How to Install an Industrial Rotary Encoder: Mounting, Couplings & Wiring Guide
Installing an industrial rotary encoder correctly is the difference between years of reliable feedback and a string of noisy signals, worn bearings and unexplained drive faults. This guide is written for maintenance engineers, electricians, OEM machine builders and anyone replacing a motor feedback device, such as an old DC tacho generator, on plant equipment. It covers how to choose a mounting location, mount solid and hollow shaft encoders with brackets, flange adapters, torque arms and couplings, and route the cable so it’s protected. If you’re working with a small panel-mount encoder for an Arduino or electronics project, this isn’t the article for you. Our focus is heavy-duty encoders on motors, gearboxes and machinery.
Need help finding a replacement encoder? Send any questions through our contact page here, or call us directly on 1300 236 467
Choosing the Right Mounting Location
Before you mount the encoder, ask yourself these questions.
Before or After the Gearbox?
Will the encoder measure accurately at this location? Consider vibration, shaft slip and the encoder’s maximum speed. Mounted before the gearbox, the encoder turns at motor speed, but any gearbox backlash sits between it and the load. Mounted after the gearbox, it measures the load directly but turns more slowly.
Protecting the Encoder from Vibration, Heat and Impact
Will the encoder be knocked or bumped because it protrudes? Is it exposed to the weather or wash-down? Will it run hot, for example when mounted directly on the back of a motor? Overlooking these factors shortens the life of the encoder and can also affect its accuracy.
Solid Shaft vs Hollow Shaft Encoders: Which Should You Use?
Encoders come in a range of mechanical designs, so buy from a supplier that can offer every option suited to your application. A solid shaft encoder connects to the machine shaft through a coupling. A hollow shaft encoder slides directly over the machine shaft and is held in place by a torque arm.
Blind Hollow Shaft vs Through Hollow Shaft
Many modern programmable and magnetic encoders use a blind hollow shaft, which stops partway into the encoder body because of the electronics behind it. This limits mounting options compared with a traditional through hollow shaft encoder (usually an optical type), where the machine shaft can pass all the way through.
Servo Flange vs Clamping Flange
Solid shaft encoders are usually mounted by one of two flange styles. A servo flange is held by clamps or cleats around its rim, which lets you rotate the encoder body to fine-tune its position before tightening. A clamping flange is bolted through threaded holes in its face, with a centring spigot locating it on the mounting surface.
PCA Encoders stocks the following mounting accessories.
Rotary Encoder Mounting Brackets
An encoder clamp bracket lets you mount a rotary encoder securely to a flat surface. Clamp brackets are available to suit all the standard encoder body diameters, including 58 mm, 70 mm and 90 mm.
Rotary Encoder Flange Adapters
Flange adapters convert one mounting style to another. They let you fit an encoder whose native flange doesn’t match your machine, or simply use a more readily available encoder.
For example, the tacho generators used on DC motors in years gone by often had a REO flange. The AF90-REO adapter lets a standard modern 90 mm body encoder fit a REO flange mounting. The adapter is tightened around the encoder body with a clamp bolt.
Torque Arms for Hollow Shaft Encoders
Do Hollow Shaft Encoders Need a Torque Arm?
When a hollow shaft encoder is mounted on the rear shaft of a motor, it doesn’t need to be bolted to the motor frame. It can float on the shaft without affecting the accuracy of its readings. However, something must stop the encoder body rotating with the shaft and the cable wrapping around it. A torque arm (also called a torsion arm) does this job. Its length is adjustable so the encoder is held square.
Rotary Encoder Couplings
When you join two solid shafts (the machine shaft and the encoder shaft), a coupling:
connects the two shafts
absorbs small amounts of misalignment so the encoder bearings aren’t loaded
can act as a reducer between different shaft sizes
limits backlash
A good encoder supplier will stock couplings in many combinations of shaft sizes.
Backlash is “play” in the drive train, like the slack in a car’s steering wheel. You notice it most at rest and when changing direction, when there’s a delay before the response. In precision motion control, backlash can cause instability, so encoder couplings are designed to be flexible while still transmitting rotation accurately.
