300 max value on Simulated 1126? RPM questions...

[Ralph@NES]

Hello

I'm trying to develop an instrument to do the following:

-Take 8 distinct RPM measurements using  what will probably be a TTL style sensor output.

Actually that's about it for the time being.  I need to add switching later but I have that part figured out.

Labview 8.21, PCI-6221 DAQ, SCXI 1001 chassis, 1349 Cable adapter and I'm planning on a 1126 frequency module with a 1327 terminal block.

I'm working on this VI right now on a completely divorced system with a totally simulated (NI-DAQ MX 8.5) hardware profile; the PCI-6221, SCXI Chassis, SCXI-1126 and 1327 are all in there, as simulated hardware.  I need to have functionality established before the boss is going to cut a check for the module so this is the best way to do it.

My sensors will likely be magnetic in nature, reading one pulse per revolution at 6000-12000 RPM, ergo a 6k-12k HZ input signal.

My issue is that no matter what combination of settings in the DAQ assistant, or for that matter using the 'Acquire Frequency' Example VI that came with Labview, I never get a reading above 300 from my simulated SCXI-1126.  No matter where I set ranges, anything, I get an output of what's basically the average between my low setting and 300.

MAX doesn't have the settings as if there were an actual hardware unit attached; no filters or ranges settable there.

Is this some quirk of using the Simulated devices or is there something I'm not seeing here?

I'll attach my simple DAQ asst-graph-indicator VI so that someone might be able to run it and see.

Thanks in advance for any and all help,

Ralph

[Matt_A]

Hell Ralph,

I'm not sure how you are reading any value from the counter of a simulated device. The NI-DAQmx Help file says the following about data from simulated devices:

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Reading and Writing Data with NI-DAQmx Simulated Devices

All NI-DAQmx simulated devices return analog input data in the form of a full-scale sine wave with 3% of full-scale noise. When multiple channels are in the task, the data for each channel is offset 5 ° in time. Digital data is always returned as if each eight-bit port were a binary counter. Counter data is always returned as 0.

Data written to an NI-DAQmx simulated device is scaled as if the device were real.

---

Just to verify this behavior, I simulated a PXI-6221 and tried to read from the counters. Whether accessing the device through test panels in MAX or with example programs in LabVIEW, I always read 0 from the counter inputs.

For anyone interested, this topic is also being discussed in another forum here.

[Ralph@NES]

Hi again Matt

I'm not sure if this is really counter or not?  Doesn't the 1126 work on something besides counter?

I'll attach my VI tomorrow at work and maybe you can get my gist...  I hope...  Thanks.  Haha.

[Ralph@NES]

Here's my barebones 'lets gauge the output' VI that's showing me a 300 max value.

[Matt_A]

Hello Ralph,

I apologize for my mistake before; I misunderstood your application and thought you were using the counters to measure frequency. The SCXI-1126 is an analog input module and would, therefore, use the analog input lines on the PCI-6221. However, the same idea about the simulated signal holds true. As stated in my previous post:

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@matt A wrote:

... All NI-DAQmx simulated devices return analog input data in the form of a full-scale sine wave with 3% of full-scale noise ...

---

Adding simulated SCXI chassis and modules will change the conditioning and scaling of the signal, but the same basic signal is simulated by the driver. If you examine a test panel for the simulated PCI-6221, you will see that the simulated signal on an analog input channel is a +/- 10V (full-scale) sine wave. The SCXI-1327 extends the input range to 300 Vdc, which therefore extends the full-scale to the 300V you indicated. The signal you are seeing is a result of the behavior of simulated signals in NI-DAQmx and not of any settings in the DAQ Assistant. I hope this clears things up.

[Ralph@NES]

Been a while since I had to address this, but yes--that cleared it up nicely.  Thanks Matt.