There is no way to turn the system on based on work entering the tank. Also, conductivity controls have two main disadvantages. First, they require very clean water to operated unless you do a regular preventive maintenance program which cleans the electrodes weekly. Second, you can reset the setpoint easily at the tank, so an operator who thinks the water is too dirty, can increasethe setting which will increase water use. It is very easy to set a conductivity controller so it is on all the time.
Flow controls piddle a little bit of water into a rinse tank continuously.
They are not meant to be turned on and off. Unless you do every line in a shop, what happens is that any lines still open flow at full bore all the time, and you see very little change in water flow. One way to look at it is if you are using 30 gpm and you put 15 flow restrictors at 2 gpm on 15 rinses, you still flow 30 gpm. Timers determine water flow based on line size, water pressure,and time. Once you put timers on, the first thing you notice is that your water pressure returns to normal.