PA101 photoacoustic gas analysis module

User manual

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Version 0.23,

12 September 2011 Table of contents 1.   Unpacking ................................................................................................. 4  

1.1.   Package list ......................................................................................... 4  1.2.   Damage inspection .............................................................................. 4  1.3.   Unpacking the module ......................................................................... 4  1.4.   The transportation mode ..................................................................... 4  

2.   Technical specifications ............................................................................ 4  3.   The front and rear panel connections ........................................................ 6  4.   Connecting PA-101 to a FTIR instrument ................................................. 8  

4.1.   Setting up the module and position adjustment .................................. 8  4.2.   Electrical connections ........................................................................ 11  4.3.   Optical connection ............................................................................. 11  4.4.   Sample gas connections ................................................................... 11  4.5.   The normal operation of the PA101 gas analysis module ................. 11  

5.   Operation of the controller unit ................................................................ 12  5.1.   The internal tubing of the gas sampler .............................................. 12  5.2.   The controller user interface .............................................................. 13  

5.2.1.   The parameters and actions ....................................................... 15  5.3.   The gas exchange procedure ............................................................ 16  5.4.   The gas exchange procedure with target pressure ........................... 17  5.5.   The flush procedure .......................................................................... 18  5.6.   The triggered operation ..................................................................... 18  5.7.   Gas sampling examples .................................................................... 19  5.8.   The gas exchanger performance ...................................................... 19  5.9.   Operating the temperature controller ................................................ 20  

6.   Operating the DSP module ..................................................................... 21  6.1.1.   Setting the DSP analog output gain factor .................................. 21  6.1.2.   Operation modes ........................................................................ 21  6.1.3.   Reset button ............................................................................... 22  6.1.4.   Switching between modes .......................................................... 22  

7.   Purging .................................................................................................... 22  8.   FTIR instrument parameters ................................................................... 23  9.   User adjustment and servicing ................................................................ 23  

9.1.   Changing the window ........................................................................ 23  9.2.   The particle filter ................................................................................ 23  

10.   Service .............................................................................................. 23  10.1.   Contacting Gasera Ltd. for service .................................................... 23  10.2.   Shipping the module for service ........................................................ 24  

Annex 1   Opus settings for Bruker Tensor and Vertex FTIR ..................... 24  OPUS Advanced window ........................................................................ 24  OPUS Optic window ................................................................................ 25  OPUS Acquisition window ....................................................................... 25  OPUS FT window .................................................................................... 26  

Annex 2   Thermo OMNIC settings for Thermo/Nicolet FTIR ..................... 27  

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OMNIC Collect window ........................................................................... 27  OMNIC Bench window ............................................................................ 27  OMNIC Quality window ........................................................................... 28  OMNIC Advanced window ...................................................................... 28  

Annex 3   Perkin-Elmer Spectrum settings (the older version) ................... 29  Spectrum Instrument tab in Instrument setup window ............................ 29  

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1. Unpacking

1.1. Package list

• PA101 Photoacoustic Gas Analysis Module • Signal cable with BNC and FTIR specific connectors • Power supply for the PA-101 Gas Analysis Module • Purge tube • User Manual • Extra particle filter

1.2. Damage inspection

After receiving the PA-101 product please inspect the product case(s) and inform the freight company and your supplier in the case of shipping damage.

1.3. Unpacking the module

Carefully unpack the PA-101 delivery package and use the package list to verify that all are included. Please, read the instructions carefully before operating this instrument.

1.4. The transportation mode

The PA-cell inside the cover of the PA101 is automatically secured for transportation. The transportation mode is active when PA101 is not placed on the mounting plate and when it is placed on the mounting plate the pins on the plate release the PA-cell to be supported by the vibration isolation system.

2. Technical specifications 1. Materials in contact with gas in the PA cell:

• FPM (seals, solenoid valves) • NBR (solenoid valves, gas connectors) • PPA, PBT (solenoid valves, gas connectors) • PPS, EPDM (gas pump) • Stainless steel (solenoid valves, gas connectors) • IR-window of the cell: BaF2, KBr or other specified • Gold (cantilever and PA cell) • Glass (BK7) (beamsplitter of the optical microphone) • Nickel (gas exchange unit block, gas connectors) • PTFE (tubes, particle filters) • PP (particle filters)

