Ruska Instrument 7252 User manual

DIGITAL PRESSURE CONTROLLER
MODEL 7252
MODEL 7252
i
USER’S MANUAL
RUSKA INSTRUMENT CORPORATION
10311 WESTPARK DR., HOUSTON, TEXAS 77042
[phone] FAX: [phone]
e-mail: [email protected] http://www.Ruska.com
Release: 7252-1D01
Revision: A
Date: 09/16/03

WARRANTY
Ruska Instrument Corporation warrants its products to conform to or exceed the
specifications as set forth in its catalogs in use at the time of sale and reserves the right,
at its own discretion, without notice and without making similar changes in articles
previously manufactured, to make changes in materials, designs, finish, or specifications.
Ruska Instrument Corporation warrants products of its own factory against defects of
material or workmanship for a period of one year from date of shipment.
Liability of Ruska Instrument Corporation under this warranty shall be limited to
replacing, free of charge (FOB Houston, Texas), any such parts proving defective within
the period of this warranty, but will not be responsible for transportation charges or
consequential damages.
This warranty is not made for products manufactured by others which are illustrated and
described in Ruska catalogs or incorporated in Ruska products in essentially the same
form as supplied by the original manufacturer. However, Ruska Instrument Corporation
agrees to use its best efforts to have original suppliers make good their warranties.
INTRODUCTION
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COPYRIGHT NOTICE
Copyright © 1997 by Ruska Instrument Corporation. All rights reserved. This document
may not be reproduced in part or in whole without the express written consent of Ruska
Instrument Corporation.
DISCLAIMER
No representations or warranties are made with respect to the contents of this user’s
manual. Further, Ruska Instrument Corporation reserves the right to revise this manual
and to make changes from time to time in the content hereof without obligation to notify
any person of such revision.
TRADEMARK NOTICE
® is a registered trademark of Ruska Instrument Corporation.
Trademarks or tradenames are subject to state and federal laws concerning their
unauthorized use or other infringements. The fact that the product marks or names in
this manual do not bear a trademark symbol DOES NOT mean that the product name or
mark is not registered as a trademark or tradename. Any queries concerning the
ownership or existence of any trademarks or tradenames mentioned in this manual
should be independently confirmed with the manufacturer or distributor of the product.
INTRODUCTION
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REVISION NOTICE
RELEASE
NUMBER
REV. DATE OF
RELEASE
DESCRIPTION
7252-1D01 A 09/16/03 Original release. See DC/RO 23958.
INTRODUCTION
-iv-

REVISION HISTORY
RELEASE 7252-1D01 Revision A (09/16/03)
Original release See DC/RO 23958.
INTRODUCTION
-v-

7252 – Change Language
Hold key for 5 seconds
mode
enter
INTRODUCTION
-vi-

SAFETY SUMMARY
The following are general safety precautions that are not related to any specific
procedures and do not appear elsewhere in this publication. These are recommended
precautions that personnel must understand and apply during equipment operation and
maintenance to ensure safety and health and protection of property.
KEEP AWAY FROM LIVE CIRCUITS
Operating personnel must at all times observe safety regulations. Do not replace
components or make adjustments inside the equipment with the voltage supply
connected. Under certain conditions, dangerous potentials may exist when the power
control is in the off position due to charges retained by capacitors. To avoid injuries,
always remove power from, discharge, and ground a circuit before touching it.
DO NOT SERVICE OR ADJUST ALONE
Do not attempt internal service or adjustment unless another person capable of rendering
aid and resuscitation is present.
RESUSCITATION
Personnel working with or near dangerous voltages shall be familiar with modern
methods of resuscitation. Such information may be obtained from your local American
Medical Association.
ELECTRO STATIC DISCHARGE SENSITIVE PARTS
CAUTION: Electrostatic discharge sensitive (ESDS) is applied to low power, solid-state
parts which could be damaged or destroyed when exposed to discharges of static
electricity. Maintenance personnel are often not aware that an ESDS part has
been damaged or destroyed because electrostatic discharges at levels less than
4,000 volts cannot be seen, felt, or heard.
