Analog Input voltage readings into USB 6008

[VeeJay]

HI,

I am trying to read 2 voltages into Analog Inputs (ai0 and ai5) . One is an Inclinometer which works on 12V supply to give a voltage output based on the angle (60mV/deg) and the other is a sensor that works on 24V supply and based on distance of transmitter and receiver, will give a voltage between 2 and 7V. Both work on separate power supplies.

I know that we have to create the same task to read multiple analog signals and thats what I did. here's what happens now. When the 24V supply is turned off, ai0 (Inclinometer ouptut) is read in correctly but when I turn on the 24V supply, Sensor voltage is correct but inclinometer voltage shows as -10.4 if I set the voltage range as 0-10V and -5.2V if the range is 0-5V. Is there something wrong I am doing in terms of reading in the values?

Thanks!

VJ

[VeeJay]

Attaching the VI. Hope it is correct.

Thanks!

[Dustin_D]

Hi VeeJay, 

Your code looks ok, other than you want to put a clear task instead of the stop task.  You may run into resource errors eventually otherwise.  It seems like you may have things not connected properly.  First look at this link, The NI Field Wiring Guide.  It will show you the best way to make connections and explain the different connection types.  The best type of measurement that you could use would be a differential voltage.  You'll need to be sure its connected correctly to your DAQ board. Usually the positive side of the signal would go to AI0 and the negative to AI8, for instance.  If you are still having trouble after revisiting this please post some more details about your hardware and your desired configuration.  Good luck!

Regards,

[VeeJay]

Thanks Dustin!! I think I have the circuit cables connected properly. I am using single ended measurements. So, for the sensor, positive goes to ai5 and negative is grounded. Similarly, I have the positive of the inclinometer going to ai0 and negative grounded. I dont see any mistakes in that because it is very trivial. Although, what labview outputs looks like a pattern. When both power supplies are on, ai0 gives -10.4 when range is 0-10V and -5.2 when range is 0-5V. -10.4/2=-5.2 (0-10V / 2 = 0-5V)

Vj

[Dustin_D]

Vj,

Would it be possible for you try and operate one sensor at a time?  Also the range setting is to configure the internal amplifier so you may want to leave it at -10 to 10 until you are sure that your signal falls completely within some other bounds.  Also if you can use a multimeter to verify that your polarity and voltage of your outputs are what you expect.  If you still are having problems taking a measurements, test with a AA battery to see if you can correctly measure that.  Keep us updated!

Regards,

[jyang72211]

Hi Vj,

Have you tried to used a DMM to verify your setup?  If not, just a DMM for your DAQ set up and make sure that you are actually getting what you think you are getting at the AI0 and AI5.  From the values that you are getting, I think there is a problem with the way that the grounds are hooked up.

Yik

[VeeJay]

Thanks for your help!! I have tried what you said Dustin. Separately, each channel is measuring the right voltage. but, when the 24V supply is on, the other voltage reads as described before. And I have tried the same thing with a DMM. Separately, they read the right voltage at the screw terminals. But, again wrong voltage is read at ai0 when the 24V supply is switched on to read ai5 (range is 0-10V).

VJ

[Dustin_D]

Vj,

Can you post a diagram of your setup? I'm still unclear why this power supply changes your input.

Thanks,

[VeeJay]

@Dustin . Please find my circuit setup attached. I quickly put together this diagram using Paint. It is not the way to do it, but I just wanted to convey the message. The 2 12V sources are small batteries. The 24V source is a regulated power supply that is used for the entire system.

Thanks!

Best Regards,

VJ

[VeeJay]

@ Yik, I thought so too.. . I have posted the circuit. Please let me know what you think as well.