Varec 4000 manual Theory of Operation, CPU Board

4000 Theory of Operation

7 Theory of Operation

7.1Overview

The Advanced Technology Transmitter (ATT) represents a flexible system for use in liquid level measurement and/or other measurement applications.

The Advanced Technology Transmitter (ATT) collects measurement information from compatible devices and transmits this information over a field communications bus.

Check disk
4 slots			Batteries
Increment disk
128 slots			3 Volt Lithium
			cells
Shaft Input connected to			-
Model 2500			+
					CPU Board
				LED Power	Current
					Controlled
Dual		Single			Switching
					Power		64 K
					Supply
	Optical					EPROM
Sensor	Sensors
Board			Power				2 K
			Switching				RAM
			Circuits
	Signal
	Conditioning		Battery and Power
			Monitor
			Check Disk Signal					HART Bus	To ATTI
					8031			Interface	Bus
								Circuit	and
					Micro-				Handheld
					Processor				Interface
Increment		16-Bit	Power-		I/O
			Down
Detector		Binary	Isolation		Ports
	Logic	Up-Down						HART
		Counter		Count
								Modem
	Shielded Counter Section
					Interface Module
					Assembly		To	L&J Tankway
								Whessoe Bus Current loop
					Mark/Space		Host
								Mark Space Matrix
					EIA-485		Interface	GPE Current loop
					TIWAY
					Plug-In Communications Board

Figure 7-1: ATT Block Diagram Table

7.2CPU Board

The ATT uses the Phillips 80CL31 CPU with 64K of ROM and 8K of RAM.

The microprocessor assembly contains the CPU, power supply, and interfaces necessary to manage operation. The power conditioning circuitry also detects a battery low condition.

The CPU monitors the count maintained in a 16-bit register. The register stores pulse information from the sensor assembly. A check disk pulse from the sensor assembly is used to verify the count at 1/4 of a disk revolution. The CPU maintains an absolute level measurement based on the level calibration count provided by the ATT and the count provided by the count register. Circuitry is provided to monitor the health of the back-up battery. When the battery voltage indicates the battery is near the end of its life, the CPU transmits a battery low indication to the ATT.

The power supply converts input power from the ATTI bus into the voltages necessary for normal encoder operation. The power supply limits input current from the ATTI bus to 8 mA.

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