Manual for AFS LLC1 Nitrogen Liquid Level Controller Sn 101 - 8/12/99

Skip to [Overview | Features | Setup and Installation | Operation | Optional Outputs | Specifications | Warranty]

OVERVIEW

The LLC1 is an analog liquid level controller using thermistor based sensors. The thermistors exhibit a large resistance change for small changes in temperature near liquid nitrogen temperature. The heat created by passing a small current through the thermistor is absorbed more readily by the liquid than by the vapor causing the thermistor to run slightly warmer in the vapor. This small difference in temperature causes a large resistance change that is picked up by and drives the circuit.

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FEATURES

Thermistor Probes

The probes are constructed from color coded (red high, white low), shielded teflon cable. Each thermistor probe is equipped with dual sensors, separated by 25mm.

Sensing Circuit

Each thermistor is connected to an independent sensing circuit that monitors the state of the sensor. In addition to liquid and vapor phase sensing, the circuit continuously checks for an open or shorted sensor.

Alarm Circuit

An alarm will sound, the remote alarm contacts will switch, and the alarm LED will light for the following conditions. Low Alarm if the liquid level falls below the low alarm sensor. Hi Alarm if the liquid level rises above the high alarm sensor.

The alarm will sound, the remote alarm contacts will switch, and the alarm LED will flash if an open or shorted sensor is detected.

The remote alarm contacts will also switch on loss of power to the unit, and automatically reset upon restoration of power.

For actual alarm conditions the alarm conditions (buzzer, LED and remote contacts) will remain on until manually reset.

Mute/Reset Switch

The audible alarm can be muted for ~15 minutes by pressing the Mute/Reset switch. If the alarm condition is not corrected the LED will remain lit and the alarm contacts will remain switched. The audible alarm will remain muted, even if another alarm condition occurs within the 15 minute window. Once the alarm condition has been corrected pressing the Mute/Reset switch will reset all alarm outputs.

Control Outputs

The LLC1 will initiate an automatic fill sequence, switching 24 vdc to the Fill Valve Output, when the liquid level falls below the Low Sensor or Low Alarm Sensor. Power to the Fill Valve Output will switch to zero, terminating the fill sequence, when the liquid level reaches the Hi Sensor or High Alarm Sensor. Shorted or open sensors will activate the alarm, but will not initiate or terminate a fill sequence.

There are two auxiliary outputs activated by the alarm circuit. 24 vdc will be switched to the Low Liquid Level output when the liquid level falls below the Low Alarm Sensor. The voltage switches to zero when the liquid level rises above the low alarm sensor. Similarly 24 vdc will be switched to the High Liquid Level output when the liquid level rises above the high alarm sensor. The voltage switches to zero when the liquid level falls below the High Alarm Sensor.

One Fill All Fill

The one fill all fill output will initiate an automatic fill sequence to all connected units when a fill sequence is initiated by the sensors. A one fill all fill sequence can also be manually initiated by pressing the Start button 90 seconds or more into a manual fill sequence.

Start Button

The Start Button will initiate a manual fill sequence if the liquid level is between the High and Low sensors. If the liquid level is above the High Sensor the fill valve will open as long as the Start Button is depressed (if held for more than 90 seconds the One Fill All Fill circuit will activate). The Start button will do nothing if the liquid level is above the High Alarm Sensor.

Stop Button

The Stop button will stop a fill sequence if the liquid level is between the High and Low sensors. If the liquid level is below the Low Sensor the Stop button will not interrupt the fill sequence.

Indicator LEDs

The green Power LED will be on as long as the unit is supplied with 24 vdc. The yellow Filling LED will illuminate as long as the Fill Valve Output is energized. The red Alarm LEDs will illuminate during an alarm condition and remain on until the alarm condition has been corrected and the Mute/Reset button is depressed.

