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Service Manual

Table 2A-4. Analog Measurement Processor Pin Descriptions (2635A) (cont)

Pin

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

Name

VREF+ VREF-

RAO

RA+

RA-

AFO

MOF

AFI

FAI

FAO

RMSF AGND3 RMSG2

RMSO CAVG

VSSR RMSG1

RMSI

Description

A/D voltage reference plus A/D voltage reference minus A/D reference amplifier output

A/D reference amplifier noninverting input A/D reference amplifier inverting input

Passive filter 2

Passive filter 1 plus resistance

Passive filter 1

Filter amplifier inverting input

Filter amplifier output

RMS output, filtered

(not used, connected to filtered -5.4V dc) (not used)

RMS converter output (not used)

-5.4V dc, filtered

(not used, pulled to filtered -5.4V dc) (not used)

Two separate signal paths are used, one for dc/ohms/temperature and one for ac. The volts dc (3V range and below) and temperature voltages are coupled directly to the a/d converter, while higher voltages are attenuated first. For ohms, the dc circuitry is augmented with an internal ohms source voltage regulator controlled through an extra set of switches. For volts ac, inputs are routed through the ac buffer, which uses the gain selected by the Measurement Processor (A3U8).

The a/d converter uses a modified dual-slope minor cycle method. The basic measurement unit, a minor cycle, consists of a fixed time integrate period for the unknown input, a variable time reference integrate period, a variable time hold period, and various short transition periods. A minor cycle period lasts for 25 ms or until a new minor cycle is begun, whichever comes first.

2A-50.Input Protection

The instrument measurement circuits are protected when overvoltages are applied through the following comprehensive means:

∙Any voltage transients on channel 0 HI or LO terminals areimmediately clamped to a peak of about 1800V or less by MOVs A3RV1and A3RV2. (This is much lower than the 2500V peaks that can beexpected on 240 VAC, IEC 664 Installation Category II, ac mains.)

∙Fusible resistors A3R10 and A3R11 protect the measurement circuitryin all measurement modes by limiting currents.

∙A3Q11 clamps voltages exceeding 0.7V below and approximately 6.0Vabove analog common (LO) or LO SENSE, with A3R35 limiting the inputcurrent.

∙A3Q10 clamps voltages during ohms measurements with A3RT1, A3R34,A3R10, and A3Z4 limiting the input current. With large overloads,thermistor A3RT1 will heat up and increase in resistance.

∙A3U8 also clamps voltages on its measurement input pins that exceedthe VDD and VSS supply rails. Resistors A3R42, A3R11, A3R10, A3RT1,A3Z4, A3R35, and A3R34 limit any input currents.

∙Any excessive voltages that are clamped through A3U8 to VDD or VSS,are then also clamped by zener diodes A3VR3 and A3VR2.

2A-24

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Fluke 2625A service manual 2A-50.Input Protection, Analog Measurement Processor Pin Descriptions 2635A Name
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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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