Hello,
I'm using a uCurrent Gold to measure the current flowing through an electrochemical cell (a voltage applied across two gold or palladium electrodes immersed in aqueous electrolyte solution). I have an issue with being limited to select from just three shunt resistors each three decades apart.
Let's say the maximum for a range is 1000mA but my current is 1.2mA. Tthe problem is that the output from the uCurrent is very small and noisy. I have to select the next more sensitive range. e.g., switch from the 1mV/1mA range to 1mV/uA range which allows a maximum current of 1mA. Now I am exceeding the range. I know that for some circumstances I can put a resistor in parallel across the current input terminals.
So...I have tried what I thought was the obvious, namely make a simple
voltage divider circuit to send, say, 10% of the current through the uCurrent but I cannot because the negative input terminal is connected to the output's negative terminal which, in turn, connects to ground on my analog/digital converter I'm using to record the current (it has single-ended inputs only). I'm at a loss (not being an electronics wizard) as to how to divide the current. My electrolyte solution has an impedance between approx. 100 to 10kohm. Any resistors used to divide the voltage must therefore be significantly less. 10ohm would be okay for a 10kohm solution but a 100ohm solution would need something less than 1ohm (I have a 0.15ohm shunt resistor to hand).
Sorry for the wordiness. Any guidance greatly appreciated
John.