Usb 6008 + LM35 temperature sensor problem

[AnalogKid2DigitalMan]

Is your analog input configured of single-ended mode, which is probably preferred over differential in this case.

Also, for kicks, have you tried connecting a ground to pin 1 of the 6008, though I do not think it is required, but still curious as to outcome.

[skogstrand]

Maxpower: Tested the program and got the same result as with the DAQ assistant.

Analogkiddigitalman: I have tested both RSE and differential, and it doesn't make any difference. I have connected pin 1 to ground also, and that didn't make any differense either. It's a stubbern 6008 I have....

[WM_John_Weeks]

I'd say it's looking more and more like you have a bad 6008.

[AnalogKid2DigitalMan]

I concur with John, this is looking like a bad unit.

As a sanity test, you could disconnect all your LM35 connections, and short pins 1 and 2 on the 6008 together. You should read 0 volts. Then connect a battery, a 1.5V AA for example, to pins 1 and 2on the 6008, and you should read ~1.5V.

Other than that, do you have the latest version of DAQ driver software for your device? I doubt this is the issue though.

[skogstrand]

I'm not sure i agree that my device is bad. Thats because when i connect My analog output on 6008 to my analog input on 6008, and make a VI that controls the output and measures the input, I get a change on analog in as I change the analog out.

[skogstrand]

I just conneced a humidity sensor to 6008, and it worked fine. So it must be an issue between the LM35 and usb6008. Thanks for your help so far. Maybe I'll try another temperature sensor. It had been nice to find out what the problem was though.

[WM_John_Weeks]

Then you've got a bad LM35? I know you said it worked OK when disconnected; maybe it has been damaged such that it has high output impedance or low drive (really the same thing, eh?).

Or you were dreaming and you have wrong pins on the LM35 🙂

[skogstrand]

Yea. That might be the problem. I can't think of anything else. Thank you again for trying to solve the issue.

[Adi_Nash]

Hi lads,

Im having the exact same problem trying to get my LM35 and usb 6008 DAQ to work...how did you eventually remedy this situation?

[MarkLe]

Hi,

I've worked with the LM35 in the past (not with NI hardware), and have been looking today at the LM35/USB 6008 issue.

I've found two distinct ways to get it to work (return 'sensible' values, with no saturation problems).

1) Either power the LM35 from an external supply (I used 5V bench top PSU) and connect the output across the two pins of a differential input to the 6008 (so GND from the LM35 to AI- and Vout to the AI+)

2) Or power the LM35 from the 6008's 5V line (V+ to 5V line, GND to 6008 GND), connect the Vout to AI+ and a resistor between AI+ and GND, then connect AI- down to GND with another resistor of the same value. I'm currently using 120K, but values up to 220K should work.

I get the input saturating at 0.317V whenever I use the RSE mode on the unit. I'm assuming this is either due to the sensor not being balanced with the single ended Op Amp input, or some kind of floating voltage taking the signal outside of the common mode range of the instrumentation amplifier. These devices are often sensitive to the capacitance of the load they are driving, and this could be an issue with the inputs on the 6008, as they are fairly low impedance compared to, for example a DMM at 144K.

Anyway, if anyone's still working with this device and would like to try the above configurations, please post back with how you get on.

Best wishes,

Mark

Applications Engineer

National Instruments