Hi folks,

I have a dc circuit and wish to monitor current under a variety of situations - its got switching converters with outputs of 5V and 15V and a smaller LDO outputting 3.3v - the switchers are putting no more than 1A out and the LDO circa 150mA - also I want to measure efficiency so need to monitor the input current, this will be < 2A @ 24V

I am thinking of using a NI DAQ unit to read current values, but not sure about sizing them up -- I can use a divider to reduce the 15V & 24V range to manage the DAQ AI input limit, 10V.

I think the DAQ is better than using an op amp or dvms etc as they have high impedance and should give more accurate results, plus a single breadboard can be used to access all 4 signals

How can I best size up sense resistors? or does it even matter that much as you can specify them in the labview VI

Cheers

 

If you're using grounded low burden voltage shunts you will need good low voltage sensitivity and resolution from the DAQ.
https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YI4xCAG&l=en-US
https://www.ni.com/en-us/support/do...tal/21/current-measurements-how-to-guide.html

A shunt’s identifying characteristic is its voltage drop at its maximum current, which is typically 50 mV, 75 mV or 100 mV by convention.