measure dc voltage, how? (sds 1052dl oscilloscope) - Page 1
Forum section: electronics / beginners

author: paddy
author_rank: Newbie
timestamp: September 06, 2015, 08:17:03 pm
content: I know some basic theoretical principles, but am stupmed with the practical nuts-and-bolts for how to measure DC voltage in the 300 to 400 volt range with a sds 1052dl oscilloscope. My multimeter shows 385 DC volts, and I have the manual for the oscilloscope, but I evidently need hand-holding for exactly what buttons to push and knobs to twist. I realize the oscilloscope reading would be approximate and most likely represented as a line in a display, but I am unable to obtain a reading (I have no reason to suspect the scope is bad, I just can't figure out how to use it). Please someone have pitty and walk me through every step of exactly what to do

author: electr_peter
author_rank: Unknown
timestamp: September 06, 2015, 08:27:02 pm
content: PLEASE,STOPmeasuring such a high voltage with you oscilloscope. WTH were you thinking?It is dangerous to you and your equipment.And WTH were you trying to see on such high voltage DC line with an oscilloscope? Is DMM not enough?I hope you won't injury you or do some damage with such poor knowledge of instruments and neglect to dangers of electricity.Typical oscilloscopes (as the one you got) and probes are not suited for high voltage measurements. See the specifications. There is special equipment for HV measurement.

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2015, 08:35:00 pm
content: Quote from: paddy on September 06, 2015, 08:17:03 pmWelcome to the forum.For voltages like this you would be well advised to use a 100:1 probe for additional safety margin for both yourself and your scope.For the Siglent supplied probe, first make sure it is set at 10:1.Then in the channel menu ensure the probe attenuation is set to match the probe.Channel coupling must be set to DC and at a setting of 100V/div the display will 3-4 div for your voltages.In the Measure menu, there are many user definable settinsg for OSD including voltages.For them to be accurate the probe attenuation and probe settings must match.Use the Probe compensation output for sanity checks to confirm your setup is correct.

author: grumpydoc
author_rank: Super Contributor
timestamp: September 06, 2015, 08:37:05 pm
content: It sounds like an inappropriate task for a 'scopeWhy do you want to do this?

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2015, 08:49:51 pm
content: While others warnings should be heeded this is not beyond the capabilities of your scope provided attention to detail is followed.Firstly Siglents are a 400V input capable DSO.For simple probing ensure the protector sleeve is covering the reference (GND) ring near the tip if the probe.This will prevent ot OH F**K moments if you short things out.Study and understand probe de-rating, the de-rating curves are on the probe packets.Always use equipment in a way to ensure good safety margins of at least 30%.This thread has many good links and advise:https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/

author: paddy
author_rank: Newbie
timestamp: September 06, 2015, 09:38:15 pm
content: > For the Siglent supplied probe, first make sure it is set at 10:1.There is a slider switch on the probe, I have selected 10x ... does that correspond to 10:1 ?>Then in the channel menu ensure the probe attenuation is set to match the probe.I have chose the 10x option.> Channel coupling must be set to DC...Check, that is done.> and at a setting of 100V/div the display will 3-4 div for your voltages.I understand that if the setting were 100V/div, then the display will 3-4 div for my voltages... However, I do not understand how exactly to go about setting the volts per div -- what buttons to push and what knobs to twist. I suspect that is one of my problems...> In the Measure menu, there are many user definable settinsg for OSD including voltages.I think I've found that menu, and selected "mean"> For them to be accurate the probe attenuation and probe settings must match.Hopefully that is covered (I set 10x as indicated above).> Use the Probe compensation output for sanity checks to confirm your setup is correct.I don't know what that means or how to do it... However, before worrying about that I'ld like to see a measurement on the screen... How do I acomplish that?

author: retrolefty
author_rank: Super Contributor
timestamp: September 06, 2015, 09:48:16 pm
content: QuoteI'm not sure your approach to learning electronics is on a good path. Do you have any local access to a mentor or instructor or even active hobbyist?

author: grumpydoc
author_rank: Super Contributor
timestamp: September 06, 2015, 09:48:33 pm
content: Quote from: paddy on September 06, 2015, 09:38:15 pmThe large knobs above the CH1/CH2 button select the vertical attenuator settingsIstronglysuggest that youa) sit down and read the manual (that will also explain probe compensation to you).b) play with your new 'scope with safe input voltage signals - something less than 30VYou still haven't said why you want to measure 400V DC with your 'scope. If it is just to gain practice using it please do something safer.

