Voltage signal (-0.40mV ~ 7.60 mV) to NI card and LV

LabView is software, not hardware. From your title I guess you're using a National Instruments data acquisition card. They make quite a few models. Which one are you using?

But anyway, yes, amplifying it would probably help; alternatively, you need data acquisition hardware with appropriate resolution (for instance, a digital voltmeter with a mV scale and a computer output of some sort).

Accurately amplifying a DC signal that small is not trivial. Some things you'll need to specify are:

- what resolution do you need? E.g., 10uV, 1nV, ...?

- how much drift, over time and temperature, is acceptable? (Are you trying to measure over a timespan of milliseconds or days?)

- what speed do you need? E.g., is this a slowly-varying DC signal, or a

- what is the output impedance of the signal source? (Alternately, what input impedance do you need from your amplifier?)

Are you measuring the output of a thermocouple? If not, then probably not.

But anyway, achieving fractional-mV resolution in a DC amplifier depends as much on good circuit design and layout skills as on the parts you use, and just having the right IC (even if it were, which it probably isn't) is not sufficient.

LabView 6.1 with a PCI-6024E

A Fluke 192B Scopemeter was used with success. Now the goal is to see a waveform in Labview

Steps of .70 mVols aprox but it doesn't need to be extremly accurate.

It could be nice to graph on Labview using for example a waveform. Going from aprox. -0.40 to 7.60 mV takes more or less 5 minutes.

As much as I know it is a slow varying DC signal

Unfortunatelly I don't know that.

Yes, I'm measuring the output of a thermocouple.

Thank you very much for your answer, so what would you recomend me to do?

Best Regards

Hi,

Thanks for your answer, I will look for the AD622 (cool device), if I don't find it I will try with a 741

Regards

So, the simplest and best thing you could do would be to get a DAQ card with a thermocouple input, such as the NI USB-9211, which they list at $395, lead time

Don't bother with a 741.

Look at the DC offset voltage spec.

The AD622 works for me in situations like this.

Cheers

The 622 is an instrumentation amp, not an OPamp like the 741. It has very good offset voltage typ 125uv.

You should amplify the signal to ~4v for the NI 6024. I believe this is a 16bit card. For the +/-5 volt range the resolution is

Cheers

Forget the 741.

If you just need reasonable DC precision the LM11 may fit the bill.

Graham

Hi

I have an LM311, would it help?

Regards

And the AD620?

Regards

Here I must respectfully disagree with Spehro. The LM311 is just what you need. Put it in a box - ideally, you might want to solder it to a printed circuit board, and then mount the printed circuit board in a box, so that it doesn't rattle. Also put some audio connectors in the box, and wire the input connectors to the output connectors. Now, sell the box to an audiophile, for $395 plus tax and shipping. Use the proceeds to buy a thermocouple card to run LabView with.

Sno-o-o-ort :-)

...Jim Thompson

Not at all.

Best regards, Spehro Pefhany

-- "it's the network..." "The Journey is the reward" snipped-for-privacy@interlog.com Info for manufacturers:

Oh, my GOD! I laugh at the same stuff as Thompson? Will somebody please euthanize me?

;-D Rich

(By the way, this is a joke.)

Not as much as reading the specifications- the 6024E can be programmed for FS of +/- 50mV with 0.008mV resolution and 0.106mV absolute accuracy using 100 point averaging.

Hi,

I choose the AD620 but I don't know if I wire it right

-IN and +IN are connected to the Thermocouple

-Vs and +Vs to power supply -12 and +12 Volts REF is connected to ground OUT directly to the voltmeter

The gain was set to aprox. 1000 with a 47 Ohm resistance

Is that ok? Unfortunatelly with the power supply -Vs=-5 Volts and +Vs=5 Volts the output doesn't represent a gain of 1000.

Any recomendation? Best Regards