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vetoshield:gas [2015/02/05 12:18] – [Overview of Control System] jeffvetoshield:gas [2015/07/29 13:15] (current) – [References and Additional Information] jeff
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 The shield is divided into separate panels of tubes. The gas flows into a given panel through a feed line and exits through return line. A schematic representation of the system is shown below.  The shield is divided into separate panels of tubes. The gas flows into a given panel through a feed line and exits through return line. A schematic representation of the system is shown below. 
  
-{{:vetoshield:veto_schematic.jpg?900}}+{{:vetoshield:vetoshield_gas_recirculation.jpg?900|}}
  
 The return lines from all the panels converge at a single return manifold and all the feed lines diverge from a single feed manifold. Thus, the entire shield can be thought of as a set of fluid resistances arranged in parallel between the two manifolds ((The fluid resistance through a panel is primarily caused by flow restrictors placed within the feed lines. Thus, the pressure within the tubes is very close to that of the return manifold. This makes the return manifold pressure a good indicator of the amount of gas in the system.)).  The return lines from all the panels converge at a single return manifold and all the feed lines diverge from a single feed manifold. Thus, the entire shield can be thought of as a set of fluid resistances arranged in parallel between the two manifolds ((The fluid resistance through a panel is primarily caused by flow restrictors placed within the feed lines. Thus, the pressure within the tubes is very close to that of the return manifold. This makes the return manifold pressure a good indicator of the amount of gas in the system.)). 
  
-After exiting the return manifold, the fluid is drawn through a positive displacement pump and forced through two Deoxo catalytic converters arranged in series. The Deoxos remove any oxygen that may have seeped into the gas through small leaks in the system. However, in order for oxygen to be removed, a small amount of hydrogen gas must be present.  Along the main line, upstream of the first Deoxo, there is a solenoid valve that opens to allow hydrogen to enter from a pressurized tank.+After exiting the return manifold, the fluid is drawn through a positive displacement pump and forced through two Deoxo catalytic converters arranged in series. The Deoxos remove any oxygen that may have seeped into the gas through small leaks in the system. However, in order for oxygen to be removed, a small amount of hydrogen gas must be present.  Upstream of the pump, there is a solenoid valve that opens to allow hydrogen to enter from a pressurized bottle.
  
 After passing through the Deoxos, the gas reenters the feed manifold and is dispersed back to the individual panels. During normal operation, the feed manifold has been held at roughly 1 psi above that of the return manifold. This pressure difference causes a flow rate of several liters per minute per panel ((Based on https://fireplace.soudan.umn.edu:8082/Shield/202 the pressure vs. flow relationship for a typical sized panel is p(q) = (6.58e-3)*q^2 + (1.11e-1)*q where p is the pressure difference between the two manifolds and q the flow rate in L/min.)). After passing through the Deoxos, the gas reenters the feed manifold and is dispersed back to the individual panels. During normal operation, the feed manifold has been held at roughly 1 psi above that of the return manifold. This pressure difference causes a flow rate of several liters per minute per panel ((Based on https://fireplace.soudan.umn.edu:8082/Shield/202 the pressure vs. flow relationship for a typical sized panel is p(q) = (6.58e-3)*q^2 + (1.11e-1)*q where p is the pressure difference between the two manifolds and q the flow rate in L/min.)).
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 __Solenoid Valves__- These are the six toggle switches located to the right of the pump controls. In auto mode, they are monitors that display the states of the respective valves ((There is no feedback from the solenoid valves. So the valve states as indicated here are merely the control signals the computer is sending to the valves. If everything is working properly the actual valve state should mirror the control signal and this detail can be ignored.)). Up indicates open and down indicates closed. In override, these six switches become controls allowing the user to manually open and close the valves. __Solenoid Valves__- These are the six toggle switches located to the right of the pump controls. In auto mode, they are monitors that display the states of the respective valves ((There is no feedback from the solenoid valves. So the valve states as indicated here are merely the control signals the computer is sending to the valves. If everything is working properly the actual valve state should mirror the control signal and this detail can be ignored.)). Up indicates open and down indicates closed. In override, these six switches become controls allowing the user to manually open and close the valves.
    
