Multiple strain gauges

[enderWiggin10]

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,

[Jice]

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?

[enderWiggin10]

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,

[Jice]

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

[enderWiggin10]

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,

[Jice]

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?

[johnsold]

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