2. Dimensions: 16,5 cm W x 29,0 cm H x 16,5 cm D (6,5 in W x 11,4 in H x 6,5 in D)

3. Weight: 6.0 kg 4. Total internal gas volume: 30 ml

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5. Operational conditions: • Ambient temperature range: 15 °C – 45 °C • PA101 operation temperature: approx room temperature – 50

°C • Humidity range: Below 90% RH, non-condensing • Pressure range: Ambient level • Dust/water resistance: IP20 (IEC 529) • Shock/vibration endurance: Vibrations can affect the

measurement results • Acoustical level: Loud sounds can affect the measurement

results 6. Storage conditions:

• Temperature range: -20 °C – +60 °C 7. Sample gas conditions:

• Temperature: The room temperature or below AND non-condensing

• Pressure: 300 mbar – 1500 mbar • Moisture: Non-condensing at sample temperature • Gas flow with bypass flow: approx. 1 liters/minute • Particulates size < 1 µm

8. Gas connections: • Connector type: Push-in connector • Connector size: For 6/4 mm tubing

9. Electrical connections: Power supply unit: • Input voltage: 100 - 240Vac, 50 - 60 Hz • Input power max: 60W Analog outputs: • Output connectors: BNC or D9 connector • Output signal voltage span: +- 3.3 V • Output signal frequency band: Low pass filtered, 0-10kHz • Output load: >2k resistive Trigger I/O: • Input trigger should be pulled to ground for a trigger with open

collector output or similar. 10. Measurement specifications:

• Detection limit: Gas dependent. Typically in the sub-ppm region. • Optical path length: 80 mm at optical axis • Repeatability: < 1 % of measured value in reference conditions at

the calibration concentration • Temperature stability: Ambient temperature change within the

operational temperature range will not cause drift • Recommended FTIR scan speed: 0.16 cm/s or less (2.5 kHz

HeNe frequency) 11. Compatible with following FTIRs:

• Bruker Tensor and Vertex series • Thermo Nicolet 6700/8700 and Nexus series • Perkin-Elmer Spectrum Two, Spectrum One, Spectrum 100

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• Varian/Bio-Rad 3000/4000/6000/7000 • Agilent/Varian 640/660/670/680 • Jasco FT/IR-4000/6000 • Shimadzu IRAffinity-1 /IRPrestige-21 • list is continuously growing, ask for other models

3. The front and rear panel connections

Figure 1. The front panel of the PA101.

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Table 1. The descriptions of buttons, LEDs and switches of the DSP section.

The PA-signal control section Power LED Indicates that the DSP receives power. Status LED Indicates the status of the DSP. Please, see Table 6

and section 6. MODE button Changes the operation mode of the DSP. Please, see

the section 6 for more information. RESET button Resets the DSP. GAIN selector Selects the gain for the output amplifier.

Table 2. The descriptions of buttons, LEDs and switches of the Gas exchanger section.

The gas exchanger and temperature controller section Status LED Indicates the status of the controller. The led is lit when

procedure is being executed, blinking when the controller waits for user input and not lit while inactive.

START button Starts procedures and enters to lower menu levels. Please, see the section 5.2 for more information.

CANCEL button Cancel procedures and returns to the previous menu. SELECT button Is used to enable editing mode and confirming the

values. Please, see the section 5.2 for more information.

ADJUST knob Is used for adjusting parameter values and menu items.

Table 3. The descriptions of the gas ports of the PA101.

Gas ports PURGE To purge the interiors of the PA101 with inert gas.

Please, see the section 7 for more information. SAMPLE OUT The sample gas exits from this port. Please, see

section 4.4 for more info. SAMPLE IN The sample gas is drawn in through this port. Please,

see section 4.4 for more info. This port is equipped with a particle filter which is located under the cover, see section 9.2 for more info.

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Figure 2. The rear panel connections and on/off switch of the PA101.

Table 4. The description of the rear panel switch and connections. The rear panel item On/off switch The switch is used to switch the power on or off. Power socket The power jack from the power supply is connected

into this. USB socket For service and diagnostics. Analog output 1 A BNC connector for the photoacoustic and

diagnostic signal output. Analog output 2 A BNC connector for the diagnostic signal output. I/O For I/O trigger signals.

