High voltage probes for rectified 220v AC? - Page 1
Forum section: electronics / testgear

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 23, 2014, 03:23:19 am
content: Hi folks... If anyone can help me... I just bought an Rigol 2072A oscilloscope and I read on its specifications that maximum voltage is 300V RMS..Here where i live, its 220 AC, but after rectifier on power supplies it goes to 330-350 volts DC....How can i use my Rigol 2072A scope safely to connect to MOSFETS in this rectified line ? Do i need to buy an high voltage probe ?... I am beginning with oscilloscope and I will use just for troubleshooting for repairing devices.. so... i would like not to pay much more for anything else... the scope was already hard on my pocket... So.. What should i do ? buy probe ? buy some adapters ? attenuator ? Help me out...Thanks in advanced !

author: SArepairman
author_rank: Frequent Contributor
timestamp: January 23, 2014, 11:34:51 am
content: 10:1 probes from decent probe manufacture are fine, with 10:1 your oscope will see 30V. Its probably safe up to ~450V.Hook it up and don't touch it while its on and you will be fine.I don't know if I would try this with some shit ass probe though.

author: SArepairman
author_rank: Frequent Contributor
timestamp: January 23, 2014, 11:43:58 am
content: keep in mind converting RMS to PP

author: Psi
author_rank: Super Contributor
timestamp: January 23, 2014, 11:49:51 am
content: If the probes that came with the scope have the 1x / 10x switch and you want to work with 230VAC put some tape over the switch so it will stay on x10.It's easy to bump the switch to x1 otherwise.

author: PA4TIM
author_rank: Super Contributor
timestamp: January 23, 2014, 11:51:30 am
content: This sort of info you can find in the spec sheet of the probes. I do not know about your scope but some scopes are only 300VDC if you use a 10X probe. In that case you need a 100X probe.But be carefull most scopes and probes are only stated for DC and low frequence use , the impedance decreases when frequency increases.But be very carefull when measuring mains with a scope. Use an isolation transformer or a differential probe. The scope ground is connected to the ground of the probe, so if you clip the ground probe on a live line you use your scope to test the fuse in your mains entrance.

author: Altemir
author_rank: Contributor
timestamp: January 23, 2014, 12:14:52 pm
content: tiagobarachoWe are working with HV (up to 7.5kV), using Pintekdifferential probes. In some cases we are using Tektronix TPS2024 DSO with full galvanic isolation between Ground and between channels. I recommend 100:1 probes (for example HP-9258) for your safe using. Let rememberpa4timrecommendations about grounding and isolation.N.B. For Rigol RP3300A probes - 300Vrms maximum voltage. Remember about voltage derating with frequency.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:08:45 pm
content: Quote from: SArepairman on January 23, 2014, 11:43:58 amSArepaiman, when i have a diode bridge rectifying 220AC to DC , the output it PP or RMS ?.. I have a fluke multimeter and It shows around 340 volts DC....If its PP, 300 RMS in PP would be 424 volts right ? so it would be safe to me to use my stock probes in 10x to measure ?I will never use it beyond those voltages... but i would like to operate it safely on those PWM supply boards to test the mosfets operation...

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:12:37 pm
content: Quote from: Psi on January 23, 2014, 11:49:51 amHi PSI.. thanks for your reply.... acctualy for the AC 220V i know its safe to use the probe rated to 300 Vrms.... but when there is a diode bridge rectifying to DC and the big cap after it , I do check on my fluke multimeter and it shows around 340 volts DC.... so i got worry if i can test those DC lines on my scope that is rated to 300 volts RMS.....i am a little bit confused...

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 23, 2014, 01:17:33 pm
content: Quote from: PA4TIM on January 23, 2014, 11:51:30 amPA4TIM, i read the specs.... but it shows 300 VRMS... i am not sure if rms is what i see in my multimeter or its PP.....Because i always thought that IF i have an AC line of X volts, it would not be possible to have more than X volts DC, but in fact after the diode bridge it shows around 340 DC for 220v AC input.... ( sorry i am not electrical engineer , just learned by myself and still a lot to learn..)