COMPRESSED GAS
Use of compressed gas can create an environment of propelled foreign matter. Pressure
system safety precautions apply to all ranges of pressure. Care must be taken during
testing to ensure that all pneumatic connections are properly and tightly made prior to
applying pressure. Personnel must wear eye protection to prevent injury.
PERSONAL PROTECTIVE EQUIPMENT
Wear eye protection approved for the materials and tools being used.
INERT GASES
Operation of pressure equipment may be accompanied by the discharge of inert gases to
the atmosphere. The result is a reduction of oxygen concentration. Therefore, it is
strongly suggested that exhaust gases not be trapped in the work area.
INTRODUCTION
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TABLE OF CONTENTS
WARRANTY ............................................................................................................ -ii-
COPYRIGHT NOTICE ............................................................................................ -iii-
REVISION NOTICE ................................................................................................ -iv-
REVISION HISTORY................................................................................................ -v-
CHANGE LANGUAGE........................................................................................... -vi-
SAFETY SUMMARY ............................................................................................... -vii-
TABLE OF CONTENTS ..........................................................................................-viii-
SECTION 1.0: GENERAL INFORMATION
1.1 INTRODUCTION...............................................................................1-1
1.2 GENERAL INFORMATION ................................................................1-1
1.3 FEATURES .........................................................................................1-1
1.4 STANDARD EQUIPMENT & OPTIONS ..............................................1-3
SECTION 2.0: THEORY OF OPERATION
2.1 INTRODUCTION...............................................................................2-1
2.2 POWER SUPPLY.................................................................................2-2
2.3 ELECTRONICS MODULE ...................................................................2-2
2.3.1 BACK-PLANE BOARD................................................................2-2
2.3.2 MICROPROCESSOR BOARD......................................................2-2
2.3.3 DIGITAL CONTROL BOARD ......................................................2-3
2.3.4 IEEE-488 INTERFACE ................................................................2-3
2.3.5 FRONT PANEL ..........................................................................2-3
2.4 PNEUMATICS MODULE ....................................................................2-4
2.4.1 MEASURE MODE PNEUMATICS.................................................2-5
2.4.1.1 Reference Port..............................................................2-5
2.4.1.1.1 Barometric Sensor...........................................2-6
2.4.1.1.2 Absolute with Evacuated Reference - Optional ..2-6
2.4.1.2 Test Port ......................................................................2-6
2.4.1.2.1 Single Test Port Operation Option ...................2-6
2.4.1.3 Vent Procedure ............................................................2-7
2.4.2 CONTROL MODE PNEUMATICS ........................................... 2-7
2.4.2.1 Pressure Supply Port .....................................................2-7
2.4.2.2 Vacuum Supply (Exhaust) Port .......................................2-7
2.4.2.3 Pressure Control ..........................................................2-8
2.5 CONTROL STRATEGY .......................................................................2-8
2.5.1 INNER VS OUTER CONTROL LOOP ..........................................2-8
2.5.2 NORMAL MODE.......................................................................2-8
2.5.3 FAST MODE .............................................................................2-8
2.5.4 ALIGNMENT OF INNER LOOP WITH OUTER LOOP ...................2-9
2.5.5 PID CONTROL..........................................................................2-9
2.6 TRANSDUCER MODULE .................................................................2-10
2.6.1 QUARTZ BOURDON TUBE SENSOR (TRANSDUCER01) ............2-10
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2.6.2 SENSOR BOARD.....................................................................2-11
2.6.3 LINEARIZATION TERM.............................................................2-11
2.6.4 AUXILIARY SENSORS...............................................................2-12
2.6.4.1 Case Reference Vacuum Sensor - Option ....................2-12
2.7 SOFTWARE ...................................................................................2-12
2.7.1 SOFTWARE SAFETY CONTROLS ..............................................2-12
