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What is the position (time) delay of the encoder signals?!

Changchun Rongde Optics Co.,Ltd.   Release time:2016/3/3   Browse:792


Position or time delay in signals is common to all encoders. It can be corrected if needed in the control system by putting in a factor derived from the calculated delay.

At high rotation speed a position delay between magnet position and the electrical output appears because of filtering. Filtering is carried out with an RC filter. Position delay can be calculated with formula:

Δφ = -Arctan{ƒ/ƒ0} (ƒ = ƒrequency, ƒ0 = (2πRC)-1)

For the AM256 and AM512B (8, 9 bit encoder ICs) and up to 9 bit RM/RE, the value of the resistor is 10 kΩ and the recommended value of capacitor is 10 nF.

Parameter

Symbol

Typ.

Position delay @ 10 Hz (600 rpm),
C = 10 nF

Δφpos

0.36°

Position delay @ 100 Hz (6000 rpm),
C = 10 nF

Δφpos

3.6°

For 10+ bit encoders the resistor value is 10 kΩ and the value of capacitor is 22 nF.

Parameter

Symbol

Typ.

Position delay @ 10 Hz (600 rpm),
C = 22 nF

Δφpos

0.8°

Position delay @ 100 Hz (6000 rpm),
C = 22 nF

Δφpos

7.87°

Using the above equation, we can therefore calculate the position delay in both degrees and time. In the following example we have a 10 bit encoder rotating at 1000 rpm.

1000 rpm

= 16.7 Hz

 

ƒ0

= (2πRC)-1

 

 

= (2 x π x 10 x 103 x 22 x 10-9)-1

 

= (1.38 x 10-3)-1 = 723.43

 

Δφ

= tan-1{ƒ⁄ƒ0}

 

= tan-1{16.7⁄723.48} = tan-1{0.02308} = 1.3°

@ 1000 rpm - 1 rotation = 0.06 s

 

(0.06⁄360) x 1.3 = 2.16 x 10-4 = 0.216 ms

 



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