WEBVTT NOTE This file was exported by MacCaption version 7.0.06 to comply with the WebVTT specification dated March 27, 2017. 00:00:00.209 --> 00:00:02.544 align:center line:-1 position:50% size:40% Oscilloscopes are typically used to measure voltage, 00:00:02.544 --> 00:00:06.715 align:center line:-1 position:50% size:55% but what you may not know is that you can just as easily measure current with a scope. 00:00:09.301 --> 00:00:10.552 align:center line:-1 position:50% size:14% Hi, I'm Ally. 00:00:10.552 --> 00:00:13.639 align:center line:-1 position:50% size:51% To measure current with an oscilloscope, you have a few options. 00:00:13.639 --> 00:00:17.643 align:center line:-1 position:50% size:60% You can use the Ohm's Law method to measure the voltage drop across a shunt resistor. 00:00:17.643 --> 00:00:21.063 align:center line:-1 position:50% size:65% You can use this voltage and your known resistance to calculate current. 00:00:21.063 --> 00:00:24.900 align:center line:-1 position:50% size:61% This is a nice, quick way to measure current, but it requires you to do some math in your head 00:00:24.900 --> 00:00:27.736 align:center line:-1 position:50% size:41% to interpret the waveform, and this can get pretty confusing 00:00:27.736 --> 00:00:30.614 align:center line:-1 position:50% size:50% if you have to document your waveform and share it with others. 00:00:30.614 --> 00:00:32.532 align:center line:-1 position:50% size:52% Depending on the shunt resistor you use, 00:00:32.532 --> 00:00:35.619 align:center line:-1 position:50% size:47% it can also introduce extra uncertainty into your measurements. 00:00:35.619 --> 00:00:38.163 align:center line:-1 position:50% size:44% For more accurate measurements, use a current probe. 00:00:38.163 --> 00:00:42.167 align:center line:-1 position:50% size:61% With a current probe, you'll get the measurement in amps right on your scope screen. 00:00:42.167 --> 00:00:43.752 align:center line:-1 position:50% size:31% No calculations required. 00:00:43.752 --> 00:00:46.546 align:center line:-1 position:50% size:47% There are three situations where you'll need to measure current: 00:00:46.546 --> 00:00:51.051 align:center line:-1 position:50% size:56% if you're working with really high currents, really low currents, or something in between. 00:00:51.051 --> 00:00:55.055 align:center line:-1 position:50% size:53% Each one of these situations calls for a different measurement strategy. 00:00:55.055 --> 00:00:57.057 align:center line:-1 position:50% size:56% Let's start with how to measure high current. 00:00:57.057 --> 00:01:02.521 align:center line:-1 position:50% size:57% When I say high current, I mean high current, as in hundreds or thousands of amps. 00:01:02.521 --> 00:01:06.275 align:center line:-1 position:50% size:52% You'll often run into large currents like this when measuring the startup of a device 00:01:06.275 --> 00:01:08.610 align:center line:-1 position:50% size:63% or the switching of a switched-mode power supply. 00:01:08.610 --> 00:01:11.571 align:center line:-1 position:50% size:38% A Rogowski coil current probe can measure high currents 00:01:11.571 --> 00:01:15.242 align:center line:-1 position:50% size:43% because it uses an air core instead of a traditional metal core. 00:01:15.242 --> 00:01:19.162 align:center line:-1 position:50% size:49% With a metal core, we'd have to worry about too high of a current saturating it. 00:01:19.162 --> 00:01:21.248 align:center line:-1 position:50% size:54% With air, we don't have to worry about that. 00:01:21.248 --> 00:01:24.293 align:center line:-1 position:50% size:47% When current is detected, the Rogowski coil produces a voltage 00:01:24.293 --> 00:01:27.713 align:center line:-1 position:50% size:51% that is proportional to the rate of change, or derivative, 00:01:27.713 --> 00:01:30.674 align:center line:-1 position:50% size:58% of the current that's enclosed by that coil loop. 00:01:30.674 --> 00:01:33.760 align:center line:-1 position:50% size:45% The voltage is then integrated, and this allows the probe to provide 00:01:33.760 --> 00:01:38.098 align:center line:-1 position:50% size:52% an output voltage that's proportional to the input current that you're measuring. 