author: phil
author_rank: Regular Contributor
timestamp: January 23, 2014, 03:36:00 pm
content: Your meter shows RMS. Power line is a sine, that means the amplitude changes over time: From the positive peak to the negative peak. This difference is called Vpp.AC RMS equals the DC voltage you would need to get the same power through a resistor (over time). Thats because the power changes with voltage, and AC is a constantly chaning voltage - that means power also changes all the time.If you want to calculate your Vpp: Vpp=sqrt(2)*Vrms.For 230VAC: 230V * 1.41 = ~325VKeep in mind that a rectifier with filter caps will convert the negative half wave to a positive one and charge up any caps attatched to it. As long as you don't load them down too much, they will go up to Vpp. Thats why you see ~340V on them.Phil

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 23, 2014, 03:53:28 pm
content: Quote from: phil on January 23, 2014, 03:36:00 pmI thought that the AC 230v would be a sine wave with lower point - 115v, and upper point 115v, so the difference is 230 v Ac.... After rectifier, would be the same because when the wave is on positive, two diodes makes the current flow in one direction, and when the wave is on negative, the other two diodes keeps the current flowing in the same direction... and the cap is need to filter this switch point where two diodes stop working the other two begins... I just dont really get why it gets to 330-340 v DC......About the scope then.. I cannot use the probes to test any rectified line D in devices working at 220 AC v ? i have to buy a new probe or there is a device to atach to the BNC connector to make it from 10x to 100x ?Thanks

author: phil
author_rank: Regular Contributor
timestamp: January 23, 2014, 04:31:43 pm
content: Quote from: phil on January 23, 2014, 03:36:00 pmSorry, my bad. I meantVp, not Vpp. Vpp is the voltage difference between the positive peak (~325V) and the negative peak (~ -325V). As such, it's about 650V.A rectifier converts the negative half wave to a positive one, so your Vpp after the rectifier is the same as Vp on the AC side.We call it 230V because the reference is ground. In reality, the voltage switches between +325V relative to ground and -325V relative to ground.

author: SArepairman
author_rank: Frequent Contributor
timestamp: January 23, 2014, 09:18:18 pm
content: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/rectbr.htmlHave a glance at that. You have a sine wave, then you rectify it, so all your peaks are on one side. Then you smush down the wave form with a smoothing capacitor.Once you look at the pictures the voltage level differences will be obviousSo, your probe attenuates 10 times in 10:1 mode, theoretically this means you can put 3000 volts into your probe and your oscilloscope will still be ok. However, the problem is that the probe would require special design to withstand these voltages. The insulation in your probe and the capacitors must be able to withstand 3000 volts, if you tried this with an ordinary probe it is likely that something would fry (I would guess the capacitor would short out).You can get something that can work at a few thousand volts cheaply on ebay.http://www.ebay.com/sch/i.html?_odkw=high+voltage+probe&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR6.TRC1.A0.Xhigh+voltage+probe+oscilloscope&_nkw=high+voltage+probe+oscilloscope&_sacat=0However the nice really high voltage stuff will be built very weird, not just thick insulators. There is one tektronix probe that features a gas insulator, there is some kind of freon in the probe that works well as a high voltage insulator and does not effect the bandwidth of the probe much.As for your question, your multimeter in AC mode will measure RMS. As to how accurate it is, this depends on frequency and crest factor. There are different techniques for determining RMS measurements,1) make the assumption that the input waveform is a sine wave, do a Vpp measurement and then convert this to RMS using the formula using a microprocessor, cheap, fast, but it is inaccurate with anything but a sine wave2) various analog conversion methods (squaring it and averaging it, there are a few variations on this method)3) record it on an oscilloscope and do it mathematically4) thermalYour multimeter if its mega cheap will do #1, your oscilloscope will do #3, your medium to high end multimeter will do some variation of 2. Different methods have different trade offs (some might give a faster response at the cost of accuracy, others may break down at higher frequencies due to nonlinearities in the nonlinear analog circuits, and they will have different accuracies at different crest factors (how fucked up the wave form is = crest factor).The ultimate judge of RMS voltage is a thermal meter, this essentially uses your signal to heat a DC to high frequency resistor and measures the temperature change in the resistor. This method will not lie to you and it will work on really screwed up wave forms, including noise, accurately. It is not fast to respond however as you need to actually heat something up. Furthermore the bandwidth will be much wider with a thermal meter. You will notice attenuation MUCH MUCH sooner in an analog RMS circuit rater then a thermal one (your meter will sometimes have 3 db rating, the frequency at which a sine wave will by off its real RMS value by 30%, just like your oscilloscope does).As for converting RMS to Vpp, sometimes its really tricky. Consider the VPP of this waveform and its RMS reading:You need to hook up an oscillsocope :p

