There are two ways to wire an incremental encoder into a system. One is single-ended wiring and the other is differential wiring.
In single-ended wiring, each channel needs only one wire. Channels are any data streams that the encoder produces. For example, a common quadrature encoder has two channels—A and B—to track speed as well as rotational direction … so it needs two wires in single-ended wiring.
Differential wiring needs two wires per channel that reference each other. That is, the wires carry signals that are 180° out of phase. To illustrate, other incremental encoders have three channels of data transmission—A, B and Z for indexing to a setpoint. Such an encoder with differential wiring has six wires total, and each channels’ wire pairs feed twin signals to a controller that discards errors to clean the input.
Each method of wiring has its advantages and drawbacks. Single-ended wiring is usually the cheaper option. This is because single-ended wiring uses one wire per channel, with one end connected to the encoder and the other connected to the controller’s I/O system. However, it is only suitable for short runs of wire. That’s because where an encoder needs a longer run of wire—say, in an application that’s deep within a piece of machinery—single-ended wiring is more susceptibile to interference. That said, single-ended wiring is easy to implement, as there is only one wire per channel and a common ground.
Differential wiring is more immune to interference. Its wiring consists of a twisted pair of shielded wires with complementary signals.
This means differential wiring is better for longer cable runs, because it rejects common-mode interference. Common-mode refers to any interference carried on all conductors. It is easily rejected in differential wiring because a signal and its complement can be sent together, which easily allows subtracting any interference. Differential wiring’s main drawback is its higher cost and number of connections … as each channel requires two wires. This means that there are more opportunities for faults as well.
The most suitable wiring choice depends on the need for longer wiring runs, interference immunity, cost control and time between breakdowns.
When deciding which way to wire the encoders in a motion system, keep the application requirements in mind. If the design only needs short cable runs in a mostly interference-free environment, then it makes little sense to use costlier differential wiring. However, if the machine dimensions necessitate long lengths of cable, or there’s a risk of interference from the surrounding environment, then differential wiring is in order. While it’s costlier and requires more material, it would prevent signal-loss and interference headaches.
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