Factors to be considered for Selection of Encoders
Incremental vs. Absolute
Can you afford to lose position in case of power failure? If the answer is no, then you must use an absolute encoder. An incremental encoder simply generates pulses proportional to the position, whereas an absolute encoder generates a unique code for each position. After a power outage, with an absolute encoder the machine operation will pick up from where it had left off even if the encoder shaft had moved during power down which is very typical as the encoder shaft will coast to a stop when power is lost. In an incremental encoder the pulses generated are counted in a counter and at power loss it will lose the count and consequently you will have to home the machine before you can start the operation. Typical application examples for Incremental Encoders are “Cut to Length”, Conveyor Control, Augur Control, metering equipment, and machines that use lead screws for motion control such as a milling machine. Upon power down, you have to re-sync the controlled apparatus. Absolute Encoders are used when the machine/process has to know the true position all the time and re-sync is not allowed, such as a Press or Assembly machine or a Dam control or an Oil Valve control.
Also, an incremental encoder is generally more susceptible to electrical noise. Whereas absolute encoder may give you a false output under noisy conditions, the true position is restored when noise is gone. On the other hand, if you can false counts with noise when using an incremental encoder, the bad count would remain there until reset or re-synced. The absolute encoders are more expensive than the incremental encoders, therefore, a price/ feature trade-off may be worth considering.
We recomend 24VDC power and 7272 outputs for highest reliabilty and imuunity to electrical noise.