Get Started- Python and IVI
Contents
1. 8 Catching Errors with SYST ERR For a program to be reliable it is necessary to check for instrument errors The COMexception example in the above section will catch an error event but it does not report the instrument error code or description and it does not give any way to handle an error A solution to handle instrument errors is shown below The power supply has a system error queue that reports error codes and descriptions in a human readable string The IVI COM DirectIO method is used to send and read SCPI commands directly to the power supply PythonWin 2 5 2 r252 60911 Feb 21 2008 13 11 45 MSC v 1310 32 bit Intel on win32 Portions Copyright 1994 2008 Mark Hammond see Help About PythonWin for further copyright information gt gt gt from comtypes client import CreateObject gt gt gt gt gt gt gt gt gt 0 gt gt gt gt gt gt 0 gt gt gt 0 gt gt gt uro gt gt gt gt gt gt gt gt gt 0 gt gt gt PS PS PS1 CreateObject LambdaGenPS LambdaGenPS In next step do not enable driver to do QueryInstrStatus PS1 Initialize GPIBO 6 INSTR False False Enable the error queue and clear it 1 System DirectIO WriteString SYST ERR ENAB 1 System DirectIO WriteString SYST ERR PS1 System DirectIO ReadString No error Now send an illegal setting PS1 Output CurrentLimit 1000 PS1 System DirectIO WriteString2. 6 The Initialize Step Once the COM object is created the first step is to initialize it An example is shown in the third command in Figure 5 PS1l Initialize GPIB 6 INSTR False False W This important step will 1 Use a resource descriptor to a Identify the port type IEEE RS 232 485 or LAN b Describe the instrument s address on the bus 2 Optionally verify the supply s identity 3 Optionally reset the supply 4 Optionally set IVI options such as simulation and error checking The initialize step will also verify that communication can be established with the power supply A Parameter 1 Select the Instrument This is a string name that specifies the Genesys port type and address The name may be one of 1 VISA resource descriptor If you only have the VISA runtime engine installed you must use this form Examples of use are For the IEEE bus GPIB 6 INSTR for Supply at IEEE address 6 For the RS 232 485 bus ASRL1 INSTR for supply connected to the computer s serial port 1 The address and Baud rate are given in the option string which is the fourth parameter CoM1 is an alias which can usually be used for the computer s serial port 1 The address and Baud rate are given in the option string which is the fourth parameter Page 9 of 16 for the Lambda Genesys Power Supply For the LAN bus TCPIP 192 168 47 92 INSTR for a supply
3. SYST ERR PS1 System DirectIO ReadString u 222 Data out of range address 06 gt gt gt Figure 10 Using SYST ERR to Catch Errors Note that setting CurrentLimit 1000 is not an error for the IVI driver so no COMexception was thrown It is however an error for the power supply so the system error queue reported it The response from the ReadString may be managed using the normal Python string functions Page 14 of 16 L AMBDAA Getting Started with IVI COM and Python for the Lambda Genesys Power Supply 9 Programming with the RS 232 485 Port Writing IVI COM programs for the RS 232 485 ports is the same as the example above for the IEEE interface The only change is in the initialize option string A RS 232 Initialize For the IEEE Initialize the entire connection is defined in the VISA resource name string For the RS 232 485 port The VISA name only selects the computer s COM port COM1 COM2 etc The Genesys address and the Baud rate are specified in the fourth parameter of the call to Initialize This fourth parameter is an option string In the example below the following settings are shown ASRL1 the computer s COM1 port is selected DriverSetup is the required start of the RS 232 string SerialAddress 6 is the Genesys front panel address setting It may be a number from 0 to 30 BaudRate 9600 is the Genesys front panel seria