2.7.1.1 Preventing Operator Errors.........................................2-12
2.7.1.2 Pneumatic Errors........................................................2-12
2.7.1.3 Shutoffs .....................................................................2-12
2.7.1.4 Oven Control ............................................................2-12
2.7.1.5 Pressure Reading and Correction ................................2-13
SECTION 3.0: INSTALLATION
3.1 INTRODUCTION...............................................................................3-1
3.2 UNPACKING THE DPC .....................................................................3-1
3.3 CAUTIONS .....................................................................................3-2
3.4 POWERING UP THE DPC ..................................................................3-2
3.4.1 OBSERVING THE DPC’S FULL SCALE RATING ............................3-2
3.5 PNEUMATIC CONNECTIONS...........................................................3-2
3.5.1 PRESSURE SUPPLY PORT............................................................3-2
3.5.2 EXHAUST PORT ........................................................................3-3
3.5.2.1 Absolute Models ..........................................................3-3
3.5.3 TEST PORT................................................................................3-3
3.5.3.1 Single Test Port Operation - Option ..............................3-3
3.5.4 REFERENCE PORT .....................................................................3-4
3.5.5 VACUUM TRANSDUCER INSTALLATION ....................................3-5
3.5.6 VACUUM SENSOR OPTION......................................................3-6
SECTION 4.0: LOCAL OPERATION
4.1 TUTORIAL .....................................................................................4-3
4.1.1 SELECTING LANGUAGE ...........................................................4-6
4.1.2 SELECTING MODE OF OPERATION ..........................................4-6
4.1.2.1 Simulated Absolute Instruments.....................................4-6
4.2 MAIN MENU .....................................................................................4-7
4.3 CONTROLLING PRESSURE................................................................4-7
4.3.1 SETTING THE PRESSURE SETPOINT............................................4-8
4.3.2 ENTERING/EXITING CONTROL MODE......................................4-8
4.4 VENT .................................................................................................4-8
4.5 STEP | JOG .....................................................................................4-8
4.5.1 STEPPING.................................................................................4-9
4.5.1.1 Setting Step Size...........................................................4-9
4.5.2 JOGGING................................................................................4-9
4.6 MENU ...............................................................................................4-9
4.6.1 MENU | SETUP.......................................................................4-10
4.6.1.1 Menu | Setup - Limits.................................................4-10
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4.6.1.1.1 High Limit ....................................................4-10
4.6.1.1.2 Low Limit......................................................4-11
4.6.1.1.3 Auto Vent .....................................................4-11
4.6.1.1.4 Control Band................................................4-11
4.6.1.1.5 Control ........................................................4-12
4.6.1.1.6 Slew Rate .....................................................4-12
4.6.1.1.7 Slew Limit.....................................................4-12
4.6.1.1.8 Access..........................................................4-12
4.6.1.2 Menu | Setup - User...................................................4-12
4.6.1.2.1 Step Size ......................................................4-13
4.6.1.2.2 Bar Graph Maximum ....................................4-13
4.6.1.2.3 Ready Tolerance ...........................................4-13
4.6.1.2.4 Gas Head Pressure Correction.......................4-13
4.6.1.2.5 Atmosphere..................................................4-14
4.6.1.2.6 Pressure Filter ...............................................4-14
4.6.1.2.7 Changing the Number of Decimals................4-14
4.6.1.2.8 Key Click......................................................4-14
4.6.1.3 Menu | Setup - Units..................................................4-14
4.6.1.4 Menu | Setup - Remote ..............................................4-16
4.6.1.4.1 GPIB Address................................................4-16
4.6.1.4.2 Protocol........................................................4-16
4.6.1.4.3 Serial Interface Set-Up...................................4-16
4.6.1.5 Menu | Setup - System ...............................................4-16
4.6.1.5.1 Date | Time..................................................4-17
