Theory Of Operation - Emerson Rosemount 3101 Quick Start Manual

September 2018
The Rosemount 3101, 3102, and 3105
The Rosemount 3101, 3102, and 3105 are 4–20 mA loop-powered level
transmitters designed for continuous liquid level measurements in tanks or
open flow channels.
They can be connected directly to a plant control system, or used with a
Rosemount 3490 Series Control Unit for programmable control functionality.
The Rosemount 3105 may be mounted in a hazardous area if powered from a
protected power supply.
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Theory of operation

The 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
and outputs the level as a 4–20 mA signal (and a digital HART
3102 and 3105).
The 3101 measures level only. The 3102 and the 3105 can calculate
distance-to-surface, contents (volume), or open channel flow, and then output
the result as a 4–20 mA signal and a digital HART signal.
An LCD screen inside the enclosure displays the selected measurement.
Programming is achieved using integral buttons inside the enclosure (all
models) or by remote communication using HART (on the 3102 and 3105 only).
(Figure 1) – the transmitter calculates the liquid depth (level)
Quick Start Guide
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signal on the
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