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NI-FGen and Amplitude Vp-p
Chris Lincoln
Member
09-27-2002 03:50 PM
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A customer of ours sent us their PXI 5401 so we could write a C++ application with it. I put the 5401 in a chassis along with a 5102 and fired up the soft panels for the two devices. When I output a waveform, say 1 kHz with an amplitude (p-p) of 1V, it actually generates a 2V p-p signal (according to my eyes and the VirtualScope software ). I'm a software person that only knows enough about electronics to ruin them, so treat me kindly if I am mistaken. It would seem that the two devices would agree on the definition of V p-p.
Q. Do I have a basic misunderstanding of the definition of peak-to-peak?
Q. I can simply cut the desired amplitude P-P in half before sending to the NI-FGen API, but wouldn't I run the risk of only generating ha
lf the amplitude if NI decides to change their implementation in the future?
Q. The board has a metrology lab sticker on it from the customers cal. lab. Is it possible that their cal lab is the one with the inconsistent definition of Vp-p and calibrated the thing off by 100%? (that would seem pretty remarkable error correction).
Thanks for your patience and help,
Chris Lincoln
ULTRAX, Inc.
Q. Do I have a basic misunderstanding of the definition of peak-to-peak?
Q. I can simply cut the desired amplitude P-P in half before sending to the NI-FGen API, but wouldn't I run the risk of only generating ha
lf the amplitude if NI decides to change their implementation in the future?
Q. The board has a metrology lab sticker on it from the customers cal. lab. Is it possible that their cal lab is the one with the inconsistent definition of Vp-p and calibrated the thing off by 100%? (that would seem pretty remarkable error correction).
Thanks for your patience and help,
Chris Lincoln
ULTRAX, Inc.
GDEV
Member
09-27-2002 05:24 PM
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What you see is the correct behavior from both hardware and software.
The NI 5401 creates the signal with the assumption of a load impedance equal to its output impedance of 50 ohm. The NI 5102 on the other hand as a input impedance of > 1Mohm.
When you use the Sources SFP you can select Edit>>Device Configuration and set the load impedance to > 1Mohm. The 5102 will then read the same voltage level you selected in the Source SFP.
If you program the 5401 from C++ it depends on the input impedance of the device/s you have your 5401 connected to. If your load impedance is effectively > 1Mohm, yes you can divide the amplitude by two before sending it to the NI-FGEN API (That is in fact what the Source SFP does).
Regards,
Marian Koop
Software Engineer
N
ational Instruments
The NI 5401 creates the signal with the assumption of a load impedance equal to its output impedance of 50 ohm. The NI 5102 on the other hand as a input impedance of > 1Mohm.
When you use the Sources SFP you can select Edit>>Device Configuration and set the load impedance to > 1Mohm. The 5102 will then read the same voltage level you selected in the Source SFP.
If you program the 5401 from C++ it depends on the input impedance of the device/s you have your 5401 connected to. If your load impedance is effectively > 1Mohm, yes you can divide the amplitude by two before sending it to the NI-FGEN API (That is in fact what the Source SFP does).
Regards,
Marian Koop
Software Engineer
N
ational Instruments
