Reading multiple strain gauges (10 to 20 strain gauges)

[cyotani]

This is strating to sounds more possible now.  

The precision resistors to complete each of the strain bridges have already ben ordered and I will be using a quarter bridge configuration for everything. 

So it sounds like the U3 does NOT come with any internal gain or amp to amplify the strain voltage which would require a few LJTick-InAmps to amplify it and give me a between resolution. While the U6 DOES have an internal amplifyer post multiplexer which takes care of all of my strain bridge amplifactaion and give me the ability to read the ("Analog Input Ranges of ±10, ±1, ±0.1, and ±0.01 Voltages").

The frequency we want to sample at least 100 Hz. Now I'm leaning toward getting a U6 and configuring it to read 5 strain readings for one corner of the car first to get comfortable with the hardware. Then adding the Mux80 to read all 20 strains in one system. 

What is your contact info to discuss this further?

Thanks for the support!

[LabJackSupport]

Correct in your U3 versus U6 reasoning.  A bridge circuit provides a small differential voltage signal, so you need amplification and differential inputs.  The U3 low-voltage analog inputs do support differential, but do not have any amplification, so you need the LJTick-InAmp.  The U6/T7 analog inputs do support differential and do have amplication options of x1, x10, x100, and x1000 (corresponding to input ranges of +/-10V, +/-1V, +/-0.1V, and +/-0.01V).  In addition to the amplification, the U6/T7 analog inputs are 16-bit (or more) class, whereas the U3 as 12-bit class analog inputs.

A couple details to discuss more are excitation voltage, and max data rates which will be limited by the extra settling required at higher amp gains.  You can contact us at support@labjack.com, or I suggest you start a topic on our forums at forums.labjack.com.

[cyotani]

I just wanted to update this with the solution that our team is going with to solve this probelm in case anyone searches and stumbles upon this thread.

After talking with the LabJack support team, they suggest using a LabJack U6 DAQ. In order to get a good sampling rate and resolution, their in line amps will be used to amplify the signal as well as provide the excitation voltage source. 350 Ohm strian gauges will be used instead of the original 120 ohm ones to not exceed the current rating of the device. 

For every 2 strain readings I will need 1 LJTick-InAmp and a total of 3 analog inputs. With the labjacks 14 analog inputs this alows me 8 strain readings which is enough to read a corner at a time for the initial stages of this product.

In order to read the strian of the whole car, (24 gauges) a Mux80 expansion board will be used to provide the additional analog inputs.

Thank you LabJack Support team for all the help and support of my School's FSAE team project, as well as the other members who posted in here with suggestions!