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 23, 2014, 11:06:33 pm
content: Quote from: SArepairman on January 23, 2014, 09:18:18 pmMannn.. now you clarified me.... The 300 VRMS on the scope specification does not mean that the maximum voltage i can check with the probe is 300, but that on the scope BNC connector should arrive maximum 300 Vrms, right ?I am not at all into high voltage... the maximum i need is just to be able to test components after the rectified bridge on 220 AC devices... and since i checked on the multimeter 340 volts DC after rectified i was worried the scope could not handle..The probe that came with the rigol DS2072a is RP3300A. this is the specshttp://www.rigol.com/download/Oversea/DS/User_guide/RP3300A_UserGuide_EN.pdfIts says Maximum input CAT II 300VAC .... Does it mean it only can be used for AC probing ? I did not find any info about DC ..What i finally want to be able to do is get a LCD TV power supply and be able to probe around and be safe.... Since i saw the 300rms limit, i was wondering if i needed another probe or something else..Do I need to get one DC probe ?Thanks very much

author: kg4arn
author_rank: Unknown
timestamp: January 23, 2014, 11:25:58 pm
content: Health insurance = differential probehttp://www.probemaster.com/product_info.php?cPath=21&products_id=289&osCsid=8c32a1eb741884fe7972443e0bfda081

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 24, 2014, 02:59:26 am
content: Quote from: kg4arn on January 23, 2014, 11:25:58 pmUsing this differential probe, i would limit my scope to be a 25 mhz scope? ... man.. that thing this expensive !!!My full scope was 788 with shipping.. and the 100mhz probe 700 v is 895 USD..... i have not more money to spend on it......

author: PA4TIM
author_rank: Super Contributor
timestamp: January 24, 2014, 08:40:46 am
content: TV inverters can be a quick way to kill a scope. I use HV probes for that (and if I'm not sure about voltage I first use my 547 with a CA plugin that is very hard to kill)The voltage of a starting inverter, or trying to start, can be over several kV and while running around 500V.Diff probes are expensive, even second hand. And not every diff probe is a HV diff probe. Most are not. Jim Wiliams has written an app note about inverters for CCFL. He gives lots of information about measuring inverters and makes a diff probe amplifier for this that uses two of these Tek HV probes. And he had all the gear you can dream of, so if he makes these for use on his hard to kill analog Teks, you do not want to probe around with the standard, not very accurate speced probes of you scope.Measuring DC after a recifier with a DMM in DC is no problem. DC will be indeed around 350V in 230V systems. But if the capacitor is dead you have a pulsing voltage and most multimeters then give the avarage voltage and that will be much lower, that is, if the CMRR is high enough for measuring nearby RFI producing inverters.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 24, 2014, 11:47:06 am
content: Quote from: PA4TIM on January 24, 2014, 08:40:46 amI am not going to test iverters output....I just wanted to probe pwm power supply....never the high voltage side of inverters....The probe that came with just says maximum of 300rms Ac .... Does it means i cannot use on dc?

author: lewis
author_rank: Frequent Contributor
timestamp: January 24, 2014, 11:59:32 am
content: Has anyone mentioned the scope's ground?The oscilloscope probe ground is connected to mains earth. If you connect the probe ground to the negative of rectified mains... BANG. Forget about the probe tip, the ground is the bugger.Alwaysuse a differential probe if working on non-isolated mains voltages and are notabsolutely surethe voltages you're measuring are referenced to mains earth. They are expensive, but at least you don't necessarily die. There are some here:http://uk.rs-online.com/web/c/test-measurement/oscilloscopes-accessories/oscilloscope-probes/?searchTerm=differential+probe&sort-by=P_breakPrice1&sort-order=asc&pn=1

