.7 CORRECTIONS.....................................................................................................................................16
2.7.1 δN1...............................................................................................................................................................16
2.7.2 δN2...............................................................................................................................................................16
2.7.3 δN3...............................................................................................................................................................17
2.8 COMPLETE DIFFERENTIAL PRESSURE EQUATION ........................................................................ 18
3. VLPC THEORY OF OPERATION.......................................... 19
3.1 OVERVIEW............................................................................................................................................ 19
3.2 SUPPLY AND REGULATION................................................................................................................20
3.3 FLOW CONTROL..................................................................................................................................20
3.4 RANGE RESTRICTIONS.......................................................................................................................21
3.5 CONTROL..............................................................................................................................................21
3.6 READY/NOT READY.............................................................................................................................22
Page III © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
4. GETTING STARTED .......................................................... 23
4.1 OVERVIEW............................................................................................................................................ 23
4.2 INSTALLING FPG TOOLS ....................................................................................................................23
4.3 SETTING UP FPG TOOLS ....................................................................................................................24
4.4 BASIC FPG HARDWARE SETUP.........................................................................................................25
4.5 SETTING UP THE PISTON-CYLINDER................................................................................................26
4.6 CONNECTING THE FPG MANIFOLD AND VALVES...........................................................................26
4.7 SETTING UP THE FPG FOR OPERATION...........................................................................................28
4.8 SETTING UP THE VLPC .......................................................................................................................29
4.9 INTRODUCING GAS TO THE FPG.......................................................................................................29
4.10 CONNECTING A DUT............................................................................................................................30
4.10.1 GAUGE MODE.............................................................................................................................................30
4.10.2 ABSOLUTE MODE......................................................................................................................................30
4.10.3 ABSOLUTE DIFFERENTIAL MODE...........................................................................................................31
4.11 CONNECTING THE DUT MANIFOLD...................................................................................................32
4.11.1 SETTING UP THE TURBO PUMP ..............................................................................................................33
4.11.2 CONNECTING THE ION GAUGE ...............................................................................................................33
4.12 CHANGING LUBRICATION GAS..........................................................................................................34
4.12.1 PURGING THE LUBRICATING VOLUME WITH A NEW GAS ................................................34
4.12.2 PURGING THE TEST PORT.......................................................................................................................35
5. SYSTEM OPERATION........................................................ 37
5.1 OVERVIEW............................................................................................................................................ 37
5.2 ZEROING THE FPG...............................................................................................................................37
5.2.1 ZERO CONDITION ......................................................................................................................................37
5.2.2 STABILITY TEST.........................................................................................................................................38
5.2.3 STORE ZERO DATA...................................................................................................................................38
5.3 INTERNAL CALIBRATION....................................................................................................................38
5.3.1 DETERMINING CALIBRATION MASS VALUE..........................................................................................38
5.3.2 ACTIVATING NEW CALIBRATION ............................................................................................................39
5.4 SETTING A MEASUREMENT MODE....................................................................................................41
5.5 USING A DUT WITH FPG TOOLS.........................................................................................................41
5.6 ZEROING THE DUT MANIFOLD...........................................................................................................42
5.7 CHANGING PRESSURE WITH THE VLPC...........................................................................................42
5.7.1 SETTING 0 PRESSURE..............................................................................................................................43
5.8 LOGGING DATA WITH THE FPG.........................................................................................................43
5.9 SHUTTING DOWN THE FPG ................................................................................................................44
6. FPG TOOLS ..................................................................... 45
6.1 OVERVIEW............................................................................................................................................ 45
6.2 MAIN MENU...........................................................................................................................................46
6.3 MAIN DISPLAY ......................................................................................................................................46
6.3.1 STATUS BAR ..............................................................................................................................................47
6.3.2 RUN DISPLAY.............................................................................................................................................47
6.3.3 TARE DISPLAY...........................................................................................................................................49
6.3.4 PLOT DISPLAY ...........................................................................................................................................50
6.3.4.1 CUSTOM PLOTS .....................................................................................................................................50
6.3.4.2 STRIP CHARTS .......................................................................................................................................51
6.3.5 LOGGED DATA...........................................................................................................................................52
6.3.6 VLPC CONTROL.........................................................................................................................................54
6.3.7 RUN DIAGNOSTICS....................................................................................................................................56
6.3.8 DUT MANIFOLD..........................................................................................................................................59
6.4 TOOLBARS ...........................................................................................................................................60
6.4.1 WINDOW DISPLAY TOOLBAR ..................................................................................................................60
6.4.2 FUNCTIONS TOOLBAR..............................................................................................................................61
6.4.3 VALVE CONTROL.......................................................................................................................................64
© 2007 DH Instruments, a Fluke Company Page IV
TABLES AND FIGURES
6.5 [RUN] .....................................................................................................................................................65
6.5.1 RUN MODE INITIALIZATION......................................................................................................................65
6.5.2 [RUN MONITOR] .........................................................................................................................................66
6.5.3 [RUN W/POINT LOG]..................................................................................................................................66
6.5.4 [RUN TEST SEQUENCE]............................................................................................................................66
6.6 [CONFIG]...............................................................................................................................................68
6.6.1 [SETTINGS].................................................................................................................................................68
6.6.2 [SYSTEM SETUP] .......................................................................................................................................69
6.6.2.1 <SETUP> .................................................................................................................................................69
6.6.2.2 <OPTIONS> .............................................................................................................................................70
6.6.2.3 <DATA FILE> ...........................................................................................................................................72
6.6.3 [FPG CALIBRATION SETUP].....................................................................................................................73
6.6.4 [INTERNAL LIMITS]....................................................................................................................................75