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2015, 10:00:39 pm
content: 10x is 10:1, most know this but to avoid confusion you should always use 10:1 meaning division not multiplication.The Vertical attenuator sets the V/div displayed.With the Measure menu enabled and OS menus visible the voltage will be displayed in the box you have selected "mean".Probe comp is a 1KHz 5V squarewave from the metal terminal at bottom right below the Trigger level knob.The SDS1072CNL i have setup ATM shows a 4V mean reading from the Probe comp terminal.A higher voltage should be more accurate.Take some more time to familiarise yourself with scope usage before you tackle more advanced or dangerous tasks.Study the datasheet or manual to see the factory stated accuracy and know your equipments limitations.RTFM.

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2015, 10:13:43 pm
content: Quote from: grumpydoc on September 06, 2015, 09:48:33 pm+1

author: AG6QR
author_rank: Frequent Contributor
timestamp: September 06, 2015, 10:37:14 pm
content: Quote from: tautech on September 06, 2015, 10:13:43 pmAgree wholeheartedly. At the very least, try measuring a 1.5V AA battery, and a 9V transistor radio battery. Maybe pairs of batteries in series. Maybe a couple of wall wart power supplies, as well. Only after you really and thoroughly understand what you're doing with those should you consider attempting a voltage above 25 or so volts, where there is potential danger.And as others have said, a multimeter is a much more appropriate instrument for measuring steady DC voltages. It's almost certainly more accurate. It's also isolated. An oscilloscope is ground-referenced, meaning you have to be very careful and thoroughly understand what you're doing when you measure mains-connected devices. Watch the "how NOT to blow up your oscilloscope" videos.

author: paddy
author_rank: Newbie
timestamp: September 06, 2015, 10:41:50 pm
content: > 10x is 10:1, most know this but to avoid confusion you should always use 10:1Check.>The Vertical attenuator sets the V/div displayed.There must be some indication somewhere of what the current setting for V/div is... but where? In the lower left hand corner of the display I find the signal coupling symbol (indicating DC status) the vertical scale factor (10.0). I twist the Volt/div knob, but nothing seems to happen; in particular, the the lower left hand corner of the display does not change.Perhaps I need to be in some mode (or not in some mode) for it to function? An anology might help here: pressing on the gas pedal is how to make a car go, but there are exceptions; the car must be in gear, and even that won't work if the engine is not running... Might I need to push some special buttons (or not have pushed others) first?Some buttons are lit in green: CH 1, Display, Run/Stop. When I have CH1, Measure, Run/Stop highlighted, the behavior is the same: I twist the Volt/div knob, but nothing seems to happen; in particular, the the lower left hand corner of the display does not change.>With the Measure menu enabled and OS menus visible the voltage will be displayed in the box you have selected "mean".I noticed that, but it says 47.2 volts whereas my multi meter says 385v (which is reasonable given the power supply I'm attempting to measure). Moreover, I see no line in the display...>Probe comp is a 1KHz 5V squarewave from the metal terminal at bottom right below the Trigger level knob.I previously accomplished the "Probe Attenuation Setting" as indicated in section 1.3.2 (page 7) of the manual (UM01011-E05A).>Take some more time to familiarise yourself with scope usage before you tackle more advanced or dangerous tasks.Point taken, but should measuring DC be hard/advanced? I suspect that must somehow be simple... it certainly is within the limitations of the sds 1052dl

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2015, 11:12:00 pm
content: Quote from: paddy on September 06, 2015, 10:41:50 pmCheck that you have not selected "Fine" adjustment of the vertical attenuator.Toggle back to "Coarse" with a push of the attenuator knob.QuoteCheck in the Trigger menu thatAutois selected NOT Normal where the waveform will only be displayed if the Trigger level is set within the amplitude of the waveform to be displayed.This is all pretty basic stuff but if this your first scope and in particular a DSO, then all this is not always apparent. CRO's can give a better grounding for newbies to scopes however DSO's have a much better feature set.Do spend some time in the Oscilloscope traing class I linked before and watch as many vids as you can fit in.

