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Instrument Control
Controlling GPIB, Serial, VXI, PXI, & Compact PCI Instruments
Agenda
• Description, History, Technologies, and Future of– GPIB– VXI– CompactPCI/PXI
• About GPIB communication and configuration• About LabVIEW instrument drivers• How to use instrument driver VIs• About Virtual Instrument Software Architecture• How to use the VISA functions• About serial port communication
What is Instrument Control ?
• The term instrument control refers to the act of using software on a PC to remotely control an instrument over an instrument control bus
Integral Components of Instrument Control
• 1. Programmable Instrument• 2. Instrument Bus• 3. Instrument Control Software
Part-1 : Programmable Instrument
Types of Instruments
1.Conventional Instruments[Standalone]- Manual Control
- No Communication Interface2.Programmable Instruments - Controlled by Instrument specific commands. - Remote controlled.
RS-232 Instrument
RS-232 Cable
PC SerialPort
Types of Programmable Instruments
• Card Based Instruments[Faceless / Naked Instrument]
• Programmable Instruments with conventional Front Panel
Difference
• Card Based Instruments reside inside PC/Controller cabinet.
• Control software is the face of the instrument Must.
• Programmable Instruments with conventional Front Panel are desktop based.
• Control software is optional manual control is also possible.
Virtual Instrument
• VI is Software face of the programmable instrument.• User takes control over the underlying hardware my manipulating VI Software.
Part-2 : Instrument Bus
Instrument Bus Types
• Stand alone Buses : used to communicate with rack and stack instruments
• Eg : RS232,GPIB etc
• Modular buses : incorporate the interface bus into the instrument itself
• Eg : PCI,PXI,VXI
Stand alone Buses : GPIB
• The General Purpose Interface Bus (GPIB) is one of the most common I/O interfaces available in stand-alone instruments.
• Originally designed by Hewlett Packard • GPIB is a digital, 8-bit parallel communications interface with data transfer rates of up to 8 Mb/s.
• The bus provides one system controller for up to 14 instruments, and cabling is limited to less than 20 m.
GPIB Hardware Specifications• Defined by IEEE 488.1• 24 Lines• Cable Specifications
– Max cable length between devices = 4 m (2 m average)
– Max cable length = 20 m– Max number of devices = 15 (2/3
powered on)• Talker/Listener/Controller• System Controller/Controller in
Charge
1
12
13
24
DIO5DIO6DIO7DIO8RENGND (TW PAIR W/DAV)GND (TW PAIR W/NRFD)GND (TW PAIR W/NDAC)GND (TW PAIR W/IFC)GND (TW PAIR W/SRQ)GND (TW PAIR W/ATN)SIGNAL GROUND
DIO1DIO2DIO3DIO4EOIDAV
NRFDNDAC
IFCSRQATN
SHIELD
GPIB System ConfigurationsLinear ConfigurationLinear Configuration Star ConfigurationStar Configuration
Configuring GPIB Board and Instruments
Measurement & Automation Explorer (MAX)
GPIB Configuration with MAX
Use MAX to examine the GPIB board settings and communicate with an instrument.
OB
JEC
TIVE
RS232 Serial Interface for Instruments
Serial Communication• Popular means of communication between computer and
peripheral device• Data sent one bit at a time across the cable• Used for low transfer rates or long distances• Only a cable is needed since most computers have at least
one available serial port
RS-232 Instrument
RS-232 Cable
PC SerialPort
Serial Hardware Connection• RS-232
– DCE or DTE configurations
– 9-pin or 25-pin• RS-422
– DCE or DTE– 8-pin
• RS-485
– Multidrop
Pin DTE DCE
1 DCD Input Output2 RxD I O3 TxD O I4 DTR O I5 Com - -6 DSR I O7 RTS O I8 CTS I O9 RI I O
Serial Communication
Terminology• Baud rate – bits per second• Data bits – inverted logic and LSB first• Parity – optional error-checking bit• Stop bits – 1, 1.5, or 2 inverted bits at data end• Flow control – hardware and software handshaking options
Using the Instrument I/O Assistant with Serial
• Select COMX as the instrument address
• Use the I/O Assistant as done with GPIB
Serial VIs and Functions
• Found in Serial subpalette under Instrument I/O
• Based on VISA functions
• Serial VIs and functions also work with parallel port communication
Serial I/O Example
• Initialize the serial port settings• Write commands to the device• Read device response• Check for errors
Exercise
Serial Write & Read VI
To build a VI that communicates with an RS-232 device.
