Why do I need to connect QTR and S+ directly on the strain gage?

[LA Tech]

I connected two wires with a 2" 120-ohm strain gage. Later, connect these wires to a strip connector. Now connect the red wire from NI system (SCXI-1314 which is already converted for 120-ohm) to red in the strip. This red is P+ in SCXI-1314. Now I connect the black (QTR in SCXI-1314) and white (S+ in SCXI-1314) to the white wire on the strip connector. Unfortunately this did not work. I got a constant strain output. But when  I connect the black (QTR in SCXI-1314) and white (S+ in SCXI-1314) to the strain gage directly it works fine.

I tried with 4 strain gages and got the same result.

It will be great if any one can tell me what went wrong?

[aNIta B]

Hi LA Tech,

         It sounds to me like there is something wrong either with your strip connector or with the connections to it.  I would recommend trying a different strip connector, and re-doing your connections.  Have a great weekend!

[LA Tech]

Hello,

It seems to me there is no problem with the strip connector, as we have connected our test strain gage on that one and it worked fine. The only difference is the length of the wire. Moreover,  we have connected two more strain gages on the same strip connector on different location and they were working fine.

Do I need to connect any signal amplifier or any type of amplifier as the length of wire is 10'-0"? It will be great if you please advise once.

Best regards,

Shaurav.

[aNIta B]

Hi LA Tech,

          As a general rule, your cable length shouldn't be more than 2 meters.   If you're needing to keep your cable length that long, I think you will need some sort of signal amplicifation.  I'm curious though, if you connect shorter wires to the same strain gauge using that connector- do you still get good values?  

[LA Tech]

Hello,

We used a new batch if strain gage and believe that the previous batch was damaged some how. However, I will be grateful if you can advise me some amplifier type that might be helpful to use. I also believe that the length is making a big difference.

Best regards,

Shaurav.

[aNIta B]

Hi LA Tech,

         I assume you are using the SCXI-152, in which case you have built in amplification in the module.  This gain is typically configured automatically, but is also software-configurable.  You can read more about this feature HERE. Have a good one!

[LA Tech]

Hello,

Good morning and thank you very much for your help.

I am afraid, we are using NI PXI 1052 and SCXI-1314. I hope you can inform me more.

Have a nice time and best regards,

Shaurav.

[aNIta B]

Hi Shaurav,

            Sorry, in my last post, I meant to say "SCXI-1520", which I am assuming you have  because you have the 1314 terminal block.  The SCXI-1520 has programmable gain, as mentioned HERE.  Also, I recommend looking at THIS discussion forum post becauseit talks about the different ways to set that gain.  Have you tried applying a gain in Measurement and Automation Explorer?  How are you programming this?  Thanks!