Cleverscope CS300 Reference Manual v2.11
Page 96 www.cleverscope.com ©Cleverscope 2004-2015
17 Frequency Response Analyser FRA [View Menu]
The Cleverscope Frequency Analyser (FRA) is a tool set you can use to measure Power Supply performance
(Gain/Phase response, Input and Output impedance and Power Supply Rejection Ratio) and the impedance and
phase of Power input filters, feedback networks, transformers, PCB power planes, and the LCR values of
capacitors, resistors and inductors. It can be used for both narrow band swept frequency measurements, and
wideband single shot spectral measurements. Values can be displayed in ohms, Farads, Henry's and degrees or
radians.
Measuring the performance of switched mode power supplies using traditional methods is difficult because of
the switching noise generated by the supply. The FRA uses narrow band frequency domain measurements to
synchronously measure the signal generator stimulus and response without being affected by the switching
noise. This makes possible the use of low amplitude stimulus signals which do not interfere with the normal
working of the power supply - the supply can be measured loaded, and in use.
The FRA is equally useful for measuring the impedance and phase of components such as capacitors, inductors,
PCB power planes, transformers, filters and resistors. The gain/phase function can be used to measure the
response of networks such as filters, amplifiers, transformers, and mechanical systems.
The FRA is based on a standard CS320A/CS328A oscilloscope, with a CS701 isolated sig generator plugged in..
The CS701 has 300V Class II reinforced isolation, a capacitance of 16 pF to ground when mounted in the
CS328A, and negligible series inductance. The CS701 has a frequency range of 0 - 65 MHz, and includes DC
offset. For Power Supply work an isolation transformer is not required. The isolation transformer has a more
limited frequency range, and introduces higher parasitic capacitance and inductance. The CS701 can be used
for Gain/Phase, and low current PSRR measurements. It can be safely used on Mains power supplies up to 230
VAC.
To measure high current PSRR, or find the Input or Output Impedance and phase of live power supplies you
will also need the CS1070 power amplifier. It has a 1A capability from -18 to +36V, with a frequency range of 0
- 52 MHz. It can be operated isolated, with care!
You can use the existing CS700A for FRA work, but it is not isolated and so cannot be used for PSU
Gain/Phase, and has a more limited frequency range of 0 - 10 MHz.
The FRA is useful for measuring the performance of Power Factor Correction controllers (0.1- 2 Hz), switched
mode PWM power controllers (10 - 500kHz), effects of line frequency and harmonics (50 - 10 kHz), PWM
Switching Frequency analysis (100k - 2 MHz), EMC (300k - 100 MHz), and LC/Transformer and filter
resonances on the power supply voltage rail.
This frequency range is also useful for characterizing anything from power supply bulk capacitors (0.1 - 1000
Hz), to small pF capacitors, nH inductors and ferrite beads at up to 65 MHz.
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