OB
JEC
TIVE
Part-3 : Instrument Control software
Choose Your Development Software
• Instrumentation software designed for test and measurement– LabVIEW Graphical Programming– Measurement Studio
• General Purpose Software– Other C/C++ environments
• MS Visual C/C++, Borland C/C++, …
What is the Instrument I/O Assistant?
• Accessed through a LabVIEW Express VI
• Sets up device communication and data parsing step by step through a configuration interface
Communicating with an Instrument
Exercise
Using the Instrument I/O Assistant
Use the Instrument I/O Assistant to communicate with the NI Instrument Simulator.
OB
JEC
TIVE
VXIVXI
www.ni.com
VXI Mechanical Specifications
• Four VXIbus Module Sizes– A – 3.9 x 6.3 in (VME single-height)– B – 9.2 x 6.3 in (VME double-height)– C – 9.2 x 13.4 in– D – 14.4 x 13.4 in
• VXI MainframesVXI Mainframes– Maximum of 13 slotsMaximum of 13 slots– Same sizes as VXI ModulesSame sizes as VXI Modules
(A, B, C, D)(A, B, C, D)– Adapt smaller modules to larger Adapt smaller modules to larger
mainframesmainframes
B
D
C
VXI Electrical Architecture
Slot 0Controller
Instrument Buses
Computer Bus
Instrument Triggering and Timing Buses
VXIInstr.
VXIInstr.
VXIInstr.
VXIInstr.
Local Bus
Slot Identification - MODID
Conclusion – The Future of VXI• Well established standard
– Especially in high channel count applications, but • Growth challenged by
– Cost of VXI– Vendor production of new instruments– Need for faster test times– Smaller instrument solutions– Ease of multi-instrument integration– New platforms such as PXI and CompactPCI
PXI and CompactPCIfor Measurement and Automation
CompactPCompactPCI CI CompactPCompactPCI CI
Pri
ce
Performance
Desktop PC
VXI
Modular Instrumentationfor Mainstream Users
Control Panel
Flow
Pressure Alarm Conditions
STOP
Temperature
Filling the GapFilling the Gap
CompactPCI puts PC technology in a CompactPCI puts PC technology in a small, rugged package by combining small, rugged package by combining three standards:three standards:
PCI busPCI bus
EurocardEurocardpackagingpackaging
Better IEC Better IEC ConnectorsConnectors
CompactPCompactPCICICompactPCompactPCICI
PXI Starts with CompactPCIPXI Starts with CompactPCI
Why use Eurocard Packaging?
• Proven over decades of use in industrial applications (VME, VXI, etc.)
• Defined by IEEE 1101 Standard• Readily available mechanical components• Excellent thermal properties• Modular, rugged, and compact
PXI Combines Standard TechnologiesPXI Combines Standard Technologies
bus
CompactPCompactPCICICompactPCompactPCICI
PPCICIPPCICI
PXI and PC Software is IdenticalPXI and PC Software is Identical
• Operating systems and application software run unchanged on PXI systems
• Configuration tools recognize PXI modules as PCI devices
• Operating systems and application software run unchanged on PXI systems
• Configuration tools recognize PXI modules as PCI devices
Trigger Bus
Sys
tem
Co
ntr
oll
er
Sta
r T
rig
ger
Co
ntr
oll
er
Per
iph
eral
Per
iph
eral
Per
iph
eral
10 MHzCLK
132 Mb/s, 33 MHz, 32-bit Computer Bus
Star Trigger
Local Bus
Electrical ExtensionsElectrical ExtensionsPXI timing and triggering improves performance:PXI timing and triggering improves performance:
Local Bus Triggers Clock Star Bus
VXI 12 lines 8 TTL, 2 ECL 10 MHz ECL D-size only
PXI 13 lines 8 TTL 10 MHz TTL 1 per slot
PXI Leverages VXI FeaturesPXI Leverages VXI Features
Timing and Triggering Extensions in PXI and VXITiming and Triggering Extensions in PXI and VXI
PPCICI IIndustrialndustrial CComputeromputer MManufacturersanufacturers GGrouproup• Governs the core CompactPCI specificationGoverns the core CompactPCI specification• Focus is on telecommunications infrastructureFocus is on telecommunications infrastructure• Online product directory contains 100s of productsOnline product directory contains 100s of products• Over 500 company membersOver 500 company members
www.picmg.orgwww.picmg.org
The CompactPCI Specification Body
• Charter of this group is to:Charter of this group is to:- Promote PXI- Promote PXI- Ensure Interoperability- Ensure Interoperability- Control the PXI Specification- Control the PXI Specification
