Flow controllers and RGA setup  

Instructions Written by Nebojsa Marinkovic (Ned)

 

Two identical systems are available, one for each hutch. The procedures below explain operation on any of them.

Up to four gases can be simultaneously regulated and/or mixed using the flow controller setup. If you need to connect more than four gases at any time, check with beeline staff.

 

Mass Flow Controllers and Purification system operation

  1. Go inside the hutch and locate: a) the plate with four Brooks mass flow controllers (MFCs) and b) gas purification rack. In the X18b hutch, both are placed below the Io ion chamber. In the X19A hutch, the mass flow controllers’ plate is sitting on the lower shelf next to the hutch door (on the left hand side), and the purification system is on the left wall (see Figs. 1 and 2).

 

Figure 1. (below left) Mass flow controllers in X19A hutch, showing color-coded gas inlets. Brown stainless steel tubing is reserved for He through purifiers, other three can vary. The MFC outlet (white PVC tubing) should be connected to your reactor system.

Input 3-way valve
 

 

 

 

 

 

 

 

 

 

 

 


Figure 2. Gas Purification system with moisture cartridges (first two on the left) and oxygen cartridges (two on the right).

 

 

 

 

  1. Check that all MFCs are connected to tubes and all inlet valves before MFCs are open. Remember the order of color tubes (green, red, yellow and brown in Fig.1). The brown stainless steel tubing is used for the carrier gas and goes through the purification system. We normally use He as the carrier gas. Thus, the purifier cartridges are saturated with He. If you want another carrier gas, check with beamline staff. Also, check that each MFC has a grey electrical cable connected.
  2. Rotate the input 3-way valve on the gas purification rack to ‘Bypass’ as in Fig.2.
  3. Outside the hatch, connect all gases to color tubes. Make sure that the pressure on the gas regulator is at least 17 PSI (the check valves before MFCs open at pressures reater than 14.7 PSI, or 1 atm).
  4. Check that the electronic MFC regulator box outside the hutch (Fig. 3) has four gray cables connected on the back. Turn the box on.

 

Figure 3. Electronic MFC regulator box on X18b.

 

 

 

 

 

 

 

 

 

 

 

 

 


Each channel on MFC regulator box (above) controls one MFC. Channel 4 is reserved for the carrier gas; other three can vary by the user. Channel 1 is the one closest to you (the first one in Fig.1, connected to the green tubing).

 

  1. Test the flow controller electronic box. Press channel selector key until  ‘ > ’ symbol appears next to Channel 4. Then, press ‘Open,close, reg.flow’ key repeatedly until it changes to ‘ V+ ’. and quickly press ‘Enter’ key. The valve is now fully open, i.e. the flow rate is > 50 mL/min. If there is flow through the MFC #4, it will be displayed.
  2. While channel selector key still points to Channel 4, press ‘Open,close, reg.flow’ key repeatedly until it displays ‘ V0 ‘ and press ‘Enter’. The MFC is now in regulated mode. Using the up or down arrow keys, select the desired flow and press ‘Enter’. The flow is expressed as the percentage of the maximum flow rate of the MFC (50 mL/min). Thus, 20% corresponds to 10 mL/min, 30% corresponds to 15 mL/min, etc. 
  3. Close Channel 4 by pressing ‘Open,close, reg.flow’ key repeatedly until it displays ‘ V- ‘ and press ‘Enter’. Move the selector key to another used channel (e.g. channel 1) and test its flow. Test all other used channels using the procedure above.
  4. If you want to use purification system, rotate its three-way valve to ‘On’. Open the two slave valves by rotating them 90o so that they are vertical, i.e. in line with the tubing (both are closed in Fig. 2). Remember to close them when you no longer need the purifiers, or at the end of your run.

 

 

 

 

 

 

 

 

 

 

Residual Gas Analyzer setup and operation

 

Figure 4. Residual Gas Analyzer

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Residual gas analyzer (RGA) is usually on and ready for use. In an unlikely case that you find it off, it may need several hours before it gets in operating mode. You may want to check with the neighboring beamline users (X18B or X19A) to see if they are using the RGA and whether it is on. If their RGA is ready but not being used, you can roll it to your beamline and use it within an hour. If you need to move the RGA, start from ‘turning RGA off’. If you want to power on your RGA, start with ‘setup’. Start with ‘operation’ if it is ready.

 

Powering RGA off

The turbo pump must stop spinning before you can move the RGA cart. It takes about 30 min to spin it down.

  1. Close the vacuum valve by rotating it 90o clockwise.
  2. Turn off the whole unit by pressing the main switch on the power strip on the bottom of the cart. After the rotary pump stops, the only sound coming from the system is your turbo pump. Wait until you can hear the sound no longer (about 30 min). 
  3. Disconnect gas lines connected to the RGA cart. Input line is connected through the filter just left to the flow meter, exhaust line is connected to the bubbler (see Fig.4). Unplug the power strip and the RS232 cable from the RGA head.
  4. Roll the RGA to your beamline and connect it to the input and exhaust gas lines. Connect the RS232 cable to the RGA head.

