EEVblog 1604 - BEWARE! Multimeter Burden Voltage
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- เผยแพร่เมื่อ 9 ก.พ. 2025
- Burden Voltage is a BIG trap with Multimeters, don't get caught out!
A short video demonstrating the impact of Burden Voltage / Shunt Resistance on current measurement.
Mutlimeter Shunt Tutorial Part1: • EEVblog #929 - Designi...
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This is one reason why I am thankful to have gone to school when we started out using analog multimeters and burden resistors and resistor loads for voltage readings had to be accounted for. I remember the old simpson multimeter had an input resistance of only about 100 kohm while measuring voltages. It meant that you really had to be careful and know what you were doing. Like my old professor always said. You can never measure anything without effecting it.
Affecting
Decades ago, I calibrated an industrial control loop that had a poor design to produce the 4-20mA signals. The before and after calibration data was all over the place, depending on the techs that calibrated the loop. The equipment had to be labeled and tagged to a matching calibration procedure document. We had to use a specific multimeter on a fixed range to get repeatable results and good loop operation. Fortunately, the control loop was not for any critical operations in the power plant.
Cool story!
Almost sounds like my time working on AB 1771 IFE when I was servicing them.
If the current is different with every multimeter why bother? Just use the analog input it's connected to
@@bene5431 The measurement/calibration/verification procedures in place at that time required 4-20mA measurements. Once a specific meter and current range was defined the problem was addressed.
Burden Voltage Avoidance Step 5: Don't measure the amperage at all. Just assume everything needs 10 amps and let the PSU and PCB guys deal with it
Would be nice if everyone used the exact same PSU
I sure hope the PCB guy won't be angry with me if I don't bother with proper measurements.
Plot twist - I'm also the PCB guy
Exactly!
Sounds like a BGA PCB design challenge.
That's what I was also saying
It makes perfect sense once pointed out, but I'll admit to having never considered it. Now added to my bag of tricks.
In case you didn't think of it, a similar idea applies to measuring voltage, although you are placing a resistor in parallel with the measurement instead of parallel. However, the impact is usually negligible in voltage measuring.
It makes much more sense to me to talk about this phenomenon as "burden resistance" as that's what causing the inaccuracy in the assumption of the circuit elements.
This is one of the reasons it's handy to have a clamp meter for measuring higher currents. Just don't forget to zero it before making a DC measurement.
How much "higher" we're talking about? Anything over the maximum value of miliampere range?
@@offspringfan89 Yes, I typically use a clamp meter when I need to measure more current than the milliamp range can measure unless I need more accuracy or resolution than the clamp meter has. There are some clamp meters like the Uni-T UT210E that can measure milliamps, but they are very sensitive to magnetic fields when measuring DC.
I haven't used a multimeter to measure amperage in ages.
I always use a clamp meter and a special clamp meter designed for 4-20mA signals.
@@offspringfan89 I only use a clamp meter for currents I expect to be > 100mA. Unless you have a clamp meter specifically designed for low current, most are designed for measuring high currents and tend to be really jumpy.
@@rocketman221projectsI see, thanks.
You don't have to calculate the shunt resistance (although working out 1V / 9.8mA - 100R = 2R isn't exactly taxing), the table shown at 2:52 is telling you precisely what the shunt resistance is. For the 60mA range, the burden voltage is given as 2.0mV/mA, but since voltage divided by current is resistance, that's just another way of writing 2 ohms - the shunt resistance for that range. Similarly you can see that the shunt resistance on the 600μA range is 0.2mV/μA or 200R; and it's 0.03R on the 6A range.
On the first equation you subtract 100Ohms to make it match the mV/mA, example
(1V/9.8mA) - 100R = 2R
2mV/mA = 2R
But on the second equation you don’t subtract the 100R or it doesn’t make sense to me example,
(1V/4.996mA) - 100R = 101R
0.2mV/uA = 200R
Can you help?