6.6.4.1 <SETUP> .................................................................................................................................................75
6.6.4.2 <PRESSURE> .........................................................................................................................................76
6.6.4.3 <TEMPERATURE> ..................................................................................................................................77
6.6.4.4 <HUMIDITY>............................................................................................................................................78
6.6.4.5 <MASS> ...................................................................................................................................................79
6.6.4.6 <PURGE> ................................................................................................................................................80
6.6.4.7 <VLPC>.................................................................................................................................................... 81
6.6.5 [DUT SELECTION]......................................................................................................................................83
6.7 TEST SEQUENCE EDITOR...................................................................................................................84
6.7.1 TOOLBAR....................................................................................................................................................84
6.7.2 <POINTS> TABLE.......................................................................................................................................85
6.7.3 [POINTS] TAB .............................................................................................................................................87
6.7.4 <SEQUENCE> TAB.....................................................................................................................................88
6.7.5 <CONTROL> TAB.......................................................................................................................................89
6.7.6 <CYCLE> TAB.............................................................................................................................................90
6.8 DUT DEFINITION EDITOR ....................................................................................................................91
6.8.1 TOOLBAR....................................................................................................................................................91
6.8.2 DUT DEFINITION SELECTOR....................................................................................................................92
6.8.2.1 [HEADER] TAB ........................................................................................................................................93
6.8.2.2 [CORRECTION] TAB ...............................................................................................................................94
6.8.2.3 [RANGE] TAB...........................................................................................................................................95
6.8.2.4 [TOLERANCE] TAB .................................................................................................................................96
6.8.2.5 [READ] TAB .............................................................................................................................................97
6.8.2.6 REMOTE COMMAND EDITOR ...............................................................................................................99
6.9 [UNITS] ................................................................................................................................................102
6.9.1 [USER DEFINED UNITS] ..........................................................................................................................102
6.9.2 [ABSOLUTE MODE], [GAUGE MODE]....................................................................................................103
6.9.2.1 [GAUGE MODE].....................................................................................................................................103
6.9.2.2 [ABSOLUTE MODE] ..............................................................................................................................104
6.10 [CHANGE USER LEVEL]....................................................................................................................104
6.11 [TOOLS]...............................................................................................................................................105
6.11.1 [REMOTE COMMUNICATIONS]...............................................................................................................105
6.12 INTERNATIONAL ISSUES ..................................................................................................................105
7. PISTON-CYLINDER MAINTENANCE ...................................107
7.1 OVERVIEW..........................................................................................................................................107
7.2 REMOVING THE PISTON-CYLINDER FROM THE MOUNTING POST .............................................109
7.3 REMOVING THE PISTON FROM THE CYLINDER.............................................................................111
7.4 CLEANING THE PISTON AND CYLINDER ........................................................................................112
7.5 PUTTING THE PISTON INTO THE CYLINDER...................................................................................113
7.6 INS T A L L IN G T H E P I S TO N - C Y L I ND E R I N T HE M O U N TI N G P O S T ............................................114
7.7 RESTORING PISTON-CYLINDER LUBRICATION AND MOBILITY..................................................115
7.7.1 OVERVIEW................................................................................................................................................115
7.7.2 PISTON CENTERING AND LUBRICATING METHODS ..........................................................................115
7.8 DETERMINING EFFECTIVE AREA..................................................................................................... 117
7.8.1 SETTING UP THE SYSTEM......................................................................................................................117
7.8.2 GENERATING A PRESSURE...................................................................................................................118
7.8.3 ADJUSTING THE NEEDLE VALVE..........................................................................................................118
7.8.4 TAKING DATA (FOR EACH PRESSURE)................................................................................................119
7.8.5 CALCULATING THE EFFECTIVE AREA .................................................................................................119
Page V © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
8. GENERAL MAINTENANCE ................................................121
8.1 OVERVIEW..........................................................................................................................................121
8.2 REFILLING THE BUBBLER ON THE FPG.........................................................................................121
8.3 ZEROING THE VACUUM SENSOR....................................................................................................122
8.3.1 SET – UP....................................................................................................................................................123
8.3.2 WARM-UP..................................................................................................................................................123
8.3.3 TEST THE ZERO OF THE VACUUM SENSOR........................................................................................123
8.4 CALIBRATING THE INTERNAL CALIBRATION MASS.....................................................................125
8.4.1 INITIAL PREPARATIONS .........................................................................................................................125
8.4.2 REMOVE THE LOAD CELL COVER ........................................................................................................125
8.4.3 REMOVE THE CALIBRATION MASS AND DRIVE..................................................................................126
8.4.4 DETERMINE THE TRUE MASS VALUE OF THE INTERNAL CALIBRATION MASS............................126
8.4.5 PUT THE MASS BACK INTO THE DRIVE ASSEMBLY ..........................................................................127
8.4.6 REATTACH THE LOAD CELL COVER....................................................................................................127
8.4.7 FINAL STEPS............................................................................................................................................127
8.5 MOUNTING POST PRT CALIBRATION..............................................................................................128
8.5.1 REMOVE THE PRTS.................................................................................................................................128
8.5.2 CREATE THE PRT CABLE ADAPTER ....................................................................................................128
8.5.3 DETERMINE THE RO VALUE ..................................................................................................................129
8.5.4 ENTER THE RO VALUE INTO THE FPG TERMINAL..............................................................................129
8.5.5 REATTACH THE PRTS TO THE FPG ......................................................................................................130
8.6 PREPARING FOR STORAGE / SHIPMENT........................................................................................130
8.6.1 FPG8601....................................................................................................................................................130
8.6.2 VLPC..........................................................................................................................................................130
8.6.3 3-DUT MANIFOLD.....................................................................................................................................131
9. DATA FILES ...................................................................133
9.1 OVERVIEW..........................................................................................................................................133
9.2 POINT LOG DATA FILE (*.DAT).........................................................................................................133
9.2.1 NAMING AND STORING DATA FILES ....................................................................................................133
9.2.2 FILE FORMAT ...........................................................................................................................................133
9.3 INTERNAL CALIBRATION LOG FILE................................................................................................133