4.6.1.5.2 Reset ............................................................4-17
4.6.2 MENU | CALIBRATE ................................................................4-17
4.6.2.1 Calibration Password .................................................4-17
4.6.2.2 Zeroing .....................................................................4-18
4.6.3 MENU | PROGRAM - STORING A SEQUENCE IN MEMORY .....4-18
4.6.3.1 Preparing to Program.................................................4-19
4.6.3.2 Entering a New Program ............................................4-20
4.6.3.3 Automatically Generating a Program ..........................4-21
4.6.3.4 Changing the Name of a Program..............................4-22
4.6.3.5 Changing an Existing Program ...................................4-23
4.6.3.6 Changing the Configuration Stored with a Program.....4-24
4.6.3.7 Running a Program....................................................4-25
4.6.4 MENU | TEST .........................................................................4-25
4.6.4.1 Menu | Test - Sweep Test ...........................................4-26
4.6.4.2 Menu | Test - Self Test................................................4-27
4.6.4.3 Menu | Test - Remote Test ..........................................4-27
4.6.4.4 Menu | Test - Shop 1 .................................................4-27
4.6.4.5 Menu | Test - Control.................................................4-28
4.6.5 MENU | DISPLAY....................................................................4-28
4.6.5.1 Menu | Display - Blank ..............................................4-29
INTRODUCTION
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SECTION 5.0: REMOTE OPERATION
5.1 CAPABILITIES ....................................................................................5-1
5.1.1 IEEE-488 ..................................................................................5-1
5.1.2 RS-232.....................................................................................5-1
5.2 REMOTE/LOCAL OPERATION...........................................................5-2
5.3 CONFIGURATION ............................................................................5-2
5.4 DEVICE MESSAGES...........................................................................5-3
5.4.1 SCPI COMMAND FORMAT .......................................................5-3
5.4.2 SCPI RESPONSE FORMAT..........................................................5-3
5.4.3 ANSI/IEEE 488.2-1987 COMMAND SUMMARY .........................5-4
5.4.4 SCPI COMMAND SUMMARY.....................................................5-4
5.4.5 EXAMPLE SCPI COMMANDS .....................................................5-8
5.4.6 SCPI STATUS REGISTERS ...........................................................5-9
5.5 SERIAL OPERATION........................................................................5-11
5.6 SAMPLE PROGRAMS .......................................................................5-11
5.6.1 SAMPLE PROGRAM 1 - 7252 GPIB (IEEE-488) - CONTROLS
PRESSURE TO 20.000%FS .......................................................5-11
5.6.2 SAMPLE PROGRAM 2 - 7252 GPIB (IEEE-488) - ZERO
SEQUENCE ............................................................................5-13
5.6.3 SAMPLE PROGRAM 3 - 7252 SERIAL (RS-232) - CONTROLS
PRESSURE TO 20.000%FS ......................................................5-17
5.6.4 SAMPLE PROGRAM 4 - QBASIC EXAMPLE FOR 7252 ...............5-21
SECTION 6.0: MAINTENANCE
6.1 INTRODUCTION...............................................................................6-1
6.2 OBSERVING THE SOFTWARE VERSION NUMBER............................6-1
6.3 PREVENTIVE MAINTENANCE ...........................................................6-1
6.3.1 INITIATING THE DPC'S SELF TEST ..............................................6-1
6.3.2 REMOVING THE DPC'S COVER .................................................6-2
6.3.3 MOISTURE FILTER .....................................................................6-2
6.3.4 PARTICLE FILTERS .....................................................................6-2
6.3.5 VACUUM PUMPS......................................................................6-2
6.3.6 PROCESSOR BATTERY...............................................................6-3
6.4 CALIBRATION ...................................................................................6-3
6.4.1 CALIBRATION INSTRUCTIONS ..................................................6-3
6.4.1.1 Preparation..................................................................6-4
6.4.1.2 Storing the Coefficients.................................................6-6
6.4.2 VACUUM (NEGATIVE GAUGE) CALIBRATIONS ..........................6-7
6.4.3 RPT CALIBRATION - SIMULATED ABSOLUTE ..............................6-8
6.4.4 VACUUM SENSOR CALIBRATION - OPTIONAL CASE
REFERENCE SENSOR.................................................................6-9
6.4.5 EDITING THE CALIBRATION COEFFICIENTS ..............................6-9
