VB Virtual Absolute Interpolating Decoder
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The credit-card-size Model VB interpolating decoder is used with selected housed encoders to form an absolute rotary or linear system with resolution up to 20 bits. Maximum resolution depends on which encoder is used with the VB .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 specific encoder 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 Virtual Absolute , you know exactly where you are. In a rotary technology.)The VA , this initialization angle is typically about one degree, depending on the encoder's line count; in a linear 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 Model VB 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. > 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

InputDifferential buffered sinusoidsUse with encoder modelVL18 linear; Vx20, Vx35 rotaryMax code length on disc or scale15 bits (32,768 cycles). See encoder data sheet.Interpolated resolution5 bits (32 steps per optical cycle)Max final resolution20 bits (1,048,576 steps)Absolute outputNatural binary byte-wide multiplexedMax input frequency200 kHz disc/scale data rateMax update rate (see note 1)At least 1 MHz, user dependent. See timing diagram.Auxiliary output (see note 2)Quadrature square waves plus index at disc/scale resolutionMax input cable length (see note 3)50 ft (15 m) Operating...

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 track is coded...

A GPI Virtual Absolute encoder system can be in any one of 3 distinct operating modes: Wait mode: 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 Model VB reports a fault condition while it is waiting for a full tag to be acquired. Search mode: Having acquired a complete new tag from an initialization sweep, it may be busy pinpointing the absolute position of that tag in the overall code sequence. How long this...

Outline Dimensions 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 Page 7 of 8 VB V3.1 GPIGPI > IIIIIIIIIIIIII size="-2">

OUTPUT C 3-byte-wide multiplexed output INTERP 05 5 bits of interpolation INPUT M Printed circuit board assembly onlyBoard assembly with aluminum mounting plate and standoffs Fully enclosed electronics (case grounded aluminum cover) Differential buffered sinusoids TEMP PKG 01 2 CA 0C to +70аC-40C to +85аC SF #N Issued at time of order to cover special customer requirementsNo special features > 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 V3.1