User Manual PA301

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Table of contents 1. Delivery content ........................................................................................ 3 2. PA301 photoacoustic detector .................................................................. 3

3. Getting started .......................................................................................... 4 3.1. Package inspection ......................................................................... 4 3.2. Connecting detector to the FTIR instrument ................................... 4 3.3. ............................................................................................................... 5 3.4. Measuring the spectrum .................................................................. 5

4. Setting up the detector .............................................................................. 5 4.1. Optical connection .......................................................................... 5 4.2. Electrical connections ..................................................................... 6

4.3. Gas connections ............................................................................. 7 4.4. The PA module connections ........................................................... 7

5. Detector operation .................................................................................... 8 5.1. Gain control and DSP-module operation......................................... 8

5.1.1. Setting the DSP analog output gain factor ................................... 8 5.1.2. Operation modes .......................................................................... 8 5.1.3. Reset button ................................................................................. 9 5.1.4. Switching between modes ............................................................ 9

5.2. Rear lever operation of the photoacoustic detector ......................... 9 5.3. Sample loading ............................................................................. 10

5.4. Purging .......................................................................................... 11 5.5. FTIR measurement parameters .................................................... 13

5.6. Test procedure .............................................................................. 13 5.7. Optional heater module ................................................................. 13

6. Service .................................................................................................... 14 6.1. User adjustments .......................................................................... 14

6.1.1. Window replacement. ................................................................. 14

6.1.2. Sample holder tightness adjustment .......................................... 14 6.2. Contacting Gasera Ltd. for service ................................................ 14 6.3. Shipping the module for service .................................................... 14

Annex 1 Opus settings for Bruker Tensor and Vertex FTIR ........................ 15 OPUS Advanced window ........................................................................ 15

OPUS Optic window ............................................................................... 15 OPUS Acquisition window ...................................................................... 16

OPUS FT window ................................................................................... 16 Annex 2 Thermo OMNIC settings for Thermo/Nicolet FTIR ........................ 17

OMNIC Collect window ........................................................................... 17

OMNIC Bench window ............................................................................ 17 OMNIC Quality window ........................................................................... 18

OMNIC Advanced window ...................................................................... 18 Annex 3 Perkin-Elmer Spectrum settings (the older version) ...................... 19

Spectrum Instrument tab in Instrument setup window ............................ 19

Perkin-Elmer initialization and icon files installation ................................ 19

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1. Delivery content

Photoacoustic detector with focusing mirror

Removable sample cups for solid, semi-solid, and liquid samples

Black reference sample

Vibration isolated detector mounting

Digital Signal Processing -module

Power supply (+12 VDC)

Cables to connect the modules and to connect to the FTIR instrument

User manual PA301, (this document)

Storage case

2. PA301 photoacoustic detector PA301 photoacoustic detector is an accessory device to the FTIR interferometers, which can be used for measuring photoacoustic spectra of solid, semi-solid, and liquid samples. Versatile analysis The PA301 detector improves laboratory productivity and safety by enabling extremely versatile and rapid analysis of solid, semi-solid, and liquid samples in any form without sample preparation. The insensitivity to sample surface morphology, the depth profiling capabilities, and sample heatability provide wide applicability in many areas of chemical and biological research which no other single accessory can match. Due to the ultra-high sensitivity of the Gasera novel cantilever sensor, ambient air can be used as the carrier gas to obtain a signal-to-noise ratio (SNR) that is still significantly better compared to other commercial photoacoustic detectors used with helium carrier gas. The quickness and the ease of use make the PA301 a must-have accessory for every lab. Photoacoustic detection Photoacoustic spectroscopy directly measures a sample’s infrared absorption. The absorption of infrared radiation in the sample creates heat which is transferred into the surrounding gas and a photoacoustic signal is generated via thermal expansion. Thus the measurement is non-destructive and the signal is independent of the surface roughness. The measurement depth can be controlled by varying the mirror velocity or phase angle of detection, and thus depth-varying information can be obtained.