6.4.6 ZEROING ...............................................................................6-11
6.4.6.1 Gauge and Vacuum (Negative Gauge) Instruments .....6-11
6.4.6.2 Absolute Instruments ..................................................6-12
INTRODUCTION
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6.4.6.3 RPT - Simulated Absolute Instruments ..........................6-13
6.5 SENSOR PHOTOCELL ZEROING.....................................................6-13
6.6 OPTIMIZING CONTROL..................................................................6-15
6.7 FAN OPERATION............................................................................6-17
6.8 SYSTEM SOFTWARE UPDATE PROCEDURE ....................................6-18
6.9 REPLACEMENT PARTS.....................................................................6-19
SECTION 7.0: PREPARATION FOR STORAGE & SHIPMENT
7.1 DISCONNECTING THE DPC .............................................................7-1
7.2 PACKING INSTRUCTIONS................................................................7-1
7.3 SHIPPING INSTRUCTIONS ...............................................................7-3
APPENDIX A: SUMMARY OF SPECIFICATIONS
A.1 UNCERTAINTY ANALYSIS.................................................................A-1
A.2 SPECIFICATIONS ..............................................................................A-5
APPENDIX B: SUMMARY OF ERROR MESSAGES ....................................B-1
LIST OF FIGURES
FIGURE 2-1: DPC BLOCK DIAGRAM .......................................................................2-1
FIGURE 2-2A MODEL 7252 DPC GAUGE PNEUMATICS DIAGRAM ...........................2-4
FIGURE 2-2B MODEL 7252 DPC ABSOLUTE PNEUMATICS DIAGRAM TO 50 PSIA .....2-5
FIGURE 2-3: PRESSURE CONTROL NORMAL MODE ................................................2-9
FIGURE 2-4: PRESSURE CONTROL FAST MODE.......................................................2-9
FIGURE 2-5: SHAFT/MAGNET SECTION................................................................2-10
FIGURE 2-6: PHOTOCELL/LIGHT SPOT.................................................................2-11
FIGURE 3-1: MODEL 7252 BACK PANEL .................................................................3-5
FIGURE 4-1: MODEL 7252 FRONT PANEL...............................................................4-1
FIGURE 4-2: MENU TREE .....................................................................................4-2
FIGURE 6-4: VACUUM (NEGATIVE GAUGE) CALIBRATION ......................................6-7
FIGURE 6-5: PHOTOCELL LOCATION...................................................................6-15
LIST OF TABLES
TABLE 1-1: OPTIONS LIST FOR THE MODEL 7252 ................................................1-3
TABLE 2-1: CONVERSION FACTORS.....................................................................2-4
TABLE 2-2: SOLENOID VALVE STATES...................................................................2-5
TABLE 3-1: GENERAL SPECIFICATIONS: GENERAL PARAMETERS............................3-1
TABLE 6-1: ELECTRONICS SELF TEST ....................................................................6-2
TABLE A-1: PERFORMANCE SPECIFICATIONS........................................................A-6
INTRODUCTION
-xii-

SECTION 1.0
GENERAL INFORMATION
1.1 INTRODUCTION
This manual contains operation and routine and preventive maintenance instructions for
the Model 7252 Digital Pressure Controller (DPC) manufactured by Ruska Instrument
Corporation, Houston, Texas. This section of the manual provides general information
about the DPC and presents its features and options.
1.2 GENERAL INFORMATION
The Ruska Model 7252 DPC uses force-balanced, fused-quartz Bourdon tube technology
to provide the precise measurement of pressure. During normal operation, the DPC
performs in either Measure mode or Control mode.
In Control mode, the DPC simultaneously measures and controls pressure. Control
mode is commonly used in the calibration and testing of pressure gauges, transducers,
pressure switches, and production pressure instruments.
In Measure mode, the DPC measures pressure. Typically, Measure mode applications
are found in research laboratories, wind tunnel testing, power plant testing, and bubbler
tank volume accountancy systems. It is also used to monitor barometric pressures,
vacuum systems, and differential pressure devices.
The 7252 has two full scale pressure ranges and two pressure controllers integrated into
one instrument.
1.3 FEATURES
The following features are available on all Model 7252 DPC’s.
Fused-Quartz Bourdon Tube Technology: (0.36 - 2500 psi full scale ranges) Ruska’s
force-balanced, fused-quartz Bourdon tube sensor makes use of the stability, high
elasticity, low hysteresis, and excellent fatigue strength of fused quartz. This time-proven
technology eliminates the need for gear trains, bearings, shafts, and other moving parts
that can wear out or introduce hysteresis or deadband into the process.
Mercury-Free: All components in the DPC are mercury-free.
