I'm having some issues with the results I'm getting when performing AFE measurements over a large range of frequencies. I'm attempting to make 7 measurements (Channels 1-7 with 8 as the common reference for each) for a frequency range of 100Hz to 60kHz. I've noticed two things:
1. Low frequency measurements seem to be inconsistent. This is a 4.7kOhm resistor between CH4 and CH8
2. I'm getting odd results at both the bottom and top end of the range for my RC circuits. Here is the plot of a 4.7kOhm || 0.1uF circuit between CH7 and CH8. Below about 500Hz, the impedance is somehow higher than the resistor, and above 40kHz we start seeing it spike again.
I'm using the 2-wire sample as a basis and have edited the sequence using the tool, and I see similar but not as exaggerated results with the EKSP tool. ( 4.7kOhm || 0.1uF )
Any thoughts on what could be causing this? The connection is via the 0.1" headers with soldered through-hole