MTEC PAC300 User manual

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MTEC PAC300
Photoacoustic Detector
Operating Instructions
August, 2023
MTEC Photoacoustics, Inc.
3507 Oakland St.
Ames, IA 50014 USA
Telephone: [phone]
www.mtecpas.com
[email protected]

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Table of Contents
1. First and Foremost: Three Key Precautions to Protect PAC300 from Damage
1.1 Protecting Microphone during Purging ………………………………............3
1.2 Caution to Avoid Breaking Window ……………………………………………….3
1.3 Protecting Window from Moisture Damage …………………………………..3
2. Unpacking
2.1 Unsealing the Hermetically Sealed Shipping/Storage Case ……………..3
2.2 Packing List …………………………………………………………………………………...3
2.3 Damage Inspection …………………………………………………………………………4
3. PAC300 Description
3.1 Introduction to the PAC300 ………………………………………………………………….4
4. Set-Up Directions
4.1 Insert Rear Lever …………………………………………………………………………….5
4.2 Mounting and Alignment of the PAC300 in the FTIR ……………………..…6
4.3 Electrical Connections …………………………………………………………………….9
4.4 Purge Gas Connections …………………………………………………………………..10
5. Operation
5.1 Preamplifier Gain Control …………………………………………………………..….10
5.2 Rear Lever Operation …………………………………………………………………….11
5.3 Sample Cup Loading ……………………………………………………………………..11
5.4 Sample Cup Insertion …………………………………………………………………..…13
5.5 Purging ………………………………………………………………………………………....14
5.6 FTIR Spectrum Acquisition Parameters ………………………………………..…14
5.7 Test Procedure ……………………………………………………………………………….15
5.8 Acquiring and Normalizing a Sample Spectrum …………………………..…15
5.9 Advanced Methods of Photoacoustic Spectroscopy ……………………...16
5.10 Storage of the PAC30 ……………………………………………………………………16
6. User Adjustments and Servicing
6.1 Setting the Sample and Reference Cup O-ring Seal Compression …..17
6.2 Window Replacement ……………………………………………………………………17
7. Service Assistance
7.1 Returning Units for Factory Servicing ……………………………………………..19
7.2 Foreign Returns ……………………………………………………………………………….19
8. Product Warranty and Disclaimer …………………………………………………………………..….20

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1. First and Foremost: Three Key Precautions to Protect PAC300 from Damage
1.1 Protecting Microphone during Purging
Purging with zero grade helium gas is used to enhance the sensitivity of photoacoustic
measurements and to reduce the moisture level in the sample chamber which
superimposes a water vapor spectrum on the sample spectrum and also interferes with
condensed sample signal generation. However, a too high gas flow rate can easily damage
the PAC300’s sensitive microphone. Accidental high flow rates may occur when gas valves
are being opened or adjusted. The PAC300 microphone is protected from gas flow surges
as long as the rear lever is in the SEAL position.
1.2 Caution to Avoid Breaking Window
Do not place samples in the brass sample cup that extend above 1 mm from the top of the
cup. Samples that extend above the top of the cup will break the PAC300’s window.
1.3 Protecting Window from Moisture Damage
The PAC300’s KBr window is moisture sensitive. The window can be protected from
moisture damage by storing the unit in its hermetically sealed case with a 10 g packet of
indicating silica gel ( http://silicagelpackets.com/indicating-silica-gel-packets/indicating-
silica-gel-packets/10-gram-indicating.html ).
2. Unpacking
2.1 Unsealing the Hermetically Sealed Shipping/Storage Case
In cold weather, it is advisable to let the case warm up for 24 hrs. before opening to
prevent moisture condensation on the KBr window.
2.2 Packing List
All PAC300 photoacoustic accessories include:
1. PAC300 with focusing mirror and KBr window.
2. Black handled sample holder (inserted in PAC300) with brass sample nest, five
small and five large removable sample cups, five nest spacers to elevate samples,
sample cup fixture and funnel, tweezers and Allen wrench to adjust cup o-ring
compression.
3. Carbon reference sample mounted in black handle.
4. Liquid crystal for imaging IR beam position.
5. Helium flow meter.
6. Hermetically sealed shipping/storage case

