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4294A DC Bias constant current not working - please help

Question asked by TonyGraham on Mar 20, 2009
Latest reply on Mar 26, 2009 by TonyGraham
The DC Bias mode of my 4294A seems to have problems in the constant current (CURR and C-CURR) modes. The Operation Manual is very vague in this section so does not help. I wish to simply bias a resistive load (7.5k resistor) with 4mA. This should give approximately 30V. It works ok with constant voltage mode so the problem seems to be with constant current facility, as follows:

1. If I set the DC Bias mode to CURR (as per page 107 of the manual) and set 'Current Level' to force 5mA, I do not get 5mA but more like only 15uA and ~125mV. (The bias monitor agrees with an external ammeter so this is a true reading). Why am I only getting this small current instead of the set 5mA?

2. So I have also tried C-CURR mode instead (The manual doesn't explain the difference - see #3 below). This has a different problem where the 4294A ramps the current extremely slowly towards 5mA and takes ~30 seconds to reach the setting! This is far too slow for my application where I need to quickly reach the 5mA setting, or my experiment (which is time dependent) is no good.

3. Generally, can anyone explain the difference between the DC bias CURR and C-CURR modes?

Thanks for your help.
p.s. the application is electrochemistry where the item under test varies over time. That is why I cannot wait the 30s for the dc bias ramp in C-CURR mode. I need to ramp in something more like <5 seconds.