@@shawnphillips8707 I think you have to remember that there are tolerances on the power supply voltage, the multimeter display and on the 100R resistor. Nevertheless, let's see what we get in the first case if we take the readings at face value: We have a displayed supply of 1.008V and a current of either 9.795mA (from the PSU display) or 9.793mA (from the multimeter display). So the total circuit resistance is somewhere between 1.008/0.009795 = 102.91R and 1.008/0.009793 = 102.93R. That means that the shunt resistance (which has to be the total resistance minus the load resistance) works out to be 102.92 - 100 = 2.92R, give or take 1 digit in the last place. The table at 4:10 indicates a shunt resistance of 1R but I'm afraid I can't tell you why the total circuit resistance appears to be close to 103R, not the 101R that would be expected from that table. Either there is a 2% cumulative error somewhere in the voltage, current or resistor measurements (or maybe even contact and lead resistance is significant), or the table at 4:10 is wrong. Sadly there was no explanation of where it came from.
For the second case on the microamp range, we get 1.008V driving a current of either 4.969mA (PSU display) or 4.966mA (MM display), which corresponds to a total circuit resistance somewhere between 1.008/0.004969 = 202.85R and 1.008/0.004966 = 202.98R. The load resistance is still 100R, so the shunt resistance has to be 102.9R, give or take 1 digit in the last place. That at least, has a reasonable correspondence with the table shown at 4:10 although closer examination seems to indicate that it may be for a different multimeter with a full-scale reading of 5, 50, 500 rather than the BM786 which clearly has FS readings of 6, 60, 600.
Checking back to the table shown at 2:52 it indicates that the BM786 has shunt resistances of 200R (0.2mV/μA on the μA ranges), 2R (2mV/mA on the mA ranges), and 0.03R (30mV/A on the ampere ranges). Why these don't correspond to the measurements in the video, I can't tell you. That's really a question only Dave can answer.
Agreed, I like the more general case of "Anytime you make an observation, the act of observing changes the conditions." Same problem with voltage measurements, at least with high impedance circuits.
Believe it or not, I really like this short video. Thank you.
"short videos" are fine. Shorts? Yeah nah
beats a 1/2 hour multimeter infomercial
I literally was talking to a fellow engineer about this and I was troubleshooting their setup.
It's common.
I design hybrid tube/solidstate hifi gear, I find myself almost never using the multimeter to measure current, because all the places I wan t to measure current are across a resistor in the circuit anyway.
Measuring voltage drop along a PCB track is fun, especially when you are talking about microvolts. Cascaded pair of op-amps on an isolated supply does the job there.
Very easy to over come the current meter in the supply, just by measuring the voltage the other side on the current meter and not on the power supply. the best way is to design in a current shunt which remains in circuit all the time, so measuring the current by measuring the shunt voltage has little or no affect on the circuit being measured.
At lest nowadays we don't have to keep thinking of the ohms/volt when taking very voltage reading. 🙂
The new guys have it so easy 🙂
Your suggestion works when you are dealing with low resistance circuits, but goes wrong when making measurements on high resistance circuits because the current drawn by the voltmeter is then an appreciable part of the total current measured. Once the circuit impedance starts to be significant compared to the input impedance of the voltmeter used, then you are better off measuring the voltage across the ammeter and the circuit together since the burden voltage will be insignificant and the current will be accurate.
@@RexxSchneider but part of the roll of beening an engineer is ķnowing the affects of the test equipment on the circuit and maybe having to calculate the correct value. When I was training it was part of what we had to learn but that was pre digital age. Where ohms/V had a big affect on readings and you had to use the mirror on the meter.
@@TheEmbeddedHobbyist I doubt you were trained in the "pre-digital" age, since I bought my first logic ic around 1965. Nevertheless I'm well aware of the limitations of analogue meters. It doesn't change the basic principle that in low impedance circuits you can ignore the current drawn by the voltmeter and in high impedance circuits you can ignore the voltage dropped by the ammeter.