author: kg4arn
author_rank: Unknown
timestamp: January 24, 2014, 12:33:27 pm
content: Quote from: lewis on January 24, 2014, 11:59:32 amWell put. Like most of us when we start out, money is in short supply. But it is the beginner who is the most likely to make an expensive or fatal mistake.My advice to the OP fwiw: If you are truly inexperienced and you cannot afford to do it the "safest" way, then don't do it at all until you have the proper experience or you can afford it.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 24, 2014, 12:47:14 pm
content: Quote from: lewis on January 24, 2014, 11:59:32 amI know.....The most affordable differential probes are 25 mhz, around 300 and something dollars....... My scope is 70 and can be hacked to 200mhz....Anyone have any idea of how many MHZ the power switch from LCD TVs or computer power supply operates?( I mean the frequency the Mosfet switchs ?)You guys convinced me... I would like to buy one... but i cannot aford the 100 mhz version... and if i dont need on those power supply.. i would the the 25 mhz version for around 300 usd....... but it that enough?

author: PA4TIM
author_rank: Super Contributor
timestamp: January 24, 2014, 01:02:43 pm
content: Quote from: PA4TIM on January 23, 2014, 11:51:30 amYep, someone dit mention groundbut better twice because measuring mains with a scope and not enough knowledge is a potential deadly combination.TS:If the scope or probe specs are not clear you have a problem. You will never know what they "forgot" to state. Most times they state AC pp and DC.For instance I grabbed a manual that I had on hand from a Tektronix plugin and that states, voltage 600V combined DC + AC peak, or 600 V AC peak to peak. So that is very clear. Do not go over 600V. And then there are statements about max voltage and frequency.In a case of a scope it is not about the input power (except in the 50 Ohm position) but pure about peak voltage because things like caps can not handle it or input resistors in the attenuator, swtiches etc have a max voltage or ander isolation related thigs.If they tell it is 300Vrms then I do not know what they mean. 300VDC must be possible but for the rest? . I think to play it save and keep 300Vpp as the max. 300Vrms on its own does not tell much for the Vpp. The formula Vpp = Vrms x 2 x squareoot(2) is for perfect sinewaves only and a scope can show all sorts of signals. For instance 300VAC with a 100V DC offset. The voltage and current is switchers is far from a nice sinewave.Here you see a trace from 230VAC mains Voltage and current draw by a switching powersupply.The yellow trace is current. Look at the Vrms of that. If this was Voltage the Vpp would have been much more as the Vrms x 2 x 1.4.I know that what you need is to expensive and that is no problem as long as you stay away from those applications. It is like jumping parachute, if you think that parachute is to expensive it is not wise to jump with an umbrella as a parachute.Your scope, your probes and your knowledge are not suited or made for mains or HV applications. The things you need are expensive, if they build your scope so it would survive that, it would have been much more expensive. These scopers are for low voltage student or hobby use and everything that can makes them more expensive is left out. Just like cheap multimeters lack blast shels around a fuse, the special fuses, mov's and more HV high energy safety things. Budget scopes are not an other class, they do the same thing as with multimeters. They are sold mainly on price, bang for bucks etc. And you know, that does not tell a thing. Very bad for even less money is still a very good bang for buck ratio, but still can be garbage.Just measure behind a mains to 24V or 12V transformer. It is not ideal but a lot safer.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 24, 2014, 01:27:08 pm
content: Quote from: PA4TIM on January 24, 2014, 01:02:43 pmPA4TIM, my scope is a Rigol Ds2072A... think its not at all bad and cheap scope... Dave did a teardown on a ds2000 serie and show how good they are...I know a scope around 788 usd cannot be compared to 5000 USD scopes but it´s not those cheap chinese brand like many that there is.. Its a Rigol...As i said before.. i will never work on hig voltage stuff , more than the power supply for home appliances that here work on 220v ac... mostly I will use it on the low voltage side.... but i may need to probe the live side, as for knowing if standby mosfet are working, or if signals are ok for those mosfets...As i just said... you guys convinced me to buy a differential probe... i just dont want now to buy a cheap one and will not work well, or buy a too expensive one that will be a overkill for my use...Do you think 25 mhz is enough this kind of job ? like this onehttp://www.probemaster.com/product_info.php?cPath=21&products_id=289&osCsid=8c32a1eb741884fe7972443e0bfda081Any specific recommendation for a good differential probe bot not so expensive.Thanks