Table 5. The pinout of the D9 I/O connector. Pin Function Pin Function 1 Trigger input – connect to

open collector output. 6 NC

2 NC 7 NC 3 NC 8 NC 4 NC 9 NC 5 GND - -

4. Connecting PA-101 to a FTIR instrument

4.1. Setting up the module and position adjustment

The PA-101 photoacoustic gas detector includes a highly sensitive pressure sensor for detecting small pressure pulses inside the closed sample cell, which are generated by the absorption of infrared light in the sample gas. In

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order to achieve optimal signal-to-noise ratio, the amount of vibrational noise should be minimized. For vibration isolation, springs are used in the detector support structure inside the analysis module. With these springs the PA cell has a resonance frequency of about 8 Hz and noise caused by vibration is effectively attenuated above this frequency. The acoustical attenuation of the cell is about 80 dB, but still loud human voice, for example, can be detected in the noise spectrum of the detector – the detector is capable to detect sound levels of approximately -20 dB. Therefore, for ultimate performance all acoustical noise sources should be isolated. The PA101 is supplied with a mounting part which fits into the sample compartment of your FTIR instruments. First the mounting part is inserted into your FTIR instrument after which the PA101 is lifted on top of the mounting parts so that the pins fit. The position of the PA101 can be adjusted from the two adjustment screws at the mounting part which are shown in the Figure 3. When all the cables are connected and system is turned on, the FTIR control software is turned on and set in the monitoring mode. One gas exchange is done for PA101 by pressing the “START” button when the display shows the text “GasExhng”. More accurate description of the gas exchanger operation is given in the section 5. The gas exchange will make sure that the PA-cell contains the compounds H2O and CO2 of air. Then the screws height and depth, which will move the PA101 in the corresponding directions, see the Figure 3, are adjusted so that the maximum signal of H2O or CO2 is obtained. In practice the optimum ranges of the screws for the maximum signal are quite wide so the adjustment might be not necessary at all, see the figure Figure 4.

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Figure 3. The position adjustment screws of the PA101 are shown.

Figure 4. The optimum range is quite wide for the height and depth adjustment so in many cases no adjustment is required.

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4.2. Electrical connections

The power supply should be connected to the power network with 100-240 V and 50-60 Hz. The cable of the power supply is connected to the +12VDC input at the rear panel of the analysis module. The LED with text “POWER” in the front panel of the gas analysis module are lit when power is switched on from “POWER” switch on the rear panel. The coaxial cable with a BNC and FTIR specific connector, e.g. D15 or D9 connector is used to connect the detector to the FTIR instrument. The BNC connector is connected to Analog Output 1 and the other connector is connected to the connector located usually in the sample compartment or on the rear panel of the FTIR instrument.

4.3. Optical connection

The PA101 is mounted to the sample compartment of the FTIR instrument. The diameter of the photoacoustic cell in PA101 is 8 mm and IR beam from the FTIR is guided into the cell with an elliptical mirror with imaging ratio of 0.5. E.g. if the IR focus size in the sample compartment is 12 mm, the size of the image at the PA cell window is 6 mm which in this case would give a tolerance of 2 mm in total.

4.4. Sample gas connections

The PA101 gas analysis module is equipped with push-in input and output gas ports for a tube with the outer diameter of 6 mm. The input side should be connected to the gas supply with pressure between 300 mbar and 1500 mbar. The factory default gas exchange procedure, for the parameters and procedure see Table 8 and Figure 7, consumes about 35 ml of gas which should be provided by the sample gas reservoir during the whole gas exchange procedure within the required pressure limits. The external particle filter should be always used with a mesh of <1um. This particle filter is located inside of the filter block. Otherwise there is danger of contamination of the gas cell and the particles can get jammed into the cantilever gap. The particle filters are available from Gasera or from your supplier.

4.5. The normal operation of the PA101 gas analysis module

When the PA101 is powered on, it starts an initial calibration procedure which takes about 30 s and is indicated with blinking blue status led of the DSP. When this is done the status LED of the DSP is constantly blue and the photoacoustic signal is provided from Analog Output 1.

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Table 6. The operational modes indicated by the status led of the DSP.

The status LED of the DSP

The status of the system

Constant blue Normal operation. The photoacoustic signal is provided from Analog output 1.

Blinks with blue and off The initial calibration after signal is recognized. Executed every time after the power up.

Red two blinks occasionally while constant blue

The signal level is too high and the Analog output signal is saturated. Use lower gain. This is usually seen at the position of the interferogram center-peak if the gain is too high.

Blinks with green and off Gas exchange procedure is active. No output is provided from analog outputs.

Blinking with red and off constantly Error status. Contact service.

