![Sense Amplifier Section](/images/new-backgrounds/15349/15349179x1.webp)
5725A
Instruction Manual
∙Serial Interface/Guard Crossing Section
The serial interface/guard crossing section consists of an
∙Analog Input Switching Section
The analog input switching section consists of a bank of relays that route ac and dc voltages and dc currents from the 5700A to various functional blocks inside the 5725A. Assemblies that receive inputs from the Analog Input Switching Section are the High Voltage Amplifier assembly (A3); the Current Amplifier assembly (A2); and the sense amplifier section of the High Voltage Sense assembly.
∙Control Section
The control section is implemented with a bank of four latches connected to the microprocessor data bus. A pair of latches with their integral drivers control relays, a pair of latches control the
∙AC Line Voltage Switching Section
The ac line voltage switching section is independent of the other five sections of the High Voltage Sense assembly. The ac line voltage section contains three switches (labeled S2, S3, and S4 on the rear panel) that configure the input to the transformer to accept one of eight nominal line voltage levels. Also included in this section are a simple unregulated power supply and a time delayed relay driver circuit. These circuits control a shunt switch around a pair of surge
Caution
To avoid meter damage, do not measure the ac line voltage section unregulated supply with a meter tied to earth ground.
Sense Amplifier Section |
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Op amp U102, transistors Q100 through Q103, and their associated parts comprise the forward gain elements of a precision ac amplifier. Since this monolithic device does not accept supply voltages large enough to accommodate output swings of ±15.6V, a quartet of discrete transistors is configured as an output stage with voltage gain. This provides the necessary output swing of 11V rms as well as limits the additional forward gain of the overall amplifier to simplify frequency compensation.
Inputs to the output voltage stage are derived from deviations of the supply current of U102 from its quiescent value. This topology depends on the increase in current from a particular power supply as the output of the monolithic op amp moves toward the value of that power supply. This increasing current develops a drop across R108 for positive output voltages or a drop across R116 for negative output voltages. These drops are amplified by Q100 and Q103. Transistors Q101 and Q102 buffer the output signal to present a low source impedance to the load.
Overall gain at low frequencies is controlled by Z100, a resistor network designed for good ac frequency response, low power coefficient, and low thermal settling time. This network provides a feedback ratio of 0.99, or a