VG Virtual Absolute Decoder
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Virtual Absolute The VG Virtual Absolute technology is a unique encoding method that combines the opto-mechanical simplicity of an incremental encoder with the system reliability and interfacing ease of an absolute encoder. Please refer to the decoder is used with the Model 7700 Model 7700 modular encoder to form an absolute rotary or linear system with resolution up to 12 bits (14 bits is optional). GPI's data sheet for full details on the encoder.The disc or scale in a Model VG provides patented high-speed circuitry to decode the special serial index track and interpolation to increase the final resolution up to 12 bits total. In addition to the natural binary position output, a Status bit tells you when the encoder is initialized. This bit is at a logic high whenever the supply voltage has been interrupted, when the initializing motion is not yet complete, or when some other effect such as electrical noise, damage, or fouling of the disc interferes with the proper code sequence from the index track. When these self-tests are all satisfied and the encoder is initialized, the Status bit is low, indicating the position data output is valid. Virtual Absolute (VA) encoder is similar to an incremental disc or scale in that both contain a cyclic track and an index track. In an incremental encoder, the index occurs at one place in the full travel, but in a VA encoder, the index track is a continuous serial code (similar in appearance to a bar code). You don't know position immediately upon power-up, as you do in a conventional absolute, but after a very short travel, in either direction and starting from anywhere, you know exactly where you are. The > Gurley Precision Instruments514 Fulton StreetTroy, NY 12180 U.S.A.(800) 759-1844, (518) 272-6300, fax (518) 274-0336, Online at www.gurley.com, e-mail: info@encoders.com ingenuity@work

PinNameTypeDescription 1StatusOutput0 = Data output valid, 1 = Data not valid 2OELInputLow byte Output Enable, latch current position 3OEHInputHi byte Output Enable 4D7OutputData bit, MSB 5D6OutputData bit 6D5OutputData bit 7D4OutputData bit 8D3OutputData bit 9D2OutputData bit 10D1OutputData bit 11D0OutputData bit, LSB 12ResetInputReset decoder by external control, 0 = Reset 13VCCPowerSingle +5VDC supply 14GroundPowerSupply Return > Gurley Precision Instruments514 Fulton StreetTroy, NY 12180 U.S.A.(800) 759-1844, (518) 272-6300, fax (518) 274-0336, Online at www.gurley.com, e-mail:...

Theory of Operation Gurley Virtual Absolute (VA) encoders employ an optical encoding technique which is still relatively new to the motion control industry. Like an incremental encoder, the VA disc (or scale, in a linear encoder) uses only incremental and index code tracks. The incremental track is structured and read by quadrature sensors in the usual way, but neither the encoder nor the host system accumulates incremental counts as the disc turns. Instead, the quadrature signals control the spatial timing for sampling the index track, where the absolute position code is stored. The index...

A GPI Virtual Absolute encoder system can be in any one of 3 distinct operating modes: Wait mode: Model VG reports a fault condition while it is waiting for a full tag to be acquired. Aware of an interruption of power or some other interference to normal operation which it interpreted as an invalid tag, it waits until a (re)initialization traverse has been executed to refresh the code tag in the decoder. The Virtual Absolute decoder locates the Status bit at the MSB position to offer a simple mechanism for a microprocessor-based host system to quickly assess data validity. Most processors...

Timing Diagrams Reset timing Read timing requirements Forward Motion Encoder Signals Reverse Motion Encoder Signals > Gurley Precision Instruments514 Fulton StreetTroy, NY 12180 U.S.A.(800) 759-1844, (518) 272-6300, fax (518) 274-0336, Online at www.gurley.com, e-mail: info@encoders.com

CODE ##10 (1024) are standard consult factory for other resolutions OUTPUT B2-byte-wide multiplexed output INTERP 022 bits of quadrature decode INPUT TTTL compatible input, single-ended PKG 0Printed circuit board assembly only (standard ֖ call factory for mezzanine) TEMP CA0C to +70аC-40C to +85аC SF #NIssued at time of order to cover special customer requirementsNo special features > SPECIAL CAPABILITIES WARRANTY For special situations, we can optimize catalog encoders to provide higher frequency response, greater accuracy, wider temperature range, reduced torque, non-standard line counts,...