The brass blocks are manganin current shunts. These are about $50 from Newark (I think) and have tempcos of less than 25 PPM/deg C. For 150 amps you will want to use a 100 micro-ohm or 250 micro-ohm shunt. The distance between the viewing terminals is about 3 inches and the inductance will be about 30nH. So, the corner frequency of the 100u ohm shunt is 500 Hz. This is the main drawback to these low-R shunts- poor frequency response and the inability to measure transient events. The other issue is that the oscilloscope will not have enough common mode rejection if the shunt is in the high side of the circuit- unless the 'scope is running on batteries and is floating. For DC measurements these shunts are great. If you want transient data you can connect a current-viewing transformer such as those made by Pearson. The small Tektronix AC transformers also work if you precede them with a homebrew transformer to step down the current. But for DC to MHz the Tektronix active current probes work well.
Dave Cuthbert Micron Technology From: [email protected] [mailto:[email protected]] On Behalf Of Gary McInturff Sent: Tuesday, February 17, 2004 2:11 PM To: 'Price, Ed'; 'EMC PSTC' Subject: RE: DC Current Probes I was wondering the same thing. You can get brass blocks that drop mV per lots of amps linearly. They come in different sizes and offer almost no impedance at DC or higher freq's. DVM's or O-scopes are hooked in parallel with the blocks and the small voltage drop monitored. They handle lots of power and are pretty cheap. Am I missing something (again?) Gary From: Price, Ed [mailto:[email protected]] Sent: Tuesday, February 17, 2004 7:52 AM To: 'EMC PSTC' Subject: RE: DC Current Probes >-----Original Message----- >From: Finlayson Joseph-G3162C [mailto:[email protected]] >Sent: Tuesday, February 17, 2004 5:54 AM >To: 'EMC PSTC' >Subject: DC Current Probes > > > >Group, > > I am looking to source a DC current probe to measure >steady state as well as inrush currents for a modular chassis >up to 100 Amps DC. Joe: Do you REALLY need a current probe? Can't you do this with a resistive shunt and an oscilloscope, using either differential inputs or simply floating the scope? That said, some of the widest bandwidth current probes (like 3 dB down at 5 Hz, very flat response, 1% accuracy) are available from Pearson Electronics: http://www.pearsonelectronics.com/ . Unfortunately, I don't know of a 100 Amp DC current sensor; all the Tek or HP probes (Hall effect or magnetoresistive) that I've seen are limited to about 6 Amps or so. Ed Ed Price [email protected] WB6WSN NARTE Certified EMC Engineer & Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military & Avionics EMC Is Our Specialty This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
