Electronics > Beginners

Keysight EL34143A CP Range issue


I am a bit confused by the following issue I am experiencing when trying to draw a 2.8W load using a Keysight EL34143A DC load.

I have set the range to low (8.16W).
CP mode
I provided power using my DC bench power supply and a fully charged battery as two separate tests to ensure it is nothing funny with the power source
When I try to apply 2.8W CP, the actual power draw drops to 0.8682W.  When I draw say 350mW, it works perfectly.  250mW works too.  2W does not. 

If I switch the unit to Medium range (35.7W), then 2.8W works without issue on the same source.  Surely 2.8W << 8.16W, and looking at the specs in CP mode, Low is rated for 0.01W - 8.16W.  Why would 2.8W not work in low range mode but it does in medium?

See below.  Any ideas what I am missing?  Perhaps slew rate on the current draw?  It is set to maximum.

It appears that CL+ shows up (top right of screen) when I cross 0.8W.  Sounds to me like a off by factor of 10 error?

I think I figured it out.  Might be obvious to some but not to me initially. 

The device has CP ranges 8.16W, 35.7W and 357W (Low, Medium, High).  It also has CC ranges 0.612A, 6.12A and 61.2A.  Murphy had me pick a voltage that resulted in current close to the cut off range for CC mode when in CP mode.  In other words, in my test 0.8W resulted in 0.617A (presumably just below the current threshold), and 0.9W resulted in 0.62156A (above the threshold).  I think in CP mode the range must be set based on the maximum power AND the resultant maximum current drawn for the voltage the DUT is at.  It is not enough to look at the power draw alone.  The unit will not give you 8W in low range CP mode if your current exceeds the low range value of 0.612A.  Therefore 8W will only work on low range mode when V > 13V as I will then be < 0.612 (the upper limit for low range).

Unless I missed it, it would have been helpful as a footnote in the manual.

Keysight confirmed:

--- Quote ---    Thanks for contacting Keysight Technologies. My name is *** and I am an application engineer with the KeysightCare technical support team. The CL+ indicator means you are hitting a current limit. If you select the load settings menu you will see the current limit setting. You will need to adjust that higher if you want to set a higher constant power value.

--- End quote ---


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