9.4 SYSTEM ZERO LOG FILE ..................................................................................................................134
9.5 ERROR LOG FILE...............................................................................................................................134
10. TROUBLESHOOTING .......................................................135
10.1 OVERVIEW ..........................................................................................................................................135
11. APPENDIX ......................................................................137
11.1 INTERNAL VALVES............................................................................................................................137
11.2 UNIT CONVERSIONS..........................................................................................................................139
11.3 FPG8601 PRESSURE CALCULATIONS ............................................................................................140
11.3.1 COMPENSATED PRESSURES ................................................................................................................140
11.3.2 DIFFERENTIAL PRESSURES ..................................................................................................................140
11.3.3 CORRECTI ON TE RMS..............................................................................................................................140
11.3.4 THERMAL TRANSPIRATION CORRECTION..........................................................................................141
11.3.5 SAMPLE CALCULATIONS.......................................................................................................................144
11.3.5.1 GAUGE PRESSURE..............................................................................................................................144
11.3.5.2 ABSOLUTE PRESSURE .......................................................................................................................145
11.3.5.3 ABSOLUTE DIFFERENTIAL PRESSURE.............................................................................................146
11.3.5.4 INTERNAL CALIBRATION (KCAL)........................................................................................................147
11.4 DECLARATION OF CONFORMITY..................................................................................................... 147
11.5 GROUNDING / ELECTRICAL SCHEMATICS.....................................................................................147
11.5.1 SYSTEM LEVEL GROUNDING.................................................................................................................148
11.5.2 FPG GROUN D DIAGRAM.........................................................................................................................149
11.5.3 VLPC POWER DIAGRAM.........................................................................................................................150
12. WARRANTY STATEMENT .................................................151
13. GLOSSARY
© 2007 DH Instruments, a Fluke Company Page VI
.....................................................................153
TABLES AND FIGURES
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Table 1. Nominal VLPC
Table 2. Nominal VLPC Ranges, 15 kPa Unit ........................................................................................... 21
Table 3. Equipment for Basic FPG Hardware Setup ................................................................................ 25
Table 4. Internal Calibration Results Options ............................................................................................40
Table 5. <Run Display> Labels.................................................................................................................. 48
Table 6. <Tare Display> Labels ................................................................................................................. 49
Table 7. <Custom Plot Properties> Tab Fields .......................................................................................... 51
Table 8. <Logged Points> Labels .............................................................................................................. 53
Table 9. <VLPC Interface> Options ........................................................................................................... 55
Table 10. <Diagnostics Display> Options.................................................................................................. 56
Table 11. <DUT Manifold> Color Scheme ................................................................................................. 59
Table 12. <DUT Manifold> Display ............................................................................................................ 60
Table 13. Window Display Toolbar Options............................................................................................... 61
Table 14. Functions Toolbar Option........................................................................................................... 61
Table 15. System Settings ......................................................................................................................... 68
Table 16. <System Setup><Setup> Options .............................................................................................69
Table 17. <System Setup><Options> Options .......................................................................................... 71
Table 18. <Options>, <Data File> Tab Fields............................................................................................ 72
Table 19. <FPG8601 Calibration Setup> Options ..................................................................................... 74
Table 20. <Internal Limits> <Setup> Options ............................................................................................75
Table 21. <Internal Limits> <Pressure> Options .......................................................................................77
Table 22. <Internal Limits> <Temperature> Options ................................................................................. 78
Table 23. <Internal Limits> <Humidity> Options........................................................................................ 79
Table 24. <Internal Limits> <Mass> Options ............................................................................................. 80
Table 25. <Internal Limits> <Purge> Options ............................................................................................ 81
Table 26. <Internal Limits> <VLPC> Options ............................................................................................ 82
Table 27. <DUT Selection & I/O Setup> Options....................................................................................... 83
Table 28. Test Sequence Editor, <Toolbar> Options ................................................................................ 84
Table 29. Test Sequence Editor, <Points> Options................................................................................... 86
Table 30. Test Sequence Editor, <Points> Tab Fields .............................................................................. 87
Table 31. Test Sequence Editor, <Sequence> Tab Fields ........................................................................ 88
Table 32. Test Sequence Editor, <Control> Tab Fields............................................................................. 89
Table 33. Test Sequence Editor, <Cycle> Tab Fields ............................................................................... 90
Table 34. DUT Definition Editor, <Toolbar> Features ............................................................................... 91
Table 35. DUT Definition Editor, [Header] Tab Fields ............................................................................... 93
Table 36. DUT Definition Editor, [Correction] Tab Fields........................................................................... 94
Table 37. DUT Definition Editor, [Range] Tab Fields................................................................................. 95
Table 38. DUT Definition Editor, [Tolerance] Tab Fields ........................................................................... 97
Table 39. DUT Definition Editor, [Read] Tab Fields................................................................................... 98
Table 40. Piston-Cylinder Maintenance Equipment................................................................................. 107
Table 41. Effective Area Calculation Variables........................................................................................ 119
Table 42. Sample Effective Area Spread Sheet ...................................................................................... 120
Table 43. Bubbler Maintenance Equipment............................................................................................. 121
Table 44. Vacuum Reference Zeroing Equipment List ............................................................................ 122
Table 45. Vacuum Reference Zeroing Equipment List ............................................................................ 125
Table 46. Effective Area Calculation Variables........................................................................................ 127
Table 47. PRT Calibration Cable Connections ........................................................................................ 128
Table 48. Effective Area Calculation Variables........................................................................................ 129
S
Ranges ................................................................................................................ 19
Page VII © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
Table 49. Troubleshooting Tips ............................................................................................................... 135
Table 50. Internal Valve Descriptions ...................................................................................................... 138
Table 51. Unit Conversion Factors .......................................................................................................... 139
Table 52. FPG Defined Pressure Calculation Variables.......................................................................... 142
Table 53. DHI Authorized Service Providers ...........................................................................................151
F
IIGGUURREES
F
Figure 1. FPG8601 Terminal Front Panel.................................................................................................... 5
Figure 2. FPG8601 Terminal Rear Panel
Figure 3. FPG Platform Front View
Figure 4. FPG Platform Back
Figure 5. VLPC Rear Panel.......................................................................................................................... 9
Figure 6. Piston-cylinder Lubric
Figure 7. Internal Calibrat
Figure 8. FPG Forc
Figure 9. Gauge Mode VLPC Block Diagram
Figure 10. Absolute Mode VLPC Bloc
Figure 11. VLPC Ready Criterion
Figure 12. FPG8601 Syst
Figure 13. FPG8601 Mani
Figure 14. Internal Calibration Res
Figure 15. FPG Tools
Figure 16. <Status
Figure 17. <Run Display>
Figure 18. <Tare Display
Figure 19. <Plot Data>
Figure 20. <Custom Plot Properties>
Figure 21. <Logged Point
