NF FRA5014, Instruction Manual

Page: 45 / 107

4.2 Servo System Measurements
FRA5014 4-3
4.2 Servo System Measurements
With the FRA5014
’s oscillator inserted in a control loop, servo system loop gain A

is able to be
determined by measuring the previous and subsequent signals V
1
and V
2
.
Figure 4-1. Connections for Servo System Measurement
⚫
If the control loop is cut off, a large output may occur, which could damage the system
under test and/or pose hazards for users. Always use a signal injection resistor so that the
control loop is not left open when the
FRA5014
’s oscillator is disconnected. This resistor
should be attached securely so it does not come loose.
⚫ If the injected signal’s level (AC amplitude, etc.) becomes too high, a large output may
occur, which could damage the system under test and/or pose hazards for users. To ensure
safety, always start with a low signal level and raise it gradually.
⚫
When connected to the FRA5014 , the system under test may have abnormal operations due
to oscillation, etc. The analyzer’s input and the oscillator’s output each have several
hundreds pF of floating capacitance (capacitance with the case), and when combined with
the floating capacitance of the connecting cable, it can cause instability in the system under
test.
The
FRA5014
’s maximum output current is

100 mA.
Unless there is a major impact on the characteristics of the system under test, the signal
injection resistor that is inserted into the circuit should be rated at 50 Ω or higher. During
measurements, a value that is parallel to this resistance value and the oscillator’s output
resistance (50 Ω) is inserted into the control loop. If inserting a lower resistance value, set
the AC amplitude and/or the DC bias to keep from exceeding the maximum output current. A
safe setting is one that prevents the combined peak value from exceeding

5 V.
(OSC: OSCILLATOR)

A
V
1
V
2
CH1 CH2 OSC
FRA
SUT : System Under Test
A

= V
2
/ V
1
Resistor
Resistor for signal injection
CH3 CH4
！
WARNING
！
CAUTION