2000 Sep 05

4

Philips Semiconductors

Product specification

Rotational speed sensor

KMI15/4

FUNCTIONAL DESCRIPTION

The KMI15/4 sensor is sensitive to the motion of ferrous

gear wheels or reference marks. The functional principle is

shown in Fig.3. Due to the effect of flux bending, the

different directions of magnetic field lines in the

magnetoresistive sensor element will cause an electrical

signal. Because of the chosen sensor orientation and the

direction of ferrite magnetization, the KMI15/4 is sensitive

to movement in the ‘y’ direction in front of the sensor only

(see Fig.2).

The magnetoresistive sensor element signal is amplified,

temperature compensated and passed to a Schmitt-trigger

in the conditioning integrated circuit (Figs 4 and 5).

The digital output signal level (see Fig.6) is at a fixed level

independent of the sensing distance. A (2-wire) output

current enables safe sensor signal transport to the

detecting circuit (see Fig.7). The integrated circuit housing

is separated from the sensor element housing to optimize

the sensor behaviour at high temperatures.

The strength of the magnetic field caused by the

Ferroxdure 100 magnet in the different sensor directions,

measured at the centre of the magnetoresistive bridge, is

trimming process.

Fig.2 Component detail of the KMI15/4.

handbook, halfpage

y

z

xx

IC

sensor

magnet with

direction of

magnetization

MBH779

Fig.3 Functional principle.

handbook, full pagewidth

gear wheel

magnet

magnetic

field lines

(a)

(b)

(c)

direction

of

motion

(d)

MRA957

sensor

y

z