Gurley Precision Instruments VJ User manual

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Gurley
Precision Instruments
VJXXXXXXXXN
S.N.
xxxxxxx
Model VJ
Virtual Absolute Interpolating Decoder
USER'S MANUAL
REV 6 JULY 12, 2 16

2
Overview
The model VJ Interpolating Decoder is designed to be used with the Gurley
77 A 2 48R12U or 77 A 1 24R12U read heads. The VJ will decode absolute
position from a Virtual Absolute disk ( 1 or 11 bits) and interpolate the analog signals
to get an additional 8 bits of resolution for a total of 18 or 19 bits. Data is read over a
serial RS422 interface. The interface can be used as standard SSI with a single input
CLK signal (differential pair) and single output DATA signal (differential pair). There is
an optional Sync input (differential pair) that allows for compatibility with other common
serial interfaces.
SPECIFICATIONS
POWER: 5. VDC @ 15 mA Min = 4.75 VDC, Max = 5.25 VDC
INPUT: 1-2 µA photocurrents from 77 A read head
RESOLUTION:
VJ1 = 262144 measuring steps
VJ11 = 524288 measuring steps
TEMPERATURE RANGE:
Code C = to 7 C
Code A = -4 to 85 C
OUTPUT INTERFACE:
CLOCK = RS-422 input
DATA = RS-422 output
SYNC = RS-422 input (optional)

3
Figure 1: Board Layout
GND
VCC
R -Reference
S -Sine
C -Cosine
I -Index
A -
Interpolated Sine
B -
Interpolated Cosine
Z -Digital Index (Code track)
Y -Digital Cosine (1X)
X -Digital Sine (1X)
S - Data valid when high
GND
J2
OUTPUT CONNECTOR
J1
INPUT CONNECTOR
LED D1
DIGITAL TEST POINTS
ANALOG TEST POINTS
INSTALLATION
Connect a 77 A readhead to connector J1. Power and RS-422 serial interface is
provided by J2. See Figure 2 and Table 1.

4

5
FIGURE 2: Output connector J2
1
2
3
4
5
6
7
8
9
TABLE 1: J2 connector definition
PIN NAME DESCRIPTION
1 VCC 5Vdc power input.
2 -SYNC Optional RS422 input .
3 -CLOCK RS422 input, SSI clock.
4 +CLOCK RS422 input, SSI clock
5 CHASSIS Chassis or shield connection
6 GND power and signal ground
7 +SYNC Optional RS422 input .
8 -DATA RS422 output, SSI Data
9 +DATA RS422 output, SSI Data
The serial interface timing is shown in figures 2 and 3. Figure 2 shows standard SSI
timing. The Sync input can be left disconnected or set to logic 1. (+SYNC voltage greater
than -SYNC voltage). Figure 3 shows the timing when using the optional Sync pulse.
Data is sampled on the falling edge of SYNC.

6
FIGURE 2: SSI timing diagram
STA DMSB DMSB-1
PARITY
Flag1
Flag2
Flag3
DLSB
CLOCK
DATA
Tcd
Tclk
T
wait
Tm
SYMBOL
DESCRIPTION
MIN TYP MAX UNITS
Tclk
Tcd
Clock period 0.3 15 uSec.
Clock to Data Valid
200
1
100
Tm
Monostabe time 16 20 25 uSec
T wait
Wait Time 0
uSec
Tc
Tcl
Clock ig time 120 nSec.
Tcl
Clock low time 120 nSec.
FIGURE 3: Timing diagram when using optional SYNC input
STA
D
MSB
D
MSB-1
PARITY
Flag1
Flag2
Flag3
DLSB
CLOCK
DATA
STA
Tcd
Tclk
Tsc
Tsync
SYMBOL
DESCRIPTION
MIN TYP MAX UNITS
Tclk
Tsc
Clock period
0.3
uSec.
nSec.
1
100
Tcd
Clock to Data Valid
200 nSec
Tsync
Sync Pulse widt 100
nSec
100
SYNC
Clock ig time 120 nSec.
Tcl
Clock low time 120 nSec.

