How do I set the filter frequency of SCXI 1125 with NI-DAQmx?

[CoastalMaineBird]

I am a newbie at NI-DAQ mx.

The SCXI 1125 module advertises a programmable filter at either 10000 Hz, or 4 Hz.
But under MX, there seems no way to access it.

On page D-4 of the SCXI-1125 user manual is this:

In LabVIEW, can I use a VI to change my filter setting?
No, currently there is no VI available to do this. You must use the
configuration utility in the Measurement & Automation Explorer to
configure each channel’s filter setting.

But if you go to MAX and rummage around, the only reference to a channel filter is in the properties of the module under TRADITIONAL NI-DAQ.

There is no such reference in the MX section.

Changing the traditional setting has no effect on the MX program I'm testing.

So do I have a useless feature, or what?

I'm on LV 7.0 Win2k, MAX 3.0.0.3014

[EdDickens]

I don't know if this will do it or not (I don't have an 1125 here to try) but there is a DAQmx Channel property node that lets you set the Lowpass Cutoff Freq for a filter.

The image shows the sub menu path to get to it. Might be worth a try.



Ed

Message Edited by Ed Dickens on 05-24-2005 12:24 PM

[LV_Pro]

Are you using either NI-DAQmx tasks or Global Channels? If so, when you configure the channel(s) in MAX's "Data Neighborhood" you should get to a screen that looks like the attached. It will give you the option of setting the frequency. I will caution that I recently had problems with having values set in MAX for attenuation on a SCXI1327 (I think) accessory (on a SCXI1126) would remain set. If I changed them in Max and then exited the would revert to the default when I looked again. This was a problem in NI-DAQ 7.2, which was resolved by downloading NI-DAQ 7.4. It is a really big (~700Mb) download, but if you get the quarterly updates it was included in the recent on. It also allows you to tell Max to simulate various NI DAQ boards, allowing you to do some of the MAX configuration "stuff" without having the board installed (as I did with this example).

Hope it helps, if not keep asking!

Putnam Monroe
Certified LabVIEW Developer

[LV_Pro]

I will also mention that this filter is on the output of the 1125, rather than the input, if I'm not mistaken. That means that it is before the input of which ever DAQ board you have connected to your SCXI chassis though.

Putnam Monroe
Certified LabVIEW Developer

[CoastalMaineBird]

YES, that works. Although not quite the way I expected.

If I set the property AFTER I add the Thermistor channel, it complains if I set ENABLE to TRUE
If I set the property BEFORE I add the Thermistor channel, it complains if I set the ENABLE to FALSE.

I guess that makes sense: you can't turn the filter OFF for a regular channel, you can't turn it ON for a CJ channel.

Any value 4.0000001 or above sets the cutoff to 10,000 Hz.
Any value 4.0000000 or below sets it to 4.0 Hz.


The way I'm doing it, it applies to all channels. Now I need to figure out how to assign it to a channel individually (if possible).

I realize that I could specify the channels as "SC1Mod1/ai0:1" in this example, but I'm coming from a (working) program where the channels can be in any order; modules intermixed, channels intermixed, whatever. I want to feed them one at a time into NI-DAQ - let it sort them out.

Thanks for your insight.

[CoastalMaineBird]

If so, when you configure the channel(s) in MAX's "Data Neighborhood"

I don't like using that global stuff, and neither does my client. The problem is that it's outside the program. My program handles a bunch (200+) of channels, some that LabVIEW knows nothing about (from TCP instruments, and other places). But they're all specified in a (relatively) common format, in a common place. So it doesn't make sense to go outside the program to change parameters for them.

I want to specify everything about the channels from code.

Thanks for your ideas, though.

[CoastalMaineBird]

I'm not sure what your point is.
According to the block diagram, there are 8 filters on the isolated side and 8 filters on the non-ISO side. My guess is that the iso filters are 10 kHz, and the common side filters are 10kHz / 4 Hz, although the filter switch is not shown.