Gated event counting for a finite time

[UMeng]

I am using a PCI 6110 card for gated photon counting. The digital signal is coming from a single photon counting module, which generates a single TTL pulse upon receiving a photon.  It also generates ~100 dark count /sec.  To get rid of the dark counts, I use gate pulses with very small duty cycle.  In this way, the dark counts are suppressed.  I want to operate for a fixed time interal with a resolution of ~1ms.  My gate pulses are at 800kHz.  Their duration is on the order of 10ns. Is there a way that I can perform gated counting for only 10000 gate pulses?  Thanks.

[NI-Bongo]

Hello UMeng,

I don't completely understand exactly how your setup is configured.  Are you using an edge counting task with a pause trigger?  If so, what are you using for the gate signal?

If you are using this method, you could use one counter to do the event counting and the other to generate a finite pulse train to act as you gate signal.  Simply generate gate pulses with the duty cycle you want and set the number of pulses to the number you want.  In LabVIEW Example Finder, there is a VI in Hardware Input and Output»DAQmx»Counter Measurements»Count Digital Events called "Count Digital Events-Pause Trig.vi" that you could modify a bit to do this.

Also, how long are the counts and are the dark counts and real counts the same duration?  Let me know if this helps or if I'm not understanding what you are trying to do.


Message Edited by NI-Bongo on 03-04-2008 12:21 PM

[UMeng]

Thanks for your reply.  My gate pulse is coming from our Laser pulse picker.  It generates one TTL pulse for every laser pulse.  The pulse picker is running at 800kHz.  I do not have an easy way to control the pulse picker and make it generate finite number of laser pulses.  So our gate signal is fixed.

One laser pulse may or may not generate one photon at the sample. But the photon counting device generate ~100 dark counts/sec.  To suppress the dark count from the photon counting device, I have to use the gated counting mode.  The gate pulse from the laser pulse picker has a very small duty cycle (<1%), which can eliminate most of the dark count and preserve the true signal.

I wonder if there is a way I can make my pci-6110 card to only collect counts over (for example) 10000 gate pulses.  I know in finite buffer event counting, the number of gate pulses can be specified.  But the gate pulse is no longer a real gate. If I use method like "BUFFERED_SEMI_PERIOD_MSR", 0 count during a gate may cause trouble, because a laser pulse has cerntain possibility of not generating a photon from the sample.




Message Edited by UMeng on 03-04-2008 12:51 PM

[NI-Bongo]

Hi UMeng,

Your question stirred up an interesting discussion at the office.  You can't do gated, buffered counting as the gate input is used to trigger the latch to the buffer.  We came up with a couple of ideas here, but neither are perfect.  It is important to also consider that you are running right at the specifed minimum pulse durations for the gate and source pulse durations for the 6110, which is 10 ns. 

NI PCI-6110/6111 Specifications
http://digital.ni.com/manuals.nsf/websearch/A9694D34EF10469386256E3000539747

With that in mind, you could use an external high speed AND gate to generate a signal for a simple event counter to read using the laser gate and the photon detector output as input to the AND gate.

Otherwise, you could try doing gated event counting on the signal and simple event counting on the gate as long as the gate frequency is consistent.  Then you could use the frequency of the gate and number of counts of the gate to get the total acquisition time.  This will require that you start and stop both counter tasks at as close to the same time as possible.  The start could be triggered with an Arm Trigger.  Getting the values from the counters would always require 2 software calls, but the longer the acquisition, the less important this error would become.

Let me know if either of these sound appealing.

[Lexx11]

Hello NI-Bongo,

I am using one counter to do the event counting and it works great. Can you give me more details about how to use another counter to generate a gate signal, please?

Regards,

Alexey

[Finnabon]

Hi Alexey, 

Right now, I'm assuming your post is about a different issue than the above. Have you checked out the example in Example Finder called Count Digital Events - Pause Trig.vi ? It is also located here. Let me know if you need more information about this or if it doesn't work for your situation. 

Allie

[Lexx11]

Hello Allie,

I am using USB 6251 platform for photon counting. The TTL pulse is coming from a single photon counting module upon receiving a photon. My goal is to count the pulses with a counter for a finite time window and then reset the count after each time window. What do you think would be the best way to implement that?

So far, I am counting the pulses countinuously using one of the counter. With the help of count digital evant-pause trig.vi example I can trigger the count by using a function generator. Can I control the counting time window internally and then reset the count?

Thank you very much

Alexey

[Kevin_Price]

You can do this by configuring a buffered period measurement task.  You just have to think about it kinda sideways is all.  You'll treat your photon signal as a timebase and some kind of timing signal as the signal whose period you're measuring.  If you simply read the count values as U32s, your measurement result will be the # of photons per interval.

Here's a recent thread on a similar topic that includes discussion and example code.

-Kevin P