Question about setting up potentiomenter.

[Krickette]

OK, forgive me, I'm completely new to this. I used labview a coupl of times in school but it's been so long and now I have a big project on my plate. I've been researching but I just can't seem to put together the information I need. 

I have

1 NI cDAQ-9178

4 NI 9237

25 or so NI 9499 

25 or so RJ50 cords

Plus I will have a boat load of potentiometers and strain guages. 

I currently am trying this out with just one pot, for simplicity. 

I have to hook up the potentiometer to the 9499. Sounds simple, right? Wrong. Can't find any useful information! I don't know what to do. 

The eventual goal is for the potentiometers to measure variable resistance which we will use labview to "convert" to degrees that the pot has been turned. We're trying to measure range of motion in joints. Eventually we will have these all rigged to a harness on a human arm, then a human leg, then something to do with a goat....

She wants them to be able to be calibrated as well. 

So we're going to synchorinize data from the potentiometers, the strain guages, and our polhemus device and have them all match up in excel and hopefully make sense. 

So please, help me figure out how to wire this thing so that I can get started? I don't know if I'm supposed to use all 3 terminals on the pot even, and I don't know if it matters which wires go in which terminals of the 9499. 

Also if anybody wants to recommend good potentiometers and strain guages for this, I need them to have linearity of 1% or less, multi or single turn, low resistance to movement... I don't even know what ohm range would be good.... 

[ShotSimon]

Hi Krickette,

Automation can be a bit overwhelming just hang in there. 

Break your problem into smaller pieces and post separately and you might have more luck getting responses on this forum.  Do some wikipedia searches regarding pots and strain gauges, typically with a potentiometer the outside terminals are the full scale resistance and the adjust is in the middle and will vary from the outer terminal.

Hope this helps,

-SS 

[johnsold]

Krickette,

How do you get informed consent from the goat?

What is a 9499?  I could not find any reference to it on NI's web site.

I can help with the pots.  You definitely need to use all three terminals on the pots.  Typically the clockwise end is connected to a positive voltage such as +5 V and the counterclockwise end to 0 V (Ground). Then clockwise rotation changes increases the voltage on the wiper.

For this kind of application single turn pots are best.  If you use multiturn pots the joint has to rotate a rather painful amount to take advantage of the pot's range.  Use pots with cermet or conductive plastic resistance elements, not wirewound or carbon composition.  Pots with metal bushings last much longer than those with plastic bushings.

A few years ago I developed a system to measure eyelid and jaw motion in rabbits. For those sensors we used a Hall effect pot.  It rotates a magnet.  The change in the magnetic field creates a chage in the resistance.  Because there is no friction between the moving parts and the resistor element, the torque to start it moving is very low compared to mechanical pots.  I am not working there any longer so I do not have direct access to the manufacturer or part number for the pots.

Strain gauges are very simple in principle and often quite tricky in implementation.  Do you have a mechanical design to which you must add strain gauges or are you still in the design phase where other options can be considered?  Do you have a good mechanical designer or engineer?  What are the ranges of load or strain you need to measure? What are the requirements on accuracy and resolution?  Will the measuements be static or dynamic? If dyanmic, how fast will the signals be changing?

Lynn