Encoder Selection Guide
An incremental encoder generates pulses on A and B channels 90° out of phase as the shaft turns; when choosing, calculate resolution (ppr) and accuracy.
This guide covers what to look at when choosing products in the Encoders category.
How an incremental encoder works
As the shaft turns, an incremental encoder generates square-wave pulses on two channels called A and B. There is a 90° phase difference between the two channels; the direction of rotation is determined by which channel leads. The third channel (Z or index) found on many models gives a signal when the shaft is at a specific reference position and is used to reset the count. Resolution is expressed as the number of pulses per revolution (ppr).
A counter or drive can evaluate the edges of the A and B channels as ×1, ×2 or ×4. In ×4 evaluation all four edges of a pulse period are counted; a 1000 ppr encoder gives 4000 counts per revolution.
How to choose the resolution
Two calculations are made together.
- Accuracy: the value of one count is the distance traveled in one revolution divided by the number of counts. On a measuring wheel with a circumference of 200 mm, a 1000 ppr encoder gives 0.2 mm per pulse in ×1 evaluation and 0.05 mm in ×4 evaluation.
- Frequency: the pulse frequency is the product of the speed (rpm) and the ppr value, divided by 60. At 1500 rpm, a 1000 ppr encoder produces 25 kHz and a 3600 ppr encoder produces 90 kHz. This value must stay below both the encoder's maximum response frequency and the frequency the counter input can count.
A ppr higher than needed raises the pulse frequency for an accuracy that will not be used. If you will connect the encoder to a PLC, check the high-speed counter input of the CPU in the PLC Systems category; if you will only display speed or length, check the counting speed of the device in the Tachometers and Counters category.
Output type, supply and cable
- Open collector: the output transistor only pulls the line to 0 V; a pull-up resistor creates the high level. The Delta ES5 open collector models in the category are supplied with 7-24 V DC.
- Totem pole: the line is driven by two transistors both to 0 V and to the supply voltage. The T in the Autonics E50S8 code indicates this output; the manufacturer states that a totem pole output can also be connected like an NPN open collector or a voltage output type.
- Line driver: gives each channel together with its inverse as a differential (RS-422 type) signal; the receiver suppresses common-mode noise. It is preferred at high frequency and where the encoder is far from the counter, and it requires a receiver with a differential input. The Delta ES5 line driver models are supplied with 5-12 V DC; they cannot be supplied with 24 V DC.
Models with 5 V, 12 V and 24 V DC outputs for the supply are in the Power Supplies category. Encoder signals are carried by shielded cable, and line driver signals by shielded twisted-pair cable; twisted-pair types are also available in the LIYCY signal cables category, and for the difference from unshielded LIYY, see the article What is the difference between LIYY and LIYCY cable?. Determine the cable type and the maximum cable length from the manufacturer's data.
Mechanical connection
The encoders in this category are shaft type: they are connected to the shaft being measured with a flexible coupling or with a measuring wheel. Take the shaft diameter, housing size, cable output direction, the load limits the shaft can take and the axial misalignment the coupling allows from the manufacturer's data sheet. The products here are external encoders; the encoder of servo motors is inside the motor and is connected to the servo drive with the encoder cable defined by the manufacturer.
Brands in this category
- Autonics: E50S8 series incremental rotary encoders. In the code, E50S indicates the shaft type with a 50 mm housing diameter, 8 indicates the shaft diameter (8 mm), the following number is the resolution, and 3 indicates A, B and Z outputs; 100, 360, 500, 1000, 2000 and 3600 ppr models are listed.
- Delta Electronics: ES5 series rotary encoders; the output type and supply voltage are written in the product name. The resolution does not appear in the name but is within the product code; verify it from the manufacturer's code table before ordering.
Ordering notes
- Products are sold per piece.
- For models listed as made-to-order, the lead time is confirmed before ordering.
- Confirm before ordering whether the coupling and mounting bracket come with the product.
- You can reach a product directly by typing the manufacturer code (such as E50S8-1000-3-T-1, ES5-06LN6842) into the search.
Comparison and selection table
| Selection Criterion | Incremental Rotary Encoder | Absolute Rotary Encoder | Measuring Wheel / Draw-Wire Encoder |
|---|---|---|---|
| Position Feedback | Pulses per revolution (PPR — e.g. 100, 1024, 2500 PPR) | Retains exact angular position after power loss (bit resolution) | Direct linear travel & web speed measurement |
| Output Circuit | Totem-Pole (Push-Pull / HTL 10–30 V) or Line Driver (5 V RS422) | SSI, BiSS, Profinet, CANopen, Modbus or analog | Quadrature A, B, Z channels (HTL / TTL) |
| Mechanical Shaft | Solid shaft (Ø6–Ø10 mm) or hollow/blind shaft | Single-turn or multi-turn optical/magnetic code disc | Spring-loaded measuring wheel or draw-wire drum |
| Typical Application | Motor speed feedback, cut-to-length, packaging | CNC axes, cranes, robotics, indexing tables | Conveyor belts, sheet metal, paper & textile lines |
Frequently asked questions
What does ppr mean on an encoder?
Ppr (pulse per revolution) is the number of pulses that come out of one channel of the encoder in one full revolution of the shaft, and it indicates the resolution of an incremental encoder. A 1000 ppr encoder produces 1000 pulses per revolution; if the counter evaluates all edges of the A and B channels (×4), 4000 counts are obtained per revolution. A higher ppr gives finer measurement, but it also raises the pulse frequency at the same speed.
How far can an encoder cable be extended?
There is no single limit value; the permitted length depends on the output type, the pulse frequency and the cable. As the cable gets longer, line resistance and the capacitance between conductors distort the waveform of the pulses; at high frequency this can cause counting errors. Over long distances and in noisy environments, a line driver output giving a differential signal and a shielded twisted-pair cable are preferred. Take the maximum cable length from the encoder manufacturer's data and route the signal cable separately from power cables.
What should I look for in a counter or PLC for a line driver output encoder?
A line driver output gives each channel together with its inverse; therefore the receiver must have a differential (RS-422 type) input. A counter or PLC input with a single-ended 24 V input cannot evaluate this signal directly. The Delta ES5 line driver models in the category are supplied with 5-12 V DC; if the enclosure has only 24 V DC, a separate supply is needed. If your input is single-ended, choose a model with an open collector or totem pole output.
Can an incremental encoder be connected to the standard digital input of a PLC?
It depends on the pulse frequency. Even at medium speeds the frequency reaches tens of kHz: at 1500 rpm, a 1000 ppr encoder produces 25 kHz. For frequencies at this level, the high-speed counter input of the PLC or a separate counter module is used; in low-speed, low-ppr applications the frequency is much lower. Verify the maximum frequency the input can count and the signal type it accepts (open collector or differential) from the PLC manufacturer's data.
Does an incremental encoder remember its position when power is cut?
No. An incremental encoder does not report absolute position; it only gives the amount and direction of movement, and the position information is kept in the counter or controller. When power returns, the axis is sent to a reference point (home) and the count is re-mapped. For axes that must report position the moment power is applied, an absolute encoder is used; the products in this category are incremental type.