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Some accessories may also include one or more of the following:
1. FTIR specific baseplate mounting.
2. Desk-top power supply.
3. Glassy carbon phase reference.
4. FTIR specific connection cable(s).
5. PAC300 elevation adjustment shims.
6. FTIR purge coupling.
7. SH003 and/or SH004 options.
2.3 Damage Inspection
Please examine items for evidence of shipping damage. Report any damage to the carrier
and to MTEC for direct purchases or the reseller that shipped the accessory.
3. PAC300 Description
3.1 Introduction to the PAC300
The PAC300 enables direct measurement by photoacoustic detection of
optical absorption spectra of s o lid s and semisolids and is primarily used in
FTIR spectrometers:
http://www.mtecpas.com/Docs/Photoacoustic%20Technology%20Overview.p
df .
The detector can be used for a wide range of measurements as described in
the applications liter atur e and literature bibliography:
http://www.mtecpas.com/applicationslibrary.html ,
http://www.mtecpas.com/Docs/FTIR%20PAS%20Bibliography%20Draft%205.pdf .
The PAC300 can also be used with nonvolatile liquid and noncorrosive gas samples which
are not toxic.
The PAC300 is designed for ease of use. It mounts in the s t a n d a r d FTIR slide-
mount fixture or on FTIR specific baseplates. Sample changing, purging,
and sealing ar e controlled by a single lever, detector preamplifier gain is
controlled by a 12 position switch on the detector, and the detector is
powered either by the FTIR or by a 115/230 V, 60/50 Hz desk top power supply
with an international standard IEC 320 input connector. This allows the power
supply to be used with appropriate cord sets for any country of the world .
Inserts into FTIR Slide Mount
Inserts into FTIR Sample compartment
PAC300 for slide mount fixture (left)
or baseplate mounting (right).

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4. Set-Up Directions
4.1 Insert Rear Lever
The stainless steel rear lever is packed separately from the PAC300 in the shipping case
and should be inserted into one of the three slots on the back of the PAC300. Use the slot
that allows the lever to rotate most conveniently in your FTIR through the 90 degrees of
rotation necessary to purge and seal the sample. Note that the sample holder can be
inserted from either side of the PAC300 to accommodate both right-to-left and left-to-
right beam directions in different FTIRs.
Purge Inlet
Sample Holder
Rear Lever
FTIR Purge
Coupler
Baseplate

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4.2 Mounting and Alignment of the PAC300 in the FTIR
The PAC300 is either mounted on an FTIR specific baseplate or in the standard sample
slide mount found in all FTIRs. Baseplate and slide mounted PAC300s are prealigned and
usually will not require the adjustments described below.
Alignment can be checked using the i nfrared heat sensitive liquid crystals supplied
with the PAC300.
Lever
Slots
Color Change Indicates
FTIR beam focal spot. If the
spot is centered in the cup,
the PAC300 is aligned.
PAC300 needs to be moved
horizontally perpendicular
to the IR beam to center the
spot in sample cup.
IR Beam
1
2

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In order to check alignment, place a liquid crystal in the sample cup following
these directions in its package:
Heat Sensitive Liquid Crystals (HSLCs)
The HSLCsare usedto alignthe photoacoustic detector in the FTIRby imaging the focal spot of the IR beam in the sample
cup. Each HSLC covers a slightly different ambient temperature range. The one best suited for a given ambient
temperature should be selected by trying each. Place a HSLC in the large sample cup supported on the foam spacer. A
brass spacer should be used under the foam to elevate the HSLC to a point near the cup rim. The heat sensitive side of
the HSCL can be identified by finger touch induced heating. The detector position should be adjusted to center the
focal spot image in the sample cup. See the Instruction Manual for additional information.
Then block the infrared beam and insert the sample holder with the li qu id
crystal into the PAC300. Fully open the aperture of the FTIR. Elevate the crystal
by moving the rear lever to the CLOSED PURGE position. Remov e the beam
block, wait several seconds, remove the sample cup, and examine the image
pattern before it fades as the temperature falls.
The types of images that may be observed are shown above. Image 1
indicates ideal alignment. Image 2 shows s ide - t o- s ide misalignment. This can
be corrected by moving the PAC300 perpendicular to the beam in the
direction opposite to the misal i gnment direction. The side-to-side
adjustment can be made as shown below either by loosening the screws on the
baseplate and sliding the PAC300 side-to-side or by adjusting the slide plate
relative to its mounting yoke.
Image 3 indicatesthat the PAC300 needs to be raised. The height of
baseplate mounted PAC300s can be adjusted with the screws that support
the accessory on the baseplate as shown below.
PAC300 needs to be
moved vertically to
center the spot in sample
cup.
3
Shims for height adjustment
Side-to-side adjustment
Side-to-side adjustment