NIST Traceability: All DPC’s are calibrated using Ruska deadweight gauges which are
directly traceable to the National Institute of Standards and Technology (NIST). Ruska is
also a NVLAP accredited laboratory and therefore can provide an optional NVLAP
accredited calibration.
Universal Power Supply: The DPC’s universal power supply accepts AC voltages
between 90 and 260 volts, and DC voltages between 100 and 370 volts. To
“reconfigure” the DPC for use in another country, the user simply changes the power
cord.
Measure While Control: The DPC simultaneously digitally displays the commanded
pressure, the actual pressure, and the difference between the two. A bar graph indicates
INTRODUCTION
1-1

how close the actual pressure is to the commanded pressure, as well as how close the
commanded pressure is to the DPC’s full scale pressure.
Friendly Display: The DPC’s color active matrix TFT display combines a bright, low-
glare readout with a wide viewing angle. During normal operation, the measured
pressure is easily visible from a distance of 10 feet (3 meters).
Adjustable Pressure Display: The pressure display may be adjusted to show one
decimal greater than or less than the default resolution.
Ease of Operation: An intuitive, menu-driven interface makes the DPC easy to use.
Frequently used selections such as the units of measure are restored to memory each
time the DPC powers up.
Easily Programmable: The DPC’s powerful microprocessor provides the basis for smart
electronics. With a few simple keystrokes, the user can set limits on the system pressure,
create unique units of measure, program a test sequence, and more.
Modular Design: The sensing element, pneumatics, electronics, and user interface are
separated into modules, making maintenance faster and easier.
Attractive Desktop Packaging: A sturdy aluminum case houses all of the DPC’s
pneumatics, electronics, and user controls. With the optional rack mount kit, this
standard 19" EIA chassis fits easily into a rack mount system.
Power On Self Test: Upon power-up, the DPC quickly tests its hardware and software.
After the DPC completes this test, the user can select more extensive self-tests for the
pneumatics and electronics.
Ease of Calibration: Calibration may be performed either remotely or entirely from the
front panel. No disassembly is required, and there are no potentiometers to tune. On
single sensor units, only a three-point calibration is required to fully characterize the
instrument. On instruments that integrate multiple ranges such as the 7252i, additional
calibration points are required.
Automatic Zero Adjust: At the user’s request, the DPC’s software automatically
performs the zero adjustment, with no potentiometers to tune.
Automatic Head Correction: The DPC automatically corrects for head pressure
between the DPC and the device under test (DUT), taking into account the density of the
test gas; e.g., air or nitrogen.
Choice of Medium: Although the DPC is not sensitive to the type of gas used within the
system, the user can select either instrumentation air or nitrogen, allowing the DPC to
automatically make pressure head corrections.
Choice of Display Units: Standard units include inHg at 0°C and 60°F, kiloPascals,
bars, psi, inH2O at 4°C, 20°C, and 25°C, kilograms per square centimeter, mmHg,
cmHg at 0°C, and cmH2O at 4°C. Altitude and airspeed units include feet, meters, knots,
and kilometers per hour. In addition to these predefined units, four user-defined units
are programmable.
Communications Interface: The DPC includes standard RS-232 serial and IEEE-488
interfaces. The user’s computer communicates with the DPC through the Standard
Commands for Programmable Instruments (SCPI) protocol.
INTRODUCTION 1-2

1.4 STANDARD EQUIPMENT & OPTIONS
A standard DPC includes this manual and a power cord. Although the standard DPC is
fully functional with just these items and the appropriate pressure and vacuum supplies,
the following options are also available.
NVLAP Accredited Calibrations - Ruska received formal accreditation from the
National Voluntary Laboratory Accreditation Program (NVLAP) which is administrated by
the National Institute of Standards and Technology (NIST). NVLAP has assigned Ruska
laboratory code 200491-0 to indicate that our accredited calibration services are in
compliance with all relevant requirements of ISO/IEC 17025:1999 and ISO 9002:1994.
Ruska's calibration laboratory can provide an optional accredited pressure calibration.
The NVLAP calibration certifications are optional and must be requested at time of order.
Rack Mount Kit: This 6.969" kit meets ANSI/EIA requirements for a 4U, 19" rack mount
kit.