Oldham Couplings
An Oldham coupling uses a plastic tongue-and-groove centre piece fitted between two clamping hubs.
Spring and Bellows Couplings
Other flexible couplings achieve the same result with a spring or bellows built into the design.
Shaft Load and Alignment
Encoder bearings are small and designed for precision, not for carrying load. Most solid shaft encoder failures are caused by side load or misalignment transmitted through the shaft.
Observe the shaft load ratings. Every encoder has a maximum radial and axial shaft load, and it’s often small (check the datasheet). Never mount a gear, pulley or sprocket directly on an encoder shaft. Drive the encoder through a coupling instead.
Use a flexible coupling. Oldham, spring and bellows couplings absorb small amounts of radial, angular and axial misalignment, so the encoder bearings aren’t loaded.
Stay within the coupling’s limits. A flexible coupling can only take so much misalignment (check the datasheet). Running at or near the full allowance wears the bearings and makes the signal drift over time.
Let the torque arm float. On a hollow shaft encoder, the torque arm should only stop the encoder body from rotating. If it’s bolted rigidly in every direction, any shaft wobble is forced into the encoder bearings.
Never force a fit. If the encoder shaft won’t slide easily into the coupling, or the encoder won’t slide onto the machine shaft, find out why rather than using a hammer or extra force.
Mounting Position for Absolute Encoders
An absolute encoder reports its true position as soon as it’s powered up, so where its zero sits mechanically matters.
Keep the rollover point out of the working range. A single-turn encoder rolls over from its maximum value back to zero once per revolution. Mount the encoder and set its zero so the machine’s normal travel never crosses that point.
Choose single-turn or multi-turn to suit the travel. If the machine moves through more than one revolution of the encoder shaft, use a multi-turn encoder, or mount the encoder after a gearbox so the total travel fits within one turn.
Tighten the coupling at a known machine position. Tighten the coupling clamp with the machine at its reference point or mid-travel, so a refit doesn’t shift your reference.
Set the zero after mounting. Once the encoder is fitted and secured, move the machine to its reference point and set the zero (see Setting the Home Position on an Absolute Encoder below).
Re-zero after any mechanical change. Replacing the encoder, coupling or gearbox, or a slipping clamp, can shift the reference.
Record the scaling and zero. Write them down so the encoder can be replaced without recommissioning the whole machine.
Step-by-Step: How to Install a Rotary Encoder
Most solid shaft and hollow shaft encoders can be mounted on motors, gearboxes and driven machinery using the steps below. Where the manufacturer’s datasheet differs, follow the datasheet.
All encoders:
Isolate and lock out. Before starting work, isolate and lock out the machine drive and the encoder power supply.
Check the encoder suits the application. Confirm the shaft type, shaft or bore diameter, flange or clamp style, supply voltage, output type and resolution are correct for the job.
Prepare the mounting surface. Clean the motor or machine face and the shaft, remove any burrs, and check the shaft for runout. Loosely fit the bracket, flange adapter or mounting plate.
Solid shaft encoders:
Fit the coupling to the encoder shaft. Slide it on by hand and never hammer it into place. Leave the clamp screws loose for now.
Position the encoder. Bring the encoder into its mounting position with the coupling over the machine shaft. Check that the shaft ends aren’t forced together or pulled apart.
Align the shafts. Keep radial, angular and axial misalignment as small as possible, and well within the coupling’s rated limits (see Shaft Load and Alignment above).
Secure the encoder. Tighten the bracket or flange bolts evenly, then tighten the coupling clamp screws to the specified torque.
Hollow shaft encoders (instead of steps 4–7):
Fit the encoder onto the shaft. Slide the encoder onto the machine shaft by hand and tighten the shaft clamp ring. Then fit the torque arm so it holds the encoder square while still letting it float with any shaft movement.
All encoders:
Wire and terminate. Wire the encoder as described in the wiring section below.
Commission and record. Restore power and complete the commissioning checks further down this article.
Encoder Wiring, Shielding and Earthing
Choosing the Right Cable
Use shielded, twisted-pair cable. On encoders with differential outputs, twist each signal with its complement (for example A with /A). On long runs, size the supply conductors so voltage drop doesn’t take the encoder below its minimum supply voltage.
