Quick Start Guide
3
August 2012
Overview of the Rosemount 2120
The Rosemount 2120 is a liquid point level switch. Based on vibrating short fork
technology, the 2120 is suitable for virtually all liquid applications.
The Rosemount 2120 is designed using the principle of a tuning fork. A piezo-electric
crystal oscillates the forks at their natural frequency (~1400 Hz). Changes to this
frequency are continuously monitored. The frequency of the vibrating fork sensor
changes depending on the medium in which it is immersed. The denser the liquid, the
lower the frequency.
When used as a low level alarm, the liquid in the tank or pipe drains down past the fork,
causing a change of natural frequency that is detected by the electronics and switches
the output state to a Dry condition. When the 2120 switch is used as a high level
alarm, the liquid rises in the tank or pipe, making contact with the fork which then
causes the output state to switch to a Wet condition.
The 2120 has a ‘heartbeat’ LED that indicates its operating state. The LED flashes when
the switch output is ‘off’ and is constantly lit when 'on'.
Figure 1. Rosemount 2120 features
A. Visible heartbeat LED G. Wetted material in 316/316L SST, solid
B. Mode switch, adjustable time delay Alloy C and Alloy C-276, or
C. Housings in glass-filled nylon, ECTFE/PFA-coated 316/316L SST
aluminum, or 316 SST H. Short fork length or extensions up to
D. Magnetic test point 157.5-in. (4 m)
E. Threaded, Flanged, or Hygienic Connections I. Two cable/conduit entries
F. ‘Fast drip’ fork design J. Direct Load, Relay DPCO, PLC/PNP,
NAMUR, or 8/16 mA electronics
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