LC10 Liquid Nitrogen Level Controller User Manual
Contents
1. Active level control will not resume until 23 seconds after all faulty sensors have been corrected The LC10 determines if each sensor is wet or dry based on the different thermal conductivities of liquid and gaseous nitrogen This is done by biasing the sensor with a small amount of heat input If the sensor is submerged in LN the heat is conducted away from the sensor with negligible temperature rise However if the sensor is not submerged a small but measurable temperature rise occurs at the end of the sensor The controller alternately energizes each sensor during 20 second intervals This minimizes the LN boil off because only one LS10 sensor is active at a time When cooled to the temperature of liquid nitrogen the total power dissipated by the sensors is 88 mW This corresponds to a quiescent boil off rate of 1 liter of LN every 3 weeks The fact that the sensors are energized intermittently does cause some latency in the controller s response to LN level changes The typical delay from when both sensor become wet and the corresponding removal of the VALVE and FILLING signals is 14 seconds The typical delay from when both sensor become dry and the corresponding application of the VALVE and FILLING signals is 29 seconds 3 1 The LINE and VALVE Terminals The line terminals LH and LN provide power to the controller and should be connected to the 120VAC mains This line voltage is also routed to the valve terminals VH and VN when t2. each sensor has a sensing tip that is covered by a splash guard The sensing tip is connected to the sensor plug by cryoflex leads The sensor plug mates with the sensor jacks provided on the LC10 circuit board Sensors are available with 2 3 or 4 foot leads CRYOFLEX LEADS 25MM PLUG x e 0 05 IN SPLASH TYE GUARD te a 0 20 IN FIGURE 3 The LS10 Sensor The LC10 is powered from 120VAC 230VAC optional and is supplied as a circuit board with screw terminals and mounting holes Features of the LC10 include 1 A watch dog timer for high reliability operation 2 A metal oxide varistor MOV to protect the controller from voltage spikes on the power mains 3 an opto isolated zero volt switching relay to prevent electrical noise and 4 A regulated 5VDC power supply that can be used to power external circuits such as lights or buzzers 2 Installation Proper site selection for the LC10 Controller is very important The controller should not be placed where liquid OR COLD VAPOR will fall on it In particular cold exhaust vapors generated during the fill operation must be directed away from the controller The LC10 circuit board has four mounting holes that accommodate 6 bolts The circuit board should not be mounted flush against a conducting surface as this will short out the traces on the bottom of the board A 1 4 inch standoff is recommended when mounting the LC10 board Position the LS10 sensors at the desired hi
3. NE G L AK NITROGEN SUPPLY LC10 CONTROLLER DEWAR LS10 SENSORS FIGURE 1 A typical LC10 application As shown in figure 2 the LC10 circuit board is equipped with two jacks that accept the LS10 sensor plugs Screw terminals are used to make all other connections to the LC10 circuit board In addition to the power and valve terminals the controller also has STATUS and FILLING outputs as well as a TOGGLE input The STATUS output indicates that the sensors are installed and operating properly If both sensors are functioning the STATUS output is connected to COMMON Otherwise the STATUS output flashes between COMMON and open to indicate a fault condition l 120 vac gt gt 2 LS10 JACK VALVE LO 1 common TOGGLE gt FILLING lt JACK alal 2 e Ja C D C FIGURE 2 The LC10 circuit board The FILLING output can be used by external equipment to monitor the LC10 s filling status This open collector output is connected to COMMON only when the solid state relay is activated The TOGGLE input permits external control over the filling process It can be used to change the controllers current state waiting or filling or to override the controller The controller uses two LS10 sensors to monitor the liquid level within the cryogenic reservoir As shown in figure 3