4. Python projects http sourceforge net project platformdownload php group _ id 78018 Used here pywin32 211 win32 py2 5 exe 3 comtypes version 0 4 2 This is a 3d party Python extension to allow early binding of COM objects with unknown interfaces http i python or i comtypes 0 4 2 Used here comtypes 0 4 2 win32 exe IVI Drivers The Lambda Genesys IVI driver package must be installed It is available as a download from http www lambda hp com product_html genesysilu htm Click on the Documentation gt Download Drivers link to register Install the file LambdaGenPS 2 x x x msi on your computer VISA Drivers The IVI drivers are built upon a layer of hardware drivers called VISA for Virtual Instrument Software Architecture These drivers may be obtained from a variety of companies who support test and measurement Page 3 of 16 Getting Started with IVI COM and Python LAMBDA A i for the Lambda Genesys Power Supply The runtime versions of the VISA drivers are acceptable but you will not have the communications utilities or the IVI configuration manager to create logical device names E Electrical Interface almost all personal computers have an RS 232 port or a local area network LAN port If your Genesys power supply uses the RS 485 or IEEE 488 IEMD option ports you will need to install these interface cards into your computer or laptop F Prior Experience with Python T
5. Session Fact E Development Environments H Reference Example 1 creating an instance of the driver directly Instrument Command Reference This example shows non interchangeable code where the driver DLL is reft LambdaGenPS IVI C Driver class is instantiated directly C import IviDriverTypeLib dll no_namespace import IviDmmTypeLib dll no_namespace imnnave Dan ATT ma mnamannanna ff mat intawn hanaan hla mimeo Figure 2 Sample of IVI Help Page 5 of 16 for the Lambda Genesys Power Supply 5 Your First Program Using Python A Launch PythonWin On the Windows Start menu launch PythonWin as shown below E ents gt GENESYS le D a If National Instruments gt m m gt 2 yore an P amp E Cyclone Max Programmer gt Microsoft Word e Agilent IO Libraries Sub X I aries Suite Calculator E Lambda gt gA Slowview i E vim 7 1 gt B winrar Se tere IDLE Python GUID Module Docs Python command line EX Python for Windows Documentation EY Python Manuals fm Programs D Documents O Settings gt Search gt Help and Support J Run Log Off HeyckW Shut Down Figure 3 Launching PythonWin Page 6 of 16 Getting Started with IVI COM and Python LAMBDAA j y for the Lambda Genesys Power Supply B Create the Power Supply Object At the Python gt gt gt prompt type the
6. connected to a local network The supply s IP address as read on it s front panel is 192 168 47 92 TCPIP GENH30 25 827 INSTR for a supply connected to a local network The supply s hostname as read on it s web LAN settings page is GENH30 25 827 2 IVI Logical Name If you have a utility that can manage the IVI configuration you can use Python to initialize an IVI logical device This allows the use of the IVI interchangeability feature which means you can swap one manufacturer s power supply for another s without changing the Python program IVI configuration utilities include the National Instruments Measurement and Automation Explorer NI MAX the Agilent VEE Pro Instrument Manager and others B Parameter 2 Identity Query If this parameter is set to True then the Initialize method will read the power supply s identity string IDN and verify that a Genesys supply is being initialized C Parameter 3 Reset If this parameter is set to True then the Initialize method will reset the power supply This includes setting the voltage and current to zero and the output off Other settings are set to the default see the User Manual D Parameter 4 Option String The fourth parameter may be empty empty double quotes a NULL string or one of the following Other parameter settings are available only the most popular are shown below See IVI Help shown in Figure 1 for mor
7. step will also verify that communication can be established with the power supply See section 6 for much more information on the Initialize step Page 7 of 16 for the Lambda Genesys Power Supply D Communicate with the Genesys Power Supply Once the Genesys IVI COM object is initialized named PS2 in the figure below you can start communicating with it The Intellisense see Figure 4 guides you through the choices of properties and methods for the PS2 object More specific details about them may be found in the IVI online Help as shown in Figure 2 PythonWin 2 5 2 r252 60911 Feb 21 2008 13 11 45 MSC v 1310 32 bit Intel on win32 Portions Copyright 1994 2008 Mark Hammond see Help About PythonWin for further copyright information gt gt gt from comtypes client import CreateObject gt gt gt PS2 CreateObject LambdaGenPS LambdaGenPS gt gt gt PS2 Initialize GPIB 6 INSTR True True 0 gt gt gt PS2 Output VoltageLimit 5 gt gt gt PS2 Output CurrentLimit 1 gt gt gt PS2 Output Enabled True gt gt gt PS2 Output MeasureVoltage Se OOLIIIS 999999993 gt gt gt PS2 Identity InstrumentModel u GEN30 25 IEMD gt gt gt PS2 Utility Reset 0 gt gt gt PS2 Close 0 gt gt gt PS2 Release OL gt gt gt Figure 5 Example Python Session Page 8 of 16 for the Lambda Genesys Power Supply