00:01:38.098 --> 00:01:41.101 align:center line:-1 position:50% size:50% Rogowski coil probes have been getting a lot of attention with engineers 00:01:41.101 --> 00:01:42.728 align:center line:-1 position:50% size:44% because they're really easy to use. 00:01:42.728 --> 00:01:45.856 align:center line:-1 position:50% size:46% The probe head is just a flexible loop that you can bend and loop 00:01:45.856 --> 00:01:48.358 align:center line:-1 position:50% size:56% around any component that you want to test. 00:01:48.358 --> 00:01:51.528 align:center line:-1 position:50% size:57% Now let's talk about how to measure currents in that in-between range, 00:01:51.528 --> 00:01:54.239 align:center line:-1 position:50% size:48% somewhere between 10 mA and 30 A. 00:01:54.239 --> 00:01:58.035 align:center line:-1 position:50% size:53% For these measurements, most engineers are using a clamp-on-style current probe, 00:01:58.035 --> 00:02:00.454 align:center line:-1 position:50% size:57% also known as a magnetic core current probe. 00:02:00.454 --> 00:02:03.832 align:center line:-1 position:50% size:60% These clamp-on-style current probes are often used to measure current consumption 00:02:03.832 --> 00:02:07.711 align:center line:-1 position:50% size:54% of things like high-frequency digital circuits, ICs, and power supplies. 00:02:07.711 --> 00:02:10.088 align:center line:-1 position:50% size:48% When you're doing this type of testing, it's often important 00:02:10.088 --> 00:02:12.007 align:center line:-1 position:50% size:50% to get accurate low-level measurements 00:02:12.007 --> 00:02:15.260 align:center line:-1 position:50% size:43% which means you need a probe with high sensitivity and low noise. 00:02:15.260 --> 00:02:18.722 align:center line:-1 position:50% size:52% One thing to note is that clamp-on probes are really easy to use. 00:02:18.722 --> 00:02:22.601 align:center line:-1 position:50% size:55% All you have to do is clamp it around a wire, and you're ready to start measuring. 00:02:22.601 --> 00:02:25.312 align:center line:-1 position:50% size:40% There are no extra components or accessories necessary. 00:02:25.312 --> 00:02:29.691 align:center line:-1 position:50% size:59% These clamp-on-style current probes have a hybrid AC/DC measurement technology 00:02:29.691 --> 00:02:32.319 align:center line:-1 position:50% size:43% which means that they have both a Hall Effect sensory element 00:02:32.319 --> 00:02:34.613 align:center line:-1 position:50% size:52% for measuring low-frequency DC contents 00:02:34.613 --> 00:02:37.449 align:center line:-1 position:50% size:42% and a current transformer for measuring those AC contents. 00:02:37.449 --> 00:02:41.536 align:center line:-1 position:50% size:58% You're able to account for the DC offset of your signal instead of the probe blocking it out. 00:02:41.536 --> 00:02:42.704 align:center line:-1 position:50% size:32% Let's look at an example. 00:02:42.704 --> 00:02:47.084 align:center line:-1 position:50% size:56% I have a couple different clamp-on-style current probes plugged into channel 1 and 2. 00:02:47.084 --> 00:02:50.253 align:center line:-1 position:50% size:52% Let's just take a look at the baseline noise of these two probes. 00:02:50.253 --> 00:02:54.299 align:center line:-1 position:50% size:57% On channel 1, I have an older Keysight probe that has a 10:1 conversion factor. 