-__Filter Display__- When this button is pressed, the front panel monitors will be low pass filtered (smoothed). The RC time constant can be changed by clicking the "Limits and Setpoints" button and then going to the Advanced tab.+__Filter Display__- When this button is pressed, the front panel monitors will be low pass filtered (smoothed). The equivalent RC time constant can be changed by clicking the "Limits and Setpoints" button and then going to the Advanced tab. The gage pressure used to compute the tube absolute pressure is filtered for at least 10 seconds before being displayed or otherwise used by the program regardless of this button's state.
  
 __Override Switches__- These switches are intended to be used in auto mode when a specific safety prevents the pump from running continuously. See the section below for more information regarding the safeties. __Override Switches__- These switches are intended to be used in auto mode when a specific safety prevents the pump from running continuously. See the section below for more information regarding the safeties.
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 __Pump Exhaust Temperature__- This monitor displays the temperature of the pipe wall a small distance downstream of the pump outlet. This should be the highest temperature in the system. Note however that this temperature responds very slowly to changing operating conditions. For example, if the pump is turned on after having been off for a long time, this temperature will take over an hour to rise and level off. The dark red bar indicates the current reading and the bright red bar indicates the upper limit which if exceeded causes the pump to shut off.  __Pump Exhaust Temperature__- This monitor displays the temperature of the pipe wall a small distance downstream of the pump outlet. This should be the highest temperature in the system. Note however that this temperature responds very slowly to changing operating conditions. For example, if the pump is turned on after having been off for a long time, this temperature will take over an hour to rise and level off. The dark red bar indicates the current reading and the bright red bar indicates the upper limit which if exceeded causes the pump to shut off. 
  
-__Pump Cabinet Temperature__-This monitor displays the air temperature inside the pump cabinet. This temperature should roughly follow, but be less than the pump exhaust temperature. The dark red bar indicates the current reading and the bright red bar indicates the upper limit which if exceeded causes the pump to shut off. +__Pump Cabinet Temperature__-This monitor displays the air temperature inside the pump cabinet. This temperature should roughly follow, but be less than the pump exhaust temperature. The dark red bar indicates the current reading and the bright red bar indicates the upper limit which if exceeded causes the pump to shut off. 
 + 
 +__Gas Use Estimator__-This displays the percentage of the time the top-up valve is currently commanded to be open. This number is proportional to the rate at which gas is being consumed by the shield. The number sometime varies considerably over a several second timescale. To get a better estimate of gas use, perform a mental average by observing it for a couple minutes. This number is periodically written to file along with other parameters, so one can calculate a more accurate average over a longer period.
  
 __O2/H2 Sensors__-These sensors indicate the O2 and H2 concentrations at the inlet of the first Deoxo and the outlet of the second Deoxo. The red arrows on the O2 meters display the user selected pump-stop thresholds. __O2/H2 Sensors__-These sensors indicate the O2 and H2 concentrations at the inlet of the first Deoxo and the outlet of the second Deoxo. The red arrows on the O2 meters display the user selected pump-stop thresholds.
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 The limits can be changed while the controller is running by clicking on “Limits and Setpoints” on the front panel. A new window will appear and all pump stop criteria is adjustable from the "Pump Stop Criteria" tab. When finished click either “Cancel” or “Accept Values” to close the window. Do NOT close the window by clicking the red “x” in the upper right corner. Doing so will require a restart of the controller program for everything to again work properly.  The limits can be changed while the controller is running by clicking on “Limits and Setpoints” on the front panel. A new window will appear and all pump stop criteria is adjustable from the "Pump Stop Criteria" tab. When finished click either “Cancel” or “Accept Values” to close the window. Do NOT close the window by clicking the red “x” in the upper right corner. Doing so will require a restart of the controller program for everything to again work properly. 
  
