Fluke 5725A, Instruction Manual, Page: 64 / 196

5725A
Instruction Manual
4-6
The 5700A/5725A system uses the following method for ac amplitude control:
1. An rms thermal sensor alternately measures two signals: an unknown but adjustable
ac signal, and a known calibrated dc signal.
2. The output of the thermal sensor is measured by the adc, allowing settling time for
the sensor each time its input is changed. The ac signal is adjusted until the thermal
sensor output is the same for both signals. Thus, the dc voltage at the output of the
thermal sensor is not important, but differences in the dc voltage when the sensor
input is switched between the ac variable and dc reference are important.
To ensure safe, reliable operation, the High Voltage Amplifier is turned on in the
following sequence:
1. The 5700A Oscillator is set to the 22V range and its output is channeled to the
5725A High Voltage Amplifier on line BOOST IN.
2. Then the output of the High Voltage Amplifier is connected to the appropriate high
voltage step-up transformer (one of three).
11A Range Functional Description 4-4.
The 5725A Current Amplifier is a transconductance amplifier that has a compliance
voltage of 3.0V rms for the ac current function and 4.0V for the dc current function. The
transconductance amplifier has a gain of -5 (e.g., 1V in gives -5A out). Either the 5700A
2V range for dc operation, or the Oscillator for ac operation, drives the transconductance
amplifier. Input voltage to the transconductance amplifier comes in on BOOST IN (for
ac current) or B-FEEDBACK (for dc current) and enters the High Voltage Sense
assembly. From there it is routed to the error amplifier on the Current assembly
whenever the 5725A is in the current function. The B-FEEDBACK line returns the
current calibration amplifier output to OSC SENSE HI during ac current operation.
The following assemblies are active in the 5725A current function:
•
In the 5700A: CPU, DAC, Oscillator, Switch Matrix, Motherboard, Rear Panel
assemblies. (Plus the Oscillator assembly in the ac current function.)
•
In the 5725A: CPU, Current, High Voltage Sense, Digital, and Power Supply.