Ohms Simplified Schematic | Fluke 2625A, 2635A instruction

Theory of Operation (2620A/2625A)	2
Detailed Circuit Description

	OHMS
	VOLTAGE
	SOURCE
	IX
					LOW
	+	A3Z4	RREF		A/D
	+	A3Z4	RREF		INTEGRATE
VR REF		REFERENCE			INTEGRATE
VR REF		REFERENCE			REFERENCE
	–	RESISTOR			REFERENCE
		RESISTOR
				A3R34
					HIGH
A3K16
A3RT1 & A3R10
	A3R11
	HI			A3R42	HIGH
	HI	A3K17		PASSIVE	HIGH
		A3K17		FILTER
				FILTER
	+	R X
VR X		R X			A/D
VR X		UNKNOWN			A/D
	-	UNKNOWN			INTEGRATE
	-	RESISTOR			INTEGRATE
		RESISTOR			UNKNOWN
					UNKNOWN
	LO				LOW
					LOW
VR X	IX•RX		RX
VR REF	= IX•RREF =		RREF
					s5f.eps

Figure 2-5. Ohms Simplified Schematic

The reference resistor for the 300-kΩ, 3-MΩ, and 10-MΩranges is the 1-MΩresistor in A3Z4, which is selected by S15. The voltage across this reference is integrated during its own minor cycle(s) and is switched to a passive filter and the A/D Converter by switches S1 and S18.

When 4-wire measurements are made on any of the six ranges, separate Source and Sense signal paths are maintained to the point of the unknown resistance. The 4-wire Source path measurement current is provided by the A3U8 ohms source through one of the A3U8 internal switches (S6, S9, S13, or S15) and the appropriate reference resistor in A3Z4. The current flows through relay A3K16, thermistor A3RT1, resistor A3R10, the HI Source instrument relay contacts (A3K1 - A3K3, A3K5 - A3K14), and the HI Source lead wire, to the unknown resistance to be measured. The current flows back through the LO Source lead wire, the LO Source path of the instrument relays (A3K1 - A3K3, A3K5 - A3K14), resistor A3R43, and analog ground, to the A3U8 ohms source.

The voltage that develops across the unknown resistance is sensed through the other 2 wires of the 4-wire set. HI is sensed through the HI Sense path made up of the users HI Sense lead wire, the HI Sense contacts in the instrument relays, resistor A3R11, relay A3K17, resistor A3R42, and Analog Processor A3U8 switch S2. LO is sensed through the users LO Sense lead wire, the LO Sense contacts in the instrument relays, protection resistor A3R35, and A3U8 switch S19.

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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.

Fluke 2625A, 2635A service manual Ohms Simplified Schematic

Models: 2635A 2625A

Figure 2-5. Ohms Simplified Schematic

2635A, 2625A specifications