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SETUP AND INSTALLATION

Probe Installation

The thermistor probes are letter coded and matched to the controller. They are interchangeable with the same letter probes without recalibration of the unit. The probes are color coded. Red is the high sensor probe, white is the low sensor probe. The lower sensor on the white probe is the Low Alarm sensor, the upper sensor is the Low Level (Start Fill) sensor. The lower sensor on the red probe is the High Level (Stop Fill) sensor, the upper sensor is the High Alarm sensor. The Low Level and High Level sensors should be positioned at least 10mm apart for normal operation. The farther apart the sensors are the more efficient the filling process will be since more liquid nitrogen is delivered to the unit at a time offsetting the initial cooldown losses of the piping. Once the sensor spacing is determined the probes should be taped together, with masking tape, at ~ 500mm intervals, to form a sensor bundle with fixed sensor spacing.

The low alarm sensor (the lowest sensor in the bundle) should be placed at a level high enough above the bottom of the tank to assure the alarm will be detected before the tank goes completely empty of liquid. For example if the liquid usage of the tank is 10mm per day and the longest period of time the alarm is unmonitored is a weekend the low alarm sensor should be placed 10 mm/day x 3 days = 30 mm above the bottom of the tank. To prevent false shutdowns (or alarms) during filling operations the sensors should be installed into a stillwell. A 12 mm, fiber tube, closed on the bottom with 2 mm holes spaced at 300mm intervals along its length, makes an excellent stillwell for the sensors. To position the sensor bundle in the stillwell measure the interior height of the tank, subtract the height the low alarm sensor needs to be off of the bottom from this interior height this will be the sensor bundle length. Measure the sensor bundle length from the bottom of the Low Alarm sensor (lowest sensor) and wrap a piece of masking tape around the bundle at this length. Mark a line on the tape with an indelible marker at this point to differentiate it from the tape holding the wire bundle together. Insert the sensor bundle into the stillwell until the mark lines up with the top of the tank (usually the same as the top of the stillwell). Bend the wire over the top of the tank and tape or clip it to fix its position. Route the sensor wires to the control box and connect. The white wire (low sensor) goes to the rightmost connector. The red wire (high sensor) goes to the middle connector.

Output Connector

The output connector switches 24 vdc to the output wires when the control box calls for a fill. Connect the red wire to the plus terminal of the device to be switched, connect the white wire to the minus terminal. If an inductive load such as a solenoid or relay is being switched a diode or surge protector should be placed across the load terminals to maximize the life of the controller contacts. The output connector attaches to the leftmost connector socket on the controller.

Power Connector

The power connector for the unit is a 5.5mm x 2.1mm x 12mm power connector. The center terminal is 24 vdc positive, the perimeter is ground. The controller is internally fused for a 3 amp load.

Remote Alarm Contacts

The four conductor terminal strip contains the remote alarm contacts and earth ground. It is recommended that shielded wire be used to connect the remote alarm. The normally open contact is open during normal operation of the unit, it closes on loss of power or when the unit goes into alarm. The normally closed contact opens on loss of power or alarm. Restoring power to the unit will reset the contacts automatically. If the unit goes into alarm, the alarm condition needs to be corrected and the Mute/Reset button pressed to reset the contacts. The shield of the remote alarm cable needs to be tied to the Ground contact. In dry areas or other areas where static electric discharges are common the Ground contact should also be connected to earth ground.

One Fill All Fill Connector

For maximum liquid conservation in multiple tank applications the one fill all fill connector can be used to minimize cooldown losses during fills by filling every tank when one needs liquid. The one fill all fill circuit uses a 6 position, 4 conductor, modular cable assembly with standard polarity. This is the same connector used to connect telephones to the wall.

DO NOT CONNECT THE CONTROLLER TO A TELEPHONE JACK, DAMAGE TO BOTH THE PHONE SYSTEM AND CONTROLLER WILL OCCUR!!

To use the one fill all fill feature simply daisy chain connect each unit to the next. For maximum effectiveness the chain should go in a circle, with the last unit in the chain connecting back to the first. The maximum modular wire length between units is 25 feet. Caution: A similar modular connector is used for computers. It is a 6 position, 4 conductor, REVERSE polarity cable. While use of this cable will not damage the circuit, the one fill all fill feature will not work.