-In certain situations, one or more safeties may need to be temporarily bypassed. Such is common if the pump has been left off for an extended period of time and an appreciable amount of O2 has seeped into the system. In this case the KR and O2 readings may be outside their limits. A safety can always be bypassed by setting the corresponding limit arbitrarily large or small. For example, if the KR is malfunctioning and reading very low, the KR Lower Limit can be set to 0 or some negative value that it will never reach. Alternatively, there are three override switches, one for the O2 levels, one for the pressure levels and another for the KR. Turing any one or more of these switches to ON will cause the controller to ignore the respective safeties. For example, the same problem with the KR could be addressed by instead turning the KR override to ON without tampering with the lower limit. The “Pressure Override” simultaneously bypasses all four pressure limits and the “O2 Override” simultaneously bypasses both O2 limits.+In certain situations, one or more safeties may need to be temporarily bypassed. Such is common if the pump has been left off for an extended period of time and an appreciable amount of O2 has seeped into the system near the KR and/or the O2 sensors. In this case the KR and O2 readings may be outside their limits. If the pump has not been running, these readings are not representative of the average gas quality throughout the shield.  A safety can always be bypassed by setting the corresponding limit arbitrarily large or small. For example, if the KR is malfunctioning and reading very low, the KR Lower Limit can be set to 0 or some negative value that it will never reach. Alternatively, there are three override switches, one for the O2 levels, one for the pressure levels and another for the KR. Turing any one or more of these switches to ON will cause the controller to ignore the respective safeties. For example, the same problem with the KR could be addressed by instead turning the KR override to ON without tampering with the lower limit. The “Pressure Override” simultaneously bypasses all four pressure limits and the “O2 Override” simultaneously bypasses both O2 limits.
  
-Unique to the KR override is an additional auto reset switch. When this switch is turned ON, the KR override will stay on only until the reading falls within the range set by the limits or a time delay has elapsed. If the pump has been off for some time, the KR reading will likely have fallen below its lower limit and the pump cannot be restarted without turning the override on. Turning the override on with the auto reset also turned on causes the controller to ignore the reading only temporarilly while the reading is climbing back toward its normal value. The time delay can be configured by clicking on the "Limits and Setpoints" button and going to the "Advanced" tab.+Unique to the KR override is an auto reset option. When this switch is turned ON, the KR override will stay on only until the reading falls within the range set by the limits or a timeout period has elapsed. If the pump has been off for some time, the KR reading will likely have fallen below its lower limit and the pump cannot be restarted without turning the override on. Turning the override on with the auto reset also turned on causes the controller to ignore the reading only temporarily while the reading is climbing back toward its normal value. The length of the timeout period can be configured by clicking on the "Limits and Setpoints" button and going to the "Advanced" tab. Its the field labeled "KR Auto Reset Delay" and sets the maximum time the KR override will remain on. The start of the timeout period is reset whenever the override switch is toggled or when the pump is started.
  
 ===Absolute Limits=== ===Absolute Limits===
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 This LabVIEW program was designed to be intuitive and user friendly. Normal operation of the system should involve minimal interaction by the user. All is fine provided the Master Control is left to Auto, the various override switches are off, the pump is running and all monitors have their limits set to reasonable values.  This LabVIEW program was designed to be intuitive and user friendly. Normal operation of the system should involve minimal interaction by the user. All is fine provided the Master Control is left to Auto, the various override switches are off, the pump is running and all monitors have their limits set to reasonable values. 
  
