[C#] Pulse Counting, maximum rate and settings

[Ben1202]

Hello,

I'm counting pulses in a C# program. The pulse rate varies between some kHz and up to 50 MHz. What is the upper limit for the count rate and can I influence it with settings?

Thanks,

Ben

[JGoebel]

Hi Ben,

this is Jan Göbel from NI Technical Support.

I don't really get your question. What kind of Hardware do you use? If you are using our X- or M-Series Multifunction DAQ Boards (62xx/63xx), 100MHz could be at the upper limit of the counter, if you tell me the specific Device I can check the specifications for you.

Best Regards,

Jan Göbel

Staff Applications Engineer

[Ben1202]

Hi Jan,

sorry for that question. I recognized that almost any information was missing when I was on my way home... So here is (hopefully) the rest of what you need:

I use a PXIe-6366 card to count the pulses. The datasheet says:

Internal base clocks

100 MHz, 20 MHz, 100 kHz

External base clock frequency

PXIe: 0 MHz to 25 MHz; 0 MHz to 100 MHz on PXIe_DSTAR<A,B>

I was wondering which frequency of the above mentioned apply in my case. The software we are using was programmed by a colleague who left and I can't find a line in the C# code or some point in NI software where any frequency is set so I was uncertain if the 50 MHz could be measured correctly. Basically it works but we are either losing pulses or counting more than are actually coming, that's why the question came up.

Thanks in advance,

Ben

[JGoebel]

Hi Ben,

first of all. The counters in our X-Series Boards are not comparable to e.g. Analog Input, when it comes to Sample Clocks. A counter (for edgecount) is basically a FlipFlop-Circuit, that does not have a clock. It will just switch his 14 Output-pins (14 bits) whenever an edge is detected. So the maximum countable frequency is just limited by the electronic RF-behaviour of the circuitboard.

Internally the Counter can count up to 80 or 100 MHz (counting 100MHz Timebase within the device). When connecting a signal via PFI, there are limitations due to the wires going from the PFI-Terminal to the Chip itself.

Sadly I cannot find a real specification on that, but I guess it should be comparable to the External Base Clock Frequency (0-25MHz), since this frequency also needs to be routed to the chip, and have to go through the same bottleneck in Bandwidth.

I cannot guarantee that, I would have to contact our R&D to get a binding answer.

But you say, that your measurement is sometimes missing counts, or counts twice? I would rather expect to miss counts, but I guess when you exceed the maximum frequency, there may different effects happening on the chip.

Could you try to decrease the Frequency to 25MHz and check if it counts correctly then? I think thats the fastest way to find out if thats the limit.

Best,
Jan Göbel

Staff Applications Engineer

[Ben1202]

Hi Jan,

thanks a lot. That's something where I can start trying to find the error. The system is on a different site to which I will have access in November again. I will setup up everything to try it with lower count rates until then. If the problem persists I will let you know.

Regards,

Ben