SCXI calibration with DAQmx

[Inpriser]

I already developed a couple of years ago a LabView program that performs SCXI 1125 calibration. At that time only traditional NI-DAQ functions were available.
We are now working on a system with 6254 M-series DAQ cards associated to a SCXI 1001 chassis, filled with SCXI 1125 cards.
As we also need to calibrate these analog inputs, I naturally wanted to use this same program again.
The problem is that M-series cards are not "seen" as NI-DAQ cards at all.

So, I tried to find DAQmx functions to do the job, unfortunately it seems that such functions do not exist to communicate with the SCXI conditioning cards...

That is a big problem for us, because we are just unable to calibrate anything on this SCXI system.
I basically need to get calibration constants from the SCXI 1125 cards and write new values back in the EEPROM if needed.

Is there a way to do that using DAQmx ?
Failing that, is it possible to make a M-series card behave as a NI DAQ device to use the old functions ?


Thanks for help.
Steph

[SanaaT]

Hello Inpriser,

The module SCXI-1125 can be used with M Series devices like 6254 and DAQmx driver.
Be sure that you will found on this driver all the functions that you need for calibration and all functions that existed on Traditionnal DAQ driver. I suggest you to see LabVIEW calibration examples that you can found on LabVIEW Help.
You will find also the calibration functions on DAQmx Advanced Palette.

Hope this help.

Sanaa T
National Instruments France

[Inpriser]

Thanks for your answer Sanaa,

I already went through the DAQmx calibration palette, but I did not find anything related to SCXI.
The examples available for SCXI 1125 calibration only shows NI-DAQ technique, that I know very well.

I guess there is maybe a DAQmx channel property that allows to read/write SCXI calibration constants, but I did not locate it. Nothing seems documented about such properties, too.

Could you please indicate me how to proceed ?

[Inpriser]

I went through the NI-DAQ 7.1 Readme file and I found this :
"NI-DAQmx and Traditional NI-DAQ Devices
The following devices are supported in NI-DAQmx and Traditional NI-DAQ. Calibration for SCXI devices is supported only in Traditional NI-DAQ."

Is there really no way to read/write SCXI 1125 calibration constants using DAQmx ?

[Logan_K]

The ability to write calibration constants for SCXI is not supported in DAQmx yet, but you can read the calibration constants in DAQmx (in fact this is what the driver does automatically every time you make a measurement). If you want to know what calibration constants the driver is using for a particular channel, then you can use the Device Scaling Coefficients DAQmx channel property: Analog Input:General Properties:Advanced: Device Scaling Coefficients: Device Scaling Coefficients.

-Logan

Message Edited by Logan K on 06-23-2005 08:55 AM

[Inpriser]

OK. That is what I was afraid of.

Do you have any idea when this function will be added to DAQmx ?
We are delivering the system to our customer, and he wants of course a acquisition chain that is calibrated...

I am not sure if it is a workaround for my problem, but when I use MAX to declare a NI-DAQ SCXI chassis there is a list of appropriate devices to control it, where M series are not listed but where PXI 6713 and PXI 6508 are listed.
These are respectively analog output and digital I/O cards used in our system, for other purposes (they use a specific conditioning, not SCXI).
I know it is possible to wire directly the appropriate digital lines of the DAQ card to a SCXI 1125 to control the chassis (serial line). Is there the same possibility with a 6713 card (as it seems stated by MAX assistant) ?
I know which lines that are to be connected on SCXI 1125 side, but which one on 6713 ? It could be PFI lines, but I did not find documentation about that.

[SanaaT]

Hello Inpriser,

You have M Series Device PCI-6254 and SCXI-1125, I suggest you to install the last version of NI-DAQ, the version 7.4 that you can download on the link below :
http://digital.ni.com/softlib.nsf/websearch/90b60d5899bcccdb86256fc700581b89

You will see on the "read file" :

Devices Supported Only in NI-DAQmx
NI PCI-6254 32 AI channel, 1 MS/s, 16-bit M Series device

Devices Supported in NI-DAQmx and Traditional NI-DAQ (Legacy)
NI SCXI-1125 isolation amplifier module

So I suggest you to install the last version of NI-DAQ (but first, uninstall the old one) and then to use calibration functions in LabVIEW.
You can found these functions on Functions Palette>>NI Measurements>>DAQmx>>Advanced>>DAQmx-Calibration.

Hope this help,

Sanaa T
National Instruments France

[Logan_K]

Unfortunately, there is no way to accurately perform the external calibration procedure for the SCXI-1125 without a 16-bit e-series DAQ board. There is actually one possible workaround for you though. Since you are performing external calibrations, then I assume you have either a high precision calibrator or a voltage output with a high accuracy DMM? If so, you could perform an end-to-end system calibration using the system calibration tool that is brand new to DAQmx 7.4. This should provide even better accuracy than only adjusting the calibration constants on the SCXI-1125 because this type of calibration accounts for errors from all elements of your system such as the M-series DAQ board and the cable, etc...

You can perform a system calibration by going to the calibration tab after creating a DAQmx global channel in MAX under Data Neighborhood. The more points you add to the calibration table, the more accurate your calibration will be.

Logan Kunitz
National Instruments
SCXI Product Support Engineer

[Inpriser]

Sanaa : I am already using DAQmx 7.4 and, except if my software installation is wrong, I have nothing related to SCXI in the DAQmx Advanced palette.
I saw this old DAQmx7.1 Readme file on the web while looking for compability information of SCXI 1125 with DAQmx.

Logan : thanks for your advice concerning the calibration tab available in MAX. This tool could be very useful and simple, but in my case it does not really help. I explain our setup : we have a SCXI 1001 chassis filled with eleven SCXI 1125 cards. We use it to perform a specific analog conditioning, and our system is a bit a mix between multiplexed and parallel mode : we use the digital lines of one PXI 6254 DAQ card only to communicate with the SCXI chassis, through one 1125 card, and therefore all cards are adressed in multiplexed mode.
When the chassis is configured, the conditioned lines are available on the HE10 connector of all 1125.
To measure these inputs, we connected direclty the analog inputs of five 6254 cards to the parallel outputs of the 1125 (one PXI card for two 1125).
This setup could seem quite complicated, but this enables us to measure all inputs at 10kHz almost simultaneously. Such a rate would not be possible in SCXI multiplexed mode.

All this to explain that we have all our channels in a parallel mode, but that is not "seen" by MAX, and hence I can not use the dedicated tool for calibration.
Again, what I need is a direct access to SCXI 1125 calibration constants. If this is possible, I would adjust my whole measurement chain by calculating myself new gain/offset parameters for each channel, as I did with traditional DAQ VIs.

[Logan_K]

I stumbled back across this post, and figured I would let you know (in case this was still and issue) that manual adjustment of the SCXI-1125 calibration constants is supported in DAQmx as of version 8.0:

http://zone.ni.com/devzone/conceptd.nsf/webmain/B3587FBEE5A1B6908625712A0074B5D8

Regards,
Logan K
National Instruments