author: AG6QR
author_rank: Frequent Contributor
timestamp: September 07, 2015, 05:44:38 am
content: Quote from: paddy on September 06, 2015, 10:41:50 pmIt's not the DC that's the problem, it's the 300V.DC is only a little harder to measure than AC, but you've been guided through the DC issues, and something is still missing.People are rightly concerned that you're having difficulty with the basics, and until you understand the basics, it's not safe to deal with high voltage or high energy circuits. Please, make all your initial mistakes using a small low-voltage battery or some other source of low power DC. (or first try an AC signal: the output of a low-voltage AC transformer, a signal generator, a computer's sound card producing output from one of the many free audio signal generator programs, an electronic musical instrument, etc.)If you can't measure a 9V transistor radio battery, you're not ready to tackle 300V. And 300V is probably inappropriate to deal with even if you CAN measure small batteries. For example, a small battery is generally isolated, so you don't need to worry about the lack of isolation in your scope. You haven't described your 300V source well enough for us to know if it can be safely probed with a non-isolated scope. Are you sure it can be? Do you know what the question means?Furthermore, some scopes can safely deal with a 9V battery using any probe attenuation, while they may require high attenuation to deal with 300V. And some probes may not be insulated properly for 300V -- check the ratings of your probes. Finally, it's not wise to use your hands to adjust probes on live circuits if they have dangerous voltages present. You should place the probes with the circuit de-energized, and then switch on the power when your hands are far from the scope and the device under test.There is much more to safety than I've covered here. 300V can easily be lethal. It can also be damaging to your scope. My advice: don't do it without professional training.

author: grumpydoc
author_rank: Super Contributor
timestamp: September 07, 2015, 06:13:56 am
content: Quote from: AG6QR on September 07, 2015, 05:44:38 am+1385V is a dangerous voltage, depending on circumstances it could be averydangerous voltage.Also a 'scope is not the correct tool for measuring DC, the clue is really in the nameoscilloscope - it is an instrument for looking at AC waveforms.At best the 8-bit ADC in the 'scope front end will give you two and a half digits of precision, usually with an accuracy no better than 1-2%.Your 'scope is not the go-to instrument for measuring DC, your multimeter is.

author: rs20
author_rank: Super Contributor
timestamp: September 07, 2015, 06:19:52 am
content: You should alsofully understandthis video before continuing with hundreds of volts of DC:

author: grumpydoc
author_rank: Super Contributor
timestamp: September 07, 2015, 06:23:57 am
content: Quote from: paddy on September 06, 2015, 10:41:50 pmWe are not worried about it being within the 'scope's limitationsWe are worried about it being withinyourlimitations.

author: timb
author_rank: Super Contributor
timestamp: September 07, 2015, 06:48:22 am
content: Quote from: rs20 on September 07, 2015, 06:19:52 amPlease do watch this video. I'm an experienced engineer, and just the other day I hooked my scope up to a circuit connected to a "floating" supply. Turns out it was floating at a -42V potential to earth ground. Sparks flew and I blew up a couple of components. I know what I'm doing and just forgot which PSU I was using.You're dealing with a *lethal voltage* and have no idea what you're doing. You could easily kill yourself. Stop, please.Sent from my Tablet

