VA Virtual Absolute Incremental Decoder0 pages

"Gurley Model VAinterpolating Decoder nn

For Use With:Models 9710, and LP10Output:Max Resolution:MultiplexedNatural Binary 20 Bits (1,048,576)Virtual Absolute

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Small Package - Big Performance

The credit-card-size Model VA interpolating decoder is used with the Model 9710 Read Head to form an absolute modular rotary or linear system with resolution up to 20 bits. GPI's 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 9710 data sheet for full details on the encoder.The disc or scale in a Virtual Absolute 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 ( 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 , in either direction and starting from anywhere , you know exactly where you are. In a rotary VA , this initialization angle is typically about one degree, depending on the encoder's line count; in a linear Virtual Absolute VA encoder, less than 1 mm of motion is needed. From then on, the encoder is truly absolute. (There are ways to build a pseudorandom encoder so that absolute information is available on power-up without initializing, but these techniques require far more complex sensing hardware; they often impose slower operation as well. And none of them offers the sophisticated built-in testing of GPI's technology.)The Model VA provides patented high-speed circuitry to decode the special serial index track and interpolation to increase the final resolution up to 20 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. >

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ISO 9001 Certified

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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

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