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OPERATION

Once setup and powered operation will be automatic. On a first fill, the low alarm will sound until liquid covers the low alarm sensor. The alarm can be muted during the filling process, but remember to reset it after the fill has progressed so that it can properly function in the event of a real alarm. The unit will fill and shut off automatically when the liquid level reaches the high level sensor. If the One Fill All Fill circuit is connected all tanks will fill automatically.

To start a fill or defog the unit press the Start button. To stop a fill cycle press the Stop button. To manually initiate a One Fill All Fill cycle press the Start button to initiate a fill, wait 90 seconds then press the Start button again (if the tank is already full press and hold the Start button for 90 seconds this will activate the One Fill All Fill for all connected tanks).

To silence the audible alarm press the Mute/Reset button. Caution: The alarm will remain muted until the alarm condition is corrected and reset, even if another alarm condition occurs. To reset the alarm circuit first identify and correct the cause of the alarm then press the Mute/Reset button. The alarm will silence and the alarm light will extinguish.

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OPTIONAL OUTPUTS

There are two optional 24vdc outputs on the output connector. The Low Liquid Level Output switches high (24 vdc) when the liquid level falls below the low alarm sensor. It can be used to switch to an alternate supply of liquid nitrogen in the event that the primary supply goes empty.

The High Liquid Level Output switches high (24 vdc) when the liquid level rises above the high alarm sensor. It can be used to power an auxiliary liquid shutoff of depressurization circuit in the event that the primary fill valve fails open.

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SPECIFICATIONS

• Operating Voltage: 24vdc +- .5 vdc
• Operating Current: 200ma, No Load
• Internal Fuse: 3 amp (Violet) Mini ATO Fuse
• Heat Dissipation Through Sensors: 15 mw each
• Sensor Response Time: <1 second liquid rising, <1 minute liquid falling
• Power Connector : 5.5mm x 2.5 mm x 12 mm. Center conductor positive
• Output Connector: Conxall, 5 Socket Mini-Con-X
  • Pin 1- 24 vdc Fill Valve Output
  • Pin 2- Common
  • Pin 3- 24 vdc Low Liquid Level Output
  • Pin 4- 24 vdc High Liquid Level Output
  • Pin 5- Shield
• High Sensor Connector: Conxall, 4 Socket Mini-Con-X
  • Pin 1- High Level Sensor
  • Pin 2- Common
  • Pin 3- High Alarm Sensor
  • Pin 4- Shield
• Low Sensor Connector: Conxall, 4 Socket Mini-Con-X
  • Pin 1- Low Alarm Sensor
  • Pin 2- Common
  • Pin 3- Low Level Sensor
  • Pin 4 - Shield

Remote Alarm Terminals: 3/8" Barrier Strip, 6-32 x 1/4" Screw Terminal Accepts 1/4" or 3/16" Spade Connector

One Fill All Fill : Dual, 6 Position, 4 Conductor Modular Jack Accepts Standard Polarity Cables, 25' Max. Length

CAUTION ON USE OF THIS DEVICE !!

This is an analog electronic circuit, and despite efforts to build in redundancy, it is subject to failure from a variety of causes. It is designed for controlling liquid nitrogen levels only. If loss of nitrogen would cause damage to materials stored therein, or cause economic loss the liquid levels should be manually checked at intervals sufficient to prevent damage or loss caused by failure of the controller or the systems it controls.

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WARRANTY

This unit has been inspected, calibrated and tested at the factory and is fully functional at time of delivery. We will further warrant the unit against defects in materials and workmanship for a period of 30 days from delivery. This warranty is limited to repair or replacement of the defective unit upon return to our factory. This warranty does not cover damages to the unit caused by improper installation, accident, fire, flood or acts of God or failure of the product if it is used for other than its intended purpose.

THE WARRANTOR IS NOT RESPONSIBLE FOR CONSEQUENTIAL DAMAGES.

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