How to determine if an encoder is counting accurately

In many cases, the encoder is not broken, but the interference causes a bad waveform, which leads to (generates, contributes to) inaccurate counting. How can I determine this? Encoder is a precision component, this is mainly because of the encoder around the interference is more serious, such as: whether there is a large motor, welding machine frequent start-up caused by interference, and whether the power line and the same pipeline transmission and so on. Select what kind of output on the anti-jamming is also very important, the general output with reverse signal anti-jamming to be better, i.e., A + ~ A-, B + ~ B-, Z + ~ Z-, which is characterized by the addition of the power supply (to the electronic equipment to provide power to the device) 8 wires, rather than 5 wires. Examples include various lifting devices, feeder trolley positioning, etc. With the reverse signal in the cable (Cable) transmission is symmetrical, interference is small, in the receiving device can also be added to the judgment. It is the encoder is also good or bad, its code disk \ electronic chip (also known as microcircuit) \ within...