Theory of Operation 4

Detailed Circuit Description

Error Amplifier Section

The error amplifier section contains three differential amplifiers and a precision high-current shunt resistor. Two differential amplifiers set the gain and uncorrected frequency response of the current amplifier. The remaining differential amplifier is used during the internal portion of 5700A/5725A calibration and during ac current operation.

Output Section

The output section contains several power transistors, a heat sink, two operational amplifiers, a current buffer amplifier, two current sensing resistors and related

components. The output stage is driven by the error amplifier section, converting a

±3V signal into a ±15A signal. The output section is powered by floating supplies that are referenced to the ICOM current common. The output stage is designed to drive inductive loads.

Monitor Section

The monitor section contains several op amps and comparators, and a thermistor. A temperature monitor circuit observes the temperature of the voltage output transistors. Excessive output compliance voltage is detected by the drive monitor circuit. Both monitor circuits send scaled voltages to a multiplexed comparator on the High Voltage Sense assembly (A6), where abnormal operating conditions are detected.

Control Section

The control section contains nine relays, a latched relay driver, several transistors, and a quad comparator. The relays and transistors switch the Current Amplifier into ac current and dc current operating states, a standby state, and several self calibration and diagnostics states during which 5725A operation is monitored and characterized by measurement circuitry and software residing in the 5700A.

Power Supply Section

The power supply section contains two bipolar power supplies. Regulated ±20V supplies and unregulated ±12V supplies are referenced to ICOM and power only the

output section. The error amplifier section and control section are powered from the

±15V and +5V 5725A system supplies.

Error Amplifier Section

4-35.

Refer to page 1 of the Current Amplifier schematic. Components U201, Z201, R235, C230, and Q211 make up the "outer loop error amplifier," a differential amplifier with high common-mode rejection ratio. The outer loop error amplifier controls a first-order feedback loop that determines the dc accuracy and uncorrected ac frequency response of the current amplifier. Q211 shuts off the outer loop error amplifier during standby and, through modulation of its channel resistance by R255 and C210, yields a soft-start transition into the operate modes.

Components U202, R232, R241, R251, R252, R234, C213, and Q213 comprise the inner loop error amplifier. The inner loop error amplifier works with the outer loop amplifier in a second-order feedback loop that significantly diminishes the effects of output stage non-linearities. Q213 reduces the inner loop gain during standby.

Refer to page 2 of the Current Amplifier schematic. Resistor R272 is a specially constructed 0.02Ω shunt resistor that senses the Current Amplifier output. U208 and Z203 comprise a gain of ten differential amplifier called the calibration amplifier (Cal Amp). The calibration amplifier scales the voltage dropped across R272, creating a signal

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Fluke 5725A instruction manual Error Amplifier Section

5725A specifications

The Fluke 5725A is a high-performance, multifunctional temperature calibration source designed to meet the demanding requirements of laboratory and industrial environments. Renowned for its accuracy, reliability, and versatility, the 5725A serves as a powerful tool for engineers and technicians engaged in temperature calibration processes.

At the core of the 5725A is its advanced measurement technology, which allows for precision temperature calibrations across a wide range. With an operating temperature range from -200°C to 660°C, it caters to various applications, making it suitable for calibrating thermocouples, resistance temperature detectors (RTDs), and other temperature measurement devices.

One of the standout features of the Fluke 5725A is its outstanding accuracy, boasting a specified uncertainty of just ±0.15°C. This level of precision ensures that users can maintain compliance with regulatory standards and regulatory requirements in fields such as aerospace, pharmaceuticals, and manufacturing.

The Fluke 5725A is equipped with dual-channel capabilities, allowing users to calibrate two devices simultaneously. This enhances productivity by minimizing downtime and optimizing workflow efficiency. The intuitive touchscreen interface simplifies operations, enabling users to view measurements, set up test parameters, and access historical data with ease.

Versatile connectivity options such as USB and Ethernet enable seamless integration into existing systems and allow for data transfer, remote control, and configuration. This feature empowers technicians to conduct calibrations efficiently, whether on-site or remotely.

The robust design of the Fluke 5725A ensures its durability in demanding environments. Built with high-quality materials, it is resistant to shocks and vibrations, making it suitable for use in manufacturing plants and laboratories where equipment may be subjected to harsh conditions.

Another notable characteristic of the 5725A is its ability to generate stable temperature outputs with minimal drift, contributing to consistency in calibration results. Its built-in self-test functionality helps ensure that the unit remains in peak operating condition, giving users confidence in their calibration processes.

In summary, the Fluke 5725A is a top-tier temperature calibration source that excels in accuracy, reliability, and user-friendliness. Whether in laboratory settings or industrial applications, its advanced technologies and features make it an essential tool for professionals tasked with maintaining precision in temperature measurements.