Processor / tank float switch

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A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other device. With any set up that contains a heating element in the liquid, it is sensible to fit a protective switch esp if methanol is present. To reduce the risk it is sensible to fit a deadlock on the heater element to ensure that it cannot be switched on unless the element is completely submerged.

Risk of methanol vapour explosion in the following circumstances:

  • liquid level drops because of a leak while the processor is unattended
  • leaving the element on when the processor is being drained
  • turning on the element when the processor is empty

Parts list

  • Solid state relay (SSR)
  • Stainless steel float switch
  • Heatsink
  • Suitable Box
  • 2.5 mm cable
  • 3 - 15 V power supply
  • Grommets
  • Connectors

Fitting instructions

First decide on the desired position of your float switch, it needs to be off in a position that leaves a few inches of oil above the heating element, then drill a suitable hole in the tank. Replace any supplied rubber washers with nylon or fibre and attatch the switch. Find a suitable place to site the box. There will be 2 cables going in (mains power and low voltage) and 2 going out (mains and float). Drill suitable holes and insert grommets (pref atex rated). Mount the heatsink and SSR inside the box and then follow the wiring diagram. Immersion heaters create a lot of heat through the SSR and require a heatsink to be fitted although a metal box attatched to the metal frame can also disipate the heat, as in the one shown here.

SSR, Solid state relay & heat sink

A solid state relay (SSR) is an electronic switching device in which a small control signal controls a larger load current or voltage. It comprises a voltage or current sensor which responds to an appropriate input (control signal), a solid-state electronic switching device of some kind which switches power to the load circuitry either on or off, and some coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

Make sure you buy from a reputable source as some imported ones can have quality issues

Heat sink

Term for a component or assembly that transfers heat generated within a solid material to air or liquid for cooling.

Quality control

Wiring Diagram

Wiring circuit

KH 21:06, 14 July 2011 (BST)