5. Operation of the controller unit While the gas exchange procedure or flush is active the PA101 gas analysis module does not produce any signal from the Analog outputs! The temperature controller starts to control the temperature when the system is powered up with the last saved target temperature.

5.1. The internal tubing of the gas sampler

The schematic of the gas exchange unit is shown in the Figure 5. The only visible parts are the sample in and out connectors which are in the front panel of the PA101. The PA cell is equipped with flow constraints which limit the rate of flow through the PA cell in order to protect the cantilever from breaking. The gas exchange system is also equipped with a mechanical gas relief valve which has the opening pressure between 0.5 and 0.8 bars over the current ambient pressure. The “Sample in” connector must be always equipped with a particle filter which is located inside the stainless steel cover.

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Figure 5. The schematic of the Gas exchange system is shown in the figure

above. All the parts shown in the figure above are inside of the PA101 except the Sample IN and EXHAUST connectors.

5.2. The controller user interface

The user interface of the gas sampler consists of three buttons, START, CANCEL and SELECT, a rotating knob, ADJUST, two LED indicator lights, POWER and STATUS, and a display. The menu diagram is shown in the Figure 6. When the controller is powered on the power led is on and the display shoes the main menu item. The main menu items are browsed with the ADJUST and by pressing the START the displayed item is chosen or procedure started. The main menu items are shown in the Table 7. All the gas exchange procedures can be cancelled immediately by pressing the CANCEL button. If the gas exchange procedure is active while the procedure is cancelled, the pump is shut down and all valves are closed. The Settings, Temperature settings and Pressure Loggings menus are accessed by pressing the START while display shows corresponding item name. The Settings display also shows the current software version. The parameters in the settings menu and data related to them are shown in the Table 8. The parameters can be browsed with the ADJUST knob and the editing mode is accessed by pressing the SELECT button which after the parameter can adjusted from ADJUST knob. The value will be confirmed by pressing the SELECT button or the value will remain unchanged if the CANCEL button is pressed. The single parameter value can be saved to memory by pressing START button for 2 seconds while the display shows the parameter.

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The gas exchange, gas exchange with target pressure and flush procedures are described in the sections 5.3, 5.4 and 5.5, respectively. The Input Pressure action opens the valves 1 and 3 and measures the pressure at the Sample IN port. This action can be used to adjust the pressure of the gas sampling system or to get the ambient pressure which can be used to set a valid value for the parameter ClsPress. The repeated gas exchange procedures, Repeatng Exchange and RptTargt Exchange, repeats the gas exchange procedure with the current parameters with the time defined with the parameter IntwTime between the gas exchange procedure starts. The gas exchange procedures are repeated a number of times defined with the parameter Repeats. If the Repeats parameter is 0 the gas exchange procedure is repeated until CANCEL is pressed. If the gas exchange procedure is active, it will be interrupted and the pump is shut off and valves are closed. Between the gas exchanges the display shows time in seconds to the next gas exchange procedure. If the IntwTime is 0, the triggered operation is activate, which is described in the section 5.6. The temperature control is operated from the Temperat Settings menu described in the section 5.9.

PARAMETERS:ADJUST  the  parameter.Pressing  the  SELECT  shortly  saves  the  change  and  CANCEL  button  cancels  the  change.  Single  parameters  can  be  saved  by  pressing  START  for  2s.

Settings  and  Temperature  settings:  Select  the  parameter  with  the  ADJUST.  Parameters  available  are  shown  in  the  other  table.  Pressure  log:  Browse  the  saved  pressure  values  with  ADJUST.

The  main  menu:

The  available  menu  items:•Gas Exchange:  Gas  exchange  procedure•TargtPrs Exchange:  Gas  exchange  with  target  pressure•Repeatng Exchange:  Repeated  gas  exchange,  also  for  triggered  operation•RptTargt Exchange:  Repeated  gas  exchange  with  target  pressure,  also  for  triggered  operation•Flush:  Flush  tubes•Input Pressure:  Open  the  input  and  measures  pressure  at  the  inlet•Pressure Loggings:  View  the  pressure  values  of  previous  gas  exchanges.•Temperat Settings:  The  temperature  controller•Settings:  Access  the  setup  and  also  shows  the  software  version

SELECT

CANCEL/SELECT

START

CANCEL

STARTProcedures  are  started.  The  CANCEL  button  cancels  the  procedures  immediately  and  returns  to  the  main  menu.

