I am working with automation using pH and EC sensors. Both are of 4-20mA communication standard. When at a time single sensor is placed in liquid(in 1000 litre tank) then everything works fine (correct value is given). But when both sensors are placed in liquid and reading is taken simultaneously from both sensors then value is unacceptable (large variation as compared to actual result). Both sensors are supplied power (24V DC) from single point and also grounded at common point. What is wrong when both sensors are placed in same liquid ?