using USB 6341 device for frequency generation but level is dropped when connect

[Nasib]

i am using USB-6341 Daq Device for frequency generation. The desired frequency is generated correctly but when i connect to other device the voltage level i means the Peak to Peak voltage of the frequency dropped to 0.6, 1 Volt and also the frequency fluctuated. As I disconnect it from the load or the device the frequency becomes constant and peak to peak voltage becomes 5.

Please some help me to resolve my problem.

Thanks

Best Regards

Naseeb

[Dennis_Knutson]

What are you trying to drive? If it requires more current than the card can source, the voltage will drop. Add an amplifier to the output.

[Nasib]

Thanks for reply. Actually it is another microcontroller based card compose of operational amplifier, transistor and so more. The input resistance of the terminal where I connected the frequency out of the daq device is 80 ohms. For matching the impedance I have used the voltage follower ckt by making single gain operational amplifiers result is slightly improved but not accurate as per requirement

please guide me what to do.

Thanks and Regards

Naseeb

[Travis_Ann_N]

Hi Nasib,

What pins are you using on the 6341? Also, can you give more information about how much the op amps you used improved the drop?

Regards,

Travis Ann

[Nasib]

Thanks for reply.

I am using Pin# 89 (PF1 12/P2.4) and # 90 as Ground for the frequency out of the USB 6341 card. I used the op amplifier as a unity gain amplifier for impedance matching. When I used the unity gain  op amplifier and connect to the input of the other ckt the voltage dropped is 1 volt less then direct connection of the DAQ card to the ckt. But the frequency continuously fluctuate. 

Best Regards

[Travis_Ann_N]

Hi Nasib,

I just wanted to clarify a few more things. Can you answer the following questions?

What frequency are you trying to generate?
When there is no load connected do you see the desired frequency?
When the load is connected, does the frequency always change to the same value or does it fluctuate within a certain range? If it fluctuates, what is the range?
Also, what microcontroller are you using?
Can you provide any images?

Regards,
Travis Ann
Applications Engineer
National Instruments

[Nasib]

I want to generate the frequency from 2KHz to 4.5 KHz, When there is no load the frequency does not fluctuate, but when the load is connected its fluctuate with in range of 300Hz on the desired frequency. But when load is not connected it perfectly give the desired frequency. When I add the unity gain amplifier between my circuit and daq pad the fluctuation is decrease and the fluctuation range in between 150Hz.

Thanks and Regards

[Travis_Ann_N]

Hi Nasib,

What task are you using to generate, maybe frequency generation or counter output task? Also, what voltage are you outputting when there is no load? Are you measuring with an oscilloscope? The max operating output current is 16mA, so it is possible that you are overloading it. 

Regards,

Travis Ann

[Nasib]

I am using the above code for frequencey generation. thanks sir for reply.

Best Regards

Naseeb

[Nasib]

As I measure the frequency on the oscilloscope the peak to Peak voltage is 5 volt of the desired frequency but when I connect the load the voltage level also decrees up to 3 volt peak to peek.

Thanks