CANCEL

START  (2s)

ACTIONS:Saveall and  Fctrydefare  executed  by  pressing  the  START  button  (2s  for  the  FA)  which  after  the  display  returns  to  the  main  menu.

Figure 6. The menu diagram is shown in the figure above. For explanation,

please, see the text and tables Table 7 and Table 8.

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The Pressure Loggings contains the pressure values saved during different phases of the previous gas exchange procedure. The phases for saving the values are marked in the diagrams in the Figure 7,Figure 8 and Figure 9.

5.2.1. The parameters and actions

Table 7. In the table below are shown the main menu items.

Action Description The main menu items. Gas Exchange

The gas exchange procedure. See the Figure 7 for details. The procedure can be cancelled immediately by pressing the CANCEL button.

TargtPrs Exchange

The gas exchange procedure which controls the cell pressure accurately at the end of the procedure as long as the input pressure is higher than the target pressure.

Repeatng Exchange

The gas exchange procedure is repeated for Repeats times or infinitely (Repeats=0). The parameter IntwTime is the time between the starts of the gas exchange procedures. The procedure can be cancelled immediately by pressing the CANCEL button.

RptTargt Exchange

Repeating gas exchange with target pressure is Repeated gas exchange with a target pressure.

Flush Tube flushing: This action pumps the gas through the tubes only effectively flushing the tubes. The procedure can be cancelled immediately by pressing the CANCEL button.

Input Pressure

With this action the input pressure can be checked. The status LED is on while this action is enabled. The valves 1 and 3 are opened and the display shows the pressure which is updated in every 0.1 s. The procedure can be cancelled immediately by pressing the CANCEL button.

Pressure Loggings

Show pressures from the last gas exchange executed. The values shown are presented in the procedure sections.

Temperat Settings

The settings menu is accessed from this display. The settings menu also displays the current software version.

Settings Sxx.xx

The settings menu is accessed from this display. The settings menu also displays the current software version.

Table 8. In the table below are shown the parameters with their

descriptions, allowed range, resolution, display units and the factory default values and Saveall and Load Factory defaults functions. These parameters and actions are accessed from the Settings menu.

Parameter Description Range Reso-lution

Display units

Factory default

PumpTime

Gas exchange pump time

1,...,200 1 s 1 s

UndrTime Evacuation time in gas exchange with target pressure.

0,...,200 1 s 0 s

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CyclCnt Gas exchange cycle count

1,...,100 1 3

WaitTime Wait time for pressure stabilization

1,...,200 1 s 5 s

ClsPress Valve closing pressure

300,...,1500

1 mbar 990 mbar

TrgPress Target pressure of the gas exchange with target pressure.

300,...,1500

1 mbar 500 mbar

RflTmrFc Refill time factor for the gas exchange with target pressure.

1,...,250 1 40

TimeOut Timeout 1,...,200 1 s 10 s IntwTime Time between the

starts of repeated gas exchange procedures.

0,...,200 0 for the triggered operation

10 s 60 s

Repeats Number of the repeated gas exchange procedures

0,...,100, 0 for the infinite loop

1 0

FlshTime Flush time 10,...,600 10 s 10 s ExecMask DO NOT CHANGE. Different service modes are

accessed by changing this value. 1

SaveAll Save the adjusted parameters to be the power on defaults. FctryDef Load the factory settings for the all parameters. The START

button needs to be held down for 2 s for activation.

5.3. The gas exchange procedure

The gas exchange procedure is described in the Figure 7. In the procedure the gas is drawn through the cell for defined time. Since the flow through the flow constraints is quite much less than the pump can draw, a low pressure is created into the volume before the pump. The pressure is allowed to rise up to pressure defined with ClosePrs parameter which after the procedure is repeated or stopped depending on the parameter CyclCnt. When the pumping cycle is done, the input valve is closed and the pressure stabilizes for a few seconds after which the final pressure is measured and saved into log and the cell valves are closed. Due to this process the last saved and displayed value represents the pressure inside of the PA-cell. The final pressure depends on the parameter ClosePrs and on the pressure at the sample input. For more accurate pressure control see the next section.

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Stop  the  pump.

Run  the  pump  for  PumpTime s.

The  process   starts  when  the  START  button  is    pressed  while  the  DISPLAY  shows  “Gas Exchange”. Open  valves  1,  4,  5  and  6.

Close  the  valve  4.

