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30 October 2012

Encoders are used in a variety of manufacturing plants, primarily to determine a motion control axis position or to obtain speed feedback....

Atraditional optical encoder is a simple sensor that uses a fixed code disc (a circular slotted ring to cyclically manipulate a light source) to produce an electrical signal, usually a square wave output. When the disc is rotated between a light source and a photodiode, the output signal corresponds to the light being passed through or blocked from the photodiode. The number of times the signal is high corresponds to the number of slots on the code disc, which is typically referred to as the line count, resolution, or pulses per revolution.

Historically, code discs contained a fixed line count, which increased manufacturing and production constraints if a different or higher resolution was required. Therefore, any changes to the application meant obtaining a new encoder. As a result, a programmable encoder. which can be programmed to any line count in either the field or during production, provides benefits to both the end user and the manufacturer. Here are five proven advantages of using programmable encoders in manufacturing processes.


 The most obvious advantage of programmable encoders is the reduction of replacement and inventory costs. Instead of stocking encoders of different line counts, one programmable encoder will suffice.

However, as any frequent user may realise, programming only the line count does not account for other parameters, such as the output signal voltage or marker pulse alignment. The best option is to obtain an encoder that offers several programmable parameters.

Sick offers a line of DFS incremental encoders that features a programmable line count as well as a programmable electrical interface.


 Setting the marker pulse – which indicates an absolute position within a revolution of the encoder – at any given point based on preference reduces setup time of an encoder. Usually, when an incremental encoder is installed, the marker/zero pulse is used as a reference signal. In some applications, an oscilloscope is used to monitor the channel so the encoder shaft can be carefully adjusted to trace the starting point.

With the DFS series, the marker pulse can be programmed via the programming interface or set remotely by applying a signal on a dedicated pin, thus saving time and energy during installation.


 Programmable encoders are an indispensable tool for OEMs and machine designers when component procurement is required for a project but the actual design requirements are not fully defined. Programmability offers the flexibility to match any changing needs of the end user.

Sick’s encoders can program any integer line count (between 1 to 65,536 on DFS60 incremental encoders and up to 18 bits on AFS/AFM60 absolute encoders) without being restricted to binary line counts only. The encoders can be reprogrammed as many times as needed.


 Programming options include DIP switches, standalone tools, serial/USB interface and control system integration using a PLC or an HMI unit. Selecting the appropriate tool is dictated by the end user’s preference, with greater prominence given to the simplicity and accessibility of the programming tool.

Users can use a USB-based tool or a portable handheld programming tool, they can automate programming through a set of commands to communicate via a PLC serial port, or they can integrate on-the-fly programming into their control system on a Windows CE-based HMI.

The most common choice among users has been the USB programming interface, which saves the settings of the encoder and makes cloning additional encoders very efficient.


 The programming software interface can be used as a condition monitoring tool as well as for monitoring parameters like position or angle during the initial integration, or when performing maintenance or making adjustments while running operations.

In addition to the benefits of programming, the DFS and AFx60 encoders offer a wide range of mechanical features, including: a metal code disc that is more resistant to shock and vibration than glass discs and withstands higher temperatures (-20 to 100˚C) than plastic discs; shaft bearings significantly spaced apart so there is no uneven loading even while running at high speeds; and an IP 65 enclosure rating and wellinsulated collets to avoid shaft leakage currents.

Key Points

• Instead of stocking encoders of different line counts, one programmable encoder will suffice

• Setting the marker pulse at any given point based on preference reduces setup time of an encoder

• Programmability offers the flexibility to match any changing needs of the end user