HYDRA

Service Manual

approximately 20 kΩ. Checking resistances between any two signals (SWR1 through SWR6) verifies proper termination by resistor network A2Z1.

2-67. Display

The custom vacuum-fluorescent display (A2DS1) comprises a filament, 11 grids (numbered 0 through 10 from right to left on the display), and up to 14 anodes under each grid. The anodes make up the digits and annunciators for their respective area of the display. The grids are positioned between the filament and the anodes.

A 5.4V ac signal, biased at a -24V dc level, drives the filament. When a grid is driven to +5V dc, the electrons from the filament are accelerated toward the anodes that are under that grid. Anodes under that grid that are also driven to +5V dc are illuminated, but the anodes that are driven to -30V dc are not. Grids are driven to +5V dc one at a time, sequencing from GRID(10) to GRID(0) (left to right, as the display is viewed.)

2-68. Beeper Drive Circuit

The Beeper Drive circuit drives the speaker (A2LS1) to provide an audible response to a button press. A valid entry yields a short beep; an incorrect entry yields a longer beep.

The circuitry comprises a dual four-bit binary counter (A2U4) and a NAND gate (A2U6) used as an inverter. One four-bit free-running counter (A2U4) divides the 1.2288-MHz clock signal (E) from the microprocessor (A1U4) by 2 to generate the 614.4-kHz clock (CLK1) used by the Display Controller. This counter also divides the 1.2288-MHz clock by 16, generating the 76.8-kHz clock that drives the second four-bit binary counter (A2U4).

The second four-bit counter is controlled by an open-drain output on the Display Controller (A2U1-17) and pull-down resistor A2R1. When the beeper (A2LS1) is off, A2U1-17 is pulled to ground by A2R1. This signal is then inverted by A2U6, with A2U6-6 driving the CLR input high to hold the four-bit counter reset. Output A2U4-8 of the four-bit counter drives the parallel combination of the beeper (A2LS1) and A2R10 to ground to keep the beeper silent. When commanded by the Main Microprocessor, the Display Controller drives A2U1-17 high, enabling the beeper and driving the CLR input of the four-bit counter (A2U4-12) low. A 4.8-kHz square wave then appears at counter output A2U4-8 and across the parallel combination of A2LS1 and A2R10, causing the beeper to resonate.

2-69. Watchdog Timer and Reset Circuit

This circuit provides active high and active low reset signals to the rest of the system at a power-up or system reset if the Microprocessor does not communicate with the Display Processor for a 5-second period. The Watchdog Timer and Reset Circuit comprises dual retriggerable monostable multivibrator A2U5, NAND gates A2U6, diode A2CR3, and various resistive and capacitive timing components.

At power-up, capacitor A2C3 begins to charge up through resistor A2R3. The voltage level on A2C3 is detected by an input of Schmitt-Trigger NAND gate A2U6-12. The output of this gate (A2U6-11) then drives the active high reset signal (RESET) to the rest of the system. When the voltage on A2C3 is below the input threshold (typically +2.5V dc) of A2U6-12, A2U6-11 is high. As soon as A2C3 charges up to the threshold of A2U6-12, A2U6-11 goes low. The RESET signal drives NAND gate inputs A2U6-1 and A2U6-2 to generate the active low reset signal (RESET*) at A2U6-3.

When the RESET signal transitions from high to low (A2U5-1), the Watchdog Timer is triggered initially, causing A2U5-13 to go high. This half of the dual retriggerable monostable multivibrator uses timing components A2R2 and A2C2 to define a nominal

2-30

Page 78
Image 78
Fluke 2635A, 2625A service manual Display

2635A, 2625A specifications

The Fluke 2625A is a sophisticated data logger designed for a wide range of industrial and laboratory applications. This versatile instrument excels in capturing and monitoring temperature and voltage measurements with precision and reliability. One of its standout features is its ability to record data from various sensors, making it ideal for environments where comprehensive data acquisition is critical.

Equipped with a large LCD display, the Fluke 2625A provides clear and user-friendly access to real-time measurement data. Its graphical interface allows users to visualize trends and monitor readings easily, which significantly enhances usability. The device supports a variety of input types and can connect to thermocouples, RTDs, and other sensors, offering great flexibility for various measurement tasks.

The Fluke 2625A employs advanced measurement technologies that ensure accuracy in data logging. With a high sampling rate, it captures fast-changing signals while maintaining data integrity. The device features a built-in memory that allows for extensive logging, accommodating long-term monitoring tasks without requiring constant oversight. Users can set it to log data at specified intervals, offering customizable solutions for different monitoring needs.

Another significant characteristic of the Fluke 2625A is its robust communication capabilities. The device supports USB and RS-232 interfaces for easy connectivity with computers and other devices, making data transfer and analysis seamless. This feature is especially beneficial for users who need to compile or analyze large sets of data quickly.

Furthermore, the Fluke 2625A is designed with durability in mind. Its rugged construction makes it suitable for challenging environments, including those with high levels of vibration, dust, or moisture. This reliability ensures that the device can withstand the rigors of fieldwork while still delivering accurate measurements.

In summary, the Fluke 2625A is a powerful data logger that combines versatility, accuracy, and reliability. Its user-friendly interface, advanced measurement technologies, and robust design make it an essential tool for professionals in various industries, from manufacturing and HVAC to research and development. Whether monitoring temperature changes in a laboratory or assessing voltage levels in an industrial setting, the Fluke 2625A stands out as a trusted solution for effective data logging and analysis.