Can I control Gain amplifier USB 6251!

[nguyenmanhcuong]

Hi all,

I have own USB 6251, I want to know if amplifier gain (PGIA) can controlled programmably?

Thanks in advanced

MC

[Dennis_Knutson]

The gain of the DAQ is controlled by setting the high and low limits of the DAQmx Create Channel.

[nguyenmanhcuong]

Hi Dennis

Thank for you reply,

As I know,  the gain of the DAQ is controlled by using channel property node and select Analog Input>> General Properties>> Advanced>> Gain>> Gain Value.

Simly I do not know if we can control amplifier gain in USB 6251? (I couldn't find information about this).

Thank so much!

MC

[Dennis_Knutson]

THE GAIN IS SET WITH THE LIMITS INPUTS OF THE DAQMX CREATE CHANNEL!!!

This sets the range of the DAQ. If you want to set the gain with a property node, you will have to use the correct property. I don't know why you say you know when you are specifiying an invalid property. You could at least explain why you don't want to use the normal method of setting the gain.

[nguyenmanhcuong]

Hi Dennis

Thank you,

What I attached in the previous message was in this topic.

I'm newer in Labview, even I don't understand how DAQ set the gain

Examples:

                + If limits inputs is (-10V, +10V)---> Gain=??

                + If limits inputs is (-5V, +5v) ------> Gain=??

                + If limits inputs is (-2V, +2V)-------> Gain=??

.............................................

So that I decided use "channel property node" and I can myself write Gain (= 1, 2, 3,...) to the property node. This may be bad way?!!

Can you explain or show me document, which introduces in details basic knowledge of the gain, how choose valid property for gain.

Thank so much 

MC

Message Edited by nguyenmanhcuong on 06-15-2009 12:59 PM

Message Edited by nguyenmanhcuong on 06-15-2009 01:02 PM

[Dennis_Knutson]

The gain is automatically set when you select the limits. You do not need to select the gain and I don't see the property you mentioned. The driver will select the best range that fits the limits. Why do you need the gain information? Do you want to know the actual range that is being used?

Message Edited by Dennis Knutson on 06-15-2009 12:16 PM

[Brad_K · Accepted solution]

Hi nguyenmanhcuong,

In DAQmx, all analog input devices support the AI.Max/Min properties that Dennis suggested (which are the maximum/minimum values on the DAQmx Create Channel VI). These properties also take the sensor scaling into account (and for SCXI, terminal block scaling). For example, if you are performing a thermocouple measurement, AI.Max/Min are in temperature units (deg C, deg F, K). If you are performing a voltage measurement, AI.Max/Min are in volts.

There are also lower-level properties:

• MIO devices like the USB-6251 also support the lower level AI.Rng.High/Low properties, which do not take sensor scaling into account. They do not support AI.Gain.
• DSA devices like the NI 4462 also support the lower level AI.Rng.High/Low and AI.Gain properties. The NI-DAQmx Help file that is on the start menu explains these in the section named "Gain for DSA Devices".
• SCXI devices like the SCXI-1102 also support the AI.Gain property, and some SCXI terminal blocks like the SCXI-1313 also support the AI.Atten property.

Since you are using a USB-6251, AI.Gain is not supported for your board. Use AI.Max/Min to set the input limits (the range of voltages that you want to measure), and NI-DAQmx will pick appropriate hardware settings. If the range that you specified is not available, NI-DAQmx will select a wider range. You can read AI.Rng.High/Low to find out what hardware settings NI-DAQmx chose.

Brad

[nguyenmanhcuong]

Thank for all! Now I undertand. Your explains are very usefulness for me!

MC

To Dennis:  I want to attenuate signal, other words I want to cut off the peak of the signal before it comes to ADC block.

Message Edited by nguyenmanhcuong on 06-15-2009 01:32 PM

Message Edited by nguyenmanhcuong on 06-15-2009 01:36 PM

[Dennis_Knutson]

I'm not sure you can use the range of the DAQ to do this. You've only got a few ranges. It's not really something you have much flexibility in adjusting.