Cornell High Energy Synchrotron Source
Doc#: SOP-OPS-014 ||
Procedure: F2 Cryo System ||
Prepared by: EE |
Rev.: 2 ||
Revision Date: 02/05/14 ||
Date Effective: 02/05/14 ||
Date Expires: 02/07/14 ||
Approved by: ZB |
To give an overview of the operation of the F2 Cryo System. Safety
- Cryogenic Helium gas and Liquid Nitrogen: Users of this document should be familiar with the Cryogenic Safety section of the CLASSE Safety Handbook
- Restricted Areas: Some of the cryo equipment is located on the roof of the F-hutches. Access to this area depends on the running status of ERL and CESR.
The F2 Monocromator crystal is cooled to liquid nitrogen temperatures (80 K) via helium gas circulated though the crystal bender assembly in the mono box. The mono box is held under an insulation vacuum of 50 mTorr or better to prevent condensation and ice buildup on the cooled parts. The helium starts at room temperature and is provided by the LEPP Cryo group. The gas travels though copper pipe from the Cryo mezzanine behind the CESR control room to the CHESS East Roof. On the East roof the helium gas flows into a vacuum insulated heat exchanger can. In the heat exchanger can the helium flows though flat plate heat exchangers set up in cross flow configuration. The cross flow takes warm incoming helium gas and cools it down with the cold helium gas returning from the mono box. While this is happening the cold gas returning from the mono box is warmed by the incoming warm helium and is retuned back to the LEPP Cryo group only few degrees cooler than what it was supplied at. The warm helium that is cooled in the cross flow exchanges is then transferred via vacuum insulated line to a heat exchanger that is installed in a liquid nitrogen dewar. The dewar is kept full of liquid nitrogen via an auto fill system. The helium flowing into this heat exchanger is cooled to liquid nitrogen temperatures and exits the dewar via a vacuum insulated transfer line that goes to the F2 mono box. In the mono box the cold helium travels though the crystal mount, removing heat from it and cooling it. From here the helium travels back to the heat exchange can via a vacuum insulated line. In the heat exchange can the helium is warmed by the incoming helium and exits though insulated pipe to be returned to the LEPP Cryo Group.See Figure 1
The helium gas is supplied at ~ 200 psi from the LEPP Cryo group and is stepped down to ~150 psi via a pressure regulator. A needle valve is installed on the return line coming from the heat exchange can and going back to the LEPP Cryo group. The needle valve is used to control the flow rate of the system. The designed flow rate is 2 grams/sec of helium. The restriction that needle valve creates plus that of the pipe returning the helium back to the LEPP Cryo group drops the pressure to < ~8psi.
The cryo system is controlled by a PLC based touch screen controller. System status and control are handled by a touch screen mounted on the cabinet. The control cabinet (Fig. 2
) houses the plc, touch screen and associated electronics is located in the F station control area. This system takes in protection interlocks for the cryo system and sends the ok to the F-line ANN box in the CHESS ops area. To allow F1 and F3 to run when F2 is not being cooled, a slit may be parked to block beam from striking downstream components. This slit has a limit switch that is closed when the slit is parked. When the system is in this condition a warning signal can be sent to ANN in CHESS ops to alert the operator of potential issues. This ANN box only sends alerts to the pager and does not close beam stops. If a warning alarm is received the operator should check the touch screen on the control box to see what the issue is. Below is a list of signals that are used for control of the system and protection of personnel and equipment.
- LN2 Autofill –status of auto fill system located on the east roof
- Cryo Pressure Switch – trips if helium return line goes above 8psi, contact Lepp Cryo
- Dump Button – located in F-Cave on low oxygen alarm
- Dump Button – located on the F-line roof are near the search button
- Low Oxygen Sensor - located in F-Cave
- E-Stop Button-located in F - Control area on the control box (Fig. 2)
- Heat Exchanger Can Vacuum-trips if can vacuum is above 1x10-3 Torr
- F2 Mono Vacuum - trips if mono vacuum is above 50 mTorr
- Cryo Helium Flow - trips if the difference in helium supply and return flows is >30 slpm
- Cryo Temperature - trips if the crystal return temperature is above -170 °C
- Dewar overflow sensor – trips if LN2 is overflowing from the dewar
The liquid nitrogen auto fill system resides on the east roof and F2 station control rack . This system keeps the dewar full and checks for overflow via a temperature probe located in the pan that the dewar sits in. Should the autofill system fail to shut off, a manual valve (Fig. 8) located on the roof of F-line will stop the flow. In this case contact a member of the safety committee to arrange access and a second person to close the valve.
