High current pulse measurement - Page 1
Forum section: electronics / testgear

author: Hawaka
author_rank: Regular Contributor
timestamp: July 29, 2023, 09:41:46 am
content: Hello,For work I'm looking to replace our high current pulse measurement setup. We are currently using a CT5 Tektronix with a TCP312A current probe and a TCPA300 amplifier. The current pulse are max 1600Apeak, rise time 20A/us (might be higher as this could be limited by the measurement setup), tpulse max 50ms. The measure needs to be isolated, as the current conductor is about 500V above earth.I am aware that what we are trying to measure is outside what the probes are design for, but we don't have anything better…The PEM CWT15 / CWT mini 15 (https://tinyurl.com/28p9bphw) or a Pearson Electronic (maybe a 4418) (https://tinyurl.com/4c6fmjcu) would be a good choice, but these are pretty expensive.Do anyone knows a better way to measure such current? A shunt with an amplifier would be for sure easy and affordable, but the isolation is missing...

author: voltsandjolts
author_rank: Unknown
timestamp: July 29, 2023, 10:02:40 am
content: Quote from: Hawaka on July 29, 2023, 09:41:46 amAdd the isolation after the shunt / amplifier / digitiser and use a floating supply for it (battery?).

author: Hawaka
author_rank: Regular Contributor
timestamp: July 29, 2023, 10:10:44 am
content: We use a scope as a digitiser, so not really an option....

author: nctnico
author_rank: Super Contributor
timestamp: July 29, 2023, 11:10:00 am
content: I'd use a shunt and an isolation amplifier for these sort of measurements. An oscilloscope with isolated inputs is even more convenient. I have a Yokogawa oscilloscope with isolated inputs and 12 bit resolution.

author: dmendesf
author_rank: Frequent Contributor
timestamp: July 29, 2023, 11:30:21 am
content: Shunt+AMC3302 = WIN

author: TurboTom
author_rank: Super Contributor
timestamp: July 29, 2023, 11:59:15 am
content: The high dynamics and short duration of the current pulse seem to be perfect conditions for utilizing a Rogowski coil followed by an integrating amplifier. You can either DIY such a contraption (which may turn out tricky) or buy one ready-to-use. Just search the web (or this place) for it...

author: PartialDischarge
author_rank: Super Contributor
timestamp: July 29, 2023, 01:09:43 pm
content: Quote from: TurboTom on July 29, 2023, 11:59:15 amNot really, Rogowski coil integrators have large droop, 50ms is a lot. Also he mentions that the shunt is floating, so the coil has to be shielded, which is not that common, otherwise the common mode switching will show up as interference.

author: Hawaka
author_rank: Regular Contributor
timestamp: July 31, 2023, 02:32:58 pm
content: Quote from: dmendesf on July 29, 2023, 11:30:21 amI'm using a AMC1301 for another project, didn't think that a IC in that family would have enough bandwidth. But after finer datasheet reading the AMC3302 does look like a really good candidate. Thanks

author: paul@yahrprobert.com
author_rank: Regular Contributor
timestamp: July 31, 2023, 03:32:55 pm
content: LEM makes some feedback current transformers that use hall effect devices to zero the magnetic field in a magnetic core. Very fast, accurate, response down to DC, but expensive.Using shunts for fast signals is tough because of magnetic pickup in your sensing circuit. I've used a clever shunt that had a coaxial geometry that kept the field out of the sensing loop. That was a custom made item, however.I once made a custom shielded rogowski with an op-amp integrator that worked pretty well. The active integrator gets rid of the droop problem but you will have to be careful with the drift due to offsets. I've heard of people doing it the modern way and digitizing the rogowski output and integrating in software, and given a fast enough sample rate and good shielding that seems to be a good solution.

author: jonpaul
author_rank: Super Contributor
timestamp: July 31, 2023, 03:52:47 pm
content: For professional use and AC only the Pearson are the best, in a wide range of types and peak I, someties on epay or at ham fleas.The TEK are classics and also can be found used but any clampon TEK has a fragile core in the tip, often damaged by a single fall.Unfortunately the CM noise and self L of the shunt in a 1500 A system will be a huge issue with any shunt, regardless of the diff amp employed. Thus shunts are used mostly if DC responseis required.The Hall effect devies have mv of output and drift and the ams and Hall device response times seem too slow for this use.SLAC, CERN, Harwell and otheratomic research facilityes often publish paers on measuremens and may have some tips on such a problem.We have both Pearson, TEK CT-5 and Yokogawa probes and CTs.But never had a 1500 A pulse to measure!Bon Chance,Jon

author: nctnico
author_rank: Super Contributor
timestamp: July 31, 2023, 04:26:42 pm
content: Quote from: paul@yahrprobert.com on July 31, 2023, 03:32:55 pmI have implemented something like that for measuring energy in welding systems (tens of kA). It is nice to have a trigger signal to reset the integrator. But getting rid of the common mode noise from the welding inverter was a PITA though.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 31, 2023, 04:44:34 pm
content: I have use Pearson current probes successfully for several thousand amperes and rise times of less than 100 nsJust make sure to insert an insulation ring into the circular opening.Pearson makes them as a special shielded version for fast pulses in the low ns range.But these have a real high price.

author: johansen
author_rank: Super Contributor
timestamp: July 31, 2023, 06:22:14 pm
content: 20A/uS is rather slow, 12500hz at 1600 amps peak.The lem closed loop hall effect sensors with 100,000khz bandwidth should be good enough.Rowgowski coils will work too, and you can buy integrators for them that are accurate enough to make a dc measurement by simply wrapping the coil around the conductor (2 seconds approximatly).

author: slugrustle
author_rank: Frequent Contributor
timestamp: August 02, 2023, 11:38:32 pm
content: I'm not so sure the AMC3302 is fast enough for what you want. Double check the bandwidth, delay, step response, and rise time specs in the datasheet and application information. Also note that these isolated amplifiers have a noise hump that starts to rise at around 100kHz; see "Figure 6-27. Input-Referred Noise Density vs Frequency" in the datasheet.These AIT1500-SG and AIT2000-D70 units from Hangzhi at stratatek look promising, but I wish the spec sheets were more detailed.https://www.stratatek.com/product-page/hangzhi-ait1500-sg-1500a-high-precision-analog-current-transducer-10ppmhttps://www.stratatek.com/product-page/hangzhi-ait2000-sg-200a-high-precision-analog-current-transducer-10ppm