I have a question regarding connecting a Standard magnetic float switch with a relay to control a waterpump.

Relay being used is RM22LG11MR from Schneider with datasheet here

My setup looks like as shown in figure enter image description here (Brown line is standard 220 V, and blue is the Nuetral)

Under normal conditions, the relay is in Normally Open (12) state. But when the water level in the tank goes down, the float sensor overrides the relay default setting by bringing it to Normally Closed (14) state, and this should start the pump to fill the tank.

The timing diagram of the relay is also shown below enter image description here The relay has two modes, i.e., a fill mode and an empty mode. I am using it in fill mode, so that as long as water tank is not full, the magnetic flow sensor activates the pump.

My question, is that the sensor has only three cables, one is neutral, one is ground, there is only one cable left which i am connecting to "Max" as shown in the figure, i could connect to Min as well. My concern is that in either case on of MAx or Min would be left Open due to the sensor and relay setup i am using, and now i am wondering how to correctly setup this sensor and relay together to make it work for my usecase. Any help will be highly appreciated

  • \$\begingroup\$ It looks like your controller aka "relay" is designed to work with an electrode style probe, and you are attempting to use it with a magnetic float (not flow) on/off switch? Is that correct? What is "state of the art" about it? Sounds like a 1930s reed switch and floating magnet. \$\endgroup\$ Commented Dec 25, 2020 at 23:39
  • \$\begingroup\$ Sorry about misleading terms. I corrected that now \$\endgroup\$
    – Mark Jeep
    Commented Dec 26, 2020 at 7:33

1 Answer 1


Your title and post mention a "flow sensor". Your diagram shows a float switch which is something completely different. That technology will be at least a hundred years old - so hardly "state of the art" so I'm not sure what point you're trying to make there. You also stated, "But when the water level in the pump goes down, ..." and this should probably be "when the water level in the tank goes down, ...".

The diagram you are using is for a 2-level-sensor arrangement using both minimum and maximum level sensors. Since you have only one level sensor that's the wrong diagram to use. You're looking for the diagram for one minimum level sensor and running the device in "fill function" mode.

enter image description here

Figure 1 (the fourth on page 12 of the datasheet) shows that the tank minimum level input is monitored and when it turns on the relay output will turn on after a time delay, Tr.


  • Set the top switch anti-clockwise for fill mode.
  • I suspect the sensitivity adjustment is for an analog sensor. Since you're using a switch the setting may not matter. Adjust until you get it to work.
  • Set the Level switch to 1 as you only have one level being monitored.
  • Buzz out the float switch to figure out which wires you require and wire these to the min input.

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