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Ultra-sensitive optical microphone The heart of the system is the patented optical microphone comprising of a MEMS cantilever coupled with a laser readout interferometer that can digitally measure microscopic movements of the cantilever sensor, having a dynamic range greater that any analog circuitry can ever obtain.

Technical specifications

Minimum detectable pressure variation in the sample cell: 2 x 10-6 Pa/√Hz (RMS)

Rapid sample change without breaking the purge seal

Analog interface: BNC cable to detector input on the FTIR

Analog output: +/- 2.5 VDC interferogram signal

DSP analog output gain range: 0.02 - 20 in 10 steps

Spectral range defined by window material (UV to far-IR)

Maximum sample size: 10 mm diameter, 9 mm height

Slide mountable

Option for helium purge with automatic purge valve operation

Option for sample heating up to +60 °C

Note: sample compartment baseplate mountings available for most FTIRs

Power supply inlet: 100 - 240V, 50 - 60 Hz, 0.7 A

3. Getting started

3.1. Package inspection

When receiving the analyzer please examine the package and contact the freight company in case of a shipping damage. Carefully unpack the device and refer the content of the delivery package to the packing list.

3.2. Connecting detector to the FTIR instrument

In order to align the detector to the FTIR interferometer the cover of the detector must be removed. Set the detector in the sample compartment of the FTIR instrument, so that the beam from the interferometer is in the centre of the hole in the detector cover and the distance of the focal point from the detector focusing mirror back plate is 48 mm. The PA301 detector connected to the baseplate with correct pre-adjustments are available to the major models of several FTIR instrument manufacturers.

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FIG 1. Position of the detector relative to focus of the FTIR interferometer.

Adjust the exact position using the liquid crystal. The detailed instructions are presented in chapter 4.1. Connect the RJ45 cable from the detector to the optical microphone DSP-module, the signal cable from DSP-module to FTIR-instrument signal input connector and the power adapter cable to DSP module’s 12 VDC connector in the back panel of the module. Turn on the power.

3.3.

3.4. Measuring the spectrum

Set the FTIR instrument mirror velocity as low as possible and aperture to maximum. The photoacoustic absorption spectrum is the single-beam spectrum. Load the sample in the detector and start the measurement. Helium purge can be performed to the cell in order to maximize the signal. The spectra can be normalized by dividing the spectra with the spectrum of black reference sample provided with the detector. The detailed measurement instructions are presented in chapter 5.

4. Setting up the detector

4.1. Optical connection

The focusing mirror of the detector focuses the infrared beam from the FTIR instrument to the sample in the photoacoustic cell. The detector should be

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mounted in the sample compartment so that the distance from the focusing mirror backplane is 48 mm from the focus and the centre of the hole in the cover on the optical axis of the beam. Then the detector is roughly on the correct position. The precise alignment is done by adjusting the finger screws of the mounting plate. The coloured spot on the crystal is observed and the detector is moved according its position. When the spot is in the centre of the crystal the alignment is correct. If the spot is in left, viewed from the direction of the FTIR interferometer infrared beam, the detector has to be moved to opposite direction (right). If the spot is behind the centre, the detector has to be raised.

FIG 2. The grey area is the liquid crystal and the green spots are the

focus points at different detector positions. When the focus is at the left side of the incoming IR beam (point 2.) the detector is adjusted to right until the focus is in the middle of the liquid crystal in the left right direction. If the spot is behind the centre (point 3.), the detector has to be raised until the focus is as close as possible of the center of the liquid crystal.

For Thermo-Nicolet FTIR, please, see the section Error! Reference source not found..

