Voltage not 0 in analog inputs (USB 201)

[OscarP]

Hello, I have a problem with my USB 201. I connected my sensors to the DAQ and after that I noticed that the readings were wrong. So I opened Instacal and checked the measured value of a channel that had not connections, and it was giving a value of 1,74v aprox. Finally, I removed all connections and checked all channels, getting the same value on all of them.

I guess the voltage without any connection should be 0, right? How could I solve this?

Thank you.

Edited June 6 by OscarP

[JRys]

You can test the input (CH0) by connecting it over to the +V pin, which is +5 volt signal. Then connect the input to the ground (AGND) and it should read close to zero. Assuming this all work, connect your sensor's -U to AGND and +S to the input. 

[JRys]

It is normal for a USB-201 input to charge to 1.7v when left unconnected. It has to do with the low pass filter before the A/D converter. You can make the inputs read zero by connect them to the ground. It good practice to do this with unused channels. 

[OscarP]

On 6/6/2024 at 3:00 PM, JRys said:

It is normal for a USB-201 input to charge to 1.7v when left unconnected. It has to do with the low pass filter before the A/D converter. You can make the inputs read zero by connect them to the ground. It good practice to do this with unused channels. 

Oh, thank you very much! So it was not wired correctly.

If I have a pressure sensor that has a + wire and a - wire. Should I connect + to an analog channel, - to GND and then another GND from USB201 to ground? See attached picture for a visual explanation.

 

PD: I've put GND in the last AGND but as fas as I know they all are connected so I could connect it everywhere.

 

 

Edited June 10 by OscarP

[JRys]

Not all pressure sensors are compatible with the USB-201. Send me the datasheet so I can see what you have.

 

[OscarP]

19 hours ago, JRys said:

Not all pressure sensors are compatible with the USB-201. Send me the datasheet so I can see what you have.

 

Ok, see them attached. I have 2 types. Both have a 0-10v output (WIKA one was bought with this output already and the other one can be selected in their config app). I also attached the wiring diagram.

 

OMEGA differential pressure gauge:

OMEGA DPG409_DIFF.pdf

 

WIKA Pressure Sensor:

WIKA ds_pe8160_en_co.pdf

ds_in0050_en_co.pdf

 

Both have an external power supply.

Edited June 11 by OscarP

[JRys]

Your sensors should work. I only wanted to make sure you didn't have the type that output millivolts or current. 

[OscarP]

7 hours ago, JRys said:

Your sensors should work. I only wanted to make sure you didn't have the type that output millivolts or current. 

So connecting sensors like I said before is ok, right? I mean, + from sensor to CH0 (for example), - from sensor to AGND and then another AGND to ground.

 

Thabk you very much for your help!

Edited June 11 by OscarP

[OscarP]

I just disconnected everything in the analog side and connected AGND to ground and the DAQ is showing me a value of 1,74v. Should I connect both, input and ground?

Edited June 12 by OscarP