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AO Port Output impedance

Dear all,

 

I used the HP33120A (Function Generator) to make a square wave signal of 900Hz/Vpp/Offset as a referenced signal in my test system, the test system works well. Now I try to replace HP33120A by NI PCI-6229, and use AO port to make same signal as the referenced signal, but the test system doesn't work. I used the Oscilloscope to compare the wavefrom from the HP33120A and PCI-6229, it seems to be same.

 

I noted that the output impedance of HP33120A is 50R, and it's 0.2R for PCI-6229. I guess this is the problem for my test system, how to solve this problem with PCI-6229, please give me some help, thanks.

 

Evan 

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Have you made the measurement 'in situ'  ?

The 33120 will create voltage levels according to the specified output load. See Manual Chapter 3 Output configuration.

What load do you have? What load is setup in the 33120?  50Ohm termination ?

To create a output impedance of 50 Ohm you can put 2 paralleled 100Ohm SMD resistors in series to your DO output, but keep in mind that you will get only half the level when the other end of the cable (your input) is terminated with 50 Ohm.

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Dear Henrik,

 

Thanks for your help.

 

For the 33120, setting is square, 900Hz, Amp 4.0Vpp, Offset 2.0VDC and 50OHM termination, so my test system works well as this referenced signal by 33120.

 

For the 6229 AO Port, I used to put 50OHM resistor in series to the AO port before, and write the DAQmx software with square, 900Hz, Amp 4.0Vpp, Offset 2.0VDC, and then connect this signal by 6229 to my test system, but it couldn't work. According to you mean and 33120 Manual, my problem is wrong AMP and Offset for my 6229, it just double the Amp and Offset (8.0Vpp, 4.0VDC) if make the test system to work well. Am I correct or not?

 

Best regards,

Evan

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There are many things that can go wrong..... Murphy 😉

 

Some tests I would do:

 

Measure with an scope (10Meg input, 10:1 ) the signal at the (connected!) receiver (if possible during runtime). For both setups.

 

To exclude the software (assuming that there are two versions (generator/DO) ) you can setup the generator to create a single pulse ( length 1.111 ms, same amplitude and offset) and use the DO to trigger the generator.

 

For the AO level: When you setup the generator with an output load of 50 Ohm, the amplifier of the generator will generate twice the defined output voltage since he know it's internal output impedance (50R) ;). 

 

 

 

 

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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