Additional Power Cords: Additional power cords are available for most countries. All
options are summarized in Table 1-1. To order these items, please contact Ruska
Instrument Sales in the U.S. at [phone].
TABLE 1-1
OPTIONS LIST FOR THE MODEL 7252 DPC
Option Ruska Instrument Corp.
Part Number (RIC #)
LabView Driver (National Instruments) Downloadable from World Wide Web
Rack Mount Kit - Cabinets 18-24 inches deep 7250-903
Vacuum Pump
115 VAC 50/60 Hz
230 VAC 50/60 Hz
99877-800
99877-860
Power Cord - USA, Canada, Central Europe 16-81, 16-81, 16-86
Power Cord - India, Japan, Israel 16-96, 16-93, 16-97
Power Cord - Australia/New Zealand 16-95
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NOTES
INTRODUCTION 1-4

SECTION 2.0
THEORY OF OPERATION
2.1 INTRODUCTION
The DPC’s power supply, electronics, pneumatics, and sensor combine to form a
complete, stand–alone, measure and control instrument. This section of the manual
describes the DPC’s component modules (Figure 2–1) and provides a general discussion
of each. The 7252 has two pneumatic control and two primary transducer modules.
DIGITAL
CONTROL
BOARD 1
Section 2.3.3
INNER LOOP
SENSOR
Primary Transducer Module 2
Photo
Sensor
TUBE
CASE
SENSOR
BOARD
Section
2.6.2
SENSOR
Section
2.6.1
Pneumatics Module 2
Reference Port
Test Port
Supply Pressure Port
Exhaust Port
PNEUMATICS
Section 2.4
IEEE-488
RS -232
Electronic Module
INNER LOOP
SENSOR
Primary Transducer Module 1
Photo
Sensor
TUBE
CASE
SENSOR
BOARD
Section
2.6.2
SENSOR
Section
2.6.1
Pneumatics Module 1
Reference Port
Test Port
Supply Pressure Port
Exhaust Port
PNEUMATICS
Section 2.4
AC
POWER
Secti no
2.2
FRONT
PANEL
Section
2.3.5
IEEE
CARD
Section
2.3.4
MICROPROCESSOR
BOARD
Section 2.3.2
POWER
SUPPLY
Section
2.2
BACKPLANE
BOARD
Section 2.3.1
DIGITAL
CONTROL
BOARD 2
Section 2.3.3
FIGURE 2-1
DPC BLOCK DIAGRAM
2.2 POWER SUPPLY
THEORY OF OPERATION
2-1

The DPC’s universal power supply accepts AC voltages from 90 to 260 volts at 47-63 Hz.
and DC voltages from 100 to 370 volts. This quad–output supply produces +5 VDC,
+/-12 VDC, and 24 VDC which are distributed to the Control and Backplane Boards.
2.3 ELECTRONICS MODULE
2.3.1 BACK-PLANE BOARD
The Back-plane Board is used to interconnect all of the plug-in electronic boards and
distribute power. The Microprocessor Board, the Digital Control Board, and the IEEE–
488 Interface all plug into the Back-plane Board. The Front Panel communicates with the
Microprocessor Board via cables. The Sensor Board communicates with the
Microprocessor board through an internal RS-485 serial communication bus.
2.3.2 MICROPROCESSOR BOARD
All of the DPC’s software resides in nonvolatile, programmable, read–only memory
(Flash EPROM) on the Microprocessor Board, which plugs directly into the Back-plane
Board. This software contains all of the instructions that operate the DPC, as well as the
conversion factors that the DPC uses to translate the internal pressure unit-of measure of
kPa into the units selected by the user. These factors are given in Table 2–1.
Data that is subject to change after the DPC leaves the factory are held in electrically
erasable, programmable, read–only memory (EEPROM). This includes the current units
of measure, the coefficients from the zeroing process, the current pressure medium,
calibration coefficients, and the conversion factors for the four user–defined units of
measure.
When the DPC powers up, its software is loaded into random access memory (RAM), also
on the Microprocessor Board. At the same time, the values stored in EEPROM Board are
restored to memory.