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 07, 2015, 10:21:16 am
content: Well... this is an interesting thread -- and a kind of scary one.Quote from: paddy on September 06, 2015, 10:41:50 pmYes, the lower left hand corner of the display will indicate that CH1 is active, the channel coupling (AC or DC) and the present setting of the Volts per Division (vertical scale factor as you have called it) as well as whether Bandwidth Limiting is in use.When CH1 is active, turning the big CH1 V/div knob (labelled V - mV) should change the V/div setting as shown in the lower left hand corner. Pushing on this knob as a button should change the function of the knob from the usual 1-2-5 "coarse" increments (1V/div, 2V/div, 5V/div, 10V/div etc.) to a "fine" adjustment (smaller increments in V/div) and back again. You should be seeing the actual V/div setting indicated in the lower lefthand corner of the screen display.QuoteTry pushing the V/div knob as a button, to change from Fine Adjust to Coarse Adjust mode. Then see if it changes the display when you turn the knob. If the CH1 button is lit this should mean that the channel is active and it should respond.QuoteThe "numbers in boxes" will generally only be accurate for the portion of a signal that is displayed on the screen. No line on the display = no accurate "numbers in boxes."Have you perhaps already damaged your scope? Let's hope not. Take the advice of the other commenters and _learn to use_ the scope's basic functions _before_ you attempt to make measurements of high voltages.QuoteThis is not the probe compensation setting. Read 1.3.3 on the next page. In the copy of the manual that I have, the scope photo on Page 2, Picture 1.1-1 is mislabelled, the item at bottom right should read "Probe Compensator" output rather than "Probe Component". This is where the scope sends a signal of known voltage and frequency to a probe, so that the probe's "compensation" or capacitance can be adjusted to give a proper waveform display on the screen. Please read the directions in the Manual here andpractice so that you can display this Probe Compensator signal properly on the screen at several different timebase (horizontal) settings and V/div settings.QuoteThe problem here is not the measurement in particular, but rather that you are a novice at using the scope at all. Yes, making a DC measurement is simple (as long as proper precautions are taken concerning the HV which you desire to measure) IF and only IF you understand how to use the scope in the first place. So back up a little bit, and do not even consider trying to make this 300-400 volt measurement until you are familiar with the basic operation of the scope, as well as the safety precautions you (and everyone else) need when dealing with HV.If you can give some more details about the circuit you are going to be measuring _once you know how to use the scope_, you will get more advice on how to do it safely. If all you are concerned about is the magnitude of a voltage that you know to be pure DC, then a DMM is a better choice than an oscilloscope for making the measurement, as others have said above. BUT... suppose you need to measure the ripple or other noise sitting on top of such a (mostly) DC voltage? Then you will definitely need to use a scope, and you will definitely need to know what you are doing and how to go about doing it safely.Practice, practice practice. Measure some simple and low DC voltages first, like from batteries of different types. Measure the Probe Compensator output at different timebase and V/div settings. Once you know how to use the basic controls of the scope and you are getting readings that make sense on these "known" signals, then you can move on to actual use of the scope on unknowns.

author: Gyro
author_rank: Super Contributor
timestamp: September 07, 2015, 11:12:42 am
content: There's a useful sticky post on High Voltage practice over on the DIY audio Tubes forum that might be helpful to you:http://www.diyaudio.com/forums/tubes-valves/30172-safety-practices-general-ultra-high-voltage.html

author: vk6zgo
author_rank: Super Contributor
timestamp: September 07, 2015, 11:59:17 am
content: The moment measurement of voltages of this order are mentioned,people are prone to run around like Chicken Little,demanding that you don't test such dangerous voltages!It is quite common to look at high voltages with Oscilloscopes-----how do people think fault finding in tube equipment was done?That said,you don't quite seem to know how to do it.With an analog 'scope.all that you do is to let the display "free-run",so there is a line across the screen.I think amodernDSO will do something similar,but the 1980s & '90s ones didn't seem to.If you can get a line across the screen with no input,the next thing is to connect a "X10"(10:1 division) probe.In many cases you have to remember that the displayed voltage is one tenth of that which you are probing.In some cases,the 'scope will do this for you,but I'm not sure whether your 'scope does it.Now,ensure your 'scope is set to "DC coupled".The Oscilloscope will display a dc voltage as a vertical shift of the horizontal line.This shift will either appear as a change of voltage of one tenth of the voltage you are probing,or a corrected version giving the correct voltage.As suggested by others,it is a good idea to try this with lower voltages so as to "get a handle" on the process.In the case of the 400v supply,sometimes these may be directly connected to the AC Mains,presenting the possibility of connecting Active to Earth via the probe "earth clip",causing a large BANG!A more insidious possibility is where you have old wiring in you house without a proper Earth connection.In this case,you may elevate your 'scope metalwork to the Mains Active voltage with resultant danger of electrocution.A"tube-style" power supply, will usually be isolated by a transformer,& will usually have one side of the supply returned to the Device cabinet,which is in turn connected to the building Earth via the power lead,,as is the 'scope Earth clip.

author: rs20
author_rank: Super Contributor
timestamp: September 07, 2015, 12:21:04 pm
content: Quote from: vk6zgo on September 07, 2015, 11:59:17 amYou must have missed the part where the OP chose 400V DC as hisfirst test signal to use when learning to use an oscilloscope. If you don't think that's a poor choice, then that's a bit nuts.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 07, 2015, 01:23:25 pm
content: " If you don't think that's a poor choice, then that's a bit nuts."Yes,but us old blokes who regularly looked at voltages of this level when you were "but a glint in your Daddy's eye" are all a bit nuts!We even learnt with valve (tube) HT lines of that order----most of the old radios we could afford to mess with had "385 volts a side" centre-tapped power transformers,giving dc HTs of around 350--375v (bit of volt drop in the valve rectifiers).Where did he give any inkling that he was using the 400v supply as a "test signal" to learn how to use the 'scope?I quote the OP in its entirety:-Quote from: paddy on September 06, 2015, 08:17:03 pmHe just wants to measure it--------having already measured the voltage with a DMM without vapourising himself,perhaps he isn't quite so fumble fingered as you assume.

