convert counter rate to DC analog

[NSL]

hi,all

    I use PCI 6601 and NI BNC-2121 to count the pulse from avalanche photodiode( APD,PerkinElmer SPCM AQR 14). The photon intensity detected by APD can be displayed on the labvew software. It works well.  But previous members in my lab did the build-up job. I am new to NI hardware and labivew.

  Now I am trying to feed the TTL signal from APDs （SPCM AQR 14) to an Atomic force microscopy (AFM)  controller. But only DC signal can be fed to the BNC channels  on that controller.  So  I need to not only count  pulses but also convert the TTL  pulses into a DC voltage depending on the pulse rate. The DC voltage can then be fed into the controller.  Is there any solution offered by NI?

  Thanks!

[Kevin_Price]

To solve this with LabVIEW and NI hardware, you'll need an additional DAQ board as the 6601 has no analog outputs.  I would tend to recommend an X-series board.  I believe they support the ability to perform fixed-rate sampling on a variable TTL frequency though I haven't exercised that capability personally.

In general terms, one of the banes of frequency measurement is how to handle long-ish intervals without pulses.  It's usually important to recognize those intervals and sometimes appropriate to report a 0 frequency. 

There will then be some programming to do.  You'll need to consider your requirements for sampling/update rates as well as latency (time between a measured frequency interval and the update of the analog output value).

Having said all that, you might also want to look into stand-alone frequency-to-voltage converters.  That'd be a nice direct way to convert TTL frequency to an analog voltage without a DAQ board or any programming.  You'll still have to pay attention to the device's behavior at low or zero frequency though.

-Kevin P

[Dennis_Knutson]

NI has numerous devices that can output a dc signal. You can search the products page yourself to find a device with the specs you need (and have not provided) or contact your local Sales Engineer for assistance.