Ametek 7270 Instruction Manual page 60

Chapter 5, FRONT PANEL OPERATION
5-12
The Reference Channel menu has five controls affecting the instrument's reference
channel. Changes to the setting of these controls can be made by using the adjacent
keys.
REF SOURCE
This control allows selection of the source of reference signal used to drive the
reference circuitry, and has three settings:-
INT
The lock-in amplifier's reference is taken from the instrument's internal
oscillator. Note that this setting gives the best phase and gain measurement
accuracy under all operating conditions, and it is always to be preferred, if
possible, to design the experiment so that the lock-in amplifier acts as the source
of the reference signal.
EXT–rp
In this setting the reference channel is configured to accept a suitable external
reference source applied to the rear panel TTL REF IN input connector
EXT–fp
In this setting the reference channel is configured to accept a suitable external
reference source applied to the front panel REF IN input connector
REF HARMONIC
This control allows selection of the harmonic of the reference frequency at which the
lock-in amplifier will detect. It can be set to any value between 1st and 127th, but
most commonly is set to 1st. Note that the "2F" setting commonly found on other
lock-in amplifiers corresponds to setting this control to 2nd.
REF PHASE
This control allows the reference phase to be adjusted over the range -180° to +180°
in 1 m° steps.
REF PHASE ±90°
This control allows the reference phase to be adjusted in steps of ±90°.
Figure 5-8, Reference Channel Menu