Wait  until  pressure   is  equal  or  more  than  ClosePrs mbar  or  until  timeout  TimeOut s.  Add  one  to  the  loop  counter:  N  =  N+1.N  P CyclCnt ?

Yes

No

Close  the  valve  1.

Wait  for  WaitTime s  and  measure  the  pressure  after   that.

Close  valves  5  and  6.

DISPLAY/PRESSURE  LOG  VALUES

The  last  measured  pressure   at  the  pressure  sensor   is  shown  before  the  closing  of  the  cell  valves  5  an  6.  Pressing   the  CANCEL  button  returns   to  the  main  menu.  Pressure   value  saved  to  ResPrs#3.

FUNCTION

Loop  counter  N=0.

The  actual  pressure   at  the  pressure  sensor   is  shown  throughout  the  whole  process.Pu

mp  

sequ

ence

Pressure  value  saved  to  ResPrs#1.

Pressure  value  saved  to  ResPrs#2.

Figure 7. The gas exchange procedure diagram is shown above.

5.4. The gas exchange procedure with target pressure

The gas exchange procedure with a target pressure has two differences to one described in section 5.3. In the procedure shown in Figure 8 the final pressure is controlled more accurately and before the pumping sequence shown in Figure 7 the gas from the PA-cell is evacuated with input valve closed. The PA-cell pressure can be set from 300 mbar up to 1500 mbar, while the accuracy depends on the parameter RflTmrFc. The twait parameter shown in the Figure 8 is calculated from the equation

where TrgPress and RflTmrFc are defined in the settings menu and p   is the current pressure with units of mbar. The optimal performance of this procedure depends on the value of the RflTmrFc and it has different values depending on the target pressure. The default value 40 works for the low pressures, <400 mbar, and should be increased when higher pressures are used.

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Do  the  pump  loop,  see   the  gas  exchange  procedure  description.

Run  the  pump  for  UndrTime s.

The  process   starts  when  the  START  button  is    pressed  while  the  DISPLAY  shows  “TargtPrsExchange”. Open  valves  4,  5  and  6.

Open  valve  1.

Close  1  and  open  valve  3.  

N  P CyclCnt ?

Yes

No

Pump  for  1  s.

Open  valve  1  and  wait  for  twait  ,  see  text  for  the  formula  and  close  valve  1.

Close  valves  5  and  6.

The  last  measured  pressure   at  the  pressure  sensor   is  shown  before  the  closing  of  the  cell  valves  5  an  6.  Pressing   the  CANCEL  button  returns   to  the  main  menu.  Pressure   value  saved  to  ResPrs#4..  

FUNCTION

Loop  counter  N=0.

The  actual  pressure   at  the  pressure  sensor   is  shown  throughout  the  whole  process.

Close  valves  3  and  4.

pressure  >  TrgPress ?No

DISPLAY/PRESSURE  LOG  VALUES

Figure 8. The gas exchange with target pressure diagram is shown above.

5.5. The flush procedure

The flush procedure draws the gas through the tubes and bypasses the PA-cell. The procedure can be used to flush the tubes or to circulate gas if headspace analysis is done. The  process   starts  when  the  START  button  is    pressed  while  the  DISPLAY  shows  “Flush”.

Run  the  pump  for  FlshTime s.

Open  valves  1,  3  and  4.

Stop  the  pump.Wait  until  pressure   is  equal  or  more  than  ClosePrs mbar  or  until  timeout  TimeOuts.  

Close  the  valves  1,  3  and  4.

FUNCTION

The  last  measured  pressure   at  the  pressure  sensor   is  shown  before  the  closing  of  the  valve  3  and  the  value  is  saved  to  ResPrs#3.  Pressing   the  CANCEL  button  returns   to  the  main  menu.

Pressure  value  saved  to  ResPrs#1.

Pressure  value  saved  to  ResPrs#2.

DISPLAY/PRESSURE  LOG  VALUES

Figure 9. The flush procedure diagram is shown above.

5.6. The triggered operation

The gas exchange procedure can be started also with an external trigger. External trigger operation is activated by setting the parameter IntwTime to 0.

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When the repeated gas exchange or repeated gas exchange with target pressure procedure is started the controller waits for trigger for the procedure start. Trigger is activated pulling the pin 1 at the I/O connector to ground, pin 5, for the trigger. While the gas exchange procedure is active pulling the trigger to ground has no effect.