-To maintain the gas quality in the veto tubes, the pump doesn't need to run 24/7. However the pump should be left running at least 50% of the time over a week timescale. The pump can be manually stopped by simply clicking on the Pump Stop button on the program front panel. After the pump is off, the pump bypass valve (PBV) will begin to open. The pump cannot be restarted until this valve is all the way open as indicated by the position monitor on the front panel. This restriction is hardwired into the AC controls and cannot be changed through the software. After the PBV is fully open, the pump can be easily restarted by clicking Pump Start on the program front panel. If the pump has been left off for several hours, an appreciable but non-hazardous amount of O2 will have seeped into the system through small leaks in and around the pump. This may cause the O2 and KR readings to be outside their limits. In this case the pump can still be restarted by temporarily turning on the KR and/or O2 overrides. After the pump has been running for about a minute, the bad pocket of gas will be pumped away through the Deoxos and the O2 reading will return to normal. At this point, the O2 override can and should be turned off. The same is true for the KR but it often takes more than 10 minutes for its reading to return to normal.  If the pump is left off for several days or longer, a good amount of O2 will have seeped into the system and it will take longer for the O2 and KR readings to become normal after the pump is restarted. +To maintain the gas quality in the veto tubes, the pump doesn't need to run 24/7. However the pump should run at least 50% of the time each day. The pump can be manually stopped by simply clicking on the Pump Stop button on the program front panel. After the pump is off, the pump bypass valve (PBV) will begin to open. The pump cannot be restarted until this valve is all the way open as indicated by the position monitor on the front panel. This restriction is hardwired into the AC controls and cannot be changed through the software. After the PBV is fully open, the pump can be easily restarted by clicking Pump Start on the program front panel. If the pump has been left off for several hours, an appreciable but non-hazardous amount of O2 will have seeped into the system through small leaks in and around the pump. This may cause the O2 and KR readings to be outside their limits. In this case the pump can still be restarted by temporarily turning on the KR and/or O2 overrides. After the pump has been running for about a minute, the bad pocket of gas will be pumped away through the Deoxos and the O2 reading will return to normal. At this point, the O2 override can and should be turned off. The same is true for the KR but it often takes more than 10 minutes for its reading to return to normal.  If the pump is left off for several days or longer, a good amount of O2 will have seeped into the system and it will take longer for the O2 and KR readings to become normal after the pump is restarted. 
  
 In any case, one should avoid letting the pump run unattended with any of the overrides switched to on. As an exception, the KR override can be left on provided its auto reset switch is also on.  In any case, one should avoid letting the pump run unattended with any of the overrides switched to on. As an exception, the KR override can be left on provided its auto reset switch is also on. 
  
-The program itself should be left running nearly 24/7 regardless of whether the pump is on. Even when the pump is off, the program opens and closes the top-up valve to maintain correct pressure in the return manifold. Of course its ok to temporarily quit with dignity and close the program to do computer maintenance such as installing OS updates. However, avoid leaving the program off more than a few hours at a time.+The program itself should be left running nearly 24/7 regardless of whether the pump is on. Even when the pump is off, the program opens and closes the top-up valve to maintain correct pressure in the return manifold. Of course its ok to temporarily quit with dignity and close the program to do computer maintenance such as installing OS updates. However, avoid leaving the program off more than a few hours at a time. Any event in which the program is not running for more than a couple hours at a time, the data analysis team should be notified that pressure regulation was temporarily lost, usually by submitting an ELOG entry.
  
-A known issue with system is the tendency for sensors to hiccup. The voltage output of a sensor as read by the computer will sometime abruptly jump well outside the limit set for the sensor. In these cases, the actual condition at the sensor is ok and there is nothing wrong with the gas system itself. The duration of these hiccups are usually short enough such that they will not pass through the software's low pass filter. However this is not always the case and these hiccups can trigger the pump to go into emergency shutdown. In these cases the pump can be restarted as outlined above.  +When the pump shuts down it's ok to try restarting it as the cause of shutdown may have been an erroneous sensor hiccup. However, if there is a new leak, the o2 levels will remain high and will not start to come down after a few minutes of running. In this case the pump should be turned off as to deter the spreading of O2 from the leak site to other places in the system.
- +
-In any case when the pump shuts down it's always ok to try restarting it as the cause of shutdown was most likely an erroneous sensor hiccup. However, if there is a new leak, the o2 levels will remain high and not come down after a few minutes of running. In this case the pump should be turned off as to deter the spreading of O2 from the leak site to other places in the system.+
  