00:02:54.299 --> 00:02:58.845 align:center line:-1 position:50% size:55% This means that we're only able to go down to 10 mA per division on the vertical setting. 00:02:58.845 --> 00:03:02.099 align:center line:-1 position:50% size:52% This really isn't good enough for most low-level current measurements, 00:03:02.099 --> 00:03:06.478 align:center line:-1 position:50% size:47% but with the probe on channel 2, we can go down to 1 mA per division. 00:03:09.272 --> 00:03:13.860 align:center line:-1 position:50% size:56% With this high sensitivity, we can measure low-level currents with much more accuracy. 00:03:13.860 --> 00:03:18.365 align:center line:-1 position:50% size:64% I've also set up peak-to-peak measurements so we can compare the two probes' baseline noise. 00:03:18.365 --> 00:03:21.034 align:center line:-1 position:50% size:50% You'll notice that the probe on channel 2 is giving us 00:03:21.034 --> 00:03:24.663 align:center line:-1 position:50% size:36% about 5-6 times less noise than the probe on channel 1. 00:03:24.663 --> 00:03:26.957 align:center line:-1 position:50% size:37% With this increased sensitivity and lower noise, 00:03:26.957 --> 00:03:29.501 align:center line:-1 position:50% size:39% we're going to be able to make more accurate measurements. 00:03:29.501 --> 00:03:31.837 align:center line:-1 position:50% size:39% When you go to pick a clamp-on-style current probe, 00:03:31.837 --> 00:03:34.172 align:center line:-1 position:50% size:38% make sure you choose one with an appropriate noise level 00:03:34.172 --> 00:03:35.715 align:center line:-1 position:50% size:52% for the measurements you need to make. 00:03:35.715 --> 00:03:38.593 align:center line:-1 position:50% size:38% This is especially important if you care about signal detail. 00:03:38.593 --> 00:03:39.928 align:center line:-1 position:50% size:32% Let's look at an example. 00:03:39.928 --> 00:03:43.014 align:center line:-1 position:50% size:56% If you're working with something like this CAN bus that I have on screen here, 00:03:43.014 --> 00:03:45.767 align:center line:-1 position:50% size:50% you can start to see how the noise level of your current probe 00:03:45.767 --> 00:03:47.561 align:center line:-1 position:50% size:47% can really affect your measurements. 00:03:47.561 --> 00:03:49.521 align:center line:-1 position:50% size:53% With the older current probe on channel 1, 00:03:49.521 --> 00:03:52.524 align:center line:-1 position:50% size:45% we can barely make out the edge crossings of this CAN bus. 00:03:52.524 --> 00:03:54.526 align:center line:-1 position:50% size:45% With the newer probe on channel 2, 00:03:54.526 --> 00:03:58.196 align:center line:-1 position:50% size:52% we can clearly define all of the bits and make more accurate measurements. 00:03:58.196 --> 00:04:01.074 align:center line:-1 position:50% size:44% Generally, clamp-on current probes don't have much bandwidth, 00:04:01.074 --> 00:04:04.953 align:center line:-1 position:50% size:42% but the current probe we're using on channel 2, the N7026A, 00:04:04.953 --> 00:04:08.123 align:center line:-1 position:50% size:61% has the highest bandwidth available at 150 MHz. 00:04:08.123 --> 00:04:10.542 align:center line:-1 position:50% size:48% The third type of current measurement is low current, 00:04:10.542 --> 00:04:14.045 align:center line:-1 position:50% size:48% and when I say low current, I mean in the microamp to amp range. 00:04:14.045 --> 00:04:17.299 align:center line:-1 position:50% size:48% Measuring low-level current like this is often necessary when testing things 00:04:17.299 --> 00:04:20.594 align:center line:-1 position:50% size:45% like battery-powered devices, charging devices, or memory chips. 00:04:20.594 --> 00:04:24.681 align:center line:-1 position:50% size:50% Engineers are always looking for ways to maximize battery life of their devices. 