I meant the digital voltmeter, we used Avo 8's and worked on valves ;+) in day release to the local college from school. Well I've always had to calculate the affects of test equipment placement on the circuit, and taken this in to account when writing the test specifications. I need to be able to set the limits so any component or equipment being out of tolerance is detected in the test results
@@TheEmbeddedHobbyist Schematic diagrams with voltage readouts and test points tended to be specified for a particular sensitivity of VOM; typically a Simpson 260, 20k ohms per volt. The loading by the meter was part of the test process. Using a different meter would likely produce different results.
Burden voltage is why i always use the 10A range. The current shunt resistor is very low resistance. Its basically a copper wire.
Probably actually something like Nichrome.
Good luck with getting any sensible MilliAmp measurement at 3.3V with that setup.
@@johncoops6897 At 1.0V Dave demonstrates in the video getting a more accurate reading from the highest range (mid value 10.05mA, than the 9.793mA original one. Latter has extra digits but they are useless beyond the first unless you have time/motivation to do the correction calculation.
Starting at the highest range also protects the meter (lower fuse!) from any unexpected high currents.
@kevinwalters5160 - that may, or may not, be the case in THIS video with THAT meter.
However what you are not grasping is that a typical handheld multimeter on 10A range is using a 0.01 Ohm shunt.
To measure 1mA that requires the meter to accurately measure 10 MicroVolts (uV) and it takes some serious ADC power to get a sensible and accurate measurement at those tiny voltages.
The WHOLE idea of having ranges in a multimeter is so you can adjust your settings get your measurements into the sweet spot between accuracy, precision, resolution and burden voltage.
Yes, it's always wise to _START_ at the highest Amp Range, but that's just the starting point.
@@johncoops6897 It's quite easy if you have a precise enough meter. The hard part is having a precise enough meter that's still handheld. But I suppose you *can* hook a power tool battery up to an inverter and duct tape it all to a 5.5-digit bench meter, and then hold the whole setup in your hand with a bit of exercise, so for certain silly versions of "handheld" it's possible.
I never really understood why people are talking about "burden voltage" instead of just speccing the input resistance, just as they do with the voltage terminals. The latter are never referred to as burden current or something. Actually I'm not even sure if---just like with the ACV terminals---the ACI resistance is higher/lower and has an inductive part or so, so the resistance is also not the same over frequency.
Keep in mind that the more digits or the more precise the multimeter is, the higher the input resistance. Keithley DMM6500 has I believe 12k (!) of resistance at the lowest range.
There are some interesting ways of dealing with noise. For an AC signal, a lock-in amplifier may be used to modulate the input signal and then filter out the resulting side bands generated. There’s a good video presentation on the subject by Zurich Instruments available on TH-cam titled, _Boost your Signal-to-Noise Ratio with Lock-in Detection_ . The system won’t allow me to paste the URL.
It looks like my previous reply was auto deleted. I am not an expert in the field of metrology. I wrote that lowering input resistance is a way of combatting thermal (Johnson) noise generated in the input network. For an ideal resistor, the noise power generated in the resistor is P=kTB, k=Boltzman’s constant, T=absolute temperature, B=bandwidth. Thus, the RMS noise voltage generated is v=sqrt(4kTBR).
People who work in RF often use the approximation for the noise voltage added by a 50 Ohm input at room temperature as -174 dBm/Hz of input bandwidth.
Congratulations! You have made a concise, detailed, intelligent, technical video in less than a minute ! Feels good, init?
You right mate?
No actually, I hated the 1 minute limit. HAd to leave stuff out and speed it up 10%.
@@EEVblog Shame. Celebrate the accomplishment and move on! It is a very good video!
Learn something new every day. Part of me is like duh I should have realized this but never actually thought about it. Incredibly useful information.
Thanks Dave! Yet another thing that I've learnt from watching your channel.
Thank you. I have purchased multiple meters and dedicated displays that have a large shunt resistor (100amp claimed) because I could never get the same current readings. It makes perfect sense because of your explanation.
So now the problem for me is which meter is accurately.