author: lewis
author_rank: Frequent Contributor
timestamp: January 24, 2014, 01:56:12 pm
content: Quote from: tiagobaracho on January 24, 2014, 12:47:14 pmThe switching waveform will be somewhere between 50 and 250kHz for a standard SMPS like this, and to see the signal reliably on a scope you need at least 20 times that in terms of the scope and probe bandwidth. So 5MHz bandwidth sounds enough. But any nasties on the waveform, such as ringing, can be many hundreds of kilohertz, up into the 10MHz region. Either way, a 25MHz diff probe will be more than adequate to see what's going on for general troubleshooting. (Even if you do get ringing at 10MHz, it is generally sinusoidal and will likely have very few harmonics above the probe bandwidth.)Don't forget that a probe is usable beyond its rated bandwidth because the bandwidth is generally where a signal is 3dB down on the roll-off curve. A 25MHz probe will still showsomethingat 30MHz as there is no brick wall cutoff, but it won't be perfectly accurate.In summary, 100MHz is best, but 25MHz will be fine. I haven't used the probe in your link, but it looks decent. Don't use it with the mains adapter, run it from batteries for the best noise performance.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 24, 2014, 02:41:41 pm
content: Quote from: gazelle on January 24, 2014, 02:03:47 pmthanks very muchI guess that one of this i will buyhttp://www.tequipment.net/CalTestCT25932.htmlhttp://www.tequipment.net/CalTestCT25931.htmlANd this Instek :http://www.tequipment.net/InstekGDP-025.html?v=0.. it have 6% of EEVblog discount ..the difference seems to be 10x /100x on the 25932 and 20x/200x on the 25931..I guess the 10X/100x is enough and more sensitive for my range, right ?

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 25, 2014, 05:07:00 am
content: Quote from: gazelle on January 24, 2014, 03:40:32 pmI just bought one Pintek DP-25 here in my country.. should arrive in 7 days for 326 USD with shipping....It does use one external power supply... but i guess i will do a 3s lipo battery with 7809 power regulator to use as a clean power supply for it, instead of using the power supply.... i guess this way i will have the best possible signal....Actually.. i may test is it does make any difference.... , but i guess its even simpler to use the battery stick to the bottom of the probe box..

author: Melkor
author_rank: Contributor
timestamp: January 25, 2014, 01:38:21 pm
content: Unfortunately the voltage spec is not enough to be sure you are safe with normal probes.Check the CAT rating too. If your DUT is connected directly to mains you can get voltage spikes that are well beyond the nominal voltage.I prefer to play on the safe side so I use a small 230V/12V transformer as I don't have resources for differential probes.I don't think the shape of the signal is too far off. Probably depends on the frequency.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 25, 2014, 01:46:59 pm
content: Quote from: Melkor on January 25, 2014, 01:38:21 pmYou can only use this transformer on Ac , right? After rectifier i would not be able to use... And i guess it can change a bit some wave details, am i wrong ?

author: PA4TIM
author_rank: Super Contributor
timestamp: January 25, 2014, 03:17:18 pm
content: Tiagobaracho, you do not need to quote every post, that makes the topic very hard to read.I use an isolation transformer for every repair of instrument that are mains powered. I have Tek differential probes but they are not for high voltage use.Your diff probe is 25 MHz or so but I do not think you will get it that high without ringing or other effects with multimeter like wires. But that is not a real problem for repairing SMPS.

author: kg4arn
author_rank: Unknown
timestamp: January 25, 2014, 03:42:25 pm
content: Regarding Pintek,Sapphire Instruments, who is as far as I am aware a reputable OEM of differential probes, claims that Pintek has copied their designs without permission.http://www.sapphire.com.tw/notify.pdf

author: Melkor
author_rank: Contributor
timestamp: January 25, 2014, 04:27:47 pm
content: Quote from: tiagobaracho on January 25, 2014, 01:46:59 pmThe waveform is good enough for me but you are right about the AC only part. Your application looks like a tricky one. For both safety and accuracy it seems that you will need a differential probe after all.

