Varec 4000 - Manual (Page 47)

37
4000 Theory of Operation
7 Theory of Operation
7.1 Overview
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.
Figure 7-1: ATT Block Diagram Table
7.2 CPU 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.
To ATTI
Bus
and
Handheld
Interface
To
Host
Interface
Interface Module
Assembly
Mark/Space
EIA-485
TIWAY
Plug-In Communications Board
Shielded Counter Section
Battery and Power
Monitor
Check Disk Signal
Shaft Input connected to
Model 2500
Check disk
4 slots
Increment disk
128 slots 3 Volt Lithium
cells
Batteries
-
8031
Micro-
Processor
HART Bus
Interface
Circuit
HART
Modem
2 K
RAM
CPU Board
64 K
EPROM
Signal
Conditioning
Increment
Detector
Logic
16-Bit
Binary
Up-Down
Counter
Dual
Sensor
Board
Single
Optical
Sensors
Count
Power-
Down
Isolation
I/O
Ports
LED Power
Power
Switching
Circuits
+
Current
Controlled
Switching
Power
Supply
L&J Tankway
Whessoe Bus Current loop
Mark Space Matrix
GPE Current loop