Notes about a GPIB USB Oscilloscope acquisition application

Transcription

1 Notes about a GPIB USB Oscilloscope acquisition application This note shortly describes a data acquisition application implemented in Delphi 7 and running under windows 7 (64bit). The application takes data from a 500 MHz HP54610A Oscilloscope and presents the data graphically on the PC. The overall picture of the system can be seen in figure 1. Figure 1 Tchart Component Class Libary DELPHI 7 Code APRO ASYNC Component Class Library FTDI FT2455 Virtual COM Port Driver Figure 2 USB Driver USB GPIB Converter GPIB Driver GPIB Device (Instrument) The software stack for the communication is as in figure 2:On the top is the graphical presentation layer that presents the data in a graphical form emulating the oscilloscope screen. The Delphi 7 code glue it all together and have all the functions for initiate the communication with the GPIB (General Purpose Instrument Bus) device and to present the data. For the communication with the GPIB device Delphi uses an asynchronous RS232 driver (component) from APRO (Former Turbo Box). See references for more information. The APRO driver talks via the FTDI virtual com port driver via RS232 (V24) commands. The FTDI driver converts this to USB communication via a FT245R chip. See references. All this is built into a little converter box from Prologix. See references. The Prologix converter translates the commands coming via USB to GPIB communication which in turn speaks GPIB with the connected GPIB device (Instrument). This application has been developed with bearing on the HP54610A (Agilent 54610) oscilloscope. The application can be interacted with via a GUI (Graphical User Interface) on the Delphi application. HP54610 GPIB_USB Acquestion Application notes.docx, , page: 1 (5)

2 The Prologix USB/GPIB converter can be seen in the photo in figure 3. The cost for this device is about 150$. I did buy mine from Sparkfun US. The unit can be connected directly to the GBIP instrument or you can use an IEEE-488 cable for the connection. Software implementation The software programmed in Delphi is focused on that the operator does the measurement directly with the oscilloscope. When the operator want to capture a waveform he pushes on Figure 3 the Get Data button on the application and the data on the Oscilloscope will be captured and transferred to the PC. After this the waveform will be presented and plotted on the PC. It will look alike the Oscilloscope screen. An example can be seen in figure 4. Figure 4 A thin line with the ground level for each channel is plotted horizontally with the corresponding color for the channel. Some information about the oscilloscope settings are written at the top and bottom of the oscilloscope screen. The screen on the PC will show more or less a duplicate of what you will see on the Oscilloscope. Two small LED squares (to the right) indicate the communication with the instrument. The buttons are: HP54610 GPIB_USB Acquestion Application notes.docx, , page: 2 (5)

3 Get: Image: Data: Get data from the oscilloscope. Save the Image to the clipboard and to a file (you have to give the filename) in MS Meta Format. Save the data in text format to a file. You can easily import this data file to MS Excel for further analyze. Info: Gives a screen with details about the last data acquisition from the Oscilloscope, Se figure 5. Select: Opens a new window where you can select parameters to be measured and also setting the screen colors of the oscilloscope screen. See figure 6. Figure 5 Info Screen The info form has three tabs: Settings: Channel Data: This will show all the settings for the Oscilloscope that was valid during the data capture of the waveforms. On this tab all the data and timing points are shown in a grid. HP54610 GPIB_USB Acquestion Application notes.docx, , page: 3 (5)

4 Measurement: Here you will see a number of measurements on the waveform like; frequency, amplitude, RMS value, duty cycle, rise time, fall time etc. Figure 6 Set measurements parameters and colors In this screen you can select the parameters, for each channel (1 and 2) to be displayed under the oscilloscope screen, see figure 4. You can also set the colors for the oscilloscope screen. Just click on the color shape and you will get a color dialog where you can select a color. The default button will set the color to the default values shown in figure 4. Debugging In theory it is pretty right forward to write this software. However I had considerably problems to get it to show the correct waveforms. It took a while to figure it out by low level debugging. It showed up that the order that you do the data acquisitions commands matter. Also the manuals for the Oscilloscope directed me in the wrong direction. The main lesson is that you must get the Preamble block after the Waveform transfer. If not you will get the wrong conversion parameters for the conversion of the ADC (Analog Digital Converter) values to voltages and offset values. You also have to be careful so the instrument has the time to complete the current command before given and additional command (task). The documentation mentioned in the reference section is vital to understand and do a correct implementation of the driver/application. HP54610 GPIB_USB Acquestion Application notes.docx, , page: 4 (5)

5 Performance The performance of this software implementation is excellent. It will just take a second or so to do a complete acquisition of the instrument and have the data up on the PC screen. I have a very good experience of the Prologix GBIP/USB converter. It work correctly directly and seems to be very robust (no bugs). This in conjunction with good performance and reasonable price makes it a good choice. Download The exe file that has been tested and works under Windows 7 (64 bit version) can be downloaded from SM6FIE website, se reference section. This should probably work under 32 bit version as well as under Windows XP, but this has not been tested. The source code can be delivered after a direct request by . Conclusion This note describes an application that makes it easy to download a clone of the oscilloscope screen to the PC. From there you can cut and paste the image to any document. You can take the waveform data and import it to Excel and other programs for further calculation etc. The performance is excellent and makes it easy to document your circuits and projects. References 1. Download HP54610 EXE file 2. Programmers Guide, Agilent Series Oscilloscopes 3. Prologix GPI-USB Controller User Manual V Async Professional 4 Developers Guide 5. Async Professional 4 Reference Guide 6. Agilent Series Oscilloscopes Programmer's Reference (help File) 7. TChart Users Guide 8. TChar Reference Guide 9. FTDI Virtual RS-232 driver (VCP) 10. GPIB Communication HP54610 GPIB_USB Acquestion Application notes.docx, , page: 5 (5)