Using a Scope IVI Specific Instrument Driver to Acquire Multiple Waveforms Simultaneously Primary Software: Instrument Drivers/IVI>>IVI Class DriverPrimary Software Version: N/A Primary Software Fixed Version: N/A Secondary Software: LabWindows/CVI Development Systems, LabVIEW Development Systems
Problem: How do I use a scope instrument driver to acquire multiple waveforms simultaneously? Solution: Most traditional and IVI instrument drivers only allow you to configure acquisition channels one at a time. However, for this particular application, acquiring from multiple channels should not be a problem. If you want to acquire waveforms from channels 1 and 2 on a multichannel oscilloscope (scope) for example, first configure the vertical attributes and channel characteristics of channel 1and then do the same for channel 2. The settings for each channel are then stored in the instrument's memory, and are not lost. Most scope drivers should have high-level VIs which will allow you to do this. Next, configure the horizontal and triggering attributes of the acquisition. Again, most scope drivers have high-level VIs for this purpose. To acquire multiple waveforms using IVI drivers, DO NOT use a read waveform VI. The reason for this is because read waveform initiates an acquisition and then fetches back only one waveform on a specified channel. A waveform from another channel cannot be acquired without initiating a new acquisition. Thus, the two waveforms will not be synchronous. Instead, use the low-level acquisition VIs of initiate and fetch. First, put the instrument in its "wait-for-trigger" state by calling initiate. Then, after the instrument receives a trigger, it will acquire waveforms from all enabled channels, and place the data in its output buffer. Next, fetch the data back from each acquisition channel separately. Since a new acquisition is not initiated in the fetch waveform function VI, no new data is acquired. Thus, in this case, the data fetched from the two channels will have been acquired simultaneously. For non-IVI drivers, the names and behaviors of the high-level VIs cannot be discussed definitively since no specifications on scopes were made. However, just about all scope drivers have some sort of "read waveform" VI, but these may or may not include the initiate function. If initiate is included, then use some sort of intermediate VI calling procedure. If initiate is a separate VI, then calling read waveform twice would result in acquiring two waveforms simultaneously. Related Links: Basic IVI Class Drivers and IVI Instrument-Specific Drivers Developer Zone Category: IVI Attachments:
Report Date: 07/19/1999 Last Updated: 03/19/2008 Document ID: 1NI8LI9A |
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