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Chapter 1. Features and Capabilities
Transport® Model PT878 Portable Liquid Flowmeter User’s Manual 3
1.2.2 Electronics Package
The PT878 consists of circuits that generate, receive, and measure the travel
time of the ultrasonic pulses. It also contains a microcomputer that controls
operation and calculates flow measurement parameters. Specific circuits
function as follows:
• TRANSMIT SIGNAL GENERATOR - The transmit signal generator,
under control of the microcomputer and timing circuit, synthesizes the
signal that drives the transmitter.
• TRANSMITTER - The transmitter amplifies the signals from the
transmit signal generator to a signal that drives the transmit transducer.
• RECEIVER - The receiver amplifies the received signals to a level
suitable for the data acquisition circuitry.
• DATA ACQUISITION - The data acquisition circuitry digitizes the
received signal and stores it in a buffer for processing by the
microcomputer.
• TIMING CIRCUIT - The timing circuit generates the transmitter
frequency, receive window, controls the data acquisition circuit and the
direction of the transmission.
• MICROCOMPUTER - The microcomputer controls the PT878
flowmeter’s operation and calculates flow measurements derived from
the transmitted and digitized received signals. Also, the microcomputer
continually checks for faults and allows the use of built-in diagnostics for
troubleshooting.
• INPUT/OUTPUT - The input/output circuitry allows the flowmeter to
indicate the measured flow with the 0/4-20 mA current loop, and to
output to a printer or other remote device. The digital output supports
frequency or pulse output, as well as use as a gate input; it can also act as
a test point for triggering an oscilloscope from the transmit or receive
window.