This is great content Dave. Always nice to visit the basics and review how the act of measuring something changes the system it measures. Great review for the olde phucks like myself and nice introduction for the new people who are just starting out. Well done and thanks.
Useful video. I was hoping for the demo of the 10A range and we got it! It omitted the other trap for young players, _always return the lead to the voltage connector_ . Far too easy to pick up the meter afterwards to measure a voltage and blow the fuse.
And with an analog meter, after putting the probes in the voltage sockets also dial maximum voltage on the selector (or better, choose "off" if that's offered). That way inadvertent inserting probes into the main the meter won't explode.
Back in the good old days of tubes, with 100s of volts, small currents and low accuracy analog meters. The burden voltage did not mater.
and now it does? 0.3ma error?
Remember back in the day, multimeters were specified in Ohms per Volt? Now that even cheap meters have multi megohm inputs, you don’t see that quaint specification. My first Radio Shack meter was 50K Ohms/Volt.
No but spelling in the schematic did.
@@wtmayhew- 50k/V = Luxury!!
I am currently trying to find a cheap analogue meter for temporary use while I repair/modify my AVO Meter.
The best that I can find at a reasonable price is only 20K per Volt. 😢
@@johncoops6897 Yes, the venerable Simpson 260 was rated 20K Ohm/volt. The Radio Shack meter I had as a teenager was the Radio Shack Micronta 22-240a Range Doubler. I just found one on eBay under $20. The seller says it looks nice, but that doesn’t mean it works. 🙂
I never heard it called Burden Voltage before. I just knew it as internal resistance in the meter. When I was in school getting my EE degree, I was taught that it was usually easier to measure the voltage across a known resistor in the circuit (if one exists where you need it) than to measure the current directly. A simple Ohms law calculation is easier than calculating the addition of the meter resistor to the circuit. Plus, you don't have to worry about the extra resistance having an unintended effect on the circuit.
I now finally understand burden voltage. Thanks Dave, that was very helpful
Use a current clamp to remove burden voltage at the expense of resolution and drift.
I have groups on FB mostly for beginners. Many times I said there: (multi)meters and scopes are not magic devices. Simple sentence and most of them catches it.
When I teach Digital Circuits, I’m surprised how many students have escaped learning much about accurate measurement technique. My first lab has students measure and compare the switching current and maximum operating frequency characteristics of LS-TTL and CMOS devices. Students are frequently surprised that input capacitance of oscilloscopes is not negligible and needs to be compensated out by way of a capacitive and resistive voltage divider in a 10X probe to make acceptable high frequency small signal measurements. Several times I’ve had students comment that now they understand why their measurements were off from what they computed in the analog devices course which precedes my course. Apparently the students were just using coaxial cable with alligator clips to measure their filter and op-amp circuits.
@@wtmayhew there are some people which they fixing airplanes with ~5 $ "multimeter".
@@norbert.kiszka Some of them are at Boeing, maybe! At least if those workers took my course, they’d probably be a little careful with their technique.
@@wtmayhew BTW. Airbus (at least A320 series) have small "issue" with "redundancy". Three computers and all of them can make bad calculations. But if nr. 2 (I dont remember exact name) will fail or lose power, then pilots cant control aircraft. There was one incident because of that. Anyway, today Boeing is worse than Airbus.
@@norbert.kiszka Thank you for the reply. That’s good question - how much redundancy is enough? It is not a good day when there aren’t enough matching computations for agreement. The scary thing is now control by wire is reaching consumer automobiles. Throttle by wire has been around for almost 20 years, but if the throttle goes crazy, the driver can still control the car. Now Tesla is doing completely electric steering on the Cybertruck. That seems not so well advised. I believe it is Brembo who have a fully electric brake system. I like the idea of having hydraulics in parallel with electric assist. I had a Nissan with electric brake boost of hydraulic brakes and it had problems with the backup ultra capacitor going bad - my car had issues. In later years Nissan when back to vacuum assist boost with an electric pump to produce vacuum.
