USB-5132 as gated integrator?

[OBirer]

Greetings,

Can I use USB-5132 as a gated integrator?

I have a PMT signal with 1-10 kHz rep. rate. The signal itself lasts 2 us and I would like to slice this 2 us window into smaller bins and collect data in that specific window and integrate the signal.

I checked the manual, it looks like it does not have a built-in gated trigger mode. I am wondering if there is any wy around it...

Best regards

O.Birer

[Nathan-P]

O.Birer,

To be honest, I'm not too familiar with gated integrators/boxcar averagers.  For your question, can you explain in more detail what you are trying to do?  For example, I found this article.  Are you trying to do waveform recovery, or static gate acquisition?  

You are correct, the USB-5132 doesn't have a hardware gate-trigger, just the standard edge-trigger.  This particular unit also doesn't even have hardware trigger re-arming, which means that after each trigger is recieved, the digitizer must be re-initialized in software (which is not deterministic), and may not work at 1-10kHz since the round trip from the hardware to the driver and back may not happen that fast.  Overall, this is not a very good unit for your application from the sounds of it.  

From what I understand so far, you want to trigger from your PMT, digitize/acquire the 2ns of waveform data, and then integrate it, and do this repeatedly at 1-10kHz.  Also, from your description, you want to have some delay between the trigger and a smaller slice of your waveform that varies over the total 2ns of time, and that you will only acquire one slice per trigger (sent every 1-10kHz).  Is this all correct?  If so, I would not reccomend the USB-5132, since you will likely need the following digitizer/oscilloscope features:

• Multi-record Acquisition support (Hardware trigger re-arming)
• Trigger Delay Support (for moving the smaller slice in relation to the trigger)

Actually performing the integration must happen in software, since we have no digitizers/oscilloscopes that have hardware integrators.

I hope this helps.

-Nathan

[OBirer]

Dear Nathan,

Thank you for your answer. I already have the 5132, and I have been trying to figure this out for a while.

The PMT signal is 2 microseconds long, not ns. So I would like to perform static measurements as described in the article you linked, but do so with ~500ns gates which will be located at different positions with respect to a trigger signal other than the PMT signal. In essence, I would like to time resolve the signal which lasts for 2 microseconds. I can generate the gate signal and sweep if necesaary.

My problem is I could not figure out a way to sample the waveform within a gate. Can I use the rising edge to start acquisition and the falling edge to stop the acquisition?

Best regards

O.Birer

[Nathan-P]

To trigger the USB_5132, you cannot do gated triggers, therefore the only trigger that sounds applicable is an edge trigger.  This means that the digitizer will trigger on either a rising or falling edge of your analog signal, or you can configure it as a digitital trigger on the PFI line.  To simulate a gated trigger, you can set your acquisition properties.  For example, if you wanted a 100ns gate you could setup a the acquisiton like:

• Sample Rate: 100MS/s
• record length: 10 samples
• reference position: 0

These properties will set your "time per record" at 100ns, which would be like a 100ns gate starting at your trigger, and then ending exactly after the 10 samples were taken.  The reference position configures the digitizer to not save any pre-trigger samples, since you probably don't want any of the data before the trigger happens.  

Does this make sense?

[TimmTheEnchanter]

My problem is I could not figure out a way to sample the waveform within a gate. Can I use the rising edge to start acquisition and the falling edge to stop the acquisition?

(This is generic for all digitizers, not exclusive toe the 513x devices.)

Because digitizers/oscilloscopes take as granted that the window of time for which you wish to acquire is known at the time of the beginning of the acquisition, you cannot configure it to have a variable window size on-the-fly (without software intervention to stop and reconfigure.)  This isn't done on the fly on any oscilloscope product I've ever heard of, from any vendor.  In other words, the concept of "gating" an acquisition is not a concept natively handled by digitizers/oscilloscopes.

Work-arounds:

• If you choose the largest possible gate time and set that to be your record length, then you can post-apply software to trim the data you don't care about.
• If you can allow software/driver interaction with the instrument while your signal is generating, you can stop, reconfigure for a different record length, and re-start the instrument's acquisition again.  Expect this could take a few milliseconds or more, depending on how you implement it.

In essence, I would like to time resolve the signal which lasts for 2 microseconds.

Is your signal repetitive?  I can only imagine that acquiring several ~500ns windows of data with relative adjustments must mean your signal is repetitive.

Just for reference, see the Acquisition Engine for the USB-513x devices.  You can see you will really only have two signals to work with to manipulate this device in hardware time: there is a start trigger (must be digital) and a reference trigger (can be analog or digital).  You can send a "start" trigger or a "reference" trigger only to capture the constant amount of data which is (in some constant way) related to the trigger event you set.

[OBirer]

Thank you for your answers.

Yes, the signal is repetitive, 1-10 kHz.

I am wondering about PFI. Will this mean that the acquisition will be allowed as long as PFI is high and stops when PFI is low?

Best regards

O. Birer

[TimmTheEnchanter]

Will this mean that the acquisition will be allowed as long as PFI is high and stops when PFI is low?

No, the PFI lines have a limited set of functionality, and that kind of functionality is not included.  You can see what the PFI lines are useful for by looking at the specifications for the device in question (e.g. 5132/5133).   You can get more information on what these functions are by referencing the NI-SCOPE help documentation (including the acquisition engine state diagram).

[Nathan-P]

On the PFI line, the trigger is an edge-based trigger, not a level based trigger.  This means that the trigger is actually the transition from low to high, or high to low, rising edge and falling edge respectively.