4.2. Electrical connections

The PA301 module is connected to the optical microphone DSP Module using an STP cable with RJ-45 connectors. The output signals of the DSP module can be read as an analog signal from the port Analog Output 1. (Analog output: single ended +/- 2.5 V, Output load >2k Ohms) Connect the power adapter to the 12VDC connector at the back panel of the DSP Module. Turn on the power of the DSP module from power switch at the back panel. Wait for 30 seconds while the automatic calibration routine calibrates the laser interferometer. This is indicated by status LED blinking

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blue. When the blue status LED is not blinking, output signal is generated to the Analog Output 1 with a BNC connector on the back panel.

FIG 3. The front and back panels of the DSP module at left and right figures,

respectively.

The coaxial cable with a BNC and FTIR instrument specific connector is used to connect the optical microphone DSP module to the FTIR instrument. The BNC connector is connected to Analog Output 1 and the e.g. D15 or D9 connector is connected to the signal input connector of the FTIR instrument often located in the sample compartment or at the back panel of the instrument.

4.3. Gas connections

There is a connector for 4 mm tube for purge gas.

4.4. The PA module connections

The FIG 4 shows the back panel of the PA module. The connections are from left to right: purge input for helium, DSP connection, purge flow indicator and heater connection which are introduced in the sections 4.3 and 5.4, 4.2 and 5.1, 5.4 and 5.7.

FIG 4. The back panel connections and indicator are from left to right:

purge input for helium, DSP connection, purge flow indicator and heater connection.

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5. Detector operation

5.1. Gain control and DSP-module operation

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.

5.1.1. 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.

5.1.2. Operation modes

Normal operating mode (constant blue) The signals from the laser interferometer connected to Input are processed. The processed signal is output through the Analog Output 1 connector. 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

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tap the detector lightly with your finger to create displacement of the cantilever 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.

Calibration on/off (blinking blue or green) When the optical microphone is making a self calibration, status LED is blinking blue. During the purge the or when the sample cell is open, the calibration does not start and status LED is blinking green.

5.1.3. 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.

5.1.4. 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.

5.2. Rear lever operation of the photoacoustic detector

The rear lever has four positions:

Open. The sample holder can be loaded or removed from the detector. Purge valves are open and the gas flows out through the sample space.

Open purge. The cell is open, but the sample holder tightly in its position. Purge gas flows out from the sample cell. The gas flows

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through the gap between the sample cup holder and the body of the detector.

Closed purge, Sample holder seals the sample cell and gas flows out from the photoacoustic cell from the output valve in the balance cell. Photoacoustic cell is purged less efficiently, but the flow in sample cell is slow in order to prevent fine powders samples from contaminating the sample cell.

Sealed, The Photoacoustic cell and all the valves are closed. The measurements can be performed in this position.

FIG 5. The lever positions are shown in the figure.

5.3. Sample loading

The sample is loaded to the photoacoustic cell by setting it to the sample cup, placing the sample cup into the sample holder and inserting the holder in the photoacoustic cell and sealing the cell with rear lever. After that the measurement can be performed.

FIG 6. Dimension of the two sample cups.

The delivery of the PA301 photoacoustic detector contains large sample cups, small sample cups, and spacers for adjusting sample height. There is also a shallow sample holder for small samples that do not require space or drying,

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and a deep sample holder for larger samples and samples that are used with desiccant.

FIG 7. The crosscut of the sample cup in the photoacoustic cell.

The sample should be set to the holder using spacers and correct cups in such a way that the sample is close to the rim of the cup holder. However, the sample must not extend the rim in order to avoid the window from breaking, while the cell is sealed. The correct amount of sample is when the bottom of the sample cup is just covered. The sample should be placed in the cup before setting the cup inside the holder using tweezers in order to prevent the sample holder o-ring from contaminating.

FIG 8. A piece of flu medicine and a polyethylene foil placed in the sample

holders.

If the measurement requires drying, the desiccant can be placed in the deep sample cup in the bottom of the sample holder, and then the spacer and sample cup with the sample are set on top of it.

5.4. Purging

When helium is used as gas medium instead of nitrogen or room air, the signal is increased approximately by the factor of three. Purging can be also used for drying the sample cell together or without the desiccant.