Clamp meter needs induced current, so it must have some burden too. Could be an experiment to measure with some good multimeter.
One of the reasons Source Measuring Units (SMU) are so useful. Particularly if you're testing low power battery devices.
That's amazing Dave! I've learnt so much from your channel. I would really love to watch a video where you could find the internal resistance and compensate for that error
Please tell me, my FLUKE 87V zeroes very slowly in the manual range of 600VAC and 1000VAC. Measurement results are still accurate. I wonder if all FLUKE 87v are like this or is my 87V damaged?
This just happened with the current measurement in my Lewin ring. Instead of 10 mA I measured 6.3 mA. Solved with a 1 ohm series shunt resistor and turned to mV reading across it.
Writing this down, thanks.
@@offspringfan89 you're welcome 🤗 . I am editing in these hours the video where I show the different readings and the effect on the other voltages in the circuit.
There are only two kinds of electronic hobbyists: those who have been bitten by the burden voltage, and those who do not know they have been bitten by the burden voltage. 😁
That's how I have been measuring current with an oscilloscope. I use a 1 ohm 10 watt resistor. Sure, it affects the measurement slightly but gets the job done. Choice of resistance depends on scope sensitivity and noise tolerance. lower resistance means also lower impact but means you have to go maximum gain on the oscilloscope and that's going to be noisy.
I still do not understand why they are calling it Burden Voltage since the problem is caused by a shunt resistor. It should be called Burden Resistance. It is much easier to know what it going on with your current measurements when you know the shunt resistance on each range.
I was on twitter and saw your post then came here and it’s uploaded! 😂
Question, if it is a digital mm, do they not take the range setting and shunt resistance into account and display the calculated current ?
It’s easy to forget that multimeters are not perfect! I recently had a similar experience (but on the voltage side) where the 1 Meg input impedance of a keithley meter loaded a circuit (with 10k output resistance) enough to cause significant measurement error. Had me scratching my head until I figured it out!
just like checking voltage you are adding in a parralel impedance. knowing your meter and what its use will cause is vital especially if your use is on the edge of a circuits stability.
Hey, why don't you connect 121GW in place of this BM786 and show how this 9.793mA will change ?
Similar thing measuring voltage on voltage dividers. The measurement action will influence the produced voltage.
Every day is a school day so the saying goes. Still learning stuff at 62 haha. I just purchased a 250VA mains transformer to isolate my scope and got thinking... How do you design a transformer for a given VA? My thinking was you know the in and out voltages, and the out amps; from that you can infer the input current. I assume you then design the primary to take that current, which in my mind means using reactance to limit it - which as reactance is frequency related does that mean a transformers VA rating varies according to frequency? If you can do a video on the theory of this it would be quite interesting as its something I've never thought about before. Watching your videos tends to do that haha.
Transformer design is *very* complex. I also am going to purchase an isolation transformer for this very purpose. My analog scope has only a two wire mains connection, but modern scopes are all grounded ultimately earth grounded. For now I use an inverter and battery (a small Goal Zero) to operate the scope with no ground reference.
The "A" part of the VA specification pertains to heating of the wire in the core. That's why variable autotransformers are often simply rated in amps; that's what matters for core heating. However, magnetic saturation is a combination of voltage and current hence VA. Frequency is an issue since saturation is a function of TIME and voltage; current follows voltage (ELI the ICE man). Less voltage, less current, less core saturation. Higher frequency avoids core saturation which is why aircraft often use 400 Hz AC power allowing for small transformers.
Yeah it's better to use current probe with a scope so that it won't distort the signal much!
BTW, 00:12 - what is kamagatsa ? Maybe come a gutsa? Come your guts out?
Yes, come-a-guts-er. As in, to spill your guts, or in other words, have an accident.
