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Theoretical background of the Linear FCDT

A project log for A new high accuracy tilt sensor

This project aims to build a tilt sensor that is cheap, very accurate and has a wide measuring range (up to 360 degrees).

Aron MolnarAron Molnar 10/04/2016 at 21:540 Comments

The Linear FCDT has three coils, which take place next to each other. The primary coil is usually excited with a frequency of 1 to 20 kHz and an excitation voltage range of 1 to 24 V rms.

The structure of the Linear FCDT

The cell surrounded by the three coils is exactly half-filled with ferrofluid, so there is a volume of


ferrofluid in the cell. At any tilt of the sensor, there is always a volume of


in the primary coil. The spare volume of


is divided amongst the secondary coils depending on the tilt of the Linear FCDT.

Let's check out the left secondary coil on the picture above. Starting from α = 0 °, in cases of positive α tilt, the Vsec1 amount of ferrofluid will decrease.

Deduction of the formula can be found here: https://hackaday.io/project/11225-a-new-high-accuracy-tilt-sensor/log/47221-deduction-of-the-linear-fcdt-volume-formula

If we plot the values of Uout normalized to 1 in cases of disparate L and R rates between -90 ° and +90 ° it is noticable that the measuring range, and the sensitivity inside that, strongly depends on the L/R rate. In cases of low rate we get a relatively great measuring range, in cases of high rate we get a smaller measuring range, but higher sensitivity.

The effect of L/R rate to the characteristics of the Linear FCDT


Next log: Experimental and theoretical curves of the Linear FCDT (https://hackaday.io/project/11225-a-new-high-accuracy-tilt-sensor/log/46959-experimental-and-theoretical-curves-of-the-linear-fcdt)


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