How much resolution does my datalogger need to read the ECHO probes?
This depends on your preference. The ECHO probe changes approximately 10 mV per % change in VWC. For a datalogger with 8 bits of resolution and a range of 0 to 2500 mV, you will have a resolution of 10 mV or 1% VWC for your probe output. For loggers with 12 bits of accuracy and the same range, you will resolve greater than 1 mV or 0.1% VWC. Not surprisingly, the graphed data from the 12-bit dataloggers appears much more smooth than the 8-bit dataloggers. There are methods to double the resolution of the 8-bit loggers (to 5 mV resolution over the ECHO range) though use of operation amplifiers. Contact your datalogger supplier for details.
