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Analog Input Errors on 3 of 7 channels
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Post Analog Input Errors on 3 of 7 channels 
Hi all,

I'm setting up my RCP2 for the first time and and using some K-type thermocouples with the Thermocouple Amplifier - AD8495 from adafruit.com

The problem I have is that on channels 1-3, the dashboard software shows a value that is not the value that the input pin sees. It works properly if I connect the signal to any of channels 4-7.

It's not scaling, because I have set the inputs back to Voltage and am just looking at raw voltage. My Amp is putting out about 1.38V which is perfect for 70 degrees or so, but connected to channels 1-3, it seems to float around. If I actually hook a mulitmeter to the terminal block, it reads the correct voltage (1.38) no matter which pin its plugged into. But the channel displayed on Dashboard is not reading the same, It's generally about 0.4V off, but seems to float a bit.

Right now, it's running with nothing hooked to any input and the values for each of the analogs are as follows. (I'm powering it via USB right now, but it acts the same with 12V power)

Analog 1: 0.19V
Analog 2: 0.19V
Analog 3: 0.19V
Analog 4: 0.30V
Analog 5: 0.53V
Analog 6: 0.77V
Analog 7: 0.90V


With the header plugged back in and the K-type hooked to #6 it's as follows.

Analog 1: 0.03V
Analog 2: 0.03V
Analog 3: 0.03V
Analog 4: 0.14V
Analog 5: 0.53V
Analog 6: 1.37V (correct for Signal from K-Type)
Analog 7: 1.03V

The longer its powered up, the more the values drift up (except the one that has an actual input signal).

Any help is appreciated. My fear is that I have a defective unit.

Aaron

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Hi,

The inputs are very high impedance by design, so if they're not connected to a source, they will float and show a voltage.

Going through the inputs, if you tie each one to ground and then VRef, does it show 0v and then close to 5v, respectively? Note when running on USB only your VRef will sag below 5v a bit.


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Brent Picasso
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Brent,

I had set the project aside and worked on some other things, but I'm back looking at it again.

To answer your question, no, on channels 1 through 3, when I connect them to 5V ref or ground, they still show some sort of floating value on the display, usually around 1.4 ish when connected to 5V ref. I can confirm that the pin is seeing the 5V with a multimeter, it's just showing the wrong value in the display. Channels 4-7 work as they should.

-Aaron

brentp wrote:
Hi,

The inputs are very high impedance by design, so if they're not connected to a source, they will float and show a voltage.

Going through the inputs, if you tie each one to ground and then VRef, does it show 0v and then close to 5v, respectively? Note when running on USB only your VRef will sag below 5v a bit.


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Hi, Can you attach your configuration file here (or email us at [email protected]) so we can check it out?

We'll work to get it sorted out. Thanks!


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Brent Picasso
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Post Config File attached 
Here is my config file.

I'm worried that it's hardware, but I did take a bunch of data today and channels 4-7 seem to be working great.

Aaron

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