NI USB-6210 - screensaver causes inaccurate measurements

[corwa]

Hello!

We are designing a testing environment which includes Laptop computer, LabView and NI USB-6210 Multifunction DAQ.

Plan is to connect at least three NTC resistors to USB-6210 with proper bias resistors.

First question:

Can pin 10  (+5V) of USB-6210 be used as voltage source for our connection circuit?

Second question:

How can we eliminate screen saver's effect on measurements (other than disabling screen saver)? We wonder how it is this even possible that enabled screen saver effects on measurements so drastically as we have experienced...

If additional information was required, we'll be happy to provide them.

Regards,

Teijo Kylä-Kaila

student of Turku University of Applied Sciences

Message Edited by corwa on 11-24-2009 06:56 AM

[NIquist]

1)  You could but you'll be limited to about 50mA.

2)  The screen saver wouldn't cause this but check to see if the PC's power management settings happen to be going into a power saving mode at the same time as the screen saver starts. 

[corwa]

Thank you for your answer NIquist. We're still having serious problems with our setup.

1) 50mA provided by NI USB-6210 is adequate for our system.

---

NIquist wrote:

2)  check PC's power management settings

---

Yes, thank you for the tip. Power management issues made our measuremets go wild. We still haven't got a solid solution for these problems. We wonder why pin 10 (+5V) changes so much in accordance with laptop's power management settings. Excited voltage source isn't acceptable in our system  so pin 10 needs to be used.

Just by changing USB-cable between NI USB-6210 and laptop, we achieved voltage drop in pin 10 from 4,95 V to 4,85 V. These values aren't stable but they seem to react also in movement with USB-cable connectors. This magnitude of voltage drop is way too much for our system.

We tried external powered USB-hub but same thing happens. Tampering with USB-cable connectors cause random voltage drops.

Does anyone have any ideas how to improve our setup? Our main concern is stabilizing pin 10 (+5V) voltage.

-corwa- 

[Seth_B.]

The +5V on pin 10 is derived from the power provided by the USB bus, which is also used to power the rest of the device.  If the laptop reduces power to the bus or if the connection is disturbed, it will cause issues with the +5V output.  Additionally, low quality USB cables will have signal integrity issues and may not sit firmly in both USB ports.

First make sure you are using the strain relief options described on page 1-4 of the USB-621x manual.  Also, look for a USB cable that has a ferrite ring built in.  These are pretty common for cameras and the like.  This helps reduce external noise on the USB communication line.  Finally, you should see if your laptop has an USB strain relief options that can help the USB cable sit more securely.  You may need to implement something yourself.

Regards,

[AnalogKid2DigitalMan]

Noise generated by screensaver could be inducing noise on the power bus due to video activity causing different power consumption by the display or graphics processer creating noise on the data bus.

-AK2DM

[corwa]

Thank you for your answers! We will implement your tips and then execute some testing. We'll report back here how things went.

-corwa-