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In the case of slide mounted PAC300s, some FTI R slide fixtures have provision for
height adjustments while others do not. If th e r e is no adjustment provided
on the FTIR, height adjustments are made by placing, as shown above, small
shims provided with the detector between the PAC300 s lide mount and the
yoke coupling plate. Adding shims lowers the detector and moves th e image
in the direction of the front of the PAC300 .
In some cases it may be desirable with slide mount fixtures to support the
PAC300 directly on the FTIR’s or other instrument’s baseplate. Four 5-40
thread screws can be used as adjustable legs as shown below.
If slide mount fixture’s position is designed to be adjustable in the direction of the IR beam
, it may be observed that the infrared beam image on the liquid crystal is large
and weak. This may be caused by the PAC300 not being positioned properly relative
the IR beam’s focal spot which is normally at the midpoint of the beam’s path through the
FTIR's s a mple compartment. The PAC300’s optics require that the PAC300’s
slide plate be coincident with the FTIR’s focal plane with the hole in its slide
plate centered on the focal spot of the FTIR. To achieve this, the slide mount’s
position can be adjusted while watching the PAC300’s interferogram signal to
maximize it.
This nut is one of four used to
raise or lower the PAC300 on
a baseplate mounted unit.
Four 5-40 Screws Support
the PAC300 and allow for
height adjustment.
FTIR’s focal spot

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4.3 Electrical Connections
The PAC300 is powered either by the FTIR or an MTEC desktop power supply. The power
and signal cables are connected to the vibration isolated part of the accessory after first
being secured to the stationary part to avoid transmitting mechanical vibrations to the
PAC300’s sensitive microphone.
The desktop power supply has +15 and -15 Volt outputs and connects to either 115V 60 Hz
or 230V 50 Hz power lines. It has an IEC 320 power cord connector and an RJ9 output
connector.
The PAC300’s preamplifier gain is adjustable in 12 steps from 2X to 10,000X to
accommodate samples with different thermal properties and FTIR mirror velocities.
Power In
Signal Out
Gain Switch
On-Off switch
120/230 Volt
switch

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4.4 Purge Gas Connections
Purging with Zero Grade Helium increases the signal by a factor of 2 to 3 and helps to exhaust
moisture and CO2 from the sample chamber. A two stage gas regulator valve should be
connected to a helium tank with its output connected to the MTEC flow meter. The
flowmeter output is connected to the inlet of the stationary part of the PAC300. Its outlet is
connected to the vibration isolated sample chamber. Consult Section 5.5 before purging the
PAC300.
5. Operation
5.1 Preamplifier Gain Control
A twelve position switch controls the gain as fo llows :
step# 1
2
3
4
5 6 7 8 9 10
11
12
gain 2
5
10
20
50 100 200 500 1000 2000
5000
10,000
factor
The gain should be set high enough to give an inter f er ogr a m amplitude of
several volts but not too high to either cause preamplifier clipping (<20V pe ak -
to-peak) or to overloadthe FTIR's A to D converter.
Higher gains are used for higher FTIR mirror velocities because the signal
amplitude decreases as modulation frequency increases. Higher gai ns are
also used when sample spectra are being acquired relative to c a r bon
reference background spectra because totally absorbing carbon gener a tes
higher signal amplitudes than partially absorbing samples whichusually a l s o
have higher thermal mass.
To Gas
Cylinder
Line Pressure
Tank Pressure
Control Flow Rate
Only with this Valve
Leave This Valve
Always Open
Rear Lever Always In the SEAL
Position When Adjusting Valves
Flow Rate 10cc/s or Less