need 15V. Not listed on Terminal Block. use an unsued SCC socket?

[TAMU Student]

I'm trying to set up an LVDT for my profesors lab next semester.  It requires a dual supply, the +15V and -15V that the SCC-PWR02 supplies will work.  Only +5V is listed for the Terminal Block.  Can I wire to the +15V and -15V slots of an unused SCC Socket?

[Logan_K]

There are a couple of concerns that I would have with this approach for powering the LVDT. First, how much current does your LVDT require? Since LVDTs are usually inductive, their DC current requirements can be fairly high, which is why many LVDT readers will excite it using an AC voltage source. The PWR02 option can supply up to 300mA (minus any current that other SCC modules would be sinking). The other concern is that the 15V power source isn't intended to be a precision voltage reference, so it's accuracy could fluctuate considerably. Since the scaling of your LVDT will be based off of the amplitude of the voltage, then you will probably need a more accurate voltage reference. Have you looked at the NI SCXI-1540 module, which is designed specifically for LVDTs?

Logan Kunitz

Signal Conditioning Product Support Engineer

[TAMU Student]

I have noticed different voltage values at these pins depending on how many modules were in.  I also learned that none of the +15V slots have any voltage at all.  The -15V and +5V slots are fine for the entire board but all of the -15V are givinig readings of less than 1V. 

I am also having trouble getting any readings to the computer.  I also am setting up a strain gauge using SCC-SG02,(and I'm using SCC-AI13 for the LVDT).  After setting up the LabVIEW software, I 'TEST' it and I flex the beam it's attached to and LabVIEW does not read any change (I have it set to continous).  Could this be related to the problem with the +15V?

If anyone has any suggestions, please let me know.  Should I have someone from NI come look at my SC-2345?

[Chris Adcock]

Are you sure that the straing gauge you are using is a 350ohm quarter bridge gauge? If the gauge is not then it will not react correctly to the SG02? Also lab are you working in? I am a student at TAMU as well.

[Logan_K]

It sounds like the +15V rail is burned out. There should be 3 green lights on the side of the SC-2345, if one of them is out then that could mean that the power supply that you are using isn't working. The 15V rail is coming straight from the external power supply, so do you have a different power supply that you could try out? If any of those power lines (+-15V, +5V) aren't working then that would certainly prevent any module from working properly.

Logan

[TAMU Student]

Yes, the light next to the 15V is not on, the one next to the 5V is.  I will try and find a different power supply to use, do I need to order one from NI if i cannot find one, i suppose so.

I don't know alot about the strain gauge, Gauge Factor = 2.12, that's about it, these are left over from a few years ago.  I'm setting this stuff up in the Civil Lab Building Rm. 115 I think, It's one of the Materials labs(room where we break the concrete samples, if you know where that is).

-Steven '06

[Chris Adcock]

You need to see if you can find some specs on the strain gauge so that you can make sure to get the correct module for the carrier. If you are using the wrong module then the bridge can be unbalanced and give you incorrect data or be incomplete and not give you any data.

[TAMU Student]

I have tested my external power supply and it is working fine.  I set up the softwarein MAX using the user manules for both the SC-2345 and each of the individual modules.  It really seems that somewhere inside the boad I can't get +15V.

[e-Cash-Money]

Hello TAMU Student,

If you still can't get +15V from the SC-2345, one of the components might be failing.  I would suggest that you call NI to troubleshoot the hardware with an Applications Engineer.  Further debugging and troubleshooting with the Engineer will help to determine the cause of the issue.