Fluke 5725A instruction manual 4-3.1100V AC Range Functional Description

Theory of Operation 4

Overall Functional Description

∙11A DC Function:

The 11A dc function is implemented with a transconductance (voltage in/current out) amplifier with a gain of -5. If the 5700A outputs -2V into the 5725A, the 5725A output is 10A. (This is transparent to the user.) The output range is 0 to 11A. The 5725A delivers amplified current to either the front or rear panel binding posts of the 5725A, depending on an internal hardware setup. Reconfiguration requires removing the covers, and is described in Section 6.

∙11A AC Function

The 11A ac function is similar to the 11A dc function. The frequency range is 40 Hz to 10 kHz. The output range is 1 to 11A rms. As in the dc current function, all outputs from the 5725A either go through the front or rear panel of the 5725A. Input to the 5725A comes from the 5700A Oscillator assembly.

4-3. 1100V AC Range Functional Description

The 5700A Oscillator assembly generates the driving ac voltage, then sends it to the 5725A Power Amplifier for amplification. The 5725A returns an attenuated feedback voltage for output correction. The final output voltage is kept accurate by the high voltage sense amplifier and a real-time, software-controlled feedback loop within the 5700A, incorporating a 5700A ac/dc thermal rms converter. The 5700A Oscillator, DAC (digital-to-analog converter), and ac/dc thermal rms converter work together with the 5725A Power Amplifier and high voltage attenuator circuits to produce the desired output.

Active assemblies in the 5725A ac voltage function are as follows:

∙In the 5700A: CPU, DAC, Oscillator, Oscillator Control, High-Resolution Oscillator, Switch Matrix, Motherboard, Rear Panel assemblies.

∙In the 5725A: CPU, High Voltage Amplifier, High Voltage Sense, Signal Transformer, Power Supply, Digital, and Interconnect assemblies.

When an ac voltage in the 220 to 1100V range is selected, the 5700A calls the 5725A amplifier and leaves its own high voltage amplifier dormant. The 5725A takes over the 1100V ac range automatically. The 5725A produces ac voltage in the following sequence:

1.The 5700A sets the Oscillator assembly to the proper frequency and amplitude. The 5700A sets the initial amplitude using an 8-bit resistive hybrid dac located on the Oscillator amplifier assembly, yielding an Oscillator output accuracy of about 0.5%.

2.Next, the 5725A Power Amplifier amplifies this signal by -100 and returns an accurately attenuated signal to the 5700A.

3.The 5700A thermal sensor and adc (analog-to-digital converter) monitoring system fine tune the Oscillator amplitude. The DAC assembly output is switched directly to the Oscillator assembly, controlling the dac output amplitude. AC voltage calibration constants stored in the 5725A determine the 5700A DAC voltage setting.

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