am256l RLS, am256l Datasheet - Page 9

• Manufacturer Part Number: am256l
• Description: Angular Magnetic Encoder Ic
• Manufacturer: RLS

Data sheet
AM256LD01_03
Issue 3, 14
Hysteresis
The AM256L uses an electrical hysteresis when converting analogue signals to digital. The hysteresis
prevents the flickering of the digital output at a stationary magnet position. The effect is a position hysteresis
when rotating the magnet CW or CCW.
* The hysteresis depends on the signal amplitude. A higher amplitude means a lower hysteresis.
Position delay
At high rotational speed a position delay between the magnet position and the electrical output appears
because of filtering. Filtering is carried out with an RC filter. The value of the resistor is 10 kΩ and the
recommended value of the capacitor is 10 nF. Position delay can be calculated as follows:
The filtering capacitor value can be reduced to 3 nF to reduce the position delay. At high rotational speed
the amplitude decreases.
Nonlinearity
Nonlinearity is defined as the difference between the actual angular position of the magnet and the angular
position output from the AM256L. Readings are compared at each output position change.
Integral nonlinearity is the total position error of the AM256L output. Figure 9 (page 10) shows a typical error
plot if the recommended magnet is carefully positioned. Figure 10 (page 10) shows the error plot if the
magnet is on the limit of alignment tolerances. Integral nonlinearity includes magnet misalignment error,
differential nonlinearity and transition noise.
Differential nonlinearity is the difference between the measured position step and the ideal position step.
Figure 11 (page 10) shows a typical differential nonlinearity plot. This is a function of the interpolator
accuracy. Differential nonlinearity is repeatable to the transition noise if it is re-measured.
The difference between two differential measurements represents the transition noise. Transition noise is a
consequence of electrical noise in the analogue signals (see Figure 12 on page 10).
© 2009 RLS d.o.o.
Parameter
Hysteresis
Parameter
Position delay
Position delay
Position delay
Position delay
Amplitude decreasing
Amplitude decreasing
th
January 2009
Symbol
Hyst.
Symbol
Δφ
Δφ
Δφ
Δφ
ΔA
ΔA
Δ
pos
pos
pos
pos
ϕ
Min.
0.3
=
−
Typ.
0.36
3.6
0.1
1
0.2
15.3
Arc
Typ.
0.45
tan
3
2
1
0
Output
{
Unit
deg
deg
deg
deg
%
%
0
f
Max.
0.6
/
Fig. 8: Hysteresis
f
0
}
Note
@ 10 Hz, C = 10 nF
@ 100 Hz, C = 10 nF
@ 10 Hz, C = 3 nF
@ 100 Hz, C = 3 nF
@ 100 Hz, C = 10 nF
@ 1 kHz, C = 10 nF
1
Unit
deg
(f = frequency, f
A
2
Note
Magnet
position
3
0
= (2
π
RC)
associate company
-1
)
9