Great video for an often confusing topic
It is a normal property of measuring in physics. Every measurement is applying some inaccuracies in measured system. Only some of that can be omitted (let's say optical measurement of a pebble position, photons will not affect that position in any serious way), and some can be a problem (the same situation, but measuring a particle position - energy of the photon is comparable to a measured object and have to be accounted for). Another fun property is accuracy. You always have to account for that, even if you are using a ruler or a tape 😊That's why surveying and making measurements is so interesting, difficult and huge subject in physics and engineering.
Hah, very much a moment of "so other fields have those details too!". It's funny because on one side I'm very aware that putting any "measurement device" literally "anywhere" changes the... *system* and thus being ignorant of that basic law of the universe... Still, this instance here was _wowski!_ to me. Thanks David and best regards from Poland, not Indonesia (puntastic^2 of me!).
...I'm awaiting delivery of a thermocouple thermometer (is there a dedicated word for that?) because I found a "need" where 400°C max absolutely doesn't come even near... I'll be thinking of my confounding variables very much *more* now. Double thanks now!
American engineers don't call this a 'burden' voltage. It's just referred to as the internal resistance of the meter, in current mode. EDIT: Step 4 should be Step 2. Carry on, Dave.
It probably depends on the particular flavor of electrical engineering. I took a US machines course called Energy Conversion in the 1970s and the term, “burden,” was used.
As an aside, Fluke has on their web site an article titled _Can you live with the burden_ ? They mention the burden voltage of the 87V is 1.8 mV/mA on the 400 mA current range. The gist of the article is about the same as what Dave presented in the video.
Great Video! One questions, could you do a video about industrial high voltage transducers or/and current transducer. I would love to get more information about the technical properties in the datasheet, its hard for me as beginner to find all the information online.
That time when Dave took 6 minutes to say "Moldymeder! Buy my merch. Moldymeder!"
So Dave walks into a bar and asks if they have a moldymeder. The bartender says "We don't serve fungi here."
...And Dave replies, "But, I AM a fun guy!"
The bartender says "We don't sell fungi here ...AND you sound like you are under-age" 😂
@@Markus0021 However, remember that when someone says "you must be fungi at parties" that's sarcasm. What they actually mean is that you're sporing.
This is also true for voltages, but the high resistors in parallel makes it much less noticeable. those are actually common test questions at the university i graduated from.
I took a machines course called Energy Conversion as an EE undergrad. Much stuff in the lab was Victorian Era equipment. There were open frame 10 HP motors the size of washing machines. The Weston current meter on our bench was in a wood box with an 1897 patent date nameplate. We spent a lot of time compensating for the fact the measuring tools we had were quite non-ideal. I suppose it was a good leaning experience to have to endure the antique equipment.
I was under the impression that every current reading meter, digital or analog had a shunt resistor. This resistor is connected across the current input and the common input. This current resistor was usually a short piece of wire soldered directly to the current and common inputs. And the value could be determined and read using another ohmmeter connected to the current and common inputs. Very possibly could be read by the meter in question. Due to the manufacture and materials used the shunt resistor could become unreliable.
Burden voltage - the daily uncertainty principle that puts the cut in the Circuit Under Test
@4.56: Three decimal places in mA versus just one (not two!) decimal places (figures behind the . when the current is expressed in mA) in A range
Great lesson Dave!
Shocking multimeter on multimeter action.
If your power supply has sense wires couldn't you just measure current before the sense point in that case?
Another work-around is a power supply with sense terminals. Connect the sense terminals across the load to ensure the power supply delivers the desired voltage as measured at the load. Good quality power supplies have sense terminals. That leaves out just about all cheap Chinese bench power supplies from Amazon, eBay, etc.
@EEVblog Dave, you need to get your name onto an entry level (Good) scope that you believe will last us a good time. Multi meters are done ✅
That was quite obvious. I'm interested how current clamp affects measured circuit.
I can back this up to because I tried measuring the amp draw from a clock and found micro amp milliamp and straight amp settings on the multimeter gave different readings and power output to the little motor
Super great video thanks never realized this
Nice info
Even a current clamp causes a parasitic load.
