UPS's between AC mains and higher end DMM's - Page 1
Forum section: electronics / general

author: kj7e
author_rank: Frequent Contributor
timestamp: April 14, 2018, 12:16:19 am
content: For AC mains power I use Tripp lite Isobar noise filtering surge protection power distribution blocks. However, I live in the mountains with sometimes strong winds and wintertime ice and snow. We have only a single utility line feed to our small area and we will see brown and black outs every so often. My home computing and networking gear is all on a large UPS, but I'm considering a true sine wave (not simulated or stepped square wave) UPS for the electronics bench. Something like this;https://www.cyberpowersystems.com/product/ups/or1500pfclcd/So, my question is, when trying to make PPM or even sub PPM measurements with say a 7.5digit DMM, is this not a good idea? Or maybe it will just depend greatly on the quality of the UPS and its own noise. Curious if anyone has used a UPS to feed their higher end DMM's and noticed any additional noise.

author: quarks
author_rank: Frequent Contributor
timestamp: April 14, 2018, 04:16:26 am
content: That is a good question. So far I have not used a UPS for my DMMs.As you already wrote, avoid modified sinewave and go for pure sinewave.Because mains power is not as stable and clean as we all would like it, my guess is a good quality pure sinewave UPS should not cause much trouble. Also you can try to add a mains stabilizer (maybe something like WS-5 from Wandel & Goltermannn)

author: Andreas
author_rank: Super Contributor
timestamp: April 14, 2018, 04:53:42 am
content: Hello,is the frequency that is output of the UPS synchronized to the mains frequency?If you have more than one mains frequency in one room I could imagine that the normal mode rejection is suffering somewhat.with best regardsAndreas

author: kj7e
author_rank: Frequent Contributor
timestamp: April 14, 2018, 05:40:12 am
content: Best I can tell, it appears to essentially be synchronous in normal operation. A few nice benefits are the EMI filtering and Automatic Voltage buck/boost Regulation. It may even provide cleaner and more stable power than directly off the mains.The AVR appears to be an auto transformer type per the online info:"Automatic Voltage RegulationAutomatic Voltage Regulation (AVR) in line interactive UPS systems stabilizes the incoming AC signal to maintain output power at a nominal 120 volts by controlling high and low voltages without resorting to battery power. This significantly increases battery life and lessens the likelihood of data loss, memory freezes, and system crashes.How AVR Works in a Line Interactive UPSA line interactive UPS includes an AVR autotransformer a special type of transformer designed to switch between powered coils of wire in response to variances in utility power input, thereby increasing or decreasing the magnetic field and the resulting output voltage to connected equipment.This type of UPS tolerates undervoltage brownouts and overvoltage surges without consuming backup battery power by automatically selecting different power taps on the AVR autotransformer. During normal operation, incoming AC power bypasses the autotransformer (where voltage highs and lows are controlled) while also charging the battery. When the incoming voltage falls below the AVR range, the UPS switches to battery backup, and the DC-AC inverter circuitry is engaged. Power will continue to be supplied by the battery-inverter circuit until incoming voltage returns to the range manageable by the AVR."Well, I ordered this one so I'll try it out and report.

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2018, 05:45:07 am
content: Better yet is to get a ferroresonant power conditioner and place it either before the UPS or just use it in place of the UPS , if you can live with power failures. The ferroresonant units will typically provide a reasonably good sine wave ( though with a high third harmonic content, which actually improves the efficiency of the input bridge rectifier as it has a flatter top on the sine wave) and will both stabilise the voltage a lot, and as well filter out all the line noise the regular UPS will allow through, unless it is a dual conversion type, plus due to the core stored energy it will ride through a few cycles of power loss with little issue. They do a very good job on removing line noise almost entirely, though you can still have common mode noise go through unless you also have an input mains filter that includes an earth line reactor to remove the common mode noise.

author: Moon Winx
author_rank: Regular Contributor
timestamp: April 14, 2018, 07:08:22 am
content: We've ran our Josephson systems, our DC scaling systems, AC-DC difference systems, etc., both with and without UPSs and when even specifically looking for any detectable difference in the measurement results, I can't say I've seen one. It does allow for peaceful shut downs in case of a power outage, so there's that.

author: Andreas
author_rank: Super Contributor
timestamp: April 14, 2018, 01:17:37 pm
content: Hello,and which manufacturer/type of UPSs did you use?with best regardsAndreas

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 14, 2018, 02:04:03 pm
content: I use a double-conversion UPS on my most expensive gear. It has the advantage of always creating AC power. Eaton makes a nice model, the 9130, and I have used them at work for years now supporting medical devices. They are very reliable.

author: mcinque
author_rank: Unknown
timestamp: April 14, 2018, 02:13:47 pm
content: I have a pure sinewave UPS and no issues with my DMM (only 5 1/2 digits); tried also to look at the sinewave with FFT and DSO and it's pretty clear, I guess there will be no issues since their PSUs are built to comply with CE/FCC which involves also noise on the power line.

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: April 17, 2018, 12:25:49 am
content: Quote from: SeanB on April 14, 2018, 05:45:07 amFerroresonant power supplies are a nifty idea. I remember seeing them in rack-based minicomputers, back in the day.Just be aware that ferroresonant units are heavy e.g. 23 kg for 500 VA, 55 kg for 2000 VA:http://www.poweronaustralia.com.au/wp-content/uploads/2014/07/Power-Conditioner-Fact-Sheet.pdfDepending on your VA requirements, make sure you keep up your gym work and maintain a decent squat, deadlift, etc.