30 Degree Rate Encoder
This
encoder has wedges every 30 degrees, thus each complete revolution yields 6
pulses on your detector. (two wedges form the basis of one pulse) Using this
on your motor or wheel means you can count pulses for 1 second then multiply
by 10 to get Revolutions per minute (divide by 6 pulses per revolution,
multiply by 60 seconds per minute equals 10) Given these nice round
numbers it makes it a great basis for a tachometer.
The image above is being shrunk by your browser to be 100 pixels across, its native resolution is 600 pixels so if you print it on a 600 DPI laser printer it will be a 1" encoder and at 300 DPI a 2" encoder.