Ametek 7280 Instruction Manual page 52

Chapter 5, FRONT PANEL OPERATION
5-6
full-scale current sensitivity may be set to any value between 1 pA and 100 µA (wide
bandwidth mode), 10 fA and 1 µA (normal mode), or 10 fA and 10 nA (low-noise
mode), in a 1-2-5 sequence.
The number reported after the letters DR is the instrument's Dynamic Reserve,
expressed in decibels, as calculated by the following equation:-
DR 20 log
10
Example:-
If AC Gain = 14 dB and SEN = 2 mV then
DR 20 log
10
0.002
DR = 46 dB
TIME CONSTANT
The time constant of the output filters is set using this control, in the range 1 µs to
100 ks in a 1-2-5 sequence. Settings of 1 ms and below restrict the choice of
instrument outputs at the rear-panel CH1 and CH2 outputs to X, Y and Magnitude.
REF PHASE
This control allows the reference phase to be adjusted over the range -180° to +180°
in 1 m° steps. Adjustment is faster using the Keypad or Active Cursor controls - see
section 4.1.04.
REF PHASE ±90°
This control allows the reference phase to be adjusted in steps of ±90°.
X OFFSET and Y OFFSET
These are the manual X channel and Y channel output offset controls. The offset
levels set by these controls, which can be any value between -300% and +300% in
0.01% steps, are added to the X channel or Y channel outputs when the X channel or
Y channel offsets are switched on using the Output Channels menu. Adjustment is
faster using the Keypad or Active Cursor controls - see section 4.1.04.
The values are set automatically by the Auto-Offset function. Note that the Auto-
Offset function automatically switches on both X and Y channel output offsets.
REF HARMONIC
This control sets the harmonic of the applied reference frequency, either internal or
external, at which the lock-in amplifier's reference channel operates, in the range 1 st
(fundamental mode) to 32 nd. For example, if the control is set to 2 nd and a
reference signal of 1 MHz is applied, the instrument will measure signals at its input
at a frequency of 2 MHz.
2
ACGain (in dB)
SEN
2
14