Theory of Operation (2635A) 2A

Detailed Circuit Description

2A-62. Input Connector PCA

The Input Connector assembly, which plugs into the A/D Converter PCA from the rear of the instrument, provides 20 pairs of channel terminals for connecting measurement sensors. This assembly also provides the reference junction temperature sensor circuitry used when making thermocouple measurements.

Circuit connections between the Input Connector and A/D Converter PCAs are made via connectors A4P1 and A4P2. Input channel and earth ground connections are made via A4P1, while temperature sensor connections are made through A4P2.

Input connections to channels 1 through 20 are made through terminal blocks TB1 and TB2. Channel 1 and 11 HI and LO terminals incorporate larger creepage and clearance distances and each have a metal oxide varistor (MOV) to earth ground in order to clamp voltage transients. MOVs A4RV1 through A4RV4 limit transient impulses to the more reasonable level of approximately 1800V peak instead of the 2500V peak that can be expected on 240 VAC, IEC 664 Installation Category II, ac mains. In this way, higher voltage ratings can be applied to channels 1 and 11 than can be applied to the other rear channels.

Strain relief for the user’s sensor wiring is provided both by the Connector PCA housing and the two round pin headers. Each pin of the strain relief headers is electrically isolated from all other pins and circuitry.

Temperature sensor transistor A4Q1 outputs a voltage inversely proportional to the temperature of the input channel terminals. This voltage is 0.6V dc at 25 ºC, increasing 2 mV with each degree decrease in temperature, or decreasing 2 mV with each degree increase in temperature. For high accuracy, A4Q1 is physically centered within and thermally linked to the 20 input terminals. Local voltage reference A4VR1 and resistors A4R1 through A4R3 set the calibrated operating current of the temperature sensor. Capacitor A4C1 shunts noise and EMI to ground.

2A-63. Display PCA

Display Assembly operation is classified into six functional circuit blocks: the Main PCA Connector, the Front Panel Switches, the Display, the Beeper Drive Circuit, the Watchdog Timer/Reset Circuit, and the Display Controller. These blocks are described in the following paragraphs.

2A-64.Main PCA Connector

The 20-pin Main PCA Connector (A2J1) provides the interface between the Main PCA and the other functional blocks on the Display PCA. Seven of the connector pins provide the necessary connections to the four power supply voltages. (See the following table.)

Power Supply

A2J1 Pins

Nominal Voltage

VCC

8

+5.0V dc

VEE

6

-5.0V dc

VLOAD

7

-30V dc

FIL1 to FIL2

2 to 3

5.4V ac

Six pins are used to provide the interface to the Front Panel Switches (A2SWR1 through A2SWR6). The other seven signals interface the Microprocessor (A1U1) to the Display Controller (A2U1) and pass the reset signals between the assemblies.

2A-33

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Fluke 2625A, 2635A service manual 2A-62. Input Connector PCA, 2A-63. Display PCA, 2A-64.Main PCA Connector
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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.
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