Figure 22. <VLPC Interfac
Figure 23. <Select VLPC
Figure 24. <Diagnos
Figure 25. Window Dis
Figure 26. Window Dis
Figure 27. Manual Valve Control Tool
Figure 28. <Settings
Figure 29. <System Setup><
Figure 30. <System Setup><
Figure 31. <System Setup>
Figure 32. <FPG8601 Calibration Setup>
Figure 33. <Internal Limits>
Figure 34. <Internal Limits>
Figure 35. <Internal Limits>
Figure 36. <Internal Limits>
Figure 37. <Internal Limits>
Figure 38. <Internal Limits>
Figure 39. <Internal Limits>
Figure 40. <DUT Selec
Figure 41. Test Sequence Editor, <Tool
Figure 42. Test Sequence Editor, <Test Points> Tabl
Figure 43. Test Sequence Editor, <Points> Tab
Figure 44. Test Definition Editor, <
S
.................................................................................................... 6
.............................................................................................................. 7
View .............................................................................................................. 8
ating Flow ................................................................................................. 12
ion Mass Alignment........................................................................................... 13
es................................................................................................................................. 17
............................................................................................ 20
k Diagram....................................................................................... 20
.............................................................................................................. 22
em Schematic.................................................................................................... 23
fold Connection................................................................................................. 27
ults Window......................................................................................... 39
(Factory Mode) ....................................................................................................... 46
Bar> ............................................................................................................................. 47
.......................................................................................................................... 47
>.......................................................................................................................... 49
............................................................................................................................... 50
......................................................................................................... 51
s> Display.......................................................................................................... 52
e> ..................................................................................................................... 55
Range>.............................................................................................................. 55
tics Display> .............................................................................................................. 56
play Toolbar ........................................................................................................... 59
play Toolbar ........................................................................................................... 60
bar .................................................................................................. 65
>................................................................................................................................. 68
Setup> Tab .................................................................................................. 69
Interface> ..................................................................................................... 71
, <Data File> Tab ...........................................................................................72
.................................................................................................. 74
<Setup>......................................................................................................... 75
<Pressure>.................................................................................................... 76
<Temperature> .............................................................................................78
<Humidity> .................................................................................................... 79
<Mass> ......................................................................................................... 80
<Purge> ........................................................................................................ 81
<VLPC>......................................................................................................... 82
tion & I/O Setup>................................................................................................... 83
bar>............................................................................................. 84
e............................................................................. 85
........................................................................................ 87
Control> Tab ....................................................................................... 89
© 2007 DH Instruments, a Fluke Company Page VIII
TABLES AND FIGURES
Figure 45. Test Definition Editor, <Cycle> Tab .......................................................................................... 90
Figure 46. DUT Definition Editor, <
Figure 47. <DUT Selec
tion> Tool .............................................................................................................. 93
Figure 48. DUT Definition Editor, [Header Tab
Figure 49. DUT Definition Editor, [Correc
Figure 50. DUT Definition Editor, [Range] Tab
Figure 51. DUT Definition Editor, [Tolerance] Tab
Figure 52. DUT Definition Editor, [Read]
Figure 53. <Insert Speci
al Character> Panel............................................................................................. 99
Figure 54. <Initialization Commands
Figure 55. <Read Com
mands Editor> Panel........................................................................................... 101
Figure 56. <RS232 Settings> Panel
Figure 57. <User Defined Unit Setup>
Figure 58. <Remote Communications
Figure 59. FPG8601 Piston Assembly in
Figure 60. Removing the Mounting Post
Figure 61. Removing the Pis
Figure 62. Alignment of the FPG pis
Figure 63. FPG8601 and PG7000 Cross
Figure 64. FPG8601 Bubbling System
Figure 65. Calibration Mas
s Drive Assembly ........................................................................................... 126
Figure 66. PRT Calibration Cable Adaptor
Figure 67. FPG Internal V
alve Configuration........................................................................................... 137
Toolbar>.............................................................................................. 91
.......................................................................................... 93
tion] Tab .................................................................................... 94
.......................................................................................... 95
..................................................................................... 96
Tab ............................................................................................ 97
Editor> Panel................................................................................. 100
........................................................................................................ 101
..................................................................................................... 102
> ................................................................................................... 105
Mounting Post......................................................................... 108
.................................................................................................. 110
ton............................................................................................................... 110
ton in the cylinder ........................................................................... 113
Float Setup ............................................................................. 117
.................................................................................................... 122
.............................................................................................. 128
Page IX © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
N
N
OOTTEES
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© 2007 DH Instruments, a Fluke Company Page X
ABOUT THIS MANUAL
A
BBOOUUTT
A
This manual provides the user with the information necessary to operate the FPG8601 system. It also
includes a great deal of additional information provided to help you optimize system use and take full
advantage of its many features and functions.
Realize that the numbers on the PC software screen captures and the VLPC range information are for
example purposes only. In some cases the information required to setup the FPG is installed with FPG
Tools. In other cases, the values must be entered into the FPG calibration setup (see Section 6.6.3).
Before u
All first time FPG users should read Section 2 for a comprehensive description of general operating
prin
10 to troubleshoot unexpected system behavior b
Certain words and expressions have specific meaning as they pertain to the FPG System. The Glossary
(see Section 13) is useful as a quick reference for exact definition of specific words and expressions as
they are used
sing the manual, take a moment to familiarize yourself with the Table of Contents structure.
ciples. Section 8 provides maintenance and calibration information. Use the inform
FOR THOSE OF YOU WHO “DON’T READ MANUALS”, GO DIRECTLY TO SECTION 4 TO SET UP YOUR
FPG SYSTEM. THEN GO TO SECTIONS 5 and 6. THIS WILL GET YOU RUNNING QUICKLY WITH
MINIMAL RISK OF CAUSING DAMAGE TO YOURSELF OR YOUR FPG. THEN… WHEN YOU HAVE
QUESTIONS OR START TO WONDER ABOUT ALL THE GREAT FEATURES YOU MIGHT BE MISSING, GET
INTO THE MANUAL!
T
T
in this manual.
HHIISS
M
AANNUUAAL
M
L
ased on the symptoms of that behavior.
ation in Section
Manual Conventions
(CAUTION) is used in throughout the manual to identify user warnings and cautions.
(NOTE) is used throughout the manual to identify operating and applications advice and additional
explanations.
[ ] indicates direct function keys or menu options (e.g., [Run]).
< > indicates FPG Tools screen displays (e.g., <FPG Pressure>).
Page XI © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
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© 2007 DH Instruments, a Fluke Company Page XII
1. INTRODUCTION
.
11.
I
NNTTRROODDUUCCTTIIOON
I
N
1.1 OVERVIEW
The FPG8601 (Force-Balanced Piston Gauge), VLPC (Very Low Pressure Controller) and FPG Tools
(PC Based Software) are used in conjunction to act as a high precision pressure measurement and data
acquisition system. Operator interaction with the FPG/VLPC and its extensive capabilities is accomplished
through the PC based software from a computer via a standard RS232 port. FPG Tools also provides
features to define a test sequence, read DUT’s with a standard RS232 or IEEE-488 output, and log data
to a data file.
