Once the encoder’s resolution has been determined, its maximum speed – both mechanical and electrical – needs to be considered. For example, if the application calls for an encoder that has a resolution of 2500 PPR, but X4 encoding is being used, then the encoder’s actual resolution only needs to be 625 PPR (2500 ÷ 4). If the encoder uses X2 or X4 encoding, the encoder’s required PPR should be divided by a factor of 2 or 4, respectively. When a rotary encoder is used to measure linear distance, the required encoder resolution (PPR) can be found by dividing the lead of the screw or pulley (distance traveled per revolution) by the linear resolution required by the application.įor example, if the required linear resolution is 10 microns (0.01 mm), and a screw with a 25 mm lead is used, the encoder resolution should be 2500 PPR (or higher). Image credit: National Instruments Corporation With X4 encoding, both the rising and falling edges of channels A and B are counted. This provides a four-fold increase in resolution, since now, four edges are counted. X4 encoding counts both the rising and falling edges of both channels A and B. So a 1000 PPR encoder that uses X2 encoding has a resolution of 2000 PPR. And with twice the edges counted, the encoder’s resolution is doubled. X2 encoding counts both the rising and falling edges of channel A are counted. X1 encoding counts either the rising or falling edge of channel A. And, with quadrature output, any one of three types of encoding can be employed: X1, X2, or X4. With two sets of pulses, the encoder can determine both position and direction, based on which channel is leading and which is trailing. This is why most incremental encoders use quadrature encoding, which produces two sets, or channels, of pulses – A and B – that are out of phase from each other by 90 degrees (hence the term “quadrature”). When an incremental encoder outputs just one set of pulses, only position can be determined – not direction. The resolution of a linear encoder can also be specified in terms of microns, which refers to the distance between pulses. These square-wave pulses are very precisely spaced, and the encoder determines its position by counting the number of pulses generated during a movement. For incremental encoders, resolution is typically specified in pulses per revolution (PPR), or, in the case of linear encoders, pulses per inch (PPI) or pulses per millimeter (PPM). If the answer i calculated is indeed in the unit of degrees, would i have to convert it to rads? (which would be equivalent to 5.23 x 10^-3 rads)?ī) Minimum angular resolution i calculated to be 2.44 x 10^-4 rads using the formula 1.22(λ)/(diameter of pupil) - I'm pretty sure that this is measured in radians.Resolution is one of the most important indicators of an encoder’s performance. λ = 500 nmī) what is the MAR (minimum angle of resolution) of the mouse's eye.įor a) I calculated the answer to be 1.5 x 10^-3 however I'm not sure whether the unit for this would be in rads or degrees as the question asks for the angle? I'm aware that MAR (theta-min), the angle between two point sources needed in order for them to be resolved as seperate is measured in radians - does this hold true for the angle that the stones subtend as well? lying 200 meters from the mouse are two stones 30 cm apart.
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