 

Setup

1.      Check that the power strip on the bottom of the RGA cart is plugged in. Turn the power strip switch on. The rotary pump starts.

2.      Wait for about one minute, than press ‘start/stop’ button on the turbo pump controller (see Fig. 4). Turbo pump starts. The controller displays the rotation of the turbo pump as it accelerates. Once it reaches 56,000 rpm, the display shows ‘normal operation’. Wait another five minutes before continuing with step 3.

3.      Open vacuum valve (black round valve, Fig 4) by rotating it 90o anticlockwise, so that its line is vertical.

4.      On the ‘pressure readout’ box (fig. 4), press the red button. After its initialization (about 15 sec) the readout shows the pressure next to Pirani gauge 1 (PG 1). The Pirani gauge displays pressures from atmospheric pressure down to 10-4 torr. If the pressure is lower than its limit, it shows zero.

5.      If PG 1 reads zero, press the top black button on the ‘pressure readout’ box labeled ‘IG 1’. Ion gauge is now on. After a few seconds it displays the pressure in the RGA. Depending on how long the RGA unit was off, it may take from ½ to 24 hours before the pressure in RGA reaches 10-8 torr.  Once it does, it is ready for use.

 

Operation

It is important that the RGA sees very little atmospheric gases. Make sure that you flow carrier gas (He) for at least five minutes with the MFC fully open (V+) before opening the RGA inlet valve. Concurrently, purge the gas lines of all gases before inputting them to the RGA.

  1. Do not open the RGA input valve until you test the unit (steps 4-5). Locate the Off/On switch on the RGA head and turn it on. Green ‘Power’ LED light turns on.
  2. Trace the RS232 cable to see which computer it is connected to. Usually it is the users’ computer at X18b, and main (data acquisition) computer at X19A. Locate the RGA icon on the desktop of the computer and double-click on it. The RGA program starts.
  3. Click Utilities – RS232 Setup – Connect. If you get no error messages, your RGA is now ready.
  4. Click on the green “Go’ button on the toolbar at the top of RGA screen. You will get the message warning you that the RGA filament must be on to proceed. Click ‘Yes’ to turn it on. After a few seconds RGA starts collecting data.
  5. In the default (Analog) mode, the screen records intensity vs. atomic mass unit (amu). You will get a screen with peaks at 2, 18, 28, 32 and 44 amu, corresponding to H2, H2O, N2, O2 and CO2 gases (see Fig. 5). As the filament degases, all these peaks diminish. Depending on how long was the filament off, it may take 5 to 30 minutes before the intensity of the peaks reach steady state. It is not necessary to wait for the steady state, you can open the RGA input valve using it after 5 min.

 

 

Figure 5. Typical RGA spectrum with input valve closed. Major peaks are found at mass units of 2 (H2), 18 (H2O), 28 (N2) and 44 (CO2 and/or pump oil).

  1. With He gas flowing, carefully open the RGA input valve (see Fig. 4), making sure not to touch the glass capillary it is connected to. After the initial burst of N2 and O2 peaks (due to air trapped in the capillary), your spectrum should start to show only one major peak at 4 amu.
  2. A powerful feature of RGA program is to view the changes in partial pressure of gases as a function of time. Choose Mode – P vs. T. By default, the program registers only N2, but one can set up to 10 different gases or gas fractions by going into Scan – Table Parameters. The program can check the partial pressure every second (default) or it can accept user-defined time interval (Scan – Schedule).
  3. It may be a good idea to view/record P vs. T along with another scan, e.g. Analog scan (c.f. Fig. 5). If you are still in P vs. T mode, click Mode – Split – Analog. The window divides in two portions, the top showing the Analog scan, the bottom P vs. T. In the split mode, the time interval is defined by the longer of the two modes displayed, i.e. the Analog scan; the minimum time interval to scan 50 amu (with default speed) is 24 seconds. The speed can also be changed in Scan – Schedule.
  4. Data can be saved as a .RGA file, readable only by the RGA program, or it can be saved as a text (ASCII) file that can be processed later with a plotting program. To save it as a text, click File – Save As – ASC text. If you use split screen, the data will be saved twice, first as the top window (Analog scan), second as the bottom window (P vs. T). Make sure you give different names (up to 8 characters) for the two scans. You do not have to stop the scan while saving – the program will save all points it has in memory from the time the scan was initiated.
  5. Fig. 6 shows P vs. T scan of a 15 hour-long run with successive oxidation (with 10% O2 in He) and reduction (with 5% H2 in He) of Cu in CeO2, saved as an ASC file and plotted using Microsoft Excel. Fluctuations in partial pressures of He H2 and O2 are clearly visible, as well as the increase in water level during the reduction process.

 

Figure 6. P vs. T output of the RGA program, showing partial pressures of gases during oxidation and reduction of Cu in CeO2, plotted using Microsoft Excel.