• Focus is on Focus is on end-user success end-user success in measurement and automationin measurement and automation• Over 50 company membersOver 50 company members
www.pxisa.orgwww.pxisa.org
Systems Alliance
The PXI Specification BodyThe PXI Specification Body
PXI Systems Alliance Members• GenRadGenRad• GespacGespac• Goepel ElectronicGoepel Electronic• GDE Systems (Marconi)GDE Systems (Marconi)
• GTE-ERSGTE-ERS• Innovative IntegrationInnovative Integration• KineticSystemsKineticSystems• LeCroyLeCroy• MAC PanelMAC Panel• MEN Mikro ElektronikMEN Mikro Elektronik• Talon InstrumentsTalon Instruments
• Acqiris Acqiris • Advanced Power DesignsAdvanced Power Designs• Advanced Test MethodsAdvanced Test Methods• Alphi TechnologyAlphi Technology• AMPAMP• AnalogicAnalogic• ASCORASCOR• ARVOO EngineeringARVOO Engineering• ATEMEATEME• A&T Engineering Tech. Ctr.A&T Engineering Tech. Ctr.• B&B TechnologiesB&B Technologies• BittWare Research SystemsBittWare Research Systems• Bode EnterprisesBode Enterprises• BRIMEBRIME• C&H TechnologiesC&H Technologies• CHROMA ATECHROMA ATE• Data PatternsData Patterns• DateppliDateppli• DatumDatum• Dolch Computer SystemsDolch Computer Systems
• National InstrumentsNational Instruments• Pickering InterfacesPickering Interfaces• PX Instrument Tech.PX Instrument Tech.• Racal InstrumentsRacal Instruments• Rohde and SchwarzRohde and Schwarz• Quantum ControlsQuantum Controls• SBS GreenSpringSBS GreenSpring• Shaanxi HiTech Shaanxi HiTech • SRCSRC• TestWareTestWare• Tracewell SystemsTracewell Systems• TTI TestronTTI Testron• Vero Electronics (APW)Vero Electronics (APW)• Virginia Panel Corp.Virginia Panel Corp.• ZYNXZYNX• SchroffSchroff• Marek MicroMarek Micro• ERNIERNI• Ballard TechnologyBallard Technology
MXI-3 Benefits
• More slots for PCs and PXI/CompactPCI• Very high performance serial link• Easy to integrate — software transparent • Short and L O N G distances• Low cost
Control Panel
Flow
Pressure Alarm Conditions
STOP
Temperature
MXIMXIGPIBGPIB
bus
VXI or VME
Stand-aloneStand-alone
InstrumentInstrumentPXI SystemPXI System
ModulesModules ModulesModulesCompactPCompactPCICICompactPCompactPCICI
PXI Modules Link to Other StandardsPXI Modules Link to Other Standards
MXI-3MXI-3
PCI/PXI GPIB VXI
Transfer Width (bits) 32 8 32 or 64Theoretical Peak Throughput (Mbytes/s) 132
1 (3-w ire) 8 (HS488) 40 or 80
Relative System Price $ $$ $$$
High Performance
PCI Bus Performance• Leverages computing technology
– 32-bit data transfers at 33 MHz (132 Mbytes/sec)
• Reduced measurement time
Conclusion – The Future of PXI
• Complete system specification that extends CompactPCI for Measurement and Automation
• PXI and CompactPCI are open specifications supported by numerous vendors
• Hundreds of products are available today for configuring PXI/CompactPCI systems
• Rapid growth due to – Low cost– Faster test times– Ease of multi-instrument integration– Small size– Adoption by other industries (telelecom)
Virtual Instrument Software Architecture
• Platform independent• VISA is the backbone of the
IVI and Plug & Play Instrument Drivers
• Interface independent• Must know SCPI command
set to program directly with VISA
GPIB VXISerial PXI
VISA
Sample GPIB Code
Sample VISA CodeSample VISA Code
VISA Terminology
• Resource—Instrument, Serial Port, or Parallel Port
• Session—Connection to a Resource
• Instrument Descriptor—Resource location
• Format: Interface Type::Address::INSTR
• Examples:
Instrument Descriptor Syntax
• Resource Name contains interface info• VISA Aliases also work
Interface Resource Name Grammar
Serial ASRL[board][::INSTR]
GPIB GPIB[board]::primary address[::INSTR]
VXI VXI[board]::VXI logical address[::INSTR]
GPIB-VXI GPIB-VXI[board][::GPIB-VXI primary address]::VXI logical address[::INSTR]
VISA Resource Name
• Exact name and location of the instrument
• Use the VISA Resource Name control (like the DAQ Channel Name control)
• You can specify the full resource name or the VISA Alias
VISA Functions
Exercise 3
Programming with VISA
To build a VI that reads and writes information from the NI Instrument Simulator using VISA functions.