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Performing the purge to the photoacoustic cell is simple. First adjust roughly the correct flow from the gas bottle so that you can feel the flow coming from the tube connected to the bottle. Connect the helium bottle(or another gas bottle) to the 4 mm gas connector at the PA301 and Set the rear lever to the closed purge, open purge or open position, which opens the electronic valves controlling the flow. Adjust the flow by monitoring the green indicator LED at the PA301. The led can be off, on or blinking, which corresponds to too small flow, the correct flow and too high flow, respectively. When the flow is too high, the LED is blinking, the input valve shuts down automatically protecting the cantilever in which case the flow needs to decreased. When purge is done, set the rear lever to seal position, stop the flow, start measurement. Minimum time to purge is about 10 seconds. However, the longer purging time is recommended when the cell is initially filled with air or other gas than helium. When the rear lever is in the seal position, both valves are closed and sample holder is closing the sample cell. In closed purge position the two valves are open and sample cell is closed. Then the balance cell is purged and gas in the sample cell is changed through diffusion. Open purge allows the gas flow also through the sample cell. Closed purge can be used when the sample is e.g. extremely fine powder which could fly along the purge and contaminate the cantilever and cell walls.

FIG 9. The schematic drawing of the gas flow in the different purging

positions.

In order to adjust correct flow from the gas bottle or purge gas line, monitor the flow indicator LED on top of the detector cover, which has three possible status:

too small flow – no light – increase the flow,

correct flow – green light,

too high flow – blinking green light – decrease flow; The input valve closes automatically preventing too high flow.

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5.5. FTIR measurement parameters

The photoacoustic spectrum is measured as a single beam spectrum. Absorption spectrum is received, when the single beam spectrum is divided by the spectrum of the reference black sample. The reference spectrum should be measured using same parameters and purge than with sample measurement. Number of scans, when measuring the reference spectrum, should be high enough to avoid increasing the noise in normalization (e.g. 100 scans). Reference spectrum is measured by loading the reference black sample, using the desired purge, and starting the measurement. By default, the FTIR interferometer driving parameters for having the highest signal-to-noise ratio should be adjusted to:

Slowest mirror velocity possible, the laser frequency is typically 1.6 kHz or 2.5 kHz,

Largest source aperture,

8 cm-1 resolution,

Scan number according to required signal-to-noise ratio, which is proportional to the square root of the number of scans.

5.6. Test procedure

For testing the performance of the PA301 detector execute the following tasks.

Set the white polyethylene sample provided with the detector on the shallow sample holder and load the sample into the photoacoustic cell.

Set the gain to one (1) so that the status LED on the Optical microphone DSP module does not blink with red.

Measure the single beam spectrum using 4 scans, 8 cm-1 resolution, largest possible aperture, and 1.6 kHz or 2.5 kHz or the closest HeNe-laser frequency.

The ratio of the signal of the absorption peak at 2920 cm-1 and peak-to-peak noise between 2100 cm-1 and 2200 cm-1 should be better than 100. The actual value depends on the throughput of the FTIR instrument, which means the amount of energy the FTIR can produce for the sample.

5.7. Optional heater module

This feature will be introduced on a later occasion.

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6. Service

6.1. User adjustments

6.1.1. Window replacement.

In case of window breakage, please, contact Gasera for service.

6.1.2. Sample holder tightness adjustment

Tighten the sample holder screws symmetrically so that the o-ring is compressed and the holder is straight.

FIG 10. The sample holder tightness adjustment screws.

6.2. 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

6.3. 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

CAUTION: The window is very fragile and easily breaks when not properly handled!

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Annex 1 Opus settings for Bruker Tensor and Vertex FTIR

OPUS Advanced window

OPUS Optic window

.

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OPUS Acquisition window

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

Perkin-Elmer initialization and icon files installation

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 or from your supplier.