8. Page 1 of 16 LAMBDA A Getting Started with IVI COM and Python for the Lambda Genesys Power Supply Introduction This is a guide to writing programs using the Python language with the Lambda IVI COM drivers Python is praised for being simple but powerful It is open source and may be installed at no cost Many standard libraries and 3d party extensions are available IVI Interchangeable Virtual Instrument is a design by the global IVI Foundation to simplify the way equipment is used with computer automation programs This guide will allow you to remotely control the Genesys power supply using the RS 232 485 IEEE 488 or LAN interfaces Table of Contents 1 Introductions din tected Halen O R Riia 1 2 Table of Content wiiccisies ccc davccninsuecnar AA TEALANIN E A 1 3 Requirements Secs tewetentetadcrdcdend dred eter e EEEa 2 4 Installation INStructiOns cccceceeeee eee ee eee ee eset eee eee es 3 5 Your First Program Using Python seceeeeeeeeeeeeee ees 5 6 The Initialize Step s sssssssssersesssrnnrnnsrnnrrrrnnesrerrrennes 8 7 Catching Errors with Exceptions ccceceeeeeeeeeeeees 12 8 Catching Errors with SYST ERR cceseeeeeeeee eee eeeee es 13 9 Programming with the RS 232 485 Port assesses 14 10 Programming with the LAN Pott seceeeeeeeeeeeeee es 16 Table of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Fig
9. Python session below Notice the traceback after trying to set the supply above its rating to one thousand volts PythonWin 2 5 2 r252 60911 Feb 21 2008 13 11 45 MSC v 1310 32 bit Intel on win32 Portions Copyright 1994 2008 Mark Hammond see Help About PythonWin for further copyright information gt gt gt from comtypes client import CreateObject gt gt gt PS1 CreateObject LambdaGenPS LambdaGenPS gt gt gt Notice in line below no spaces after commas gt gt gt PS1l Initialize GPIBO 6 INSTR False False QueryInstrStatus True 0 gt gt gt PS1 Output Enabled True gt gt gt PS1 Output VoltageLimit 1000 Traceback most recent call last File lt interactive input gt line 1 in lt module gt File C Python25 Lib site packages comtypes __init__ py line 231 in setattr value COMError 2147192831 None u LambdaGenPS Instrument error detected Use ErrorQuery to determine th rror s u LambdaGenPS LambdaGenPS 1 None 0 None gt gt gt Figure 9 Using COMexception to Catch Errors Although this COMexception method will display all types of errors at any time this example does not show how to programmatically handle the exception This example also does not show how to report the instrument error code or description Page 13 of 16 Getting Started with IVI COM and Python LAMBDA A j y for the Lambda Genesys Power Supply
10. an RS 232 power supply gt gt gt from comtypes client import CreateObject gt gt gt gt gt gt COML 0 gt gt gt u Sim2 gt gt gt gt gt gt LS gt gt gt PS PS PS PS1 CreateObject LambdaGenPS LambdaGenPS lL Initialize False False Simulate True DriverSetup SerialAddress 6 BaudRate 9600 l Identity InstrumentFirmwareRevision a n3 c0 l Output VoltageLimit 100 PS L Output MeasureVoltage Figure 8 Enabling a Simulated RS 232 Instrument Page 12 of 16 for the Lambda Genesys Power Supply 7 Catching Errors with Exceptions When an IVI COM method is called it will return with a non zero HRESULT value that describes a type of COM error It will also throw a COMexception event By default COMexceptions will only report errors detectable by the computer including unopened ports cable disconnections or no responses from the power supply By modifying the Initialize step see section 6 the COMexception can be thrown for instrument errors such as an illegal command or a setting out of range To do this change the fourth parameter Option String in the Initialize step to QueryInstrStatus True This will cause the IVI driver check after every command to make sure the command was accepted by the power supply If a command error occurred then a COMexception will be thrown This method is shown in the