The autofill controller is set to maintain a level in the dewar between 20 and 26 inches of liquid nitrogen. When the level falls below 20 inches the autofill controller opens a solenoid connected to the house liquid nitrogen supply and fills the dewar until it is at 26 inches and shuts the solenoid. The frequency of the fills will depend on the heat load and boil off in the dewar.
The crystal mount base plate has a heating system with three zones of heat to keep the bearings and mechanical mechanism at ~20 °C so they do not freeze up and bind. There are five (5) foil heaters that are attached to various parts of the bender mechanism and three (3) PT1000 RTD sensors to monitor the temperature. These RTD signals are run though a signal conditioner that outputs a 0-10 volt signal. This is a linear proportional output. These signals go into the CHESS signals database and to three (3) Omega PID process controllers. The controllers are driving zero-crossing solid state relays connected to the heaters (Fig. 7
). The set point is in volts and is set to 4 volts corresponding to 20 °C (Fig. 5
). These controllers need to be in the run mode while the system is operating, this can be done by holding down the run button for two seconds on the controller. A red LED will light up beside the run label. One further step is needed to enable the heaters - the green power switch on the solid state relay panel needs to be turned on (Fig. 7
). This can also be used to disable the heaters, if this power switch is off the heaters will not work regardless of the state of the PID process controllers
The remaining temperature signals are also monitored in a similar fashion using PT1000 sensors going to signal conditioner and then into the CHESS Signal Monitoring System. The scaling for the rest of the temperature signals is as follows; -200 °C to 50 °C is output as a 10 volt to 0 volt linear signal form the signal conditioner. The gas pressures are 0 to 200 psi and output a 0-5 volt linear signal. All of the cryo system signals are collected by a UEI crate located in the F-Cave Rack. Two software generated alarms are also coming from this UEI unit. The temperature of the helium return on the crystal will open a relay that trips the cryo aux box if it is above the set point, currently -180 °C. The UEI also looks at the flow rates of the helium gas coming from two electronic mass flow meters. These meters output a signal of 0-5 volts corresponding to 0-1000 slpm. If a difference >30 slpm of supply and return flow is monitored, a relay is opened by the UEI. This relay is connected the Cryo Control Box. These software generated alarms clear without intervention, but the PLC latches on these events. Start up
To start the system up the following must be satisfied:
- Liquid nitrogen auto fill on and active, manual valve open
- Crystal bender heater system on and running
- Beam is prevented from hitting the first crystal via slit
- All interlocked conditions on the aux screen satisfied, except for crystal temperature.
With these conditions met one can start the system by pressing the push to cool button on the touch screen. Once the system is cooled the crystal temperature indicator will show ok and the beam blocking slit may be moved out of the beam and the station used. Shut Down
To shut the system down ensure the beam blocking slit is parked in place and press the push to warm button on the touch screen. If the system is to be turned off for a long period of time the liquid nitrogen auto fill should be shut off (Fig. 4)
and the manual valve (Fig. 6
) feeding the system should be turned off. The bender heater system should also be shut down by turning power off on the solid state relay panel (Fig. 7
) and putting the three controls in stop mode by holding the stop (Fig. 5
) button for two (2) seconds.
Figure 1 - System Diagram
Figure 2 – Cryo PLC controls. Located in F-Line Prep Area
Figure 3 – Low oxygen alarm and dump button. Located in F-Cave
Figure 4 - Liquid Nitrogen Auto Fill System. Located on the back of the F2 station control rack
Figure 5 - Bender Heater Process Controllers. Located in F-Cave Control Rack
Figure 7 - Heater Solid State Relay Panel and Switch. Located in F-Cave Control Rack
Figure 8 – Manual LN2 shutoff valve
Rev. 1 – Initial document (10/17/13 - EE)
Rev. 2 –Revised for PLC Controls (02/05/14 – EE)
- 30 Aug 2017