Magnetic Stirrer

Overview

A magnetic stirrer mixes a liquid by spinning a small magnet inside the vessel instead of putting a paddle into the sample. A coated PTFE Stir Bar dropped into the flask follows a magnet that turns just under the bench-top surface, so the contents are stirred without anything touching them through the glass. The hotplate version adds a heated Top Plate, letting one instrument both mix and heat a reaction.

Everything sits in a cast Chassis heavy enough to keep the unit from walking across the bench while the magnet spins. The aluminium base carries the drive, the heater, and the electronics; a molded shell closes it up and recesses the front for the controls. The operator sets a target speed and temperature on the Display Panel, drops a vessel and a PTFE stir bar onto the plate, and the controller holds both setpoints on its own.

How it works

Stirring is magnetic coupling. The Stirring Drive turns a two-pole magnet bar on a BLDC motor a few millimetres below the plate. Its field passes straight through the non-magnetic aluminium and grips the stir bar in the flask, dragging it around at the same speed. A Hall sensor feeds rotor position back to the board so the controller can lock the rpm and ramp gently, start too fast and the bar loses sync and rattles instead of spinning.

Heat comes from a resistive Heating Element clamped under the plate, switched by the Control Board. A PT100 sensor reads the plate temperature and the microcontroller drives a triac to hold the setpoint; plug a probe into the front jack and it regulates the liquid itself rather than the surface. Two independent safety layers guard against runaway heat: a resettable over-temp limiter trips first, and a one-shot Thermal Fuse cuts mains power for good if the plate ever exceeds its ceiling. The control board ties the loops together, one MCU runs the motor driver and the heater stage at once, so speed and temperature stay independent of each other.