Theory of Operation (2620A/2625A)

2

 

Detailed Circuit Description

2-44. Digital Input Threshold

2-1.

 

The Digital Input Threshold circuit sets the input threshold level for the Digital Input Buffers and the Totalizer Input. A software programmable voltage divider (A1U17, A1R35, A1R36, A1R37) and a unity gain buffer amplifier (A1AR1) are the main components in this circuit. The Microprocessor sets outputs A1U16-15 and A1U16-12 to select one of four input threshold levels. These outputs control the resistive divider (A1R35, A1R36, A1R37) via two drivers with open-collector outputs in A1U17. The voltage from the divider is then buffered by A1AR1 which sets the input threshold. Capacitor A1C29 filters the divider voltage at the input of A1AR1. Table 2-3 defines the programmable input threshold levels.

The instrument selects the +1.4V dc threshold level at power-up initialization.

Table 2-3. Programmable Input Threshold Levels

A1U16-15

0

0

1

1

A1U16-12

0

1

0

1

Input Threshold Voltage

+2.5V dc

+0.7V dc

+1.4V dc

+0.7V dc

2-45. Digital Input Buffers

Since the eight Digital Input Buffers are identical in design, only components used for Digital Input 0 are referenced in this description. If the Digital Output Driver (A1U27-

16)is off, the input to the Digital Input Buffer is determined by the voltage level at A1J5-10. If the Digital Output Driver is on, the input of the Digital Input Buffer is the voltage at the output of the Digital Output Driver.

The Digital Input Threshold circuit and resistor network A1Z1 determine the input threshold voltage and hysteresis for inverting comparator A1AR2. The inverting input of the comparator (A1AR2-2) is protected by a series resistor (A1Z3) and diode A1CR14. A negative input clamp circuit (A1Q9, A1Z2, and A1CR17) sets a clamp voltage of approximately +0.7V dc for the protection diodes of all Digital Input Buffers. A negative input voltage at A1J5-10 causes A1CR14 to conduct current, clamping the comparator input A1AR2-2 at approximately 0V dc.

The input threshold of +1.4V dc and a hysteresis of +0.5V dc are used for all Digital Input Buffers. When the input of the Digital Input Buffer is greater than approximately +1.65V dc, the output of the inverting comparator is low. When the input then drops below about +1.15V dc, the output of the inverting comparator goes high.

2-46. Digital and Alarm Output Drivers

Since the 12 Digital Output and Alarm Output Drivers are identical in design, the following example description references only the components that are used for Alarm Output Driver 0.

The Microprocessor controls the state of Alarm Output Driver 0 by writing to latch output A1U16-2. When A1U16-2 is set high, the output of the open-collector Darlington driver (A1U17-15) sinks current through current limiting resistor A1R62. When A1U16- 2 is set low, the driver output turns off and is pulled up by A1Z2 and/or the voltage of the external device that the output is driving. If the driver output is driving an external inductive load, the internal flyback diode (A1U17-9) conducts the energy into MOV A1RV1 to keep the driver output from being damaged by excessive voltage. Capacitor A1C58 ensures that the instrument meets electromagnetic interference (EMI) and electromagnetic compatibility (EMC) performance requirements.

2-15

Page 62 Page 64
Page 63
Image 63
Fluke 2625A, 2635A service manual Digital Input Threshold
Page 62 Page 64

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.
Top Page Image Contents