American Magnetics 185 & 186 Liquid Level Instruments (CE-Marked) - Manual (Page 11)

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1 Introduction
1.1 Model 185/186 Features
The American Magnetics, Inc. (AMI) Model 186 Liquid Level Controller
system is an advanced, microprocessor-based solution designed to provide
accurate and reliable level monitoring and control of virtually any
cryogenic liquid.
1.1.1 Capacitance-based level sensing
The system consists of a Model 185/186 Liquid Level Instrument, sensor,
connecting cables, and an optional solenoid-operated fill valve. The
instrument sensing element is typically a 3/8 inch (9.5 mm) OD cylindrical
capacitor constructed of stainless steel which allows a cryogenic fluid to
become the dielectric between the concentric plates. The instrument
measures the sensor capacitance which is directly related to the
percentage of the sensor immersed in the cryogenic liquid. The sensors are
normally constructed in overall lengths of up to 20 feet (6.1 m). The
maximum active length is typically 7 inches less than the overall sensor
length.
1.1.2 HI/LO level alarms
The Model 185/186 provides two alarm setpoints for both HI and LO level
indication. The HI and LO level alarms activate front panel LEDs, an
audible alarm, and two independent sets of relay contacts accessible from
the rear panel. All setpoints are continuously adjustable from the front
panel.
1.1.3 Level control
The Model 186 adds two additional setpoints which are used to specify a
control band for the liquid level. The Model 186 automatically energizes
and de-energizes a rear panel controller output receptacle which is
typically used to operate a solenoid valve. The controller output receptacle
state can be manually overridden from the front panel. A fill timeout
feature is also provided which can be used to terminate the fill function
after a user-specified period of time.
1.1.4 Convenient display
The instrument is equipped with a 4-digit LED display which provides
liquid level indication in inches, centimeters, or percent as selected by a
front panel switch. A front panel switch allows the user to adjust the
instrument length quickly and easily for a specific active sensor length.
The sensor active length can be entered in either inches or centimeters.
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