How do I connect and detect a high frquency pulse (0-3500hz) with a variable pulse voltage (0v low,5-10v high), on a SC-2345 connected to a PCI-6224?

[Labview Intern]

How do I connect and detect a high frquency pulse (0-3500hz) with a variable pulse voltage (0v low,5-10v high),  on a SC-2345 connected to a PCI-6224?  Labview doesn't generate a waveform if I try to graph the signal, and my analog input doesn'y recognize that the signal is even pulsing, only that it has a voltage.  Some advice would be much appreciated.

Thanks in advance,

Garrett

[Otis]

Hi Garrett,

It sounds like you want to do Frequency Measurements of a signal that is somewhat digital.

There are two ways you can really do this:

1. Wire your signal to the counter input and use the Digital Frequency examples (Help > Find Examples > Browse > Hardware Input and Output > DAQmx > Counter Measurements > Digital Frequency)
   
2. Continue taking analog measurements and use some sort of logic to determine where you are getting rising and falling edges.

I would recommend doing method #1, but you must determine which one is the best for your system.

If you want to connect to the counter pins then you will find the terminals located on the side of your SC-2345.  If you don't need to condition your signals then simply wire everything into the proper pins for your counter (below).

Default NI-DAQmx Counter Terminals (Connector 0)

Terminal	Counter Context (Default)	Motion Encoder Context	Signal Name
37	CTR 0 SRC	CTR 0 A	PFI 8
3	CTR 0 GATE	CTR 0 Z	PFI 9
45	CTR 0 AUX	CTR 0 B	PFI 10
2	CTR 0 OUT	—	PFI 12
42	CTR 1 SRC	CTR 1 A	PFI 3
41	CTR 1 GATE	CTR 1 Z	PFI 4
46	CTR 1 AUX	CTR 1 B	PFI 11
40	CTR 1 OUT	—	PFI 13

[johnsold]

Garrett,

If your signal can go to 10 volts, do NOT conect it directly to a digital or counter input. Doing so may destroy the device! Most digital and counter inputs have a maximum input of 5 V. Check the specs for your device.

You may be able to use a simple voltage divider or diode clamp to condition your signal, depending on speed, source impedance, etc.

Lynn

[AA Dan]

NI has 2 devices that will probably help.  Since you have a SC-2345 the newly released SCC-CTR01 will probably be the best way to connect a higher voltage digital signal to a MIO counter using J19 or J20 slots in the 2345.  The SCC-CTR01 can measure frequencies of digtal signals up to 400kHz and up to 48V in amplitude.  It can also general digital pulse trains up to 400 kHz 48V. 

The other product that has been out for a while that would be good if you need more then 2 of these (there are only 2 counter timer slots in the 2345 and only 2 counters on the E series and M series MIO devices) called the PCI/PXI-6624 with 8 isolated counter timers that can achieve up to 48V I/O at 400 kHz.

Hope that helps out.

[AnalogKid2DigitalMan]

You could also use an opto-isolator, transistor, or CMOS IC circuit to translate the higher voltage levels down to TTL compatible (0-5V) logic levels. Fairly simple and inexpensive.

[AA Dan]

Certainly custom circuitry can be a less expensive method to solving this type of application and many others.  However, if you're not an electrical engineer and are not familiar with a lot of the gotchas of electrical design then considering an out of box option is probably best.  Issues like temperature affecting accuracy, noise causing false pulses, current & loading issues with the signal source, etc.,.  Using a product that has been thoroughly tested and specified is sometimes worth the extra expense.  Especially if you're expecting to hand off the application to someone else for maintenance.

[AnalogKid2DigitalMan]

Dan:

I agree, but sometimes there are others within an organization that have the skills to come up with a simple hardware logic interface. No performance specs were supplied in the OP.

The SCC modules look like a nice complement to DAQ hardware interfacing/isolation. I may consider them in my next project, have been using Analog Devices 5B series and their large backplanes.

Any plans on providing a high-bandwidth F-V converter? The SCC-FV01 is only 100Hz, something on the order of 10KHz-100KHz is more realistic.