Thanks Shannon. I’m not positive that I need to use differential measurement… I’m approaching the edge of my knowledge as a non-EE. Turner doesn’t specify whether it’s OK to connect signal and power grounds to the same point — maybe I’ll ask their tech support. But when the sensor is on, I’m measuring around 13 mV between its signal ground and power supply ground wires. Thus when I read the measured value (voltage) across Sig+ to Sig-, it’s different than if I read voltage across Sig+ to Supply-.
I just now modified a Grove cable by disconnecting the V and Gnd lines and moving the Signal Ground so that it will connect appropriately to the ADC (see ugly drawing attached), and will test it today. I found it pretty easy to disconnect individual wires from a Grove connector, using a dental pick, so I may just go that route.