11. e VISA resource name string Below is an example if the power supply auto IP address is 169 254 7 58 PythonWin 2 5 2 r252 60911 Feb 21 2008 13 11 45 MSC v 1310 32 bit Intel on win32 Portions Copyright 1994 2008 Mark Hammond see Help About PythonWin for further copyright information gt gt gt from comtypes client import CreateObject gt gt gt PS1 CreateObject LambdaGenPS LambdaGenPS gt gt gt PS1 Initialize TCPIP 169 254 7 58 INSTR False False 0 gt gt gt Read the network hostname gt gt gt PS1 System DirectIO WriteString SYST COMM LAN HOST 0 gt gt gt PS1 System DirectIO ReadString u GEN60 85 181 gt gt gt B LAN Initialize with Hostname If the LAN power supply is connected through a network server it s hostname may be registered by the NBNS or DNS services In this case the hostname may be used in the VISA resource name string instead of the IP address Below is an example if the power supply hostname is GENH30 25 827 PythonWin 2 5 2 r252 60911 Feb 21 2008 13 11 45 MSC v 1310 32 bit Intel on win32 Portions Copyright 1994 2008 Mark Hammond see Help About PythonWin for further copyright information gt gt gt from comtypes client import CreateObject gt gt gt PS2 CreateObject LambdaGenPS LambdaGenPSs gt gt gt PS2 Initialize TCPIP GENH30 25 827 INSTR True True 0 gt gt gt PS2 Identity In
12. e options Page 10 of 16 for the Lambda Genesys Power Supply Option String Simulate True Enabling the Simulate mode allows you to run the Python program even if no power supply is actually connected to the system Commands are simulated and responses are fixed default values gt gt gt from comtypes client import CreateObject gt gt gt GenPS CreateObject LambdaGenPS LambdaGenPs gt gt gt GenPS Initialize TCPIP 192 168 14 57 INSTR False False Simulate True 0 gt gt gt GenPS Output Enabled True gt gt gt GenPS Output Enabled True gt gt gt GenPS Identity InstrumentModel u GENvvv aaa LAN gt gt gt GenPS Output MeasureVoltage 1 55 gt gt gt Figure 6 Simulating an Instrument Option String QueryInstrStatus True This will cause an ESR query to be automatically sent after every command If a command error or other error is returned a COM exception will be thrown See section 7 below for an example gt gt gt PS2 Initialize GPIB 6 INSTR True True QueryInstrStatus True 0 Figure 7 Enabling Automatic Error Query Page 11 of 16 Getting Started with IVI COM and Python LAMBDA A j y for the Lambda Genesys Power Supply Multiple Option Strings Multiple options are set by using a comma separator between the option parameter strings Below is an example of simulating
13. his tutorial assumes very little prior experience with Python programming It will do nothing more than use the PythonWin Interactive screen to create the Genesys supply IVI COM object and send a few commands Installation Instructions Download the files listed in the Requirements section above Then A Install the Python Program You will create a folder such as C Python25 B Install the PythonWin Program You will create a folder and program such as C Python25 Lib site packages pythonwin Pythonwin exe C Install the Python comtypes Extension You will create a folder such as C Python25 Lib site packages comtypes D Install the Genesys IVI Drivers You will create a folder and library such as C Program Files IVI Bin LaGen dll E Install the VISA Drivers You will create a folder such as C VXIPNP or C Program Files VISA or other Page 4 of 16 for the Lambda Genesys Power Supply F Additional Help A discussion of the Python interface for COM objects may be found at http starship python net crew theller comtypes Information on the IVI COM drivers including the commands and settings is installed by the Lambda Genesys IVI driver package A Getting Started and language reference Help is included This help file may be opened through the Start menu as shown below l C Drive Studio 2005 ae Accessories ie Documents gt Bucket Programming B Sett
14. ings gt T National Instruments 9 Search gt E Infor Worktop gt Help and Support fa Lambda fn LambdaGenPs Documentation E Run National Instruments CVI IE Undock Computer Shut Down t Programs fas 4 Windows Explorer Walter Heyck Inbo Ti Get Figure 1 Launching IVI Help Below is a sample of the Help file s contents LambdaGenPS H H ee gt k Hide Locate Back Forward Stop Refresh Home Contents index Search Favorites Qf LambdaGenPS IVI COM Driver i ee ee Getting Started with the IVI COM Driver An IVI COM driver must be instantiated before it can be initialized This sec IMI Backa create an instance of the driver ee aiiin Achieving interchangeability with the IVI Session Fac Configuring the Driver The IVI Session Factory uses the IVI Configuration Store to instantiate the Q Performing Basic Operati ith the IVI CC the driver session specified logical name This eliminates the need for a clie 7 ee one eee reference the IVI COM driver DLL and the main driver class This is useful i Creating an Instance of the Driver that want to be totally interchangeable Initializing the Driver Accessing Repeated Capabilities Using instrument specific capabilities A Accessing Instrument Specific and IVI De If the client program uses the instrument specific interfaces then the code Using Simulation interchangeable so there is nothing to gain from using the IVI
