Theory of Operation

Functional Description 2

Section 2

Theory of Operation

2.1Functional Description

The Model 943-227-15 Digital Preamplifier is an eight-decade, linear reading radiation. The preamplifier is sensitive to moisture and is mounted in a NEMA 4 sealed enclosure. The preamplifier box contains a desiccant package to remove moisture from the interior of the preamplifier. The desiccant has a color indicator to show when it should be replaced when the color changes to blue.

The detector electrometer converts the current from the detector to a voltage which is measured by the analog to digital converter of the preamplifier. Under program control, this measurement is made every 50 milliseconds on the first five decades and every 100 milliseconds on the upper three decades.

The electrometer is auto-ranging and auto-zeroing. An internal coarse zero control (factory adjusted) is provided. The microprocessor in the preamplifier performs data collection, integration and multiplication by a stored calibration factor, range changing and communication with the Model 942A-200C Digital Ratemeter or Model 960 Digital Process Radiation monitoring system.

2.2Main Circuit Boards

The wide range ion chamber detector block diagram is shown in figure 2-1. Detector electronics are contained within two circuit board assemblies located in the preamplifier enclosure: the 977-210-10 High Voltage/Communications Interface circuit board assembly and the 977-200-15 Electrometer circuit board assembly. Schematic diagrams are located in Appendix B.

The 977-200-15M Electrometer circuit board contains the microprocessor, the EPROM, the integrating electrometer, the programmable gain amplifier, the analog to digital (A/D) converter, and the auto zero DAC circuit.

The 977-210-10M Communications Interface circuit board contains the dc voltage regulator, the BDC/DC converter, the asynchronous communication interface adapter (ACIA), the Victoreen communication loop driver/receiver, the RS232 communications driver/receiver, and the communication loop fuses.

2.3 977-200-15M Electrometer

Refer to the electrometer schematic 977-200-18M located in Appendix B. Z7 is a Texas Instruments TMS 70C00 microprocessor, which is utilized to control detector operation. Z8 latches port C of the microprocessor to form the lower order bits of memory address. Z10 is a 27C64 EPROM containing the operational firmware for the detector. Z18 is an optional RAM socket which is not utilized for this model detector. Z9 is a decoder for the upper order address bits. Z11 is a latch used to store control bits to select the gain of the programmable gain amplifier formed by the combination of Z5, Z4, and RN2. Available gains are 1 through 128 in binary increments 1, 2, 4, . . . 128. Z3 is an eight-bit analog to digital converter used to digitize the output of the programmable gain amplifier. Analog switch Z17 pin 11 selects either the integrating electrometer or the high voltage sense line as the input to the programmable gain amplifier is not active in this application. Refer to Table 2-1 for preamplifier register addresses and Table 2-2 for electrometer control bit assignments.

2-1

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Fluke 943-27, 943-227-15 manual Theory of Operation, Functional Description
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943-227-15, 943-27 specifications

The Fluke 943-27 and Fluke 943-227-15 are advanced electrical testing tools designed to meet the demands of professionals in industrial and commercial settings. Recognized for their accuracy and reliability, these devices come loaded with essential features tailored to ensure optimal performance during electrical measurements.

The Fluke 943-27 is a compact yet powerful multimeter that excels in providing precise voltage and current readings. It is equipped with a large, backlit display that ensures visibility in low-light environments. The device supports a wide range of testing parameters, including AC and DC voltage, resistance, continuity, and capacitance measurements, making it invaluable for troubleshooting electrical circuits.

On the other hand, the Fluke 943-227-15 offers additional capabilities, including advanced data logging features. This multimeter allows users to record and analyze measurements over time, which is particularly useful for identifying intermittent issues in electrical systems. Its connectivity options enable seamless data transfer to a computer or mobile device, facilitating easy documentation and reporting.

Both models illustrate a robust construction built to endure tough working conditions. They meet stringent safety standards, which is critical for protecting users from electrical hazards. The ergonomic design ensures comfort during prolonged use, and features like overmolding enhance grip and durability.

One of the standout technologies in these multimeters is Fluke’s True-RMS measurement capability. This feature ensures accurate readings of non-linear loads, which are common in modern electrical systems with variable frequency drives and other electronic devices. Additionally, the built-in low-pass filter technology reduces noise in measurements, ensuring precision even in environments with significant electrical interference.

The Fluke 943-27 and 943-227-15 are also designed to be user-friendly. They feature intuitive controls and a straightforward user interface, allowing technicians to navigate functions effortlessly. The ability to perform automatic ranging simplifies measurements, eliminating the potential for errors when setting the range manually.

In conclusion, the Fluke 943-27 and 943-227-15 represent essential tools for electrical technicians who require versatility, accuracy, and durability in their testing equipment. With advanced features, reliable technologies, and a user-centric design, these multimeters not only meet but exceed the expectations of professionals in the field.
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