4. TERAGON LC10 Liquid Nitrogen Level Controller User Manual Teragon Research e 2518 26th Avenue e San Francisco CA 94116 phone 415 664 6814 e fax 415 664 6745 e www trgn com WARNING THE LC10 CONTROLLER CONTAINS CMOS CIRCUITS WHICH ARE SUSCEPTIBLE TO DAMAGE BY ELECTROSTATIC DISCHARGE ESD STANDARD ESD HANDLING PRECAUTIONS SHOULD BE OBSERVED WHEN INSTALLING THE CONTROLLER WARNING TRACES ON THE LC10 CIRCUIT BOARD CAN CARRY LETHAL VOLTAGES INSTALLATION AND MAINTENANCE SHOULD ONLY BE PERFORMED BY A QUALIFIED ELECTRICAL TECHNICIAN WHILE POWER IS APPLIED CONTACT WITH THE CIRCUIT BOARD CAN LEAD TO DAMAGE INJURY OR DEATH WARNING CONTACT WITH LIQUID NITROGEN OR COLD NITROGEN GAS MAY CAUSE SERIOUS FROSTBITE OR BLINDNESS NITROGEN GAS CAN CAUSE RAPID SUFFOCATION USE AND STORE LIQUID NITROGEN ONLY IN WELL VENTILATED PLACES 1 Overview The LC10 Liquid Level Controller uses two LS10 Sensors to maintain the nitrogen level in a cryogenic reservoir The controller uses a solid state relay to operate an external cryogenic solenoid valve A typical LC10 application is shown in figure 1 The controller has been designed so that either LS10 sensor will function as the high or low sensor Filling will begin when both sensors have become dry and continue until both sensors have become wet As a safety feature the controller will not initiate or continue a fill operation if either sensor is unplugged CRYOGENIC SOLENOID VALVE O
5. Voltage 40VDC relative to COMMON Max Current 150 mA Max Power 350 mW Input Signal TOGGLE active low Output Power Supply 5VDC 90mA max Screw Terminals Accepts 14 to 30 AWG Mounting Holes 2 5 in square pattern 0 15 in I D Specifications are subject to change without notice 5 Warranty The LC10 Level Controller and LS10 Level Sensors are warranted to be free from defects in materials and construction for 1 year from the date of purchase Neither the controller nor sensors contain any user serviceable parts and all warranty repairs must be performed by Teragon Every effort has been made to ensure the accuracy and completeness of both this manual and the LC10 system that it describes Should you discover any error in either the manual or the LC10 system we would be most grateful to hear from you regarding the oversight Please contact us at tel 415 664 6814 fax 415 664 6745 or e mail sales trgn com We thank you in advance for your assistance The quality of our products and the satisfaction of our customers are our two greatest concerns 2003 Teragon Research Firmware Rev 2 2
6. gh and low setpoints within the LN reservoir For proper operation the sensors must not be permitted to move due to the turbulence generated during the fill operation Sensors should either be anchored in place or shielded from the turbulence within a shroud or tube Anchoring can be accomplished using a length of stainless rod and nylon cable ties Suitable materials for a shroud or tube include metals PTFE FEP and phenolic Be aware that inserting a warm tube into LN is hazardous liquid will spout from the upper end of the tube due to the boiling that occurs within the tube During normal operation the solenoid is energized when both sensors become dry and filling continues until both sensors are wet Note that both level sensors are treated equivalently and either sensor can function as the high or low sensor There is no need to determine which sensor is used for the upper or the lower position Simply place the sensors at the desired high and low setpoints and then insert the sensor plugs into either jack on the controller The remaining connections to the LC10 are made using the ten screw terminals on the circuit board The following table gives the names abbreviations and functions for each of the terminals Terminal No Terminal Name Abbreviation Function 1 LINE HOT LH AC Input 2 LINE NEUTRAL LN AC Input 3 VALVE NEUTRAL VN AC Output 4 VALVE HOT VH AC Output 5 COMMON C DC Ground 6 TOGGLE T Logic In
7. he controller attempts to fill The LN LINE NEUTRAL terminal is connected directly to the VN VALVE NEUTRAL terminal on the LC10 circuit board The LH LINE HOT terminal is connected to the input of the control relay When the relay is closed by the controller the voltage applied to LH appears on VH It is important to correctly connect LH to the hot side of the mains since only this side is switched on an off by the controller 3 2 The 5V and COMMON Terminals The LC10 is equipped with a regulated 5VDC power supply that can be used to power external circuits This makes it particularly easy to add indicators lights buzzers to the controller s STATUS or FILLING outputs The COMMON terminal is the ground reference OVDC for the power supply Up to 90mA may be drawn from the 5VDC terminal and returned via the COMMON terminal The COMMON terminal can also be used to ground an external DC supply if one is used with the STATUS or FILLING outputs 3 3 The STATUS Output The STATUS output indicates if the sensors are installed and operating properly The STATUS signal is an active low open collector output If both sensors are installed and functioning properly the STATUS output is grounded i e connected to COMMON If the controller determines that either sensor is shorted unplugged or excessively noisy then STATUS flashes between ground and open The number of flashes per second indicates which sensor is faulty one flash per second for senso