author: lewis
author_rank: Frequent Contributor
timestamp: January 25, 2014, 09:04:57 pm
content: Quote from: kg4arn on January 25, 2014, 03:42:25 pmThat's a bit worrying. With a bit of kit like this you need to trust it. The diff probe appears to be rated to 600V CAT III which means it can be used directly on domestic AC mains before the socket outlet, but not at the origin of the installation (electricity meter). Off the top of my head, CAT III overvoltage is 4kV, but don't quote me on that, I'd need to look it up.I wouldn't use it in a CAT III environment though, but itshouldbe fine in CAT II (after the socket outlet). Just be careful. More info here:http://en.wikipedia.org/wiki/Measurement_category

author: jmcdonald
author_rank: Contributor
timestamp: January 26, 2014, 12:24:40 am
content: How about Doug Fords design for a 1000:1 probe on EEV episode 85.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: January 26, 2014, 05:33:06 am
content: on tequipment they have Cal Test for 288 is you quote with them... i thinks this should be the best price...i guess still have 6% of eevblog

author: PA4TIM
author_rank: Super Contributor
timestamp: January 26, 2014, 08:53:47 am
content: Quote from: jmcdonald on January 26, 2014, 12:24:40 amA HV probe is not for mains connected measurements on the mains grid side. And most are only for multimeter use. (and the multimeter must match the probes resistance for the right reading, most need a 10M multimeter. I do not know the EEV episode 85 design)Fordirect to mains connected measurements you need a diff porobe or 1:1 isolation transformer

author: tiagobaracho
author_rank: Regular Contributor
timestamp: February 01, 2014, 04:19:08 am
content: Hi guys !! I received my DS2072A .. I AM IN LOVE !!!! my first scope and seems amazing... I bought the differential probe.. Still waiting for delivery...I have one doubt...I did one test here.... The pron has 3 pins right ..... I did test with adapter not connecting the earth pin...On both positions, ( live one side and ground on the other...vice and verse) when i touch on the ground of BNC i could fell a little bit of shock in my fingers...This sometimes is common with few electronics device like computers, washing machine.... and if you plug it the other way, usually it stops..... So what i do is find this better position and then put the earth... ( usually the default position are the best)...But on this rigol, i felt the shock on both position.... Is that normal ? Because i guess first without the ground it should be isolated the BNC ground to the mains input.... but if i am feeling small shock, it means that back on the power supply live part, there should be something going through both input wires to the ground...This is the power supply from the teardown dave did... Look the C149 and C150 capacitorshttp://www.flickr.com/photos/eevblog/8022086942/#in/set-72157631618295437Both are connected to one side of the input and the other side goes to ground... So if ground is floating(not connected), the live wire( does not matter wich pins is it) will go through a capacitor and to the ground... I suppose that if I remove those caps the shock on the ground would go away.Look the picture i took just touch the probe ... It shows the 60 HZ signal from the 220v outlet because in reference to the scope BNC ground i am real earth ground and the scope ground is transmitting some of the input live...its normal and the power supply needs the earth to work well ??Thanks

author: BravoV
author_rank: Super Contributor
timestamp: February 01, 2014, 08:14:30 am
content: Quote from: tiagobaracho on February 01, 2014, 04:19:08 am... just becareful !!!Expecting next post ..... HELP !!!! My new scope is toasted !!!!! .... or .... no new post will be posted again, ever.

author: tiagobaracho
author_rank: Regular Contributor
timestamp: February 01, 2014, 11:46:51 am
content: Thanks for your reply, but i am not stupid ... I have been fixing for 13 years, and is not now that I will need this kind of beginner advice...

author: granz
author_rank: Regular Contributor
timestamp: March 07, 2014, 05:38:12 am
content: Quote from: tiagobaracho on February 01, 2014, 04:19:08 amWhat country are you in where they use 220v/60Hz ? That's fairly uncommon. (Peru?) Also, if you are swapping hot/neutral by flipping the plug around it sounds like you don't have polarized outlets... You should really replace these with newer polarized ones, or at least re-wire them to always have hot and neutral on the same sides.Yes, you do want the ground connected for a few reasons. Those two caps on the input form part of the EMI filter, and when you remove the ground connection you reduce the effectiveness of that filter, allowing more noise in (and out). Besides that, it really is a safety hazard to leave the ground disconnected, especially on a scope. Consider what happens when one of those input caps fails shorted: the BNC ground is now live as well as anything you have connect to the scope probe ground lead.

author: hibone
author_rank: Regular Contributor
timestamp: March 22, 2014, 03:03:44 pm
content: Hi everyone.I was wondering if any of the high voltage (differential) probes, available on the market, also provides galvanic isolation of the output from the input.Thank you.