Exercise 7 states: A rotary potentiometer is used as a position sensor. The maxi

Question

Exercise 7 states: A rotary potentiometer is used as a position sensor. The maximum angular displacement to be measured is 180 degrees, and the potentiometer is rated for 10 volts over a range of 270 degrees of rotation.

8. For the situation in Exercise 7, assume that the potentiometer is replaced by an encoder with 360 degree range. (a) How many slots are required on an incremental encoder in order to obtain the resolution of 0.75 degrees? (b) How many circular tracks are required on an absolute encoder in order to obtain the same resolution?

Explanation / Answer

a) For an incremental encoder,Resolution of Encoder = Range of Encoder/No.Of Slots.

Given, Resolution of Encoder = 0.75 degrees,

Range of Encoder = 360 degrees.

Let, No. Of Slots = X.

Therefore, From the above resolution formula,

=> 0.75 degrees = (360 degrees/ X)

=> X = 360 / 0.75 =36000 / 75 = 480 slots.

=> No. of Slots on Disc, X = 480 slots.

b) Absolute encoders have three or more concentric circles having slot-patterns that generate unique binary code based on the position of the shaft. Number of concentric tracks determines the number of binary bits. The optical disc of the absolute encoder is designed to produce a digital word that distinguishes N distinct positions of the shaft.

Let Absolute Encoder has Y circular tracks. i.e 2Y number of binary bits.

So, Resolution = Range of Encoder / Number of binary bits.

=> 0.75 = 360 degrees / 2Y

=> 2Y = 360 / 0.75 = 480

=> Approx. Y = 9

=> No.of Circular Tracks on Absolute Encoder is = 9 tracks.

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