how to measure inrush current using an oscilloscope

The each have their uses and depend on what you need to accomplish and what your board might face. We changed the switcher design to use an older IC from a different vendor and it worked. The devices inrush current will be completely unpredictable since it is dependent on the phase of the AC voltage. With the device to be tested turned off, turn the meter's dial to iFlex. Graphing the inrush measurements versus phase for the 12 VDC power supply reveals a trend. 1. We measure the voltage over the capacitor directly with the first channel of the oscilloscope. A clamp-on ammeter may have a digital or analog readout. Inrush current can only be measured by meters that have an inrush button. Have some patience here, some scopes take as long to boot up as an old PC. * Circuit breaker instantaneous tripping current, should it be RMS or peak current?Equipment used:* Agilent / Keysight DSO-X 2000 Oscilloscope* HT Instruments HT9022 Power Clamp Meter* Yokogawa CW10 Power Clamp Meter* Fluke 43B Power Quality Analyzer* Thermal magnetic circuit breakerUseful links:Circuit Breakers - How they Work, What's Inside :https://www.youtube.com/watch?v=u6I7dKDk7hECircuit Breakers:http://en.wikipedia.org/wiki/Circuit_breaker------------------------------------------------------------------------------------------------------My website and forum:- http://www.mjlorton.comDonations and contributions:- http://www.mjlorton.comMy techie channel MJLorton - Solar Power and Electronic Measurement Equipment - http://www.youtube.com/MJLortonMy Techie Amazon Store: http://astore.amazon.com/m0711-20My other channel VBlogMag - For almost any topic under the sun! You need to use two probes for doing this measurement and subtract the value of one from the other - DO NOT CONNECT THE GND OF THE PROBE TO EITHER SIDE OF THE RESISTOR- you will in effect cause a short circuit if you do this. The measurement diagram is shown in figure 9. Most likely, the spike was from all the bypass caps we had. No. Ultra-sensitive standby power measurement Measure according to IEC 62301 DC, or 1P2W Max. For example, if you're measuring a 1.5V AA battery, you'd select the 2V range. The devices have a capacitance of about 122F. Does a beard adversely affect playing the violin or viola? The meter probe must be clamped around the wire of the tested circuit and the knob must be set appropriately, depending on the current type: AC or DC. I also explain how an electrothermal circuit breaker works by preventing overloads and short circuits. Fig 6. Does English have an equivalent to the Aramaic idiom "ashes on my head"? Both are able to detect and capture the event waveform, though the detection timing is slightly different due to the differing . Current waveform with peak hold and steady state peak current. Last edited by GeoffS; Jul 31, 2019 at 11:36 PM. Just use a 0.1 ohm shunt resistor, and measure voltage drop across it, do some ohm's law calculation to I = E/R. Normal max. Originally Answered: How do I use osiloscope to measure current? The types of measurements you need to take, the number of tools you wish to carry to do your job, and the price you're willing to pay will dictate your choice. I got some struggle with my measurement so I changed oscilloscope to another oscilloscope of the same model, suddenly I realized that despite the setup is the . Step 4: Adjust the scope's vertical sensitivity to 1v/division. 2) Clear the peak hold measurement from the front panel. Answer (1 of 4): To measure current, you need a way to convert the current into a voltage that the scope can measure. Is it possible for SQL Server to grant more memory to a query than is available to the instance, Find a completion of the following spaces. The current clamp direction makes a difference in PQ stuff because of the relationship beteen voltage and current, voltage leads current in a inductive circuit. The steady state 2.26 A peak current drawn from the AC source. The turn-on phase can significantly affect the inrush current. www.tektronix.com/accessories7 Inrush current is measured as a peak current and is useful for sizing fuses or designing additional protection circuitry. I'll explain the two methods to measure inrush current using oscilloscopes in detail. A peak hold measurement determines the inrush current while a peak measurement is used for steady-state current. Devices with capacitive input will have low inrush currents when the voltage is turned on at zero volts. An inductive load will have its maximum inrush current at zero and 180-degrees. I'm getting confused with so many solutions as to what is best. The 12 VDC power supply output will turn on 1.3 seconds after the AC power is applied. Download Manuals, Datasheets, Software and more: Have feedback? Here are steps for measuring it, in this case when using the Fluke 381 (see illustration above): With the device to be tested turned off, turn the meter's dial to . 