Floating voltage of NI USB 6215

[96368917]

Hi,

I'm currently an undergraduate of Nanyang Technological University, Singapore and undertaking a project which involves light flickering measurement system.  This measurement system is run by LabVIEW and the DAQ system is NI USB 6215.  This DAQ device is linked through AC Programmable Source Chroma which helps to generate AC supply for my fluorescent lamp.  Testing for 22ft long tube fluorescent lamp with electronic ballast works perfectly ok but however, when the software runs with the magnetic ballast, the fluorescent lamp just blow up.  I've noticed that there is a voltage surge (spike) whenever the software tries to update a new voltage amplitude to the DAQmxWrite.VI.  This voltage spike is responsible for the "death" of the fluorescent lamp.  Even when I stop the DAQ, the device still has floating voltage which can range from 2V to 8V.  I'm wondering whether is there anyway to remove the voltage spike from NI USB 6215 without using any hardware electronics to solve the problem?

[Steven_C]

Hi,

I was wondering if you were seeing this DC offset both when your electronic ballast and magnetic ballast or simply with you magnetic ballast. Could you please confirm? Also, when you say that it can range from 2 to 8V, does this start at 2V and raise over time to 8V? Also, could you please confirm that you do not see this offset when measuring the voltage with no load. One thing you may want to consider if you are seeing a spike when connected to the magnetic ballast would be to use some additional voltage clamping circuitry.

Best regards,

Steven

[96368917]

Hi Steven C,

The DC offset will occur in both electronic and magnetic ballasts except that the electroninc ballast seems to be "immune" to the voltage spike.  The range of 2V to 8V from the NI USB 6215's output remains constant when user abort the execution of LabVIEW programme.  When there is no load, the DC offset is very small around 1.5V.

Thank you for suggesting of using the voltage clamping circuitry.  However, this will alter the previous data entries.

[tnek]

Hi,

It seems like you are seeing two problems with your current setup. The first is the voltage spike that occurs when you switch voltage levels. The second is the voltage output when the program is finished running.

The first problem may be due to either a transient effect in the ballast or glitching on the analog output of the NI-6215. Since the magnetic ballast relies on inductive effects, a sudden change in current may be damaging. The other cause may be glitching which originates at the digital to analog converter (DAC) when voltage levels change. There is more information on glitch energy found in this article. There are two solutions for glitching presented in this article but they are both require additional hardware. It may be useful to know the amplitude of the spikes that you are seeing.

The second problem is due to the fact that the analog output will continue to output the last voltage value until a new value is set or the device is reset. The can be compensated by just writing another voltage or resetting the device right before the program ends.

Regards,
Kent
Applications Engineer