METER AQUALAB TDL User manual

Operator’s Manual
METER Group, Inc.
Version: July 18, 2017 — 14:18:47

AquaLab TDL
METER Group, Inc.
2365 NE Hopkins Court
Pullman WA 99163
Phone: [phone]
Fax: [phone]
Website: www.metergroup.com
Email: support.foo[email protected] or
sales.foo[email protected]
Trademarks
AquaLab is a registered trademark of METER Group, Inc.
c
2017 METER Group, Inc.
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AquaLab TDL CONTENTS
Contents
1 Introduction 1
1.1 Customer Support . . . . . . . . . . . . . . . . . . . . 1
1.2 About This Manual . . . . . . . . . . . . . . . . . . . 1
1.3 Warranty ......................... 2
1.4 Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . 2
1.5 General Safety Information . . . . . . . . . . . . . . . 3
2 About AquaLab 4
2.1 AquaLab TDL Instrument Specifications . . . . . . . . 4
2.2 AquaLab and Water Activity . . . . . . . . . . . . . . 5
2.3 HowTDLWorks ..................... 5
2.4 AquaLab and Temperature . . . . . . . . . . . . . . . 6
3 Water Activity Theory 7
3.1 Moisture Content . . . . . . . . . . . . . . . . . . . . . 7
3.2 WaterActivity ...................... 7
3.3 Water Potential . . . . . . . . . . . . . . . . . . . . . . 9
3.4 Sorption Isotherms . . . . . . . . . . . . . . . . . . . . 12
4 Getting Started 13
4.1 Components of your AquaLab . . . . . . . . . . . . . . 13
4.2 Choosing a Location . . . . . . . . . . . . . . . . . . . 13
4.3 Preparing AquaLab for Operation . . . . . . . . . . . 14
5 Menus 16
5.1 Measurement Tab . . . . . . . . . . . