Why can't SCC-sg24 be used as a first stage in a dual stage system as documented

[storeytime]

If I put the SG-24 as the first stage (J9) for dual stage, and SCC-LP03 as second stage(J1), but only select the LP03 for J1 the voltages come out are fine.  The user manual states that it can be used that way.  You can't have the LP03 as the first stage because because the second input is the ground reference.  Differential inputs must goto the wheatstone bridge in the sg24 module.  why is the SG-24 not suppose to be the first stage according to MAX or in the document at http://digital.ni.com/public.nsf/allkb/34E477CC7C41F698862571AE0067F8D1

[Travis_W]

Hi,
The documentation you've referenced is in the process of being updated.  The SCC-SG24 can be used as either a single-stage module or as the first stage of a dual-stage configuration. 

For using the SCC-SG24 in either of these scenarios, the user manual provides the following instructions:
"Plug the SCC-SG0X or the SCC-SG24 into any SC-2345 socket J(X+1), where X is 0 to 7, and wire the bridge configuration signals to the module."

Have you tried using the SCC-SG24 in J1, and the SCC-LP03 in J9?

Have a great day!
Travis W

Message Edited by Travis W on 08-25-2006 08:01 PM

[storeytime]

yes i have but the LP03 puts out only a single signal not the differential signals needed for a wheatstone bridge. therefore it hase to go SG24 to LP03.  I have SG24 in J9 and LP03 in J1 the voltages out are fine.  Just curious why I can't select it in the MAX software.

[Logan_K]

This was a bug in NI-DAQmx 8.0, which should have been fixed in NI-DAQmx version 8.1. What version of DAQmx are you using?

-Logan K

[storeytime]

I am using NI-DAQmx 8.0.  How do I get 8.0.

I have the latest updates package we received on as of February 2006.  How do I get 8.1.  We have a license for Professional development suite.

Message Edited by storeytime on 08-28-2006 02:09 PM

[storeytime]

I downloaded Ni DAQmx 8.1 and installed it said it couldn't make any changes to MAX 4.0.3.  I still cannot add scc-sg24 to J9.  Also, none of the readme files for the NI-DAQmx software have sc-2345 listed as compatible hardware.

[Logan_K]

I am sorry - the "bug" that I was talking about before is different than what you are referring to and I think I confused us both. The SCC-SG24 module was not designed with cascading in mind, so it doesn't fully support being the 1st stage of a cascading configuration, which is why MAX won't let you select it for the 1st stage. However, due to the way that the inputs to the SCC-LPxx modules are designed, they will work with the SCC-SG24 module in a cascading configuration. The way to make this work is to configure your hardware with the SCC-SG24 module in the 1st stage, and the SCC-LPxx module in the second stage. Then, in MAX, configure the SC-2345 to have the SCC-LPxx module in the first stage, and the SCC-SG24 in the second stage. If you do this, then the scaling for both of the modules will be handled properly in the driver.

Regards,
Logan

[storeytime]

Will the .5 gain of LP03 cause any problems with the scaling?

[Travis_W]

Hi storeytime,

The scaling should be handled correctly if you employ the workaround mentioned above.  Are you seeing that there is a problem?  If so, please describe the behavior.

Have a great day!
Travis W

[storeytime]

With the SG24 in Module J9 and LP03 in J1 I was getting response much lower in the predicted gain output.  So I read the pinouts for the SG24 and the ACH (x) - and ACH(X+8) - are left floating therefore one needs to ground the - inputs on the LP03.  So I tried to ground them to AIGND on the screw terminal block of the sc-2345 as it says to do in the LPXX literature.  But in looking at the documentation for the Sc-2345 there exist no AIGND acces from the screw terminal block.  So I then preceded to read the PINOUTS for the J9-16 on the SC-2345 and grounded them to PIN 6 which is AIGND.  Is there an AI GND on the screw terminal block so I can ground there wire with a more secure means.   This problem clears up the Voltage response problem. 

So if you ground the LPXX (-) inputs you can use the SGXX as first stage in a dual stage for signal acquisition and filtering.

Am I wrong in making these assumptions?