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There 77 read head and disk should be installed according to their manual. It may be
necessary to slightly adjust the alignment of the readhead to get the signals in proper
phase shown in Figure 5. The Index signal should be at its minimum or maximum level
when the cosine signal is at it minimum. The simplest ( but not the best way) to make the
adjustment is to slightly move readhead until the LED D1 remains lit without blinking,
when slowly rotating the disk. A better method is to monitor the voltage on Testpoint U
and adjust the read head position until this voltage is at maximum. This pin will be at a
high voltage ( about 3.3V) when Index transitions occur within +/- 45 degrees of
optimum. You can also observe the signals shown in Figure 5 on an oscilloscope while
adjusting the head.
FIGURE 4: Read head and disk.
FIGURE 5: Analog test point signals. C,S,I, and R. (Reverse Direction show)

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DATA OUTPUT FORMAT
Data is output serially with the first bit being status (STA). The status bit is high when
virtual absolute position is not known. After a small initial movement the status bit
should go low and stay low. The second bit is the MSB of the position word. Following
the LSB of the position word are three flags bits. Flag 1 goes high when a decoding error
occurs. Flag 2 goes high when either the analog signal amplitudes become too low ( Sin
or Cosine < 1Vpp) or the Index signal transitions are occurring in the wrong place. Flag
3 goes high when a quadrature error is detected. This occurs if SIN and COS states
change by more than 9 degrees between a sample. A flag bit is set by an error and will
be held until a read is completed. The next bit is a parity bit. The parity of all the bits is
odd.
TABLE 2: Data format
BIT POSITION BIT NAME DESCRIPTION
Bit 1 STA VA Decoder Status Bit.
Bit 2 thru Bit (n+1) DMSB..DLSB Position bits.
Bit (n+2) Flag 3 Quadrature error.
Bit (n+3) Flag 2 Signal quality watchdog.
Bit (n+4) Flag 1 VA decoder error.
Bit (n+5) Parity Parity bit. Parity is odd.
Bit (n+6) ( bit) Trailing zero bit.
* n is the number of position bits

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WARRANTY AND RETURN POLICY
Gurley Precision Instruments (GPI) does not warrant that the hardware will work
properly in all environments and applications, and makes no warranty and representation,
either implied or expressed, with respect to the quality, performance, merchantability, or
fitness for a particular purpose of any software or documentation. GPI reserves the right
to make changes to the hardware and to User's Manual content without obligation to
notify any person or organization of the revision or change.
GPI warrants its products to conform to their published specifications and to be free from
defects in material and workmanship for a period of one year from date of shipment. This
Limited Warranty is extended to the original end user and covers parts and labor. Any
product returned under warranty is subject to inspection and testing at GPI. User must
return the product, freight prepaid, to the factory. GPI, at its option, will repair or replace
any product found defective, free of charge. Return freight charges are collect to the user.
This warranty is void if damage was caused by unreasonable or improper use, including
failure to comply with manufacturer's installation and operation instructions. Damage
from shipping is specifically excluded from warranty.
This warranty is exclusive and GPI makes no other representation of any other kind,
expressed or implied, with respect to the product, including its merchantability or fitness
for a particular purpose. Buyer's exclusive remedy to claims arising under this Warranty
shall be the repair or replacement of the product, or damages which will not exceed the
purchase price of the product. In no event, including claims of negligence, shall GPI be
liable for incidental or consequential damages.
All brand and product names are the trademarks of their respective owners.
As part of our continuing effort to improve our customer service, we have established an
RMA NUMBER SYSTEM for returned goods. If you have to send any products to us
for any reason, please observe the following procedure:
1. Before you ship us anything, call your salesperson for an RMA number. Please have
the model and serial number available.
2. Make sure your product is properly packed so it is not damaged in shipment.
3. Before you seal the box, write the RMA number on a piece of paper and put it inside
the box so it’s the first thing we see when we open it.
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a black felt-tipped marker.
5. If you contact us about the returned item or items, please refer to the appropriate
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Thank you for your cooperation.