topic Re: Multiple strain gauges in LabVIEW

Multiple strain gauges

labview.edu — Mon, 09 Feb 2009 17:14:59 GMT

Hi,

I am trying to run a simple application, where multiple strain gauges are to be read, nothing fency. I am using a Gauge indicator to dispaly the strain reading so far so good. The problem arise when I am connecting the multiple gauges, I am not sure how to assign the individual Indicators to different strain gauge, so all my gauge indicators end up showing the same value. What I want is that different gauge indicator display the reading from different strain gauges.

Hardware: Labview 8.5.1, SC-2345 connector block, SCC-SG01 Strain module, PCI-6251 DAQ Card.

Thanks,

Sine

Re: Multiple strain gauges

walter-donovan — Mon, 09 Feb 2009 17:39:57 GMT

Can you post your vi?

Re: Multiple strain gauges

RavensFan — Mon, 09 Feb 2009 18:09:11 GMT

Are you using Express VI's? If so, you will need to split the signals before sending to each indicator.

Re: Multiple strain gauges

labview.edu — Mon, 09 Feb 2009 22:10:56 GMT

How can I split the signal? I am new to the labview. I am attaching the pictures of back and front panel.

Thanks,

Sine

Re: Multiple strain gauges

RavensFan — Mon, 09 Feb 2009 23:22:33 GMT

On the block diagram, go to Express ---> Signal Manipulation.

You will see functions for merge and split signals. These are exandable. You can grab the bottom and drag them down so you can create more inputs (for merge) or outputs (for split) as needed.

Eventually you'll want to get a way from using the Express VI's, but they are good for getting a beginner started quickly.

To learn more about LabVIEW, I would recommend looking at the online LabVIEW tutorials
LabVIEW Introduction Course - Three Hours
LabVIEW Introduction Course - Six Hours

Re: Multiple strain gauges

labview.edu — Wed, 11 Feb 2009 15:11:42 GMT

Thanks to your split signal tip the gui is working! I made this GUI to null the strain gauges (manually, by turning the resistance of the strain gauge module). I am new to Labview, is there anyway I can null the strain gauge without having to adjust the delicate screw on the module?

Thanks for your help,

Sine

Re: Multiple strain gauges

RavensFan — Wed, 11 Feb 2009 16:00:48 GMT

I don't know of any other way to null the strain gages for these modules.

One thing you could do is to take an initial reading in your program with the gages unloaded, and subtract that from all subsequent readings.

Re: Multiple strain gauges

Jice — Mon, 05 Jul 2010 11:41:54 GMT

I may be a bungling idiot bt i dont seem to get a good signal from my scc-sg01, whatever i try the signal remains- -0.001700.

I've followed the manuals of both the scc-sg01, the SC2345 and my DAQ card PCI 6221 over and over again.

Can somebody help?

Re: Multiple strain gauges

enderWiggin10 — Wed, 07 Jul 2010 21:23:13 GMT

Hi Jice,

I took a look at your DAQ Assistant Setup. It appears that your signal could be railing at -0.0017 because you have set a signal input range of -1m to +1m, or -0.001 and +0.001; you will actually be able to get a signal slightly above and below this range though. Try setting a range of -0.07 to +0.07 or -70m to +70m. This might allow you to see the actual value instead of the software imposed railing value of -0.0017. Does this help?

Best,

Re: Multiple strain gauges

Jice — Thu, 08 Jul 2010 13:23:52 GMT

Thanks Adam,

It works for channel 2 however channel 1 display a value of -0,0787, i've tried the shutn calibration and the trick of changing the limits. however when I use a value above +-70m, I get an error. Is the scc-sg01's channel 1 fried or am I still doing something wrong.

With kind regards Jordy

Re: Multiple strain gauges

enderWiggin10 — Fri, 09 Jul 2010 18:30:52 GMT

Hi Jordy,

It would appear that the signal is now railing at the negative signal input range of just below -70mV. This is the lower limit of the device. Can you try to connect the signal to a handheld dmm to get a rough estimate of the actual signal? It appears that your strain signal is actually below -70mV.

Can you try to switch your signals, this will identify if the strain signal from channel one works on channel 2?

Best,

Re: Multiple strain gauges

Jice — Fri, 23 Jul 2010 09:45:21 GMT

Hi Adam,

I've switched the strain gage from channel 2 (wich worked proberly) to channel 1 and stil got -0,0787 as a result.

Any idea's?

Re: Multiple strain gauges

enderWiggin10 — Mon, 26 Jul 2010 16:33:28 GMT

Hi Jice,

It still sounds like you are saturating your input line. Can you try to read the voltage on a device with a larger input range such as a handheld DMM to find out what the actual value is?

Best,

Re: Multiple strain gauges

Jice — Mon, 23 Aug 2010 13:20:52 GMT

What exactly do i need to measure? Sorry i'm just an composite engineer with no electrical skills but with programming skills

Re: Multiple strain gauges

enderWiggin10 — Tue, 24 Aug 2010 15:40:53 GMT

Hi Jordy,

Just connect your AI+/- to a handheld DMM rather than connecting to the AI+/- of your DAQ device. Then you can find the actual voltage your device is outputting if it is out of range of your TC device.

Best,

Re: Multiple strain gauges

Jice — Wed, 25 Aug 2010 09:06:46 GMT

when i connect the DMM to the SG's I get the foollowing results

SG at AI (X)+

Voltage Strain

AI (X)+ 1.25V -0.07837

AI (X)+8 0.86V -0.07837

SG at AI (X)+8

Voltage Strain

AI (X)+ 0.86V -0.07837

AI (X)+8 1.25V +-0

What am I doing wrong here?

Re: Multiple strain gauges

johnsold — Wed, 25 Aug 2010 13:22:53 GMT

You have a differential voltage of 0.39 V and a common mode voltage of 1.06 V. You are trying to measure this with a mV range on the DAQ device.

1. Your strain gauge or signal conditioning devices are not connected properly or are defective. I am not familiar with your devices but these values seem unlikely.

2. Your DAQ device needs to be set to a range which is compatible with the output of the signal conditioning device.

Lynn