00:04:24.681 --> 00:04:29.352 align:center line:-1 position:50% size:61% To do this, you need to be able to accurately test your device's low-current states 00:04:29.352 --> 00:04:31.605 align:center line:-1 position:50% size:51% so you can optimize power consumption. 00:04:31.605 --> 00:04:35.025 align:center line:-1 position:50% size:44% To get this level of sensitivity, use a high-sensitivity current probe 00:04:35.025 --> 00:04:38.361 align:center line:-1 position:50% size:56% that allows you to measure these low signals with very low noise 00:04:38.361 --> 00:04:42.365 align:center line:-1 position:50% size:60% while maintaining a high enough dynamic range that covers the input signal. 00:04:42.365 --> 00:04:44.743 align:center line:-1 position:50% size:49% If we look at an example, on channel 2, 00:04:44.743 --> 00:04:47.287 align:center line:-1 position:50% size:43% I have that clamp-on current probe we were looking at before, 00:04:47.287 --> 00:04:49.956 align:center line:-1 position:50% size:40% and on channel 3, a high-sensitivity current probe. 00:04:49.956 --> 00:04:52.626 align:center line:-1 position:50% size:57% The true signal that we're measuring is 6 mA. 00:04:52.626 --> 00:04:56.087 align:center line:-1 position:50% size:47% We're getting almost exactly that with the high-sensitivity current probe 00:04:56.087 --> 00:04:59.007 align:center line:-1 position:50% size:61% because there's barely any noise from the probe riding on the signal. 00:04:59.007 --> 00:05:03.011 align:center line:-1 position:50% size:64% These high-sensitivity current probes are optimized to measure current flow within a DUT 00:05:03.011 --> 00:05:04.846 align:center line:-1 position:50% size:34% to characterize subcircuits. 00:05:04.846 --> 00:05:07.933 align:center line:-1 position:50% size:51% This allows you to see both large signals and small details 00:05:07.933 --> 00:05:10.769 align:center line:-1 position:50% size:40% on fast and wide dynamic range current waveforms. 00:05:10.769 --> 00:05:12.479 align:center line:-1 position:50% size:50% Often when you're doing current testing, 00:05:12.479 --> 00:05:15.023 align:center line:-1 position:50% size:40% you need to be able to make low-level current measurements 00:05:15.023 --> 00:05:17.567 align:center line:-1 position:50% size:39% while still being able to analyze those larger currents. 00:05:17.567 --> 00:05:19.361 align:center line:-1 position:50% size:41% To do this, you have two options. 00:05:19.361 --> 00:05:21.530 align:center line:-1 position:50% size:50% First, you can double-probe your signal, 00:05:21.530 --> 00:05:25.158 align:center line:-1 position:50% size:59% but this will double-probe loading and give you an inaccurate view of your signal. 00:05:25.158 --> 00:05:29.162 align:center line:-1 position:50% size:53% The other option is to use a two-channel, high-sensitivity current probe like this one. 00:05:29.162 --> 00:05:32.165 align:center line:-1 position:50% size:57% Making more accurate current measurements starts with the right probe. 00:05:32.165 --> 00:05:35.377 align:center line:-1 position:50% size:45% For more information on how to pick a probe for your measurements, 00:05:35.377 --> 00:05:37.337 align:center line:-1 position:50% size:61% check out the selection guide that's linked below. 00:05:37.337 --> 00:05:38.880 align:center line:-1 position:50% size:43% For even more probing resources, 00:05:38.880 --> 00:05:41.591 align:center line:-1 position:50% size:44% make sure you download the Probe Training Kit linked below 00:05:41.591 --> 00:05:44.177 align:center line:-1 position:50% size:48% and subscribe to our YouTube channel for more videos like this. 00:05:44.177 --> 00:05:46.721 align:center line:-1 position:50% size:45% I'm Ally with Keysight Technologies, and I'll see you next time.