1) Setting the turn-on phase from the front panel of the AC source. A series of measurements are made to determine the maximum inrush current. We can have a clear view of the inrush current by . Multimeter setup for inrush current logging In addition to measuring first peak inrush current, the GDS-3000 is also able to measure second peak inrush current to easily observe changes to instantaneous power (See figure 10). The ones I use (Fulree, $1, 3-pin, 5Volt / 2 Amp) work fine with input voltages up to 22 Volts. Testing the Speaker Ohms with Multimeter. use some low value shunt resistor in line with the power supply (as low as possible) and read the voltage across it. But you can configure the oscilloscope to measure current as well. Clamp meters measure current, voltage, resistance, and . Center the jaw or flexible probe around the device's live wire. use oscilloscope math capability (or just yourself) to do a difference between the two channels and this will be your current. (My meter isn't that fast, but I do have an analog 100MHz oscilloscope.). On the right, after 1.3 seconds, the power supply turns on and pulls steady-state current. Only after turning on its output will it be drawing steady state current. Tektronix designs and manufactures test and measurement solutions to break through the walls of complexity, and accelerate global innovation. It is also important to consider what phase the AC voltage is at when it is applied to the DUT. That would be like trying to measure current with a volt-meter. Thanks to additional test lead sockets, we can e.g. Request Repair / Calibration Using a 0.1 1W or 5W resistor. Q I want to measure inrush current using the PQ3198/PW3198. Some devices will have to be designed to limit the inrush current. This is because at a phase of zero and 180 degrees, the voltage is turning on at zero volts. In the device manager (Windows-key-> type deviceand select device manager-> scroll down to Connections (COM & LPT), unfold), make sure the IR adapter shows up with a COMport ID). the 1rst question : how much is the input resistance of my scope !!!! You probably want at least 2MSa/s and you will need to set the trigger level to go off just as the motor starts up. The typical way of measuring total power consumption is to insert a low-valued precision resistor in the power supply, then measure the voltage drop across it. Select "1x" or "10x" on the probe. The design of the device will affect the phase at which the maximum inrush current occurs. When you are doing this test on the bench, the N6705B DC Power Analyzer (DCPA) is your best bet. Current measurements can be made with ANY oscilloscope. No. Only meters that offer an inrush button can measure inrush current. Figure 4. These show the advantage of sampling at a much faster rate using an oscilloscope. If the capacitors are not being charged through any significant resistance, then inrush should be quite brief. There is . We are the measurement insight company committed to performance, and compelled by possibilities. Need help on product selection? Newsletters. Mostly the voltage is about 15 volts peak but I forgot to bump up the amplifier output as the voltage fell away slightly at high frequencies. We checked it on the 100Mhz scope and everything looked fine. I'm OK with things exploding if someone attempts to hook up a device to mains power, for example. (20 min) The inrush current is split between the supply voltage capacitor, C1, and the inductor-limited input current required by C2 and the converter (shown dotted). Asking for help, clarification, or responding to other answers. Peter Dalmaris. Light bulb as limit, to what is current limited to? http://sound.westhost.com/articles/external-psu.htm#kil, https://www.eevblog.com/forum/other-blog-specific/a/msg1341166/#msg1341166. The NTC device initially has a high impedance, which reduces the inrush current. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Wrap the jaw or flexible probe around the live wire of the device. But you can configure the oscilloscope to measure current as well. Request Technical Support PX800 is a unique power analyzer that offers accurate oscilloscope style time-based and averaging style power measurements in one unit with advanced triggering capability. lesson 2 of 6 | Oscilloscope probes connect your scope to your device under test. -- Richard Feynman. Be careful not to ground the device. Daves uCurrent is essentially a current to voltage converter. If you feed your device through the 0.1 you will drop a running max of 0.05V. Change the PWM duty cycle of the converter from 0.5 to 0.4 and 0.6 and observe how the average output voltage changes to 16 V and 36 V, respectively. Since all three methods require that the current being measured pass through . In the EVENT2-CURRENT screen, there are "Inrush" and "I peak" selections. Re: How to measure current on an oscilloscope ? For a one ohm resistor, each mV of voltage will be equal to 1mA of current. The fact that "inrush" current in a motor does not occur instantaneously. Then if you measure the voltage drop across the resistor at power up, with your scope, you will get a fair idea of the inrush current . Was Gandalf on Middle-earth in the Second Age? At zero volts a sinewave has its maximum rate of change, this change causes an inductive load to create their largest inrush current. Substituting black beans for ground beef in a meat pie. The DCPA has the scope feature which makes this a