11-15-2005 08:43 AM
12-15-2005 03:54 AM
Hi,
I do not know the trick you mentioned to amplify the clock signal.
Which NI show was it ? perhaps I could find more details if I know it
salutations,
Marc L.
NIF
12-15-2005 02:14 PM
12-19-2005 03:32 AM
12-19-2005 03:50 AM
12-19-2005 06:12 PM
I tested the attached example on a simulated device so hopefully it will work on a real one without any kinks. You didn't specify your programming environment, so I'm assuming you're using LabVIEW. If not, hopefully you can translate to the appropriate ADE based on the picture of the block diagram.
In the example, I'm using an AO task to program the analog trigger as specified. This has two consequences. First, you won't be able to perform hardware timed AO while the AI acquisition is running. If this isn't acceptable, you'll need to try the second approach described in the next paragraph. Second, you'll have to wire the signal to PFI0 instead of an AI channel. With this configuration, the signal will be seen with a +/- 10V range and referenced to AI Gnd. Since the trigger DAC is an 8 bit comparator circuit for this board, you'll have ~80 mV of resolution. You didn't mention what the amplitude or DC offset (if any) of your signal is, but hopefully this resolution will suffice. You can use the level and hysteresis properties for the analog trigger to filter out noise in the analog signal or account for DC offset.
If the constraints listed above aren't to your liking, you can try to use a second AI channel as a trigger channel. This has some advantages and disadvantages. The disadvantages are that this requires you to use a trigger with your AI task and it also requires you to acquire another channel of data. You mentioned the trigger wasn't a problem so this can probably be taken care of with simple analog start trigger. The data can easily be thrown away, but depending on your sampling rates, it might require a lot of extra bus bandwidth or processing power when scaling the data. On the positive side, it doesn't require you to use up your AO channels needlessly and you can apply gain to the input signal in order to effectively increase the resolution of the trigger circuit. You can also apply a low pass filter and different terminal configuration if desired. The gain, coupling, terminal configuration, filtering, and coupling applied to the signal is controlled by the values used in the Create Channel VI and the Channel Property node. To create an example that does this, simply start with one of the shipping examples for an Analog Start trigger, change the trigger source to one of the AI channels instead of a PFI or APFI pin, and change the clock source to the AnalogComparisonEvent as shown in the attached example.
That should do it. Good luck with your application and post back if you have additional troubles.