NF FRA5022, Instruction Manual

Page: 75 / 145

4.5 Servo System Measurement
FRA5022
4-11
■
Measurement voltage range magnification
FRA5022
’ s internal oscillator has a dialectic voltage of 42Vpk against the case. It is thus
possible directly input a signal with an electric potential of up to about
±
40V to the
circuit.
On the other side, the analyzer input voltage range is limited to
±
10V. It is not possible to
measure directly when a signal exceeds this range. Even in such cases, it is possible make
measurement by means of other methods like attenuate a signal with an attenuator or
shift the analyzer ground electric potential to an external circuit. In the case a signal is
attenuated it becomes necessary to compensate the frequency response for this
attenuation.

“4.7 Equalizer”
Figure 4-8 Measurement voltage range magnification example
4.7k
Ω
4.7k
Ω
Signal input
FRA
CH1 or CH2
input
R
1
R
2
±
10V
±
20V
150pF
Coaxial cable
1m
Characteristic impedance
50
Ω
When the signal source impedance is sufficiently low, if the
parallel values of R
1
and R
2
are set below a few k
Ω
, the
errors can be reduced.
When changing the attenuation ratio it is set to C
1
R
1
≒
R
2
C
2
. Here, C
2
= cable capac FRA input capacitance.
In the case of a 1m coaxial cable of 50
Ω
, C
2
= about 150pF.
The higher the parallel values of R
1
and R
2
and the higher
the frequency, the bigger will be the errors. Use
attenuation only after evaluating thoroughly the general
accuracy.
C
1
Power for the shift can be a battery with
low internal resistance.
When the signal level difference is big,
split the shift power for CH1 and CH2 to
prevent inter-channel interference.
Do not apply to locations where the
original voltage exceeds
FRA5022
’ s
non-destructive maximum input voltage,
±
24V.
Signal input
FRA
CH1 or CH2
input
±
10V max
0 - 20V
10V
Power for shift