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72 Series – Liquid Level Control


Pumping - brewing - measuring liquids? You have a pool or fountain?


There are numerous applications in our daily lives where the level of liquid in an industrial tank, water treatment facility or outdoor recreation, to name a few, requires controlling the amount of liquid for the end process. While some approaches can be advanced, many applications use a set of electrodes and a level control.

What about floor surface water or condensation in cabinets?


These electrodes measure the resistance in non-pressurized liquids between two electrodes at various levels. The electrodes are wired to a level control relay and when the resistance changes due to high or low levels the relay reacts. For the electrodes to measure resistance between them, the liquid needs to be non-corrosive and have suitable resistance. Some examples of both suitable and un-suitable liquids are listed below.

What kind of liquids are suitable?


Potable water Demineralized water
Well water Fuels
Water (general use) Oils
Rainwater Liquids with high-percentage alcohol
Seawater Liquid gas
Liquids with low-percentage alcohol Paraffins
Wine, beer, milk, coffee Ethylene glycol
Sewage Paint
Liquids fertilizer


Finder offers a great range of products within the 72 Series to cover wide ranging applications. There are two level control relays and numerous probe options for sensing levels in tanks to even a floor water sensor protecting investments.

Level Control Relays ...

… two versions are available in a small 35 mm package ready to mount on DIN Rail.

Type 72.01

  • Adjustable sensitivity (5 to 150) kΩ
  • Delay time (0.5 s or 7 s) switch selectable
  • LED function indication
  • Emptying or filling functions switch selectable
  • 16 A / 250 V AC rated contacts (UL 15 A 1/2 Hp)
  • UL Listed

Type 72.11

  • Sensitivity fixed at 150 kΩ
  • Delay time fixed at 1 s
  • Emptying or filling functions link selectable
  • 16 A / 250 V AC rated contacts (UL 15 A 1/2 Hp)
  • UL Listed

With two options for sensitivity, fixed or adjustable, this works well to cover various application needs. The 72.11 is fixed at 150 kΩ, whereas the 72.01 allows easy adjustability from 5 – 150 kΩ. The latter is helpful to avoid false detection of surface foam. Emptying and filling on the 72.11 is via use of Z1/Z2 terminals while the 72.01 uses an onboard selectable switch.

Both the 72 Series level control relays have ‘Positive Safety Logic’ meaning that the ‘make’ contact is closed when the monitored level is within the target range. The ‘make’ contact opens if the level is not within the range after the set time delay. This set delay offered with the 72 Series would turn the motor on or off within 0.5 s or 1 s. If there are ripples or foam on the surface this could lead to increased motor cycling or ‘hunting’. This can be alleviated with the 7 s run-on time delay offered with the 72.01 where the liquid would run past the electrode level.


Finder offers a variety of suspended or solid electrodes and a fixed floor water sensor. Some of these probes are suitable for level monitoring in food processing applications compatible with FDA title 21 part 177 as well as probes with high levels of chlorine or salt water.

Suspended cable and rod versions use a common electrode attached to B3 of the level control relay and another wired into B1. The level control relay can also accept an addition electrode into B2 allowing for 2 reference points. If the tank is metallic then the tank can be utilized as the B3 electrode. Below are two examples.

Type 072.11

In addition to the more standard electrodes, Finder offers a very unique all in one probe. The 072.11 is a floor water sensor designed to detect and report any presence of surface water. Approximately 2” x 1” in size the 072.11 can be mounted in the best area for system protection. Depending on product placement, the sensor will detect to a minimum of 1 mm from the floor. With a maximum cable length (not included) over 600 feet the applications are vast.

Product application example 1:



In refrigeration systems the potential exists for the evaporator coils to freeze up causing an ice bank. If left unchecked the ice bank would lead to undesired water in the system causing problems and down time. Using the 072.11 and a level control relay the problem can be detected and controlled.

Product application example 2:

Control panels are designed based on the environment they are in and enclosure chosen to match. Whether these are NEMA 12, 4, or 3X depending on the location, application and maintenance potential may still exist where water could egress into the enclosure.  From moisture, leak, damage or failure to secure the door properly. The 072.11 and level control relay offer a great cost effective solution for peace of mind. Mounted in a desired location at the bottom of the enclosure the floor water sensor can detect and report the presence of water working to keep your components from inadvertently swimming.

Overall the 72 Series level control relays and electrode options provide a robust solution to a vast amount of applications in numerous fields.


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