15. l bits per second It may be 1200 2400 4800 9600 or 19200 PythonWin 2 5 2 r252 60911 Feb 21 2008 13 11 45 MSC v 1310 32 bit Intel on win32 Portions Copyright 1994 2008 Mark Hammond see Help About PythonWin for further copyright information gt gt gt from comtypes client import CreateObject gt gt gt gt gt gt gt gt gt 0 gt gt gt u LA gt gt gt 0 gt gt gt gt gt gt 540 gt gt gt PS1 In next step ASRL1 INSTR is the generic name for COM1 PS1 Initialize ASRL1 INSTR True True DriverSetup SerialAddress 6 BaudRate 9600 CreateObject LambdaGenPS LambdaGenPS PS1 Identity InstrumentManufacturer BDA PS1 Utility Reset PS1 Output CurrentLimit 5 PS1l value Output CurrentLimit Figure 11 Initializing the RS 232 Port Page 15 of 16 for the Lambda Genesys Power Supply B Catching Errors For the serial RS 232 port any setting out of range or other illegal command will generate a COMexception There is no need to Initialize the driver with QueryInstrStatus True Page 16 of 16 for the Lambda Genesys Power Supply 10 Programming with the LAN Port Writing IVI COM programs for the LAN port is the same as the example above for the IEEE interface The only change is in the initialize option string A LAN Initialize with IP Address Like the IEEE Initialize the entire LAN connection is defined in th
16. lines gt gt gt from comtypes client import CreateObject gt gt gt PS1 CreateObject LambdaGenPS LambdaGenPs PS1 is an arbitrary name created to identify the reference to the power supply object You may choose any name The first time you run the CreateObject command a list of Generating comtypes notices are displayed After this when you begin to type commands to the PS1 object you will see the Intellisense list boxes appear as shown below PythonWin Interactive Window File Ed it View Tools Window Help D Sugas tarna BRERA Ss Pythonin 2 5 2 r252 60911 Feb 21 2008 13 11 45 MSC v 1310 32 bit Intel on win32 Portions Copyright 1994 2008 Mark Hammond see Help About PythonVVin for further copyright information gt gt gt from comtypes client import CreateObject CreateObject LambdaGenPS LambdaGenPs gt gt gt PS1 gt gt gt PS1 DriverOperation A Identity Initialized MultiDrop 00005 009 Figure 4 Intellisense C Initialize the Genesys Power Supply Once the COM object is created the first step is to initialize it This step is used to select the instrument including what bus it is using and it s address and do other things In the Figure 5 example below the step PS1 Initialize GPIB 6 INSTR False False W will assign a name PS1 and open communication with a Genesys power supply at IEEE address 6 This
17. strumentModel u GENH30 25 LAN gt gt gt
18. ure 8 Figure 7 Figure 8 Figure 9 Launching IVI HEIp visser cies cere eieaiccavere 4 Sample of IVI Help ssssssssssssssssnserresssrrsrnsessrrrernes 4 Launching PythonWin c eceeeeeee estes eee eee teens 5 Intellisense ind ews conse tacetntene Center i 6 Example Python Session cccceeeeeeeeeeeeeeeeeeeaeeneenees 7 Simulating an Instrument ccceeeeeee ee eee ee eee es 10 Enabling Automatic Error Query cccceeeeseeaeeneeneeas 10 Enabling a Simulated RS 232 Instrument 11 Using COMexception to Catch Errors ceeeeeeea ees 12 Using SYST ERR to Catch Errors eeeeeeeeeees 13 Initializing the RS 232 Port cceeeeeee eset eee ees 14 Page 2 of 16 Getting Started with IVI COM and Python LAMBDA for the Lambda Genesys Power Supply 3 Requirements A Windows Operating System This tutorial is written using Windows XP SP2 Because of the requirement for VISA hardware drivers and COM objects this tutorial cannot say that other operating systems are supported Python Software This tutorial requires the following downloads 1 Python version 2 5 2 Earlier versions have not been tested The comtypes package may not be compatible with earlier versions of Python http www python org download Used here python 2 5 2 msi 2 PythonWin build 211 Python extensions for Windows This is a Windows graphical development environment for compiling
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