I think, like some comments, you have to be aware of the situation and adjust your measurement tool based on the circumstances at hand. I believe there are multiple ICs for measuring different current levels and they all have a sweet spot, none have a universal measurement shunt or clamp.
Can I say that while I know about the burden voltage is I still don't understand what the video on Twitter was trying to demonstrate?
Now I'm gonna try to see if the answer is here! 😅
Less information due to the 1 minute time limit for videos there?
Are you talking about my Short , or the video I posted from a customer? With the customer video, he did the same thing using a 470ohm resistor.
@@EEVblogI'm talking about the customer video.
By watching it in my phone I wasnt able to understand what was in the breadboard, to me i seemed that the meter was directly connected to the wires coming from the top of the screen. I completly missed that there was a resistor in there.
Now it makes more sense!
Doing the math it seems that the mA range of the DMM has a resistance of 2 ohms and the uA range has a resistance of 100 ohms
Use hi-res multimeter and 10 A range. That way you'll get uA resolution with almost zero burden voltage.
Most people don't have a high end 6.5 digit bench meter
My $22 clamp meter works great.
Why are there no multimeters with hall effect sensors in them? Like the Allegro sensors, for example.
So other than being 6x longer, how much more useful information is in this 6 minute version than the 1 minute version? Asking for a friend 🙂
Looks like it's about time you invented a multimeter with the same magic as a clamp current meter Dave. Resistors smesistors
Is the continuity testing done with the amp jacks on this meter?
Wouldn't active I/V conversion solve that and still allow enough signal to get a good measurement? Quite easy to do up to a few mA, for a bench meter, it would be practical up to a few hundred mA.
That's why I invested in a DC capable clamp meter and never looked back. Measure current without breaking into the circuit. Problem came to light using a 12 volt system and an inverter drawing 10 amps. Multimeter shunt plus resistance of test leads was triggering inverter's low voltage alarm. Hopeless
To test it, you have to take it.
So can I find the mV/mA burden voltage rating of my mm and compensate the source voltage higher on a bench PSU? Or is that asking for trouble?
Yes, common technique. But if your current changes dynamically you could be in trouble. If your PSU has a sense terminal then you can use that.
I thought the same thing. Add it back if you needed accuracy. Last week I was doing parasitic drain testing on a BMW, it was 12mA, but as long as it was less then 50mA its ok, so accuracy in that instance isn't necessary.
I hope Dave responds to your question
I've realized that this is even an issue when putting a (thermal) circuit breaker in series with a 12V battery in a UPS etc. It can drop over a volt, basically to run the heater inside the breaker. Fuses of course have the same issue.
Interesting.
Coincidentally just this spring I've had to learn calculating the multimeter's error in voltage and amperage measurement. Tinkercad is a great tool to try and see some of these effects.
Where do you get the resistor box?
Just curious why a Hall effect sensor is not used on a near 0 ohm shunt for current measurement. Are they not accurate enought?
They aren't very accurate for low currents. And can also be susceptible to interference. Burden voltage is not an issue as long as you know its there and can compensate for it.
I couldn’t stop hearing Dave say “Burton voltage”. Can’t for the life of me understand why.
You need to buy an EEVblog "Mouldy Meader" to accurately measure those pesky Burton voltages.
Any opinions on using hall effect current measurement in a multimeter.
That's how a lot of amp clamps work.
One Drink for every Mouldimeter!
With analog meters (voltage wise) it is measured in ohms per volt. A good analog meter is 50k ohms/volt (low scale). This (typically) translates to 50 micro-amps full scale on the meter. So, to get 50 micro-amps for a 10 amp full scale, you need a precision small (and powerful) resistor in the mili-ohm range if now lower. When you go to smaller currents for the same deflection, you need progressively higher resistance to get full scale. All of this proves that multimeters are not "simple". They can get quite complex! Even the analog ones.
