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Tech Tip: Point Level Sensors and Pump Control

Madison’s point level float switches are designed to be simple, cost-effective, durable and reliable. If problems occur, is the root cause the float switch or the installation? Here are some tips to consider when installing a point level switch for pump control. Note: Since each circuit has unique electrical characteristics, Madison Company cannot review or be responsible for the hook-up of your circuits. In order to insure proper circuit connections and sensor life, please review all product information and consult a qualified electrical technician or engineer before directly connecting your float switch to any powered device.
 
Consider the device that the float switch will control and how it will be used
Most general purpose single point float switches can only switch single-point, low power, small electrical devices, or provide control signals to relays, PLCs or controllers. As a guideline, since most electrical circuits are inductive or capacitive and unique, a float switch rated for resistive loads should only switch general purpose electronics directly that are less than 1/5 the resistive rated watts for the switch. For example, a standard 60 watt rated float switch can typically switch on or off a valve or device directly that is rated up to 10-12 watts. This is because these inductive or capacitive loads create electrical spikes typically 5 to 10 times the rated load when switched on or off.

When a larger powered device is being used, a relay is often required to isolate the float switch from this larger device. The float switch is connected in series with the relay input coil which typically draws only 3-5 watts. When the powered switch is closed, the relay coil is activated and closes the isolated output contacts. The relay contacts turn on or off the higher current required by the controlled device.
 
High/Low, Dual Level Fluid Level Control
Another consideration when using the float switch is to minimize ‘chattering’. Since a single point float switch turns on/off within 1/16” of level change, it can ‘chatter’ on and off rapidly if used to maintain the fluid level about a point, or in moving liquids. This ‘chattering’ will cause rapidly repeated electrical spikes that will damage and can even tack-weld the switch contacts closed, as excessive heat is produced in the single switch.

In order to avoid repeated ‘chattering’ of a single point float switch when maintaining a high/low fluid level, two separated switch points are needed to allow sufficient delay between starting and stopping most electrical devices.
 
Check the Switch
After the switch is installed, connect it to an ohm meter or continuity tester to see that the switch changes state when the float is raised or lowered on its own.

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If you are experiencing issues with your point level float switch, give Madison a call at 203-488-4477 or contact us at info@madisonco.com.