FPG pressure is defined by using a high precision load cell to measure the force exerted on the effective
area of a piston-cylinder (see Section 2). Instead of rotating the piston like othe
provides sensitivity between the piston and cylinder by maintaining a constant flow through the annular
gap. This flow generates a centering force that prevents the piston from touching the cylinder during
normal operation. Noise normally associated with rotation is therefore not present.
FPG platforms are designed to maximize metrological performance and ease of operation in both gauge
and absolute modes. Many features are included to enhance the fundamental precision and stability of
pressure measurements as well as simplifying use and reducing the operator influence on the
measurements.
r piston gauges, the FPG
The VLPC generates low pressure in gauge and absolute modes (0 to 15 kPa). It is used to set and
stabilize pressure as read by the FPG so that the VLPC/FPG combination can be used to set user
specified target pressure values. The general operating principle of the VLPC is to generate a stable flow
through one of a number of restrictions depending on the range of pressure to be controlled (see Section
3.4). The pressure drop across the restriction is the controlled
FPG is used to dynamically readjust the flow to obtain the desired target pressure.
FPG Tools is the complete interface to both the FPG and the VLPC. An interface to all functional aspects
of both instruments is provided by the software. FPG Tools uses three basic modes of operation to
remotely interact with the FPG and VLPC: [Run Mode], [Run w/Point Logging], and [Run Test Sequence]
(see Section 6.5). These modes respectively allow simple monitoring of pressure, monitoring of pressure
with user dep
A DUT can be used in any run mode for real-time error determination and/or data acquisition.
endant steps and data acquisition, and monitoring with defined test steps and data acquisition.
differential pressure. Feedback from the
Page 1 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
1.2 REQUIREMENTS
FPG Tools is a PC based application designed for 32 bit versions of Windows. The PC requirements
stated below are necessary to maintain the minimum acceptable performance between the software and
related hardware components.
• Windows XP, 98, NT service pack 4 or greater
• 500 MHz Pentium Processor or compatible
• 32 Mb of Ram
• 12 Mb free hard drive space
1.3 SPECIFICATIONS
1.3.1 GENERAL SPECIFICATIONS
1.3.1.1 FPG8601 GENERAL SPECIFICATIONS
Power Requirements: 85 to 264 VAC, 50 to 60 Hz, 60 VA consumption
Operating Temperature:
Weight: Instrument platform
FPG Platform 31.2 kg (61 lb)
FPG Terminal 1.4 kg (3 lb)
Dimensions:
FPG Platform 53.4 cm H x 35.8 cm W x 35.5 cm D
FPG Terminal 12 cm H x 15 cm W x 20 cm D
Microprocessors:
Instrument Platform Motorola 68302
FPG Terminal Hitachi 64180
Communication Ports:
RS232
IEEE-488.2 Not used
Maximum Pressure Ranges: 0 – 15 kPa Gauge and Absolute
Operating Media: Gas: air or Nitrogen (N
Pressure Supplies: Lubrication port: 700 - 850 kPa (100 - 120 psi), supply
Drive In Supply: 600 to 1000 kPa (90 to 150 psi) air
Maximum Overpressure Limit: +20 kPa to –10 kPa (+3 to – 1.5 psi)
Pressure Connections:
Lubrication Supply Port
Upper Test Port
Lower Test Port
Drive In Port
Vacuum Port
CE Conformance: Not available
Driver Port (Ext Valve): Not used
15 to 35 °C
(21 in. H x 14.1 in. W x 14 in. D)
(4.7 in. H x 5.9 in. W x 7.9 in. D)
COM1: Host computer
COM2: VLPC
COM3: Not Used
)
2
must remain constant ± 1 % to meet control specifications
1/8 in. NPT
KF16
KF16
1/8 in. NPT
1/8 in. NPT
© 2007 DH Instruments, a Fluke Company Page 2
1. INTRODUCTION
1.3.1.2 AMBIENT AND INSTRUMENT CONDITION MEASUREMENTS
Temperature:
Range
Resolution
Accuracy
Relative Humidity:
Range
Resolution
Accuracy
Vacuum:
Range
Resolution
Accuracy
Ambient and Lubrication
Pressure Sensor:
Range
Resolution
Accuracy
Lubrication Pressure
[°C] [°C]
0 to 40 0 to 40
0.1 0.01
± 0.2 ± 0.1
5 to 95 %RH
1 %RH
± 10 %RH
13 Pa
1 mPa
± 20 mPa
200 kPa
1 Pa
± 0.1 kPa
1.3.1.3 PISTON-CYLINDER
Cylinder Material: Tungsten carbide
Piston Material: Tungsten carbide
Nominal Diameter: 35 mm
Nominal Area:
Mounting System: Non-rotative piston
980.5164 mm
Piston-Cylinder
2
1.3.1.4 PRESSURE MEASUREMENT
Resolution1: 10 mPa
Precision Reproducability
Uncertainty
Standard Measurement:
1. Resolution: The smallest variation in input detectable in output.
2. Reproducibility: Combined reproducibility of force measurement and long term stability of
piston-cylinder effective area.
3. Standard Measurement Uncertainty: All sources of uncertainty under typical operating
conditions are identified, quantified and combined following ISO/TAG4/WG3. The result is then
rounded upwards to provide conservative global figures for the typical user in typical conditions
of the maximum deviation from the true value of the pressure determined by the FPG8601 and
the pressure actually present at the test point.
2
:
± 20 mPa
3
:
Absolute: ± (25 mPa + 0.003 % of reading)
Gauge and absolute differential: ± (20 mPa + 0.003 %
of reading)
Page 3 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
1.3.2 VLPC GENERAL SPECIFICATIONS
Power Requirements: 85 to 264 VAC, 47 to 60 Hz, 70 VA max. consumption
Operating Temperature Range: 15 to 35 °C
Storage Temperature Range: - 20 to 70 °C
Weight: 41.6 kg (91.5 lb)
Dimensions: 30.5 cm H x 53.4 cm W x 50.5 cm D
Microprocessor: Motorola 68302, 16 MHz
Communication Ports:
RS232
IEEE-488.2
Control Specifications:
Operating Medium: Gas: air or Nitrogen (N
Pressure Supplies: SUPPLY port: 700 - 850 kPa (100 - 120 psi), supply must remain
Drive Air Supply: 600 to 1000 kPa (90 to 150 psi) air
Pressure Connections: Test (Lo) 1/4 VCO
(12 in. H x 21 in. W x 19.9 in. D)
COM1: FPG
COM2:: Not Used
Not used
± 0.02 Pa + 30 ppm of range selected
constant ± 1 % to meet control specifications
Test (Hi) 1/4 VCO
ATM 1/4 VCO
Vacuum 3/8 VCO
Supply 1/8 NPT F
Drive 1/8 NPT F
)
2
© 2007 DH Instruments, a Fluke Company Page 4
1. INTRODUCTION
1.4 FPG PLATFORM FRONT AND REAR PANELS AND VLPC FRONT AND REAR PANELS
1.4.1 TERMINAL FRONT AND REAR PANELS
1.4.1.1 FPG TERMINAL FRONT PANEL
The front panel assembly provides a 2 x 20 vacuum fluorescent display and a 4 x 4
membrane keypad for local user interface.