8. put 7 STATUS S Logic Output 8 FILLING F Logic Output 9 5VDC 5V DC Output 10 5VDC 5V DC Output Connect the solenoid valve leads to the VH and VN terminals Connect any auxiliary circuits lights switched etc to the appropriate input output terminals Finally connect the unenergized power leads to the LH and LN terminals ensure that the hot leg of the mains power is connected to the LH terminal Apply power to the power leads to begin automated filling of the LN reservoir 3 Operation When power is applied to the LC10 Controller it first runs a diagnostic to determine if both LS10 sensors are installed and functioning properly The controller checks if the sensors are shorted unplugged or excessively noisy Within 0 4 seconds the STATUS signal will indicate if the sensors are operating properly see section 3 3 If both sensors are functioning properly the LC10 begins analyzing their signals to determine if the sensors are wet or dry The first wet dry determinations require 23 seconds from the application of power after which active level control begins If either LS10 sensor is damaged or unplugged the LC10 will cease to control the LN level until the problem is remedied Power will no longer be routed to the VH terminal the FILLING signal will not be active and the STATUS signal will indicate which sensors are faulty However the controller can be forced to fill by using the TOGGLE input see section 3 5
9. r 1 two flashes per second for sensor 2 and three flashes per second if both sensors are faulty As shown in figure 4 a simple LED circuit connected between STATUS and 5V can be used to observe the STATUS signal 4 LED 5VDC STATUS 1500 FIGURE 4 Using an LED to observe the STATUS output Alternately an audible alarm can be generated from the STATUS output using either of the circuits in figure 5 The first circuit provides only the audible signal while the second provides both audible and visible signals 5VDC 5VDC ID 1500 xo AD 2KQ BUZZER A BUZZER LEDW STATUS 2N3904 STATUS 2N3904 1N4148 _ 1N4148 COMMON gt COMMON BUZZER International Comp Corp p n BRT2821P 06 Allied Elect Stock No 623 1931 FIGURE 5 Circuits that generate audible signals from the STATUS output Since STATUS is an open collector output it can be used with external power supplies in excess of SVDC The voltage applied to STATUS should not exceed 40 VDC relative to COMMON The current sunk by STATUS should not exceed 150 mA and should not dissipate more than 350 mW 3 4 The FILLING Output The FILLING output indicates if the controller is trying to fill the dewar by applying power to the VALVE terminals The FILLING output is an active low open collector output it is grounded i e connected to COMMON while the controller is filling A simple LED circuit connected between FILLING and 5V can be used to obser
10. ve the FILLING signal as shown in figure 6 5VDC 2 LED FILLING 150Q FIGURE 6 Using an LED to observe the FILLING output Since FILLING is an open collector output it can be used with external power supplies in excess of SVDC The voltage applied to FILLING should not exceed 40V DC relative to COMMON The current sunk by FILLING should not exceed 150 mA and should not dissipate more than 350 mW 3 5 The TOGGLE Input The TOGGLE input provides immediate external control over the filling process If the liquid level is between the two sensors then momentarily shorting the TOGGLE terminal to COMMON will cause the status of the controller to toggle from the filling state to the waiting state or vice versa If both sensors are dry shorting TOGGLE to COMMON will disable filling until TOGGLE is released from COMMON Finally If both sensors are wet or if either sensor is unplugged TOGGLE can be used to override the controller and force fill the reservoir Usually a normally open momentary switch is wired between TOGGLE and COMMON as shown in figure 7 AE TOGGLE e COMMON FIGURE 7 A momentary switch can be used to activate the TOGGLE input 4 Specifications Power 120VAC 3Amps 50 60 Hz 230VAC optional Size 3 13 in L x 3 0 in W x 1 5 in A Fill Relay 120VAC 2 5Amps Zero volt switching 230VAC optional Required Sensors LS10 2 each Output Signals STATUS and FILLING open collector active low Max
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