9205 module: incorect measurements

[jaraalmonte]

Hi,

I have 2 9205 32 channel AI modules in a 9074 cRIO chassis. 1 is in slot 7 and one is in slot 8. I am acessing data using the Scan Engine Advanced I/O function blocks at a sampling rate of 100Hz, with the default delay time of 8us between samples. All channels are NRSE on a 5V scale. 

Connected to each channel is the attached circuit. The current source is the output from a LEM current transducer, either module LV-20P (Rm = 140) or an LT 100-T (Rm=49.9).

I started testing by bringing channel 9 live. When the cRIO is not connected, I measure with a multimeter an output voltage of 1.19V on channel 9, and nothing but noise on any other channel. Now when I connect the 9205 module, the channel 9 value drops to 1.14V as read by a multimeter, and  more importantly, channel 25 now reads ~0.504V. If I disconnect just channel 25 from the module, the module reports an input voltage of 1.14V, the same as channel 9. If I measure the voltage with a multimeter, the DC voltage on channel 25 is only ~10mV.

I have tried both 9205 modules and they give the same results. Right now I am out of ideas, since it clearly is something internal to the 9205, and also I can't reproduce this behavior with every channel. That is, if I bring channel 8 live instead, it behaves fine, but channel 9 and 25 are always coupled for some reason.

Any ideas or suggestions? Thanks,

Jon

[Dustin_D]

Hi Jon,

I want to make sure that you have your 9205 connected properly.  This document covers the finer points of the different wiring configurations. Also the manual of the 9205 will show you the proper configuration for NRSE.

                        

 Ensure that your COM and AISENSE are connected as well as the ground terminals from all of your signals.  Also consider the length of the wire that connects your transducer to the 9505.  If you are still receiving issues try a differential measurement by connected the ground to AI8 and the signal to AI0 to see if that will give you the expected measurement.  Also as a tip, start with one channel and add them one at a time.  Reply post if you have further questions!

Regards, 

[jaraalmonte]

Hi,

As an update, I have tried everything I can think of and it is not a problem with my circuitry. I have taken a DB37 connector and connected all pins together except pins 9 (DO0) which I left unconnected, and pin 20 to which I connected an Agilent E3631A power supply set to 2V relative to the grounded pins. On all 3 of my 9205 modules (2 NRSE, one RSE) I can reproduce the behavior of channel 24 reporting 1/2 of channel 8 (so ch8 has 2V, ch24 has 1V), even though channel 24 is grounded.

I am using the recommended software set for RIO 3.0.1 with scan engine support along with advanced i/o support and the 2009f2 patch. I have confirmed that this behavior happens whether I address the channel using advanced i/o or whether I call the channel directly using the variables under the module in the project explorer. I have not tried using FPGA mode, only scan engine interface. Right now, I am thinking it is most likely a bug, but if you have any sugestions I will try them.

Jon

Edit:

 To clarify, I have the D-Sub version of the 9205 and my DB37 connector is directly connected to the module so that there are no external effects.

Message Edited by jaraalmonte on 02-24-2010 11:54 AM

[Donovan_B]

This sounds very similar to what was reported to R&D (# 130493) and was fixed in version 3.1 of the NI-RIO driver.

Is there a reason you are using NI-RIO 3.0.1 with LabVIEW 2009?  The earliest available version of NI-RIO that officially supports LabVIEW 2009 is 3.2.1 and the most current version is 3.4.  I would recommend upgrading your version of RIO to get full support for your current version of LabVIEW as well as the fix for what you are describing.

[jaraalmonte]

As far as I know, we do not have a site license for LV2009 although I might be mistaken. I am running LV 8.6.1. I will see if I we do have a copy of 2009 and try that...

Jon

[Donovan_B · Accepted solution]

I must have misunderstood. I thought you said in the previous post you were using LabVIEW 2009 with the f2 patch. You should still be able to get the fix in LabVIEW 8.6.1 by upgrading your version of NI-RIO. All versions beginning with 3.1 should contain the fix and support LabVIEW 8.6.1.  The current version, NI-RIO 3.4, also has this support.

[jaraalmonte]

Thank yon Donovan, upgrading has fixed my measurement problem. I have new problems with LV2009, but as they are unrelated to this I will start a new topic.

Jon