1. Display
2. Multi-Function Keypad
Figure 1. FPG8601 Terminal Front Panel
Page 5 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
1.4.1.2 FPG TERMINAL REAR PANEL
The rear panel assembly provides the communications connection to the FPG
platform and the power connection module.
1. Power Switch
2. Fuse
3. Power Receptacle
4. Connector for Cable to
FPG (25 pin
5. Cooling Fan
Figure 2. FPG8601 Terminal Rear Panel
© 2007 DH Instruments, a Fluke Company Page 6
1. INTRODUCTION
1.4.2 FPG PLATFORM FRONT VIEW
The front of the FPG provides the connections to the VLPC, DUT and vacuum sensor. It also
provides the electrical connection to the mounting post PRTs and vacuum sensor reading.
1. Upper Mounting Post
2. TEST+ (KF-16)
3. Mounting Post PRT Connector
4. TEST- (KF-16)
5. Lower Mounting Post
Figure 3. FPG Platform Front View
Page 7 © 2007 DH Instruments, a Fluke Company
6. Vacuum Reference Port (KF-25)
7. Mounting Post Reference
8. Vacuum Sensor Connector
9. Vacuum Sensor Port
10. Reference Level
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
1.4.3 FPG PLATFORM BACK VIEW
The FPG platform rear panels provide the connection to the FPG Terminal, remote
communication connections and supply pressure connection ports.
1. COM2 (RS232) – VLPC
2. COM1 (RS232) – Remote Host
Communication
3. IEEE-488 – Not Used
4. Absolute Mode – Lubrication
Pressure Vacuum
5. Bubbler
Figure 4. FPG Platform Back View
© 2007 DH Instruments, a Fluke Company Page 8
6. Lubrication Supply
7. Drive In
8. Coalescing Filter
9. Drivers Option Connector Not Used
10. COM3 (RS232) – Not Used
11. FPG Terminal Port
1. INTRODUCTION
1.4.3.1 VLPC REAR PANEL ASSEM BLY
The rear panel assembly provides pressure connections, communications
interfaces, the power ON/OFF module and product labeling. Pressure fittings are
internally secured to prevent loosening when making and breaking connections.
1. IEEE-488 Connector – Not Available
2. Fan
3. Power Switch
4. Label, Product
5. Pressure Connection – Drive
6. Pressure Connection – Supply
Figure 5. VLPC Rear Panel
7. Pressure Connection – Test (Hi)
8. Pressure Connection – FPG
Vacuum
9. Pass Through – ATM Ref
10. Pressure Connection – Test (Lo)
11. COM1 (RS232) – To FPG
12. COM2 (RS232) – Not Used
Page 9 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
N
N
OOTTEES
S
© 2007 DH Instruments, a Fluke Company Page 10
2. FPG THEORY OF OPERATION
.
22.
G
FFPPG
T
HHEEOORRYY OOFF
T
O
PPEERRAATTIIOON
O
N
2.1 OVERVIEW
The FPG measures low gauge and absolute pressure by using a load cell to measure the force on the
effective area of a 35 mm piston. A measurement mode specific lubricating pressure is applied to the
annular gap of the piston-cylinder to provide a centering force on the piston. Compensation for the
effects of the lubrication pressure on the load cell and piston are determined during the
manufacturing process. The output of the load cell combined with the force components associated with
the lubrication pressure determines the total force on the piston. This force divided by the temperature
corrected effective area of the piston determines the differential pressure of the FPG.
In gauge mode, the FPG differential pressure is equivalent to the gauge pressure of the system since the
lower port of the FPG is exposed to atmosphere. In absolute mode, the lower port of the FPG is
connected to vacuum. Because of the lubricating flow, a perfect vacuum can never be achieved;
therefore a high precision low range vacuum reference sensor is used to measure the residual
vacuum pressure. This pressure is applied to the FPG differential pressure to obtain the final system
absolute pressure. Absolute differential operation of the FPG is the same as absolute mode operation
without the use of the vacuum reference sensor.
To support automatic zeroing and calibration of the FPG the mounting post assembly contains several
pneumatic valves that are automatically controlled by FPG Tools. Many internal sensors are also present
to verify that the FPG is operating in the required conditions and to make pressure buoyancy corrections.
2.2 PISTON-CYLINDER
The FPG uses a 35 mm diameter, tungsten carbide piston-cylinder designed with a pressure to mass
conversion coefficient of 10 kPa/kg. The cylinder has a conical shape on its interior surface to generate a
centering force on the piston when a lubrication pressure is applied in the annular gap through the center
of the cylinder (see Figure 6). The non-rotating piston is conne
freedom mechanical assembly located at its center of gravity. This allows the piston to center itself in the
cylinder under the influence of the lubricating pressure. As a result, the piston is perfectly mobile, making
no contact with the cylinder.
cted to the load cell by a multi degree of
Page 11 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
LUBRICATING
SUPPLY
REG
FLOW
MASS
COMPARATOR
P
hi
P
lub
P
ref
Figure 6. Piston-cylinder Lubricating Flow
The piston-cylinder resides in the mounting post that provides upper and lower measurement chambers
equipped with high pressure (P
) and low pressure (P
hi
) connections at the two extremities of the
ref
piston-cylinder. The high pressure port is the measurement port of the FPG. The low pressure port is
considered the reference port of the system. When the port is exposed to atmosphere, the FPG will read
gauge pressure. If the port is exposed to vacuum, the FPG will measure absolute differential pressure.
The measured value of the low pressure port must be applied to the FPG differential pressure to get an
absolute pressure.
