03-22-2012 10:19 PM
Ok so I'll admit I'm out of my element here as an Automotive engineering student.
I'm hooking up 2 pressure transducers (http://www.meas-spec.com/downloads/M5100.pdf with the binder 3 wire connector) with a 5V source to a NI DAQPad 6015 (USB) and reading with Labview Measurement and Automation Explorer. I'm not sure how to wire these up. obviously excitation going to the transducer and then the signal going to AI of the DAQ, however what do I use for my AI ground. Can I use the casing of the pressure transducer? What ports do I use for this, AI1, AI2 and then keep going with AI3 and AI4 for the next transducer?
Any help is appreciated.
03-23-2012 11:48 AM
I have attached a document called the "Field Wiring and Noise Considerations for Analog Signals". This is a great reference for determining the proper wiring configuration for your application. In your case I would wire the excitation wire from your pressure transducer to your 5V source and then I would wire the common or black wire from your pressure transducer to the common/ground of that power source. This will ensure that your pressure transducer is properly powered and grounded. For your signal I would then take the signal out of the pressure transducer to the positive input of your AI and I would then use the same ground on the power source/pressure transducer to tie into the AI ground of the same channel.
03-23-2012 03:32 PM
I wired it up this way. Makes sense with that document now. However I think I'm getting feedback from my ground loop. I'm just using a cheap 5V power supply plugged into a regular AC circuit. When i look at results I get this
What should I be doing to correct this? Switching to a floating source like a battery?
03-23-2012 03:41 PM
So I've been playing with it and sorry to keep bugging, but I think i figured it out a bit. I have both my sensors hooked up to the same power supply. If I only have one plugged in I read a steady -10V, as soon as I plug the other in I get noise. Should I be only using 1 sensor per power source?
03-26-2012 09:26 AM
That's a very good point. I thought I was in the clear for what my power supply was, however it makes sense if it isn't. I'm going to switch power supplies and check.
Thanks for the help!
03-27-2012 01:50 PM
So I scrapped the power supply I was using and wired up my pressure transducer to the DAQ using the 5 volt terminal (as defined by the chart below from user manual DAQPad 6015).
So I have excitation for both sensors hooked up to (+) 47 (-) 63 and my signal hooked up to 1 and 4. When I start the readings I'm getting full scale 5 volts (flatline). I know this is an issue with no groud, however I have it hooked directly to the DAQ ground.
Any ideas anyone?
03-27-2012 09:50 PM
I looked over the PDF of your transducer and would like to know which one you are using. What is the full model number? Since you are using 5 volts does this mean that you have the 0.5 to 4.5 volt output? What is the pressure range?
Since you do not know if this is a transducer problem or a DAQ problem I would separate them. Take the transducer off and use a voltmeter to check the voltage between DAQ pins 47 and 63 to see if you have 5 volts. Then using a battery (between 1 to 4 volts) attach it between pins 1 and 63 and see what the DAQ reads.
To check the transducer attach a 5 volt supply (between black and red wire?) and check the voltage output (between the sig output and the ground black wire). You could also do this at different pressure inputs to the transducer.
03-27-2012 10:25 PM
Yes, it's the 0.5 to 4.5 V ratiometric with 5V in. The pressure transducer is rated to 100 psig. I used a power supply before and got the same results.(flat line)
I just measured the voltage across the pins and I get 5.03V. So I don't think it's an issue of the power supply to the transducers.
If I use the multimeter across pins 63 and 4 I get 0.49V. If I do this while blowing into the pressure transducer I get an increase in voltage. This indicates to me that the sensor side of everything is working and that my connections are good. Why would I be reading a 5V steady state voltage from a 0.5V input? Am I just an idiot when it comes to the software? These are the settings I'm using:
03-28-2012 11:32 AM
For differential, you have to connect your positive signal to AI0 (pin 1) and the negative to AI8 (pin 2).
You are probably reading a constant 5V with your current setup since the input is floating (unconnected) based on how you have your task and wiring incorrectly configured.
Refer to pg 40 (section 2-7) of the manual here:
You may need to use bias resistors, in the manual look for the wiring guidlines for differential.
Hope this relieves some of your "pressure"