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I am trying to use the PA1000 for IEC standby measurements. When using mains as source (230Vac, 50 Hz), the measured standby power is as expected, but I am having a hard time getting a pass, due to excessive THC.
I tried using an APC UPS, and got THC below 2%. The problem is, that once I disconnect the mains, and the line-interactive UPS switches to battery-mode, the measured power consumption start acting weird. Have a look at this screenshot.
Initially the DUT is powered from the UPS in battery-mode, and the measured standby power fluctuates wildly between 240 and 440 mW. At 00:00:50, I connect the mains line to the UPS, and the measurement start looking as expected.
1) Do you have any guess as to what's happening here?
2) can you recommend a cost-effective means of synthesizing the mains source (that do not result in this erratic behaviour)?
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That being said, the voltage from the regular wall socket is usually bad and has quite a lot of harmonic content leading to failure in the test as you noticed. Using an UPS system instead of an AC source is ok as far as the output voltage of UPS systems is clean enough. My guess is your UPS system is a "Standby type UPS system" that filters the AC source from the socket when connected hence giving you a decent input voltage quality. When you plug your UPS out of the wall socket, the output is completely synthesized from the battery backup so you are relying on the output power/voltage quality of the UPS which is usually choppy depending on the particular UPS model.
If you are getting decent results with UPS plugged in, I would just use that configuration to run the test or alternatively get a clean AC source that meets the requirements I listed earlier. Let me know if you have questions.
1. in mains/non battery mode, the test fail due to THC > 2%
2. In batt mode, all the requirements are met, THC<2%, Vrms within 1%, etc but as you can see, the measured power fluctuates wildly.
I am unsure what is the reason for this fluctuation. I can't really see any noise when connecting an oscilloscope. Maybe the impedance of the mains, as seen by the PSU of the DUT is fluctuating?
Anyway, I can't be sure to get good results, so I guess I need an alternative AC source.
Can you recommend a (reasonably prized) clean AC source for this purpose?
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