shunt resistor

[Dennis_Knutson]

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vadajooz wrote:

the connections are good and as i siad they were  , its not exactly the most complicated operation .

im asuming a known current because thats how shunts are rated , shunts are designed to drop 50 mV, 75 mV or 100 mV when operating at their full rated current , so if my shunt drops 75mv at 50A  using "ohms law" it has a risistance of .oo15ohms which is exactly the same thing , and i wouldnt expect it to be any thing else with current risistance and voltege related . the shunts are calalbrated on current so i would asume that the rated current is a building block for your mesurement ,

i will draw a schematic if you wish , i cant understand my mesurements alto i was speculating my answers because i know the value of the load dump .

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  You are still approching it bass ackwards. Shunts are NOT rated with a constant current. The shunt is going to drop some voltage at the max current but since you are trying to measure the current, you need to divide the measured voltage by the known resistance (which is a specification of the shunt).

Message Edited by Dennis Knutson on 05-23-2010 05:06 PM

[vadajooz]

http://radionics.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&Ne=4294922967&N...

there is a link to the radionics range of shunts ,if you think shunts arnt rated to a constant current then you should open the link ,there isnt one rated with a risistance , there all rated to max current with spicific voltdrop at that current ,so the specification of the shunt  of 75mv @ 50A will have a risistance of .0015ohms , that is what im dividing the voltege by ,

if im aproching this backwards please explain , this is why im on the fourm , but what we are talking about is exactly the same thing . either way the mesurement is not right ,

if you were conecting to the daq, would you be mesureing the volt drop on the shunt or the voltege accross the shunt

[Dennis_Knutson]

You've just agreed with what I've been saying. You have a known resistance and you should be dividing the voltage by that. You are not. Look at your code. You are dividing the resistance by the voltage!

[vadajooz]

i did say we were talking about the same thing ! i see my mistake now and feel a bit stupid i missed it !

the reading tends to jump around a lot , even when current not being drawn , is there a reason for this ,

and thanks for spotting that !

[Dennis_Knutson]

I believe you are now seeing the limitations of the 6008. It's minimum range accuracy is only 37.5mv.

[vadajooz]

thats quite a lot accross a shunt !