Earthing the Shield
Earth the cable shield to drain interference away from the signal conductors. Follow the encoder and drive manufacturers’ recommendations: many specify earthing the shield at both ends through 360° EMC cable glands, while others earth it at one end only to avoid earth loops. Keep the shield continuous through any junction boxes or connectors.
Keeping Signal Cables Away from VFD and Motor Cables
Variable speed drives and motor cables are the most common source of encoder noise. Run encoder cables in a separate tray or conduit from power cables, keep as much distance between them as practical, and cross power cables at right angles where they must cross.
Radial, Axial or Tangential Cable Exit?
Choose a radial (side) or axial (rear, in line with the shaft) cable or connector exit so the cable doesn’t protrude where it could be knocked or damaged.
A tangential cable exit combines both. One tangential exit encoder can replace either a radial or an axial exit model, which also means fewer variants to keep in stock.
Connectors, Cable Glands and IP Rating
Choose a connector or cable gland rated for the environment, and check that the IP rating of the whole assembly, not just the encoder body, suits any dust, moisture or wash-down. Fit strain relief so the cable isn’t pulling on the terminations, and a drip loop so water can’t run along the cable into the connector.
Checking Supply Voltage and Output Type Before Power-Up
Confirm the supply voltage matches the encoder’s rating, and that its output type (for example HTL push-pull or TTL/RS-422 line driver) matches the drive or PLC input. Never connect a signal output to the supply or 0 V, as this can damage the output circuit.
Commissioning and Setting the Zero Position
Setting the Home Position on an Absolute Encoder
Take a single-turn absolute encoder with a 4–20 mA output as an example. One full turn (0–360°) corresponds to 4–20 mA. The encoder has a zero input terminal: applying a positive voltage to it sets the current position as home, or zero (4 mA). Do this only after the encoder is fully mounted and the machine is at its reference point.
Post-Installation Checks
- Direction of rotation: check the count or position increases in the direction the drive or PLC expects. If it doesn’t, change the direction setting or swap the channels as the datasheet describes.
- Pulse count or position: move the machine a known distance or angle and check the reading matches.
- Signal quality: run the machine up to full speed and watch for count errors or drive faults. Check the signals on an oscilloscope if you have one.
- Clearances: check the cable and torque arm clear all moving parts through the full range of travel.
- Records: note the encoder model, resolution, settings, scaling and zero position for future replacement.
Common Encoder Installation Mistakes to Avoid
- Hammering an encoder or coupling onto a shaft
- Mounting a gear, pulley or sprocket directly on the encoder shaft
- Using a rigid coupling, or no coupling, on a solid shaft encoder
- Bolting a hollow shaft encoder rigidly to the motor frame instead of using a torque arm
- Over-tightening clamp screws beyond the specified torque
- Running encoder cable alongside motor or VFD cables
- Leaving the cable shield unearthed, or broken at a junction box
- Forgetting to re-zero an absolute encoder after a replacement or mechanical change
Frequently Asked Questions
How Do I Mount an Encoder on a Motor?
For a hollow shaft encoder, slide it onto the motor’s rear shaft, tighten the clamp ring and fit a torque arm. For a solid shaft encoder, mount it on a bracket or flange adapter and connect it to the motor shaft with a flexible coupling. The step-by-step procedure above covers both.
Why Is My Encoder Signal Noisy?
The most common causes are encoder cable run alongside motor or VFD cables, a shield that isn’t earthed correctly, and mechanical problems such as a loose coupling or worn bearings. Check the wiring first, then the mounting.
Can I Replace an Old Tacho Generator with an Encoder?
Yes. Many older DC motors have a tacho generator with a REO flange, and an AF90-REO flange adapter lets a modern 90 mm encoder fit the same mounting. Check that your drive can accept an encoder input, or ask us about the options.
Need Help Choosing Encoder Mounting Accessories?
Replacing an old tacho or encoder? Send us the shaft size, flange type and output you need, and we’ll match it. Contact PCA Encoders or call us on 1300 236 467.
Is this information useful? If so, why not share it with your peers and colleagues? Simply click the blue LinkedIn share icon below.