5.7. Gas sampling examples

In the Figure 10 are shown the two possible gas sampling schemes. In any case the gas reservoir should be capable to provide total amount of gas displaced during the gas exchange procedure, the default ~35 ml, with pressure over the parameter ClsPress or LowPress and within the time of the gas exchange procedure, default approx 40 s. This gives minimum flow of 52.5 ml/min for the flow in to the PA101 with pressure above parameter ClsPress.

Figure 10. Two possible gas sampling schemes are shown in the figure

above. In the example A) the gas is supplied directly to the SAMPLE IN and there is no constant flow of the sample gas. With the by-pass flow B) the sample flows by the SAMPLE IN and the gas is sampled from the flow every time the pump runs. The tube after the T-piece is required to make sure that in case of backflow the input sample is not mixed with the ambient gas.

5.8. The gas exchanger performance

The gas exchanger pumping performance was tested with a normal gas exchange procedure. The volume displacement was measured from the output with gas pressure of 1 atm while air was used for the tests. The tests were performed with different pumping times by varying the parameter PumpTime with one pumping cycle, CyclCnt = 1, and other parameters were the defaults. The particle filter was connected to the input of the PA101. The results of the measurements are shown in the Figure 11.

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Figure 11. The volume displacement of the gas exchanger module against

the pumping time PumpTime=1s with one pumping cycle , CyclCnt =1. During the first second of the gas exchange the pump draws gas with pressure near atmospheric pressures and after that a steady state condition is created in which the flow constraints limit the flow and the pressure next to the pump is below 0.5 atm as can be seen from the pressure display during the gas exchange procedure. The total volume displacement, V, for a gas exchange with pumping time of P1 can be calculated from equation

, so with default parameters, PumpTime = 1 s and CyclCnt = 3, the total volume displacement is about 35 ml when taking into account the fluctuations of the displacement between different pumping. The Flush procedure was tested with particle filter at the input and with tubes of 4 mm of internal diameter and 1 m length at the input and output. The measured flow was approximately 1 l/min for the flush procedure.

5.9. Operating the temperature controller

The temperature controller is accessed from the main menu item Temperat Settings. The items in this menu are described in the Table 9.

Table 9. The menu items in the Temperat settings menu. View mode Edit mode Description Cell Tmp cur ttºC

Cell T set>tt<C

In normal mode displays the current temperature of the PA-cell. In edit mode the target temperature can be set. The tt stands for digits of the temperature value.

GasExTmp cur ttºC

GasEx T set>tt<C

In normal mode displays the current temperature of the pump and valve block . In edit mode the target temperature can be set.

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When the PA101 is powered on the heating is started immediately if the set temperature is higher than the temperature of the PA101. If this not desired the set temperature should be set to a value always below the ambient temperature and the value should be saved in the memory by pressing the start button for 2 seconds while in the edit mode.

6. Operating the DSP module There are two indicator LEDs in the front panel of the DSP module: Power and Status. The Power LED indicates that there is a 12 VDC voltage in the DSP Module's power input and the power switch is turned on when the LED is lit. The Status LED indicates the current operating mode of the unit using different colors and blinking modes.

6.1.1. Setting the DSP analog output gain factor The DSP analog output gain factor is set from the selector at the front panel. This gain affects only to the gain of the D/A output in the DSP. When the output signal exceeds the maximum output voltage a clipping occurs and the status led gives a red blink. In case of clipping select the next lower gain until the status led is constant blue.

6.1.2. Operation modes

Normal operating mode (constant blue) The photoacoustic signal is outputted from the Analog output 1. A constant zero voltage is generated to the Analog Output 2.

Diagnostics mode (blinking pink) In this mode the DSP Module does not process the signals from the laser interferometer. The signals from the laser interferometer are available from the Analog Output connectors 1 and 2. If the LED is blinking and it is most of the time lit, the outputs are the calibrated laser interferometer signals. If the LED is blinking and most of the time unlit the outputs are the raw interferometer signals. When both outputs are connected to an oscilloscope, which is in the XY mode, the calibrated signal should stay on a circle with radius of 1 V. The raw laser interferometer signal should be close to a circle with some amount of elliptical shape. If the shorter ellipse half axis drops below 0.5 V, an error occurs and the PA detector needs maintenance! TIP: To see the XY signal in the diagnostic mode from an oscilloscope screen tap the detector lightly with your finger to create displacement of the cantilever

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sensor.

