Catalog excerpts
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. > 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 photocurrentsUse with encoder model9710 modular rotary or linearMax code length on disc or scale12 bits (4096 cycles). See 9710 data sheet.Interpolated resolution2 or 8 bits (4 or 256 steps per optical cycle)Max final resolution20 bits (1,048,576 steps)Absolute outputNatural binary byte-wide multiplexedMax input frequency10 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 VA 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 VA V3.1 GPIGPI > IIIIIIIIIIIIII size="-2">
(Final system resolution in bits = > CODE + > INTERP ) OUTPUT C 3-byte-wide multiplexed output INTERP 0208 2 bits of interpolation8 bits of interpolation INPUT A Printed circuit board assembly onlyBoard assembly with aluminum mounting plate and standoffs Fully enclosed electronics (case grounded aluminum cover) Differential photocurrents TEMP PKG 01 2 CA 0C to +70аC-40C to +85аC (available with > INTERP = 02 only) SPEC #N Issued at time of order to cover special customer requirementsNo special features > SPECIAL CAPABILITIESWARRANTY Gurley Precision Instruments514 Fulton StreetTroy, NY...
