Nulling strain large number of strain gauges

[Barnstyle]

I am trying to strain null 17 to 18 strain gauges at the same time.  Each gauge strain nulls individually but when I try to strain null them at the same time, the machine will not finish the null process and therefore freezes the labveiw program. 

Has there been any other problems from other customers that have encountered this and if so, how could I go about to correct this problem? 

Bernard Frankl

[pallen]

Do you have all of your strain channels in a single task?

[Barnstyle]

The strain gauges are going through a single channel.  We have three modules going into a single SCXI-1520 chasis.

Bernard Frankl

[pallen]

A single channel?  Or a single task? 

I'm also currently working on a project that is using an SCXI-1001 chassis with two SCXI-1520 modules. 

I have a single task that has multiple channels representing my load cells and LVTs.   The documentation for the Offset nulling VI seems to indicate that it can null several channels at once.  But I've yet to figure out how. 

It sounds to me like you and I both have a similar problem.  Our NI representative is supposed to be meeting with me tomorrow afternoon.  This will be one of the questions I will have for him.

[Barnstyle]

Our system is nulling the strain gauges in a single channel mode.  The three modules are channeled to a single function to strain null in the backpannel of LabView.  We also have a system that reads LVDT's, an analog input (Load Cell), thermocouples and strain gauges at the same time.  It all works together fine except for the strain gauges.  If there is less than ten strain gauges, then the systems work well together without much delay.  However, when there are a large number of strain gauges, the system will not null them at the same time.  When I disable all the systems except the strain gauges, we run into the same problem with strain nulling.  Therefore, I have narrowed it down to jus the strain gauges that are causing the problem.  I have checked each gauge individually to determine that it is a software or system problem and not the gauges themselves.  The gauges will work together when I have 17 of them when I DO NOT strain null them indicating that it is the nulling process that is not working.  When we do not strain null them, there is a large amplitude of ranges that is registering so we need to strain null them for our test.

Bernard Frankl

Thank you for your reply and your help.  It helps us greatly and maybe we can help eachother out here if we are working on the same type of system.

[pallen]

Hello Bernard,

I had my visit from my NI sales rep and he showed me how to add multiple channels to the offset null function.  

I'm including a little VI (7.1) that works for me here with 12 strain gages.  

In NIMAX I have one task that has 24 channels in it.  12 of them are strain channels that I want to null.  

Using MAX I created 12 Virtual Channels with the same name and properties as the strain channels in my single task.  I was then able to select only the strain channels as a subset of my task.  This worked well for me and didn't seem to take any longer than nulling a single channel.  

Hopefully this information will be useful to you.  

Good luck.