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Products		Absolute Encoders		Optical Rotary		A2

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Features
Additional Documentation
Description
Setup Network
Analog Output
Electrical Specifications
Absolute Maximum Ratings
Pin-out
Accessories
Compatible Cables & Connectors

Versions (ordering information)

The A2 absolute encoder is a non-contacting optical rotary position sensor which reports the shaft angle within a 360 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. The SEI-UPS will retain the muti-turn position after a power failure. 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 RS232 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 AD2-B adapter for interface to an RS232 port and the USB1 for interface to a USB port. One of these products is required in order to interface the A2T 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 comes on a CD with each product shipped or can also be down loaded from US Digital's website here. 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).

See below for the many versions available.

Analog output (A-option) is available for each of the above versions. It can stand alone (does not need to connect to a PC), providing an analog voltage proportional to the angular position, with 12-bit resolution. The A-option is fully functional with the SEI bus, but is limited to one device instead of 15 devices.

US Digital warrants its products against defects in materials and workmanship for two years. See complete warranty for details.

The analog versions of the A2 have a 12-bit DAC on the output which feeds to 2 lines that are otherwise used for the BUSY handshaking pair. This DAC has a full range of 0 to 4.095 volts which is 1 milli-volt per bit. The value which the internal microcontroller sends to that DAC is the same as the digital value that it sends to the host. Since the resolution (which represents the number of codes per revolution) is field programmable, the range of the DAC will also follow that setup. Our default resolution is 3600 codes per revolution which yields 1 count per tenth of a degree. This makes the DAC output equal to 1 milli-volt per tenth of a degree or 0 to 3.599 volts. When the DAC needs to have the full range to 4.095 volts, the single turn resolution should be set to 4096. This is easily done with the available software which runs on a PC. See below for information on the SEI-ADA absolute encoder analog adapter.

Please Note: The BUSY handshaking lines are replaced by the analog output option. This means that only one device will be able to be connected to the SEI bus when using the analog output option.