High current "probe" - Page 1
Forum section: electronics / beginners

author: Boschi
author_rank: Regular Contributor
timestamp: September 27, 2017, 09:58:38 am
content: Hi, i need to measure some low voltage (12v) high current (100-200A) stuff.If possible i want at least 10khz of bandwidth in order to measure a 1Khz square signal.I dont need high accuracy, 5% would be acceptable.I am tempted to do a DIY shunt resistor with a sheet of stainless steel with a low ohmic value (100-500 micro ohm), use a ucurrent-like circuit to amplify the voltage and calibrate the gain of the circuit until i get 1mV per A.My limited experience says that apart from the TC of the metal it would be pretty precise and with a bandwidth of about 100khz ( max4238, 1Mhz of bandwidt).Im missing something?I'll post some schematic once i get home.About calibration, i mean making about 9-10 amps flowing in the resistor, and calibrating the gain to get 1mV/A.Will it be linear enough?Thanks for the answers.Inviato dal mio A0001 utilizzando Tapatalk

author: Giaime
author_rank: Regular Contributor
timestamp: September 27, 2017, 10:05:32 am
content: For those currents, I would suggest an Hall-effect sensor, something like this:http://www.tamuracorp.com/clientuploads/pdfs/engineeringdocs/L32PXXXS05FS.pdf

author: capt bullshot
author_rank: Super Contributor
timestamp: September 27, 2017, 10:17:37 am
content: Or something similar by LEM:http://www.lem.com/hq/en/component/option,com_catalog/task,displaymodel/id,90.13.36.000.0/

author: oldway
author_rank: Super Contributor
timestamp: September 27, 2017, 11:33:07 am
content: Low cost solution is to use the voltage drop of one the cables and to amplifier and measure it.Gain of the operational amplifier must be ajusted to calibrate the signal.

author: xani
author_rank: Frequent Contributor
timestamp: September 27, 2017, 12:57:16 pm
content: Current clamp ?

author: Jeroen3
author_rank: Super Contributor
timestamp: September 27, 2017, 01:06:40 pm
content: Fluke has several current probes with BNC adapter. The i1010 for example, €400. Or the i410, but that's only 3Khz.But DIY using a shunt is certainly possible. You can just buy the shunts in the required value.

author: mk_
author_rank: Regular Contributor
timestamp: September 27, 2017, 03:55:15 pm
content: Quote from: Boschi on September 27, 2017, 09:58:38 amTake a look at sensitec-Current-sensors. If you do the math right you don`t even to calibrate (it`s more or less some kind of opamp-gain)Take care about the inductive part of your microohm-shunt.... this can result in some surprising measurements.... (t=L/R, so... if you expect something below 1uH you still have a long tau because R is very low too)

author: Boschi
author_rank: Regular Contributor
timestamp: September 28, 2017, 08:42:45 am
content: Quote from: mk_ on September 27, 2017, 03:55:15 pmThis is exactly the reason why i ask here!Im not very used to work with inductor, so ill study the math these days.I want to keep it as DIY as possible, as a student im pretty broke Anyway, this is basically the circuit, ill just connect the shunt directly whitout using any switch.Link:http://www.eevblog.com/files/uCurrentRev5schematic.pdfAbout buying the resistors, are they better? Also, here is very important using 4 wire connection, any keyword to use?If i choose to use the DIY shunt, any way to make it better about the inductance?Like giving a u shaping to the resistor in order to cacel out the magnetic flux.Some reference that i think are useful:https://meettechniek.info/instruments/shunt-resistors.htmlA u shape would be like a basic bifilar winding thing, so what culd i expect from something like that?

author: max_torque
author_rank: Super Contributor
timestamp: September 28, 2017, 02:40:37 pm
content: Check out the Sensitec range of high bandwidth current sensors:http://www.sensitec.com/products-solutions/current-measurementcan be used stand alone or shunted to increase range!

author: Jeroen3
author_rank: Super Contributor
timestamp: September 28, 2017, 07:22:54 pm
content: Played around with the sensitec CMS3005 just now. It's spot-on, and it responds to 1 mA! An 5A LEM doesn't get out of bed for 1mA.Update: 2018-11-05, Sensitec discontinued the CMS and CDS families current sensors.