US Digital A2 Absolute Optical Encoder

The A2 absolute encoder is a non-contacting optical rotary position sensor which reports the shaft angle within a 360 deg. range. As opposed to incremental encoders, the A2 reports the absolute position rather than the change in position. When powered up, it does not require a home cycle, even if the shaft was rotated while the power was off. In multi-turn mode, it tracks the position in a 32-bit counter as long as the power supply is maintained. Internally, an infrared LED flashes through a circular bar code onto a linear array sensor. The microcontroller decodes the image into a unique position. All user programmable parameters such as resolution, origin, direction and mode are permanently stored in an internal EEPROM.

The interface of the A2 utilizes our SEI (Serial Encoder Interface) bus. The SEI bus is a simple, quick, convenient network of devices interfacing to an RS-232 serial port or USB port. The SEI bus supports 1 to 15 devices on a single, 6-wire telephone-type cable up to 1000 feet long (similar to RS-485).

US Digital offers two SEI interfaces: the AD2B adapter for interface to an RS-232 port and the SEI-USB for interface to a USB port. One of these products is required in order to interface the A2 to a PC via our SEI bus. The wall-mount PS-12 power supply furnishes the power for all devices on the SEI bus.

US Digital provides software free of charge for all products which require software for operation. The software can be used as is or it can serve as an example for creating your own custom application. The absolute encoder software utilizes our SEI Explorer software to configure and communicate with the product from a PC platform.

Our absolute encoders may be used in many stand alone applications that do not require a PC interface. For these applications we provide detailed communications protocols for all of our absolute products (see the SEI Absolute Encoder Communications Protocol page).

An analog voltage output (A-option) is available for the A2. An A2 with the analog option can stand alone (does not need to connect to a PC), providing an analog voltage (0 to +4.095 volts maximum) that is proportional to the angular position, with 12-bit resolution. A2 encoders with the A-option can still be communicated with on the SEI bus, but only one device can be on the bus at a time instead of up to 15 devices.

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