4.4 P
ARAMETER
SETTINGS
4.4.1 T
IME
CONSTANT
This option selects the used time constant
t
for the low-pass filter. If applicable, the closest
approximation of the digital equivalent to an analogue Butterworth filter is used. The corner
frequency of the Butterworth filter is 1/
t
.
4.4.2 R
OLL
O
FF
The meaning of the "RollOff" is shown in the curves in this
. It equals the degree of the
lowpass filter. One can chose between 6 dB/oct (1
st
order), 12 dB/oct (2
nd
order) and 24 dB/oct (4
th
order).
4.4.3 D
YNAMIC
This switches the input amplification of the LockIn. With "high" dynamic, input amplification is 1.
The maximum signal amplitude is then +/-10 V. The "normal" input amplification is 10, which
equals maximum signal amplitudes of +/- 1 V. When the low dynamic is chosen, the resolution of
the LockIn is highest, but the signals cannot exceed 100 mV.
4.4.4 C
OUPLING
If the specification of the instrument allows it, this option switches between DC coupled input and
AC
coupled input. Note: The 3dB corner frequency of the input high pass is around 2Hz. Reference
frequencies around 2 Hz and below may cause misleading results.
4.4.5 T
HE
M
ETERS
The meters display the LockIn output channels, which are X and Y as well R and Phi, in physical
units.
Manual Anfatec PCI-Lockin Amplifier AMU2.4 – Rev. 1.10 dated 30/09/20
Page 18 (70)
Figure 8: Effect of different time constants.