© 2007 DH Instruments, a Fluke Company Page 12
2. FPG THEORY OF OPERATION
2.3 LOAD CELL
The load cell has a measurement capacity equivalent to 2 300 g with a resolution of 1 mg. A force
equivalent to 1 500 g is used for the measuring range. The rest of the measurement capacity is used to
compensate for the mass of the piston and its carriage assembly.
During the manufacturing process, the load cell is calibrated and linearized within the required specifications.
Load cell accuracy is maintained by the ability to frequently zero null force error, and by making slope
corrections using an internal calibration mass. The FPG is specifically designed to allow the internal
calibration mass to be measured in perfect alignment with the piston and cylinder (see Figure 7).
The ma
true mass value. When the mass is lowered in the operating conditions of the FPG, a correction factor is
determined to cause the buoyancy corrected output of the load cell to be equivalent to this true mass
value. Sensors internal to the FPG measure pressure, temperature and humidity around the load cell to
make the buoyancy correction. Since zeroing and running the internal calibration are integral parts of the
FPG, pneumatic valves are included with the FPG to allow the system to automatically set the necessary
conditions to perform each task.
ss value of the internal calibration mass is accurately determined and stored in FPG Tools as a
Figure 7. Internal Calibration Mass Alignment
The FPG configuration subjects the load cell to the lubricating pressure which significantly differs from
typical atmospheric conditions. The optimum environmental conditions of the balance are specified by
the manufacturer as temperature between 10 and 30 °C with relative humidity of 40 to 70 %. Typical
laboratory conditions yield the necessary temperature range. The humidity is, however, controlled to
approximately 50 % by a bubbling system internal to the FPG. FPG Tools will display a warning message
if these conditions change beyond these limits. Low humidity values cause electrostatic effects on the
load cell which have adverse influence on the zero stability of the load cell.
Page 13 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
2.4 LUBRICATION PRESSURE
Two different values of lubricating pressure are used depending on whether the FPG is working in gauge
or absolute measurement modes. These two pressures are supplied by two independent regulators
which can be connected by valves depending on the measurement mode. In gauge measurement mode,
the nominal lubricating pressure value is 140 kPa absolute which is about 40 kPa gauge. In absolute
measurement mode, the nominal lubricating pressure is 40 kPa absolute. The absolute mode lubricating
pressure reduces the lubricating flow which allows the reference vacuum or back pressure to be less than
a Pascal with most standard vacuum pumps. Higher power vacuum pumps can be used to greatly
reduce this pressure.
The lubrication pressure affects buoyancy forces on the load cell and the piston-cylinder as well as
creating a change in the dragging force on the piston-cylinder. The buoyancy effect is characterized
during the manufacturing process by varying the lubrication pressure and recording the change in load
cell output relative to the change in lubrication pressure. The drag effect is determined by maintaining a
constant lubrication pressure and changing the reference (see Section 2.7). Each time the FPG is
zeroed, the
the lubrication pressure and reference pressure since the last zero. A high quality pressure regulator built
into the FPG prevents this pressure from changing significantly when proper system pressure is applied.
As a result, the influence of the lubrication pressure on the FPG is maintained at a minimum.
The FPG is intended to be used in ambient conditions which means that the gas present in the upper and lower
measurement chambers is ambient air. It is therefore desirable to use air as the lubricating medium.
This avoids gas mixtures in the measurement chamber. However, FPG Tools supports N
Prior to changing gases, the system must be thoroughly purged. This includes the lubricating volume and
the test and reference ports of the FPG. Lack of knowledge of the constitution of the test gas complicates
the calculation of density needed to make fluid head corrections.
se effects are also set to zero. Therefore, changes in these forces are only due to changes in
as a lubrication gas.
2
2.5 VACUUM REFERENCE PRESSURE
The FPG8601 inherently measures differential pressure. When the lower mounting post is exposed to
atmosphere, the FPG measures gauge pressure. If the lower mounting post is exposed to a vacuum, the
FPG measures absolute differential pressure. To measure absolute pressure, the residual vacuum
pressure in the lower mounting post must be added to the FPG differential pressure. As a result, a high
accuracy low range sensor is included with the FPG to define absolute pressure.
Depending on the vacuum pumps used, the residual vacuum pressure will be less than 1 Pa. At this
pressure, span error in the vacuum sensor does not significantly impact the overall uncertainty of
the FPG. A 0.5 % span error at 1 Pa results in a .005 Pa error. However, zero offset in the sensor is
directly transferred to the zero offset of the FPG. Therefore, the zero of the sensor should be checked
frequently (see Section 8.3). A pneumatic valve is provided to isolate the vacuum reference sensor when
the FPG is n
change from vacuum to atmosphere. FPG Tools automatically isolates the sensor depending on the
current mode of operation.
ot under vacuum. This helps to reduce zero drift by avoiding the shock associated with a
© 2007 DH Instruments, a Fluke Company Page 14
2. FPG THEORY OF OPERATION
2.6 SIMPLIFIED FORMULA FOR CALCULATING DIFFERENTIAL PRESSURE
The calculation of differential pressure is made following the basic formula:
ΔP = F/A
eff.
(θ)
VARIABLE DEFINITION
ΔP
F Force measured by the load cell in counts (1 count = 1 mg).
A
(θ)
eff.
Differential pressure between the upper and lower chambers in Pa.
Effective area of the piston-cylinder at the operating temperature, θ.
The value is expressed in m
2
.
The force, F, measured by the load cell when it displays a number of counts, N, can be calculated using a
calibration coefficient, K
, following:
cal
F = K
cal.
. N
VARIABLE DEFINITION
K
Calibration coefficient of the load cell. This value contains any
cal.
N Number of counts output by the load cell representing the force
necessary slope correction for the load cell determined by the
internal calibration (see Section 5.3). The air density and local
gravit
y present at the time the calibration was performed are also
quantified by this value. The calibration factor is expressed in
Newtons/ Count (1 count = 1 mg).
measured. One count represents the force corresponding to a
mass of 1 mg loaded on the load cell under the calibration
conditions.
The effective area of the piston-cylinder at temperature θ, can be expressed using its value at 20 °C and
the linear thermal expansivity of the piston and the cylinder materials following:
A
(θ) = A
eff.
(20°C) . [ 1+ ( αp + αc ) . ( θ - 20 ) ]
eff.
