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System description
The RGH25F encoder system consists of a common readhead in standard or UHV compatible form,
coupled to the interface, which gives accurate, industry standard outputs. There are 10 versions of the
REF interface, offering digital resolutions of 5 µm to 5 nm, and an analogue version giving 1 Vpp output.
The digital REF interfaces are available with a variety of different clocked outputs, each interface option
having a different maximum speed and minimum customer counter clock frequency, ranging from
1 to 50 MHz.
REF interface features
n
Self-tuning active correctio
The REF interface actively corrects for input signal imperfections to optimise system accuracy.
Corrections are made for the following:
Automatic Offset Control (AOC) – adjusts offset independently for the sine and cosine signals
Automatic Gain Control (AGC) – ensures consistent 1 Vpp signal amplitude
Automatic Balance Control (ABC) – adjusts the gain to equalise the sine and cosine signals
These correction mechanisms operate over the full working speed range of the readhead. The user can
disable/enable the AGC by depressing the CALIBRATE button for greater than 3 seconds.
LED indicators
The REF interface SETUP LED provides visual feedback of signal strength, error condition and reference
mark phasing, for setup and diagnostic use.
Flashing Purple indicates high signal alarm condition
Purple indicates high signal
Blue indicates optimum signal
Green indicates acceptable signal
Orange indicates low signal
Red indicates unacceptable signal
Flashing Red indicates unacceptable signal alarm condition
Flashing Blue indicates overspeed alarm condition
Red flash when traversing reference mark indicates good phasing*
Orange flash when traversing reference mark indicates poor phasing*
Blank flash when traversing reference mark indicates phasing unacceptable*
The Yellow CAL/AGC LED indicates when the REF is in the calibration routine and whether or not
AGC is active
LED on indicates AGC active
LED off indicates AGC inactive
LED slow flashing indicates calibration routine
LED fast flashing indicates calibration failure
*NOTE: Reference mark flashes only occur up to 100 mm/s traverse speed.
Alarm output
The REF interface asserts the alarm output (E) for the following conditions:-
Incremental signal level below 20%
Incremental signal level above 135%
Readhead speed in excess of specification
Signal offset compensation of sine and cosine excessive
Signal balance compensation excessive
System installation/calibration
The calibration procedure is required to optimise the gain, balance and offset of the analogue input signals
in the REF interface. These settings are then stored and recalled for initial use at startup.
To calibrate the system, the following sequence should be carried out:
} Prior to calibration, AGC should be off. To switch AGC on or off, the CALIBRATE button should be
pressed for more than 3 seconds. When AGC is on, the CAL/AGC LED will be on and when AGC is off,
the CAL/AGC LED will be off.
} Install the readhead according to the readhead installation section below.
} Enter the calibration routine by pressing the CALIBRATE button momentarily. The calibration routine is
indicated by slow flashing of the CAL/AGC LED.
} Traverse the readhead slowly past the scale until the CAL/AGC LED stops flashing. The calibration cycle
is now complete.
>135%
If calibration fails, the CAL/AGC LED will flash quickly instead of switching off. If this happens the
CALIBRATE button should be pressed momentarily to exit the calibration routine. The calibration procedure
>110% and <135%
should then be re-tried.
>90% and <110%
If the unit continues to fail calibration, factory default settings should be restored by powering down, then
>70% and <90%
pressing the CALIBRATE button as power is re-applied. The calibration procedure should then be repeated.
>50% and <70%
NOTE: To exit the calibration routine at any time, the CALIBRATE button should be pressed momentarily.
>20% and <50%
<20%
If fitted, the reference mark should be phased (see reference mark phasing)
Mounting brackets
The bracket must have a flat mounting surface, enable conformance to the installation tolerances,
allow adjustment to the rideheight of the readhead, and be sufficiently stiff to prevent deflection of the
readhead during operation. For easier installation, adjust the roll and yaw of the bracket with respect to
the axis of readhead travel before the readhead is attached. This can be done with a clock gauge and a
precision square.
Readhead installation
To set nominal rideheight, position readhead spacer with ' L ' shaped aperture under the optical
centre of the readhead to allow normal LED function during set-up procedure. Ensure that the scale,
readhead optical window and mounting face are clean and free from obstructions.
NOTE: Ensure readhead fixing screws are tightened to 0.5 Nm-0.7 Nm.
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