Error indicator (blinking red) Blinking red color in the status LED indicates an error condition. A single blink every second indicates that the analog output signal level exceeds the output range of the DA-converters (analog clipping). If this happens when recording an interferogram, lower analog gain factor should be used. Continuous blinking means that DSP Module has not detected signals from the laser interferometer. This is a case when the PA cell is not connected to the DSP module or when the laser interferometer signal drops below 0.5 V.

Initial calibration (blinking blue) When the optical microphone is making a self calibration after power on, the status LED is blinking blue.

6.1.3. Reset button Pressing reset button in the front panel resets the DSP Module. After reset, the DSP is in the normal operating mode and automatically starts initial calibration sequence of the laser interferometer which lasts for about 30 seconds.

6.1.4. Switching between modes A single click of the Mode button switches between modes in the following order: The normal operating mode, calibrated output in the diagnostic mode, raw output in the diagnostics mode and back to the normal operating mode.

7. Purging In order to obtain all the available infrared light power into the PA-101 gas cell or to make quantitative measurements of CO2 or H2O, the optical path of the infrared beam should be purged using an inert gas, e.g. N2. The connector for purging the PA101 gas analysis module is located at the front panel of the instrument, which fits a 6 mm tube (outer diameter). The purge tube is equipped with a black soft tube that slides along the purge tube tightly against the FTIR sample compartment wall. There are two alternative ways to perform the purging: 1) If the purge gas comes through the FTIR instrument, with window removed from the sample compartment wall, no action is needed. Now the interiors of the PA101 will be purged and gas will flow out through the purge connector. 2) If FTIR has closed purge flow, you can separately purge the optical path from the sample

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compartment wall to the PA101 cell window by inserting a purge gas tube to the purge connector. Let the purging gas flow through the gap between the instrument and the soft tube.

8. FTIR instrument parameters For the optimal operation the FTIR instrument scanning speed should be 2.5 kHz (or less) in HeNe laser frequency, which corresponds to a mirror velocity of 0.1581 cm/s. The center peak in the interferogram signal is weak compared to conventional FTIR since the photoacoustic signal comes from the energy absorbed to gas and not from the energy transmitted through gas. “Autogain” is recommended for the signal gain setting. The output format of the spectrum should be selected to “Single beam”. The aperture of the FTIR should be fully open with all resolution settings in order to maximize the signal. Also, “power spectrum” output is recommended since the signal contains ranges with no signal from which a proper phase correction cannot be calculated.

9. User adjustment and servicing

9.1. Changing the window

The window change requires major disassembling of the PA101 for which reason it is recommended that you contact Gasera Ltd. for that.

9.2. The particle filter

The particle filter in the module has to be changed if the flow through the Gas exchange unit is blocked or significantly decreased or the filters are contaminated. Filters are available from Gasera Ltd or from your supplier.

10. Service

10.1. Contacting Gasera Ltd. for service

Please contact Gasera’s service department via e-mail for authorization and instructions prior to shipping any items for repair. Service e-mail address: service@gasera.fi

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10.2. Shipping the module for service

Package the return carefully in order to avoid any damage during transit and send the system including power supply and cables to address below: Shipping address for service:

Gasera Ltd. Tykistökatu 4, 20520 Turku, Finland

Annex 1 Opus settings for Bruker Tensor and Vertex FTIR

OPUS Advanced window

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OPUS Optic window

.

OPUS Acquisition window

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OPUS FT window

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Annex 2 Thermo OMNIC settings for Thermo/Nicolet FTIR

OMNIC Collect window

OMNIC Bench window

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OMNIC Quality window

OMNIC Advanced window

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Annex 3 Perkin-Elmer Spectrum settings (the older version)

Most of the parameters are automatically set when the PA101 with baseplate is inserted into the Perkin-Elmer instrument.

Spectrum Instrument tab in Instrument setup window

NOTE ! Perkin-Elmer instruments require that the files PA301.ini PA301_icon.bmp PA301_icon1.bmp PA301_icon4.bmp are copied into the computer which runs the Spectrum software. In the older system the files are copied into directory c:\pel_apps\bin while in the newer systems the directory is C:\Program Files\Common Files\PerkinElmer\BeamPath. However, the installation path can be user defined and the correct path is obtained by looking into file pel_apps.ini in the c:\windows directory, which contains the directory info as: [Data Server] Installation Directory = c:\pel_apps The required files are available from Gasera