OB
JEC
TIVE
Instrument Drivers• More than 1200 LabVIEW Instrument drivers
• Programming simplified to high−level API
Instrument Drivers
instrument addressing command string building range checking
memory storage data scaling response string parsing
instrument addressing command string building range checking
memory storage data scaling response string parsing
Test ProgramTest Program
Low-Level I/O: - ‘set:vert_div:0.001’ - ‘init:trig:arm’ etc…
Low-Level I/O: - ‘set:vert_div:0.001’ - ‘init:trig:arm’ etc…Instrument Driver: - ‘ReadWaveform’Instrument Driver: - ‘ReadWaveform’
Instrument DriverInstrument Driver
Intuitive high-le
vel functio
ns
IDNET - Instrument Driver Network
• Learn about drivers• Get help with developing drivers• Submit your driver to the network• Download drivers
Installing and Finding Instrument Drivers• Drivers available at ni.com/idnet
• Install the instrument driver VI Library into LabVIEW 7.0\instr.lib directory
• Access drivers from Functions»Input»Instrument Drivers subpalette
Instrument Driver Model
• Initialize • • •
• Configure • • • • • • • •
• Action/Status • • • • • • • • • • • •
• Data • • • • • • • • • • • • • • • • • • • • • • • • • •
• Utility • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
• Close • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
Instrument Driver VIs
Instrument Drivers
• Instrument drivers have a similar hierarchy
Instrument Driver VI Tree
Instrument Driver Inputs and Outputs
• Instrument Descriptor• VISA Sessions
- A connection or link to a specific instrument- Created after instrument is initialized- Used throughout VI whenever you communicate with that specific
instrument• Error cluster
HP34401A Initialize.vi
Putting It All Together
• Initialize instrument• Do operation(s)• Close instrument• Check error status
VISA Sessions
Error Clusters
Exercise 4
Function Generator – VI
To build a VI that uses the Function Generator instrument driver VIs to Generate Output waveforms.
OB
JEC
TIVE
Instrument Drivers
• Issues– Performance– Inconsistent structure/quality
• Additional Expectations– Instrument interchangeability– Instrument simulation– Simplification of instrument
programming– Multithreading/parallel testing
Instrument Drivers
• Interchangeability• Simulation• State caching
TraditionalTraditional
IVIIVIT
est
Tim
eT
est
Tim
eT
est
Tim
eT
est
Tim
e
Test ProgramTest Program
IVI Class Driver
IVISpecificDriver
IVISpecificDriver
IVISpecificDriver
VISA I/O LibraryVISA I/O Library
Summary• LabVIEW can communicate with any instrument that connects to your computer
if you know the interface type• Use the Measurement & Automation Explorer (MAX) to detect, configure, and
test your GPIB interface and instruments• An instrument driver eliminates the need for your to have detailed knowledge of
the specific strings used by an instrument• Instrument Library – more than 1600 instruments supported• Instrument driver VIs share a common hierarchy and come with an example to
help you get started• VISA a standard protocol for using multiple types of I/O and instrument driver
development• Serial library contains functions for serial communication• You need to know the format of the returned data string in order to convert it to
the correct values
Conclusions
• GPIB is a defacto standard here to stay
• VXI is limited in its general market acceptance
• PXI is helping to lower the cost of production test
• LabVIEW and TestStand lower development time and costs
• National Instruments is the Leader in Computer-based
Measurement and Automation solutions