author: rs20
author_rank: Super Contributor
timestamp: September 07, 2015, 01:28:02 pm
content: Not interested in such pedantry. OP clearly doesn't know basics of triggering or how to set volts/div --> Learning. Doing it with a 400V DC signal.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 07, 2015, 01:31:52 pm
content: Note this statement:QuoteThis, coupled with the fact that he sees no change in the bottom left CH1 V/div setting display when he rotates the V/div knob.... may mean he has already blown the front-end input preamp or attenuator circuitry on CH1. Even if the knob is in "fine" mode the display should still indicate a change in value when the knob is rotated.Let's see if he can get a proper display of the Probe Compensator signal on CH1 at various V/div settings.

author: grumpydoc
author_rank: Super Contributor
timestamp: September 07, 2015, 01:39:22 pm
content: QuoteProbably not but combining not having the first clue how to set a 'scope up, no information about why (s)he wants to measure 385V with a 'scope which isn't the best tool for the job (ripple measurements noted but no evidence at the moment he wants to do that) and potentially dangerous voltages (we don't for instance, know that the 385V in question isn't across the main resevoir cap in an SMPS) does not add up to a comfortable feeling.If this is just practice then the OP can do that with safe voltages. If you had a dangerous way to acomplish something and a safe way to do the same thing would youactuallychoose the dangerous one?Also, this is an Internet forum - it is typically impossible to tell the experience level of the other posters (though we seem to have a clue here) so there is a sensible tendency to be cautious with advice.QuoteThe data sheet says the inputs are good to 400V (DC+AC peak) - that should remain true even at the most sensitive vertical setting. So heshouldn'thave blown it up.....yet

author: vk6zgo
author_rank: Super Contributor
timestamp: September 07, 2015, 01:43:53 pm
content: Quote from: alsetalokin4017 on September 07, 2015, 01:31:52 pmI'm not sure that one follows from the other.Does the V/div display report what is happening in the attenuator or preamp,or does it just show what the attenuator setting is supposed to be?I would have assumed the latter.

author: rs20
author_rank: Super Contributor
timestamp: September 07, 2015, 01:48:59 pm
content: Quote from: vk6zgo on September 07, 2015, 01:43:53 pmAgreed, the CPU (and the display on screen) controls what the attenuator is set to, not the other way around.

author: Docholiday
author_rank: Regular Contributor
timestamp: September 07, 2015, 01:56:21 pm
content: Wow! 300 plus DC volts as a first measurement and not understanding you scope? Do your self a big favor at least at a bear minimum watch Daves video on how not to blow up your scope and read your scopes manual.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 07, 2015, 02:12:51 pm
content: So why doesn't the V/div display at bottom left, change at all when he rotates the CH1 V/div knob?Quote

author: rs20
author_rank: Super Contributor
timestamp: September 07, 2015, 11:45:25 pm
content: I think it would be very helpful if the OP posted a video of him supposedly rotating the V/div knob, and showing the V/div setting on the screen not changing.Quote from: alsetalokin4017 on September 07, 2015, 02:12:51 pmSeems far more likely that he's twisting the wrong knob, is deep in some menu that disables the knob, or is looking at the wrong thing on the screen. Regardless, the theory that the analog circuitry is fried is waaay down the list of explanations.

author: RogerRowland
author_rank: Regular Contributor
timestamp: September 08, 2015, 06:58:58 am
content: Quote from: alsetalokin4017 on September 07, 2015, 02:12:51 pmI assume he's tried rotating it in both directions? If he's reached one limit, no amount of rotating the same way is going to change anything ....

author: paddy
author_rank: Newbie
timestamp: September 09, 2015, 10:53:58 am
content: This post is off-topic, but:My truck broke down, so until I can fix it I will be taking a vacation from trying to sort out the power supply problems of my tube amp... till then, thanks to all