An analog encoder reports motion through an analog electrical interface. Before choosing one, establish what that interface actually carries: a scaled position value, such as 0–10 V or 4–20 mA, or a pair of sine/cosine signals that repeat as the mechanism moves. Both belong in a discussion of encoder output signals, but their receiving electronics are quite different.

The word analog does not identify the sensing technology. An optical or magnetic encoder may provide an analog output. A potentiometer measures position by changing a resistance ratio through a moving contact; it is a separate transducer, rather than the operating principle of every rotary encoder with an analog interface.

Reading position from voltage or current

A suitable absolute encoder can map a defined travel range onto 0–10 V or 4–20 mA. The controller reads an analog voltage or analog current and converts it into engineering units. Check the specified measurement range and output option: a product family offering both interfaces does not mean every unit provides both simultaneously.

Imagine a valve actuator with 180° of travel. With the example scaling below, 0° corresponds to 0 V or 4 mA, 90° to 5 V or 12 mA, and 180° to 10 V or 20 mA. The two tracks illustrate alternative output options for the same movement.

For this example, angle = 18 × V or angle = 11.25 × (I − 4), with voltage in volts and current in milliamps. More generally: position = start position + [(signal − lower limit) / (upper limit − lower limit)] × travel span. Reverse scaling, teach settings and a different travel range require different coefficients.

A full-turn device may wrap from its upper output value back to the lower value at the 360°/0° boundary. That discontinuity can be normal. Any software estimating speed or direction must account for the specified wrap behavior and sample interval.

Sin/cos feedback needs a different receiver

Common 1 Vpp sin/cos interfaces provide two signals approximately 90 electrical degrees apart. Electrical phase is not the shaft's mechanical angle: there may be many signal periods per revolution. An incremental encoder receiver uses interpolation within a period, along with period counting and the required reference information, to establish position over the travel range.

Two ordinary analog input channels are not automatically a suitable sin/cos receiver. The input circuitry, amplitude, bandwidth and simultaneous sampling must suit the signals. A resolver also uses angle-related sine and cosine signals, but has its own excitation and decoding requirements. Matching terminology does not make these interfaces interchangeable.

PLC integration: resolution is only one specification

On a PLC, select the correct channel in the analog I/O module. A voltage input and a current input are not interchangeable. Confirm the supply voltage, signal reference, input impedance and allowable current-loop load. A 4–20 mA interface is not necessarily a two-wire device; use the manufacturer's pinout.

An ideal 12-bit input spanning 0–10 V has a nominal step of about 2.44 mV. For the 180° example, that is approximately 0.044° per step. This is quantization, rather than a system accuracy guarantee. Encoder error, output resolution, input error and noise also matter. When comparing analog and digital inputs, a larger bit count cannot settle the choice by itself.

A single position reading does not directly describe speed and direction. These can be estimated from changes between successive readings, with proper timing and wrap handling. Sampling rate and filter delay therefore belong in the specification. For square-wave incremental feedback, the relevant checks include a high-speed counter, its counting frequency and, where applicable, a matching line-driver receiver.

Installation details that make the reading useful

Use shielded cable, suitable routing and the manufacturer's shield termination and grounding instructions. Maintain appropriate separation from motor and drive power wiring. Current signaling does not eliminate every source of interference. Filtering can help, but excessive filtering delays the reported movement; investigate wiring and signal levels before treating every unstable reading in software.

In this example, 4 mA is a valid zero-position reading. Reliable open-circuit or fault-current detection depends on features supported by both the sensor and input module. For the mechanical side, check hollow-shaft mounting, couplings and accessories, and the required IP protection. If the actual load moves linearly, a linear encoder or suitable draw-wire encoder may measure closer to the point that matters; motor rotation alone does not always establish load position.