breeze. In this video, we will be demonstrating how to measure inrush current using triggers and cycle-by-cycle measurements with PX800. When the power is turned on, the decoupling capacitors get charged by a large current flow. Most electronics contain switching power supplies as they are incredibly efficient. Many oscilloscope probes have a switch that allows you to switch between "1x" and "10x." If you have (or can request samples of) several PTCs spanning a range up to your power supply rating, this becomes even simpler: Use a fuse two levels higher rated than the highest PTC that trips on start-up. High Precision Power Meters - 3 - phase AC/DC. In some devices, inrush current can be surprisingly high (10x or higher than their steady current). On the meter's face, press the inrush button. Various turn-on phases of an AC voltage. At first glance, our original schematic (Figure 2) might look like it would work well. Figure 3. Best approach to design or implement short circuit protection? The current-to-voltage converter here is the humble resistor. Experiments. Here is a picture of my setup: I have several PTCs of different values on order for doing exactly what you suggest. The typical way to measure dc inrush current is to use a test setup in which a power source is applied to the input of the DUT (see Fig. The actual current value is then determined by dividing the total measured amplitude by N. Note: Winding more turns around the probe increases the insertion impedance (inductance rises as the square of the turns). A third possibility is adding a negative temperature coefficient (NTC) current limiting device to your design. Connect your probe to the first channel on your scope, and turn it on. Measuring inrush current is a task that many customers that use DC Power Supplies want to accomplish. For this kind of job I'm using LEM transducers connected to scope ( this is poor man scope current probe with bandwith about 100kHz. At my last job, our switch mode power supply wasn't working on our USB device. Using a Shunt Resistor This is perhaps the simplest way to measure current, and will be discussed here in detail. As mentioned above, any oscilloscope can measure the voltage across a resistor and therefore can be used to measure current with a shunt. @Oli I'm assuming it does not have persistence refresh. I'm measuring inrush current with a current probe ( tektronix P6303) that is connected with an amplifier between, which is powered by an AC line before it's connected to an oscilloscope. Step 3: Connect the probe's ground crocodile clip to a reliable grounding point. The shunt resistor is usually so small, that it doesn't have an impact in most applications. Measure the voltage dropped across a shunt resistor: Some power supply designs may have shunt resistors built into the design for feedback. Plug one end into the headphone . To look at inrush current, set your oscilloscope's trigger to normal mode, which is used to look at transient signals. The first one is to add a series resistor to reduce the current flow in the circuit line and the other one is to use line filter impedance in AC supply input. For that, you need to perhaps consider an overvoltage protection IC or circuit. This means simply measuring the voltage drop across a sense resistor to derive the current. My personal strategy is to simply use a cheap, high input voltage range buck regulator on the input line. To define it in a more simple form, after turning on any electrical instrument, a large current which exceeds the steady-state current value is called inrush current. The screen capture on the left shows the voltage phase and the inrush current. Here is a quick and dirty method. Most oscilloscopes only directly measure voltage, not current, however you can measure current with an oscilloscope, using one of two methods. Plug your coaxial cable into the oscilloscope. The first measurement uses a 0-degrees turn-on phase, and the second uses 10 degrees. Figure 9. 504), Mobile app infrastructure being decommissioned, PTC Fuses and Low Current Circuit Protection, Help designing an inverse polarity and overload (crowbar) protection circuit. We will explore how to use, connect, and choose the right oscilloscope probe for your measurements. Chat with Sales This content cannot be displayed without JavaScript.Please enable JavaScript and reload the page. Note that the parallel combination of inductor and capacitor as shown above acts as a second order low pass filter reducing the voltage ripple at the output. Using an NTC to reduce the inrush current into capacitive device. Another possibility is to turn on a small part of the device and synchronize the rest of the turn-on to the AC line, taking advantage of the phase with the lowest inrush. Using an oscilloscope to measure currents requires converting a current to a voltage, and this can be done a few ways. All you have to do is to so supply it with some kind of voltage signal that changes over time, and it will display it on the screen. Just get 2 probes, connect the tip to each side of the resistor, and the grounds to the actual ground. How to measure current on an oscilloscope ?

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