Another important component on the Microprocessor Board is the lithium battery. The
battery continuously updates the DPC’s date and time, even when the unit is powered
down. This battery has a varying life. If the instrument is left on 24 hours a day, it may
last 5 to 10 years. If the instrument is stored, it may only last one year.
The Microprocessor Board also supports the RS–232 serial interface that allows the user’s
computer to communicate with the DPC.
THEORY OF OPERATION 2-2

TABLE 2–1
CONVERSION FACTORS
Unless specified otherwise, conversion factors are based on ANSI 268–1982.
Symbol Description Conversion Factor
InHg inches of mercury (0 °C) = kPa x 0.2952998
InHg inches of mercury (60 °F) = kPa x 0.296134
KPa KiloPascals = kPa x 1.0
Bar Bars = kPa x 0.01
Psi pounds per square inch = kPa x 0.1450377
cmH20 Centimeters of water (4 °C) = kPa x 10.19744
inH20 inches of water (4 °C) = kPa x 4.014742
kg/cm2kilograms per square centimeter = kPa x 0.0101972
mmHg Millimeters of mercury (0 °C) = kPa x 7.500605
cmHg Centimeters of mercury (0 °C) = kPa x 0.7500605
knots indicated airspeed per NASA TN D–822
km/hr kilometers per hour = knots x 1.852
Feet feet of altitude per MIL–STD–859A
meters meters of altitude per MIL–STD–859A
User1 user defined = kPa x user defined
User2 user defined = kPa x user defined
Pa user defined (Pascals) = kPa x 1000.0
hPa user defined (hectoPascals) = kPa x 10.0
%FS percent of full scale
2.3.3 DIGITAL CONTROL BOARD
The Digital Control Board plugs directly into the Back-plane Board. This board reads a
high speed silicon strain gauge pressure transducer, PDCR, connected to the pressure
generation point. A digital controller on the board drives two solenoids in the
pneumatics section to form a high speed, closed loop controller.
2.3.4 IEEE–488 INTERFACE
The DPC’s IEEE–488 (GPIB) interface card, which plugs directly into the Back-plane
Board, provides the DPC with an IEEE–488 interface. This interface allows the user to
automate the measurement and control processes.
2.3.5 FRONT PANEL
The Front Panel contains the active matrix TFT color display, rotary knob and rubberized
keys used to operate the DPC.
THEORY OF OPERATION
2-3

2.4 PNEUMATICS MODULE
The DPC's Pneumatics Module varies depending on whether the DPC is a Gauge mode,
Absolute mode, or a Simulated Absolute mode instrument. Gauge mode DPC's
reference their measurements to atmospheric pressure, whereas Absolute mode DPC
measurements are made with respect to sealed vacuum. A Simulated Absolute mode
DPC has a barometric sensor in addition to a gauge Bourdon tube sensor. The DPC
adds the barometric reading to the Bourdon tube reading to obtain a Simulated Absolute
value. It can operate as a Gauge mode instrument if the user selects to not add the
reference pressure.
The valves, filters, and transducers that make up the pneumatics module of a Gauge
mode (or Simulated Absolute) DPC are shown in Figures 2-2a. The schematics for the
Absolute mode DPC is shown in Figures 2-2b.
In the sections that follow, the Zero, Isolation, Apply and Release valves are all
24–volt, DC solenoid valves that are either open or closed depending on the DPC’s
operational mode.Their behavior is summarized in Table 2–2.
VACUUM
SENSOR
Option V
Control Section
REFERENCE
PORT
TEST
PORT
ZERO
ISOLATION
(< 1000 PSI FS)
BAROMETRIC
REFERENCE
SENSOR
(SIMULATED
ABSOLUTE
OPTION)
A
PPLY RELEASE
EXHAUST
PORT
SUPPLY
PRESSURE PORT
INNER LOOP CONTROL SENSOR
PRIMARY SENSOR
FIGURE 2–2A
MODEL 7252 DPC GAUGE PNEUMATICS DIAGRAM
0.36 to 2500 psig (2.5 kPa to 17.2 MPa) Full Scale Ranges
Note, this diagram depicts only one of the two 7252 channels.
THEORY OF OPERATION 2-4