Theory Of Operation - Emerson Rosemount Ultrasonic 3107 Quick Start Manual

July 2016
Overview of the Rosemount 3107 and 3108
The Rosemount 3107 and 3108 are sealed 4–20 mA loop-powered liquid level
transmitters, specifically designed for use in waste water and effluent treatment plant
on aqueous applications.
These rugged UPVC transmitters are certified Intrinsically Safe for use in Zone 0 areas,
and factory fitted with up to 165 ft. (50 m) of two-core cable for simple low cost
installation in sumps, wet-wells and over open channel flow structures.
The transmitter may be mounted in a hazardous area if powered from a protected
power supply. They can be connected directly to a plant control system, or used with a
Rosemount 3490 Series Control Unit for programmable control functionality.

Theory of operation

Each transmitter is designed to be mounted above a liquid, and uses ultrasonic pulses
to continuously measure the distance to the liquid surface. The
microprocessor-controlled electronics calculates distance to the liquid level from the
time delay between the transmitting and receiving of signals.
When programmed with the bottom reference of the application – usually the bottom
of a tank – the transmitter will calculate the liquid depth (level), and output the level
(Figure 1) as a 4–20 mA signal and a digital HART
The 3107 and the 3108 can also calculate contents (volume) or open channel flow, and
then output the result as a 4–20 mA signal and a digital HART signal.
Programming is achieved by remote communication using HART.
Figure 1. Typical application
F
A. Rosemount 3108 Flow Transmitter
B. Rosemount 3490 Series Control Unit
C. 4–20 mA signal output
D. Relay
E
20mA
4mA
®
signal.
G
A
E
E. Pump
F. Transmitter Bottom Reference
G. 4–20 mA and HART signal input
Quick Start Guide
B
C
D
D
3