A Simpson 260 is rated at 20 k ohms per volt, independent of scale. So if I set the dial to 10 volt range, that inserts 200 k resistance (actually, it inserts 198 k ohms and the meter movement is 2k ohms). What is wanted is 50 micro-amps full scale meter deflection. R = E/I, so 10/0.000050 = 200000 ohms.
What a wonderful meter that 121GW is. I'd have that over any Fluke.
I forgot to mention it can display the burden voltage as well.
I bought it in 2019 and still haven't unboxed it. I don't even know if it works
@@rasimbotHa, ha, ha.. Well I'll tell you one thing in this world I'm certain of, and it isn't the sun rising in the morning... It is, Dave's 121GW WILL work.
The question now is, does Ohms mode inject any voltage or current into the circuit ?
Yes it does. You can measure it if you have two multi-meters. It's very low current and the current is limited as to not damage whatever the unit under test is.
Okay, but how many times do you need fractions of mA precision? ZERO times would be my answer so far.
How come EEVblog BM786 doesn't have the low burden option like 121GW
I did not have major design input into the 786.
Why not sell a practical mini (0-24mA) current clamp adapter? Fluke 771/772/773 market is sky high right now.
Thats why i use old fluke 895a differental volt meters. Scared of new stuff
Step5: use sense lines of your power supply?
When I worked for a company in the mid 1990s, who had a calibration lab, we had a Hewlett Packard 3458A in the lab, and you could twist a couple of bare wires together, connect them to the meter on it's most sensitive current range, and it would read a current caused by the heat from your fingers. If memory serves, it was in the nano or picoamps, whatever the lowest digits were on its most sensitive current range. 🫨
Sorry Dave, TH-cam won't allow me to double like your video, 😢 short, concise and to the point!!!! I would second @fedimakni1200 request for a video on the use on hall effect current sensors compared to a multimeter and to see what the difference would be between them and multimeters in respect to burden voltages? He said shunt resistor but I think comparing it to a multimeter would be just as interesting, NOT A CLAMP METER though, I know this is a hall sensor but would like to see the module being used instead.... Again, thank you Dave..
5 stars and 2 thumbs up!!!
I guess everybody knows... No?
This is a trap for quite a lot of folks. Judging by the comments.
@@SirMo I already noticed. How actually multimeter measures the current they think?
@@fixitalex It would be possible to measure current with very little burden voltage to where it would be negligible. You would just need a very low drift and precise meter so that you could use super low ohms shunt. Say 0.001 Ohm or something. I just don't think people consider how much burden voltage most meter have when measuring current.
Stop being a smart aleck!
So you're saying people shouldn't teach anymore because everybody should know everything already?
dave burdening everyone with "educational" content again = smart
not putting picture of his head on merch to boost sales = not smart
So that's why multimeters are chirping... They have bird'n'voltage.
Isn't such a tiny amount of discrepancy being a bit nit picky?
What circuits would require such extreme accuracy?
When you make datasheets for electrical components where you want to determine the current draw, you want it to be correct for example, and not artificially lowered because there was a sneaky resistance in series.
Good info.
Just realized, in German, the word for burden and load is the same ("Last").
How clamp meters affects this type of measurements? 😉
That is a burden!
So it went from 10ma to 9.8ma.. So a 0.0002 Amp drop.
1v / .0002 = 5000 ohms
So your internal shunt is a 5k resistor
I think not. The 1v is across the combined resistance, 100 ohms + shunt resistance. Therefore 1v / 0.0098A = 102 ohms. 102 - 100 = 2 ohms. Someone correct me if I'm wrong.
@@rogerwilco5187 You might be right.. I haven't messed with ohm's law since 1999.. lol
@@calholli Actually I'm pretty much in the same boat, but my old brain was niggling at me that something wasn't quite right with 5k and a drop of only 0.2mA.
I'm calling it "burden resistance" from now on.
Unless you use a hall effect ammeter. Ron W4BIN
Hi dave, can you make a video about the difference between measuring the current using hall effect current sensor vs shunt resistor? Thanks
Yeah..... I second that one, would be good to see the results,