VARIABLE DEFINITION
αp
αc
Linear thermal expansivity of the piston in K
Linear thermal expansivity of the cylinder in K
-1
.
-1
.
The piston and the cylinder are made of tungsten carbide therefore the thermal expansion coefficients are
the same; α
+ αc = 9 . 10-6 K-1. FPG Tools provides a single entry value for this combined effect in the
p
FPG calibration setup (see Section 6.6.3).
The sim
plified formula for the calculation of the differential pressure can therefore be expressed as:
ΔP = K
cal.
. N / A
(20°C) . [ 1+ ( αp + αc ) . ( θ - 20 ) ]
eff.
Page 15 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
In gauge measurement mode, the differential pressure is defined as being the difference between the
pressure in the upper chamber at the reference level of the mounting post and the pressure at the
corresponding level in the ambient air.
In absolute measurement mode, the differential pressure is defined as being the difference between the
pressure in the upper chamber at the reference level of the mounting post and the reference vacuum in
the lower chamber measured by the capacitance diaphragm gauge.
The reference pressure is defined as the pressure surrounding the piston when the load cell is in a zero
condition with the upper and lower chambers in by-pass condition. Therefore, the reference pressure is
atmospheric pressure in gauge mode and vacuum in absolute mode.
2.6.1 REFERENCE LEVEL
The reference level of the mounting post is defined as the height at which a variation of
density in the upper chamber will not affect the differential pressure measurement.
This position depends on the internal geometry of the piston in the upper chamber, in this
case, the piston is hollow. The position of the reference level of the FPG is 25 mm above the
center of the piston. This is approximately the bottom of the upper mounting post (see Figure 3).
2.7 CORRECTIONS
The simplified formula of differential pressure is valid only in the special case where the conditions of the
gas surrounding the load cell and the piston do not change from the time the mobile assembly (made up
of the piston and its carriage) is zeroed and the time the differential pressure measurement is made.
Although the FPG is designed to keep these conditions very stable, it cannot be assumed that they are
constant. Therefore corrections are made to compensate for the associated force changes. The force of
the differential pressure acting on the piston is affected by three different quantities: δN1, δN2 and δN3.
FPG Tools displays these corrections real time on the <Diagnostics Display> windows (see Section
6.3.7). Figure 8 displays each of these quantities.
tare and in operation after tare. N
represents the force on the load cell at the time of tare. N represents
0
This figure shows the forces on the system, both at
for force on the load cell in operation after tare.
Since the effects of buoyancy and drag at the time of tare are included when the FPG is zeroed, it is only
necessary to correct for changes in these forces due to changes in conditions after the time of tare (zero).
A δ precedes each of the corrections because they are derived from changes of conditions since the last
tare. FPG Tools provides warnings to prevent significant changes in each of the correction factors in
order to limit the magnitude of overall correction (see Section 6.6.4).
2.7.1 δN1
If the lubricating pressure which surrounds the load cell, the piston carriage and the piston
changes after the tare is executed due to drift of the lubricating pressure regulator or
temperature of the lubricating gas, the corresponding change in buoyancy force will affect the
force on the load cell. This change in force is quantified by δN1. δN1 is a function of the
buoyancy force coefficient, K
pressure and subtracting the effect due to changes in the drag force (see Section 2.7.2).
is calculated using K
δN1
zero (see Section 11.3.3).
, which is determined experimentally by varying the lubrication
b
and the change of the lubrication pressure since the last system
b
2.7.2 δN2
Due to a small amount of asymmetry of any piston-cylinder assembly, the difference between
the lubricating pressure and the reference pressure surrounding the piston creates a net
viscous drag force that acts on the piston. If this differential pressure changes after the tare
has been executed the drag force changes and the force on the load cell will be affected.
To determine δN2, a drag force coefficient, K
by varying the reference pressure while holding the lubrication pressure constant.
Subtracting the buoyancy changes due to the change in reference pressure (see Section 2.7.3),
© 2007 DH Instruments, a Fluke Company Page 16
, is determined experimentally. Kd is determined
d
2. FPG THEORY OF OPERATION
Δ
Δ
N
N
Δ
the remaining effect is the change in force due to drag on the piston. δN2 is calculated using
and the change in the difference between the lubrication pressure and the reference
K
d
pressure (see Section 11.3.3).
2.7.3 δN3
Buoyancy due to the reference pressure gas that surrounds the piston exerts a force that acts
on the piston. If the FPG reference pressure changes after the tare is executed, the corresponding
change in the buoyant force affects the force on the load cell. In absolute mode the reference
pressure is on the order of a few Pascal. Buoyancy effects related to changes in such a low
pressure are insignificant. Therefore, δN3 = 0 for absolute mode.
In gauge mode the reference pressure is atmosphere. Buoyancy effects due to changes in
atmosphere can have a measurable effect on the output of the FPG. Like the other
correction terms, δN3 quantifies the change in buoyancy due to the change in atmosphere.
Typically atmospheric changes are quite small so the change in buoyancy will also be small.
The effect of δN3 is most apparent when the FPG is zeroed in gauge mode, then the system
is changed to absolute mode without re-zeroing (not a recommended practice). The change
in reference pressure is equal to one atmosphere. The change in buoyancy force associated
with this large change is the correction. Since zeroing in each mode of operation is standard
procedure for the FPG, this extreme situation does not occur.
=mg + F
0
F
B,L
F
B,L
(δN1)
mg
F
B,R
F
B,R
(δN3)
Figure 8. FPG Forces
+ F
+ F
B,L
B,R
D
P
*A
θ
high
F
D
F
D
(δN2)
P
*A
θ
ref
Page 17 © 2007 DH Instruments, a Fluke Company
FPG8601™/VLPC™ OPERATION AND MAINTENANCE MANUAL
2.8 COMPLETE DIFFERENTIAL PRESSURE EQUATION
The combination of all corrections along with the simplified pressure equation yields the complete differential
pressure equation for the FPG. An exploded view of all FPG calculations is detailed in Section 11.3.
ΔP =
. ( N + δN1 + δN2 + δN3 ) / [A
K
cal.
(20°C) . [ 1+ ( αp + αc ) . ( θ - 20 ) ]]
eff.
In gauge measurement mode, this differential pressure is equal to the gauge pressure of the FPG.
In absolute mode, the residual vacuum pressure measured by the vacuum reference sensor is applied to
the calculated differential pressure to obtain the absolute pressure of the FPG.
© 2007 DH Instruments, a Fluke Company Page 18
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