Novatech 409B Instruction Manual page 12

9.0 Appendix B. External Reference
Option.
9.1 The /R option converts the external clock input
to a 10.00 MHz reference input (consult factory for
5.00 MHz). This option provides locking and track-
ing circuitry to generate an exact binary clock
needed to allow even output steps.
9.2 The external clock input on the 409B series is
changed to accept 10.00 MHz. A reference input
signal is automatically detected and, if within a lock
range of approximately ±5ppm, it is locked to and
tracked by the narrow-band phase lock loop.
9.3 If an input signal is not detected, the unit will
default to the internal free-running oscillator and
perform identically to a 409B without the /R option.
9.4 The front panel LED will display four condi-
tions:
Steady Green: unit is locked to a stable refer-
ence, or is using the free running clock.
Blinking Green: unit is stabilizing to a free run-
ning condition. This occurs upon power-
up or if the reference is removed.
Steady Red: unit detects an external input, but
cannot lock to it.
Blinking Red: unit has detected a change in the
reference and is attempting to lock. This
will occur if a reference is applied to a
unit that has been free running.
9.5 When changing the reference mode, the phase
lock loop may take several minutes to stabilize to
the final resolution of the 409B. Changing from a
blinking LED to a stable LED indicates that the pro-
cess is completing, but you should verify the out-
puts.
9.6 The /R option diverts the external clock line so
the "C E" command is no longer valid. The "Kp"
command should not be used. If either command is
used with the /R option, you will get unpredictable
behavior.
NOVATECH INSTRUMENTS 12 409B Manual, 17-Apr-2015