Couplings mechanically and electrically isolate the encoder from the motor. This separation helps avoid encoder signal errors such as miscounts or extra counts by reducing noise in the encoder. In addition, electrical isolation prevents damage caused by current from the motor. 
Couplings also allow the encoder to compensate for shaft misalignment. Cutouts on the coupling allow flex to occur in the coupling rather than in the motor shaft. The runout from the shaft is absorbed by the coupling to prevent physical damage to the encoder.

The four most common indications that your encoder is producing optimal output include:

Encoder tethers are designed and engineered to allow the encoder to float with the run-out of the motor shaft. If the tether is bolted too rigidly to the motor, then run-out from the motor can damage the encoder bearings. It is critical to use the parts provided with the encoder during installation to ensure the tether is properly placed. Avoid bending the tether from the position in which it is provided from the factory.

Without a functional tether, the wobble from the motor shaft will create additional wear on encoder bearings causing them to fail. Friction from bearing failure will cause encoder electronics to overheat.

A tether is an anti rotation device mounted between motor and encoder to ensure the encoder remains stationary while the motor is running.

You can calculate the number of shaft positions on your encoder with the following equation: 2^x where X = the resolution of your absolute encoder in bits.

RPM x PPR / 60 = Frequency Response in Hertz

To convert a DC tachometer to an encoder, you should consider the brackets. Beyond mechanics, you should also consider what ppr, input and output voltage, and the bore size of the motor being measured.

Many factors play a role in determining the maximum length of cable that can be used to connect the encoder to the controller. The largest problem with running long lengths of cable is that the cable becomes more susceptible to noise. This is due to the capacitance of the cable, the cable acting as an antenna, and the loss of power through the cable. The maximum distance of cable can be achieved by following some basic wiring principles. Do not run the cable near objects that create a lot of electrical noise. This includes AC motors, Arc welders, AC power lines, and transformers. Use twisted pair cabling when using the signal and its complement, and shielded cabling when running any type of signal. Use the highest voltage available for the output voltage. For example, if the encoder will output 5 to 24 volts, then use 24 volts. Use an Open Collector or Differential Line Driver output with a differential receiver (PM28S00) so that the maximum amount of current can be sink/sourced.

If you are using the encoder as an input to more than 1 controller, use a signal amplifier. This is also a good way to help increase the distance a signal can travel. Typical maximum distances for a Differential Line Driver are around 100 ft.or more when using a differential input, and for an Open Collector the distance is around 35 ft.

The A not and B not channels are the compliments of the A and B channels. This means that when signal A is high, signal A not is low and when A is low, signal A not is high. The same is true for any signal that has a compliment. This is commonly used to keep noise to a minimum. Some input cards will accept both the A and A not signal. It then compares the two signals to help eliminate common mode noise that may have been picked up on the line. This is done by accepting a pulse only when signal A is high and signal A not is low. This is true for any channel that has a compliment, signal A was used only as an example. This is commonly called a Differential Output.