[SI-LIST] Re: Current Sense Resistor Measurement
- From: Jerry Chow <ehjchow@xxxxxxxxx>
- To: ERIK KUNDRO <kundro85@xxxxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>, steve weir <weirsi@xxxxxxxxxx>
- Date: Wed, 30 Nov 2011 08:46:02 -0800 (PST)
HI Erik :
Tek has a few diff probe that can handle to +_42V ( DC + AC), the price
ranging from $1800 to $4700. Not cheap, you can almost get the lowest-end
scope with that money.
( ADA400A, TDP0500, TDP1000, P6251, P6250, 1Mhz, - 1Ghz) .
But Our PowerSupply Engineer love it and it is really handy when you need to
probe PSU.
Regards
>________________________________
> From: ERIK KUNDRO <kundro85@xxxxxxxxxxxxx>
>To: si-list@xxxxxxxxxxxxx; steve weir <weirsi@xxxxxxxxxx>
>Sent: Tuesday, November 29, 2011 8:00 PM
>Subject: [SI-LIST] Re: Current Sense Resistor Measurement
>
>Steve,
>Thanks for the quick response. My only issue with your suggestion is that by
>adding DC blocking caps I am removing the steady state value of the current
>and only viewing the AC/transient portions of the waveform. I need to know
>both steady and transient currents.
>
>So for example, if my circuit draws a steady 4A but has a 300mA fluctuation
>about that 4A... all I would get on the scope is the 300mA fluctuation
>waveform and not be aware of the 4A continuous current since the DC blocking
>caps would remove it. Basically I would see a peak current of 300mA in this
>example, when really the peak current is 4.3A. Correct? or did I misunderstand
>your suggestion?
>
>Erik M. Kundro
>
>
>
>--- On Tue, 11/29/11, steve weir <weirsi@xxxxxxxxxx> wrote:
>
>From: steve weir <weirsi@xxxxxxxxxx>
>Subject: [SI-LIST] Re: Current Sense Resistor Measurement
>To: si-list@xxxxxxxxxxxxx
>Date: Tuesday, November 29, 2011, 9:33 PM
>
>If it is not too late to alter your circuit board, then you can put down
>DC blocking capacitors on either side of your sense and terminate those
>to common. Then you can use just about any differential probe around.
>The only limitation will be on the low frequency end. You can jig such
>a thing on a small circuit board as well.
>
>With straight coax, you should use the 50 Ohm input setting on your
>scope and DC blocks. Unless you are mechanically gifted, Tek P6150A, or
>Agilent 54006 probes are a lot better than what you can put together
>yourself.
>
>Steve.
>On 11/29/2011 7:03 PM, ERIK KUNDRO wrote:
>> I am trying to measure the current going into a DC-DC converter by removing
>> a series fuse and placing a small value resistor in its place. I want to
>> make the measurement using an oscilloscope so I can get a plot of the actual
>> current waveform, not just an rms number like with a DMM (I need info like
>> peak current and the current waveform shape).
>> I'm measuring in system, so I'm in a tight space and single ended type
>> probes are too large. The input to the DC-DC is powered by 12V, but all the
>> differential probes I see do not have a common mode spec anywhere near 12V
>> (most seem to have a max common mode of about 3V). So it doesn't look like I
>> can use a differential probe to measure across the resistor since it sits on
>> a 12V line.
>>
>> I tried using two coax cables, each with one end cut and soldered from power
>> to ground on my PCB on both sides of the resistor. Then I used the scopes
>> math function to subtract one channel from another to obtain a current
>> waveform. But for some reason the coax cables seem to be causing some
>> ringing or resonance like oscillation that is greatly distorting the
>> measurement.
>>
>> I am running out of ideas here... anyone make a measurement like this
>> before? Any thoughts or suggestions? I'm getting desperate here. Seems like
>> it should be an easy measurement to make, but I can't seem to be able to do
>> it.
>>
>>
>>
>>
>>
>> ------------------------------------------------------------------
>> To unsubscribe from si-list:
>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>> or to administer your membership from a web page, go to:
>> //www.freelists.org/webpage/si-list
>>
>> For help:
>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>> List technical documents are available at:
>> http://www.si-list.net
>>
>> List archives are viewable at:
>> //www.freelists.org/archives/si-list
>>
>> Old (prior to June 6, 2001) list archives are viewable at:
>> http://www.qsl.net/wb6tpu
>>
>>
>>
>
>
>--
>Steve Weir
>IPBLOX, LLC
>150 N. Center St. #211
>Reno, NV 89501
>www.ipblox.com
>
>(775) 299-4236 Business
>(866) 675-4630 Toll-free
>(707) 780-1951 Fax
>
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>//www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
>List technical documents are available at:
> http://www.si-list.net
>
>List archives are viewable at:
> //www.freelists.org/archives/si-list
>
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>//www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
>List technical documents are available at:
> http://www.si-list.net
>
>List archives are viewable at:
> //www.freelists.org/archives/si-list
>
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
