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Model 286 Features
The American Magnetics, Inc. (AMI) Model 286 Liquid Level Controller (cryogen monitor) is a microprocessor-based instrument designed to provide multiple sensor capacitance-based monitoring and control of liquid levels. In addition to the brief feature descriptions provided below, a detailed feature matrix is provided in the Model 286 manual or the product brochure shown here.
Capacitance-Based Level Sensing
A typical control system consists of a Model 286 Liquid Level Controller, up
to four AMI liquid level sensor(s), and connecting coaxial cable(s). The primary
instrument sensing element is typically a 3/8 inch (9.5 mm) OD concentric-tube
cylindrical capacitor constructed of stainless steel which allows the fluid to
become the dielectric between the concentric cylinders. The instrument measures
the sensor capacitance, which is directly related to the percentage of the
sensor immersed in the liquid.
Multiple Sensor Monitoring and Control
The Model 286 is capable of monitoring four independent, capacitance level sensors and controlling liquid level in up to two vessels by directly controlling the actuation of two solenoid-operated flow control valves.
Factory calibrated
The Model 286 is typically calibrated by AMI for matched sensors in liquid nitrogen, and is ready for immediate use upon delivery. If the working fluid is something other than nitrogen, an approximate calibration can be performed or the customer must perform an open or closed dewar calibration after installation when the sensor can be immersed in the target fluid.
Multiple calibrations per sensor
Each of the four sensor inputs to the Model 286 can have up to four independent calibrations, which are user-selectable. The user simply selects the desired calibration using the menu-type interface. All calibration data is passcode protected and stored in nonvolatile memory.
Convenient Display and Direct Keypad Entry
The instrument is equipped with a 16-character x 2-line backlit character-mode LCD display which provides liquid level and setpoint indication in inches, centimeters, or percent as selected by the user. The default display indicates liquid level and fill/loss rate. The current liquid level is updated and visible in many of the display modes used in configuring various settings of the instrument.
The 4 x 4 keypad is provided for direct entry of values for setpoints, sensor length, and other functions. The keypad also provides a convenient menu-type interface for configuring various instrument settings that require selection from a list of options.
HI/LO Alarms
Two user-defined setpoints, HI and LO, are provided for all four channels with front panel LED indications for Channels 1 and 2. The HI and LO setpoints may also operate two pairs of low-current, rear panel relay contacts and a built-in audible alarm. The HI/LO relay contact pairs may be assigned to Channels 1 and 2, or to Channels 3 and 4.
Controller Modes
The Model 286 provides three controller modes: normal, auto-changeover, and pre-cool. The preferred mode can be selected via the front panel keypad or remote interface. The level control sequence varies based on the selected mode. See the discussion provided in the Model 286 manual or PDF format brochure for more information about the controller modes. View an on-line video of a Model 286 used on pre-cool mode to autofill a 0.25 liter nitrogen IR detector dewar - Small Dewar Autofill Video.
AMI Model 286 Auto-Changeover System with Vacuum Jacketed Manifold
Switching between LN2 supply tanks to keep critical system cold
Remote Operation
The Model 286 is capable of providing up to two analog 0-10 VDC signals, which corresponds to 0-100% liquid level, accessible from the rear panel of the instrument for use with a voltage recorder. This is a factory-installed option and should be specified at the time the instrument is purchased.
Up to two self-powered (i.e. does not require an external power supply) 4-20 mA current loop outputs can also be ordered as an option.
Additional digital interface options, including RS-232 or RS-422, are available. The serial remote interface provides a comprehensive command set for remote monitoring and configuration of all functions of the instrument.
| Level Measurements | |
| Resolution: | 0.1%, 0.1 cm, or 0.1 in |
| Linearity: | ± 0.1 % |
| Operating Parameters | |
| HI, A, B, and LO Alarms: | 0% to 100% adjustable |
| HI/LO Alarm Relay Contact Ratings: | 30 VAC or 60 VDC, 10 VA (up to 0.5 A max) [20 V at 0.5 A to 60 V at 0.167 A] |
| Controller Outputs: | AC line voltage @ 2A max current each output |
| Fill Timer: | 0.1 to 9,999.9 minutes |
| Analog Output | |
| Integral Non-linearity: | ± 0.012 % |
| Resolution: | 16 bits |
| Total Error: | ± 0.75 % for 4-20 mA output ± 1 % for 0-10 VDC output |
| Current Drift (4-20 mA): | 75 ppm / °C |
| Voltage Drift (0-10 V): | 100 ppm / °C |
| Power Requirements | |
| Primary: | 100-120 or 200-240 VAC ±10% 50-60 Hz, 4.2 A max (25 VA plus sum of controller output currents) |
| Physical | |
| Dimensions (Standard): | 97 mm H x 213 mm W x 290 mm D (3.8" H x 8.4" W x 11.4" D) |
| Weight (Standard): | 1.9 kg (4.2 lbs) |
| Dimensions (Rack Mount): | 89 mm H x 483 mm W x 290 mm D (3.5" H x 19" W x 11.4" D) |
| Weight (Rack Mount): | 2.2 kg (4.9 lbs) |
| RG-59U Extension Cable Length: | 500 ft. maximum |
| Environmental | |
| Ambient Temperature: | Operating: 0 °C to 40 °C (32 °F to 104 °F) Non-operating: -20 °C to 60 °C (-4 °F to 140 °F) |
| Relative Humidity: | 0% to 95%; non-condensing |
Model 286 Manual in Adobe Acrobat 3.0 format (981 KB)
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