 If turning on the pump CAUSES any of the pressures to rise outside their limits, the pump should be turned off immediately. This most likely indicates a mechanical blockage downstream of the pump, such as a jammed closed recirculation valve. The over-pressurization caused by running the pump under these conditions could cause a catastrophic failure and hence a huge leak.   If turning on the pump CAUSES any of the pressures to rise outside their limits, the pump should be turned off immediately. This most likely indicates a mechanical blockage downstream of the pump, such as a jammed closed recirculation valve. The over-pressurization caused by running the pump under these conditions could cause a catastrophic failure and hence a huge leak.  
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 A backup of the Gas Rack folder containing the necessary controller VIs, configuration files and the executable: A backup of the Gas Rack folder containing the necessary controller VIs, configuration files and the executable:
  
-{{:vetoshield:gasrackbackup2015-1-27.zip|}}+{{:vetoshield:gasrackbackupv2015-7-1.zip|}}
  
-The main VI (gas_rack_controller.vi) is in the folder "Controller and SubVIs" folder along with the SubVIs it directly calls. A copy of the exectuable along with the helper files is alongside these files in another folder called "builds". Some of the SubVIs outside the "Controller and SubVIs" folder are also needed while some are just testing VIs.+The main VI (gas_rack_controller.vi) is in the folder "Controller and SubVIs" folder along with the SubVIs it directly calls. A copy of the exectuable along with the helper files are inside the folder called "builds". Some of the SubVIs outside the "Controller and SubVIs" folder are also needed. There are some unused VIs. 
 + 
 +The LabVIEW code was written in LabVIEW 2012. If using the .exe instead of the VI, LabVIEW itself does not need to be installed but you must have the LabVIEW run-time engine (version 2012f3) and DAQmx 9.4.0 installed. 
 + 
 +Also included is the firmware code to program the CPLD located on the control board located inside the blue panel: 
 + 
 +{{:vetoshield:gas_rack_cpld.zip|}}
  
 For additional information on the gas re-circulation system contact Jeff Gunderson at gund0328@umn.edu or 612-669-7962. For additional information on the gas re-circulation system contact Jeff Gunderson at gund0328@umn.edu or 612-669-7962.
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 {{:vetoshield:mixer_control_board.jpg?700}} {{:vetoshield:mixer_control_board.jpg?700}}
  
-===Programming control=== +The CPLD configuration file is posted at the end of this manual along with the software written in LabVIEW.
- +
-[Joe is currently in the process of finding a copy of the CPLD programming to post right here. Upon repetitive failure to find the copy, this subsection will be omitted.]+
  
 ===Software Control=== ===Software Control===
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 ====References and Additional Information ==== ====References and Additional Information ====
  
-Here is a backup containing the VIs and the configuration file needed to run the gas mixer. The top level VI is called "Mixer Control 3.vi":+A backup of the Gas Mixer folder containing necessary software needed to run the controller: 
 + 
 +{{:vetoshield:gas_mixer_2015-7-15.zip|}} 
 + 
 + 
 +The main VI (mixer_controllerYYYY-MM-DD.vi) is included along with the necessary SubVIs. A copy of the pre-compiled executable along with a few helper files is alongside these files in another folder called “builds”. Also included are the necessary auxiliary files the controller needs access to which are the three log text files it writes to plus the config file "gas mixer.ini" and the mail list it reads from.  
 + 
 +The LabVIEW code was lasted edited in LabVIEW 2012. If using the .exe instead of the VI, LabVIEW itself does not need to be installed but you must have the LabVIEW run-time engine (version 2012f3) and DAQmx 9.5.1 installed. 
 + 
 +The CPLD firmware is also included: 
 + 
 +{{:vetoshield:gas_mixer.zip|}} 
 + 
 +There is an up-to-date version of the .jed configuration file. The source code included is not the most recent version but is the only version I have been able to find. 
 + 
 + 
  
-{{:vetoshield:mixer_backup12-13-12.zip|}} 
  
-For additional information on the gas mixing system try Joe Pastika at past0035@umn.edu. 
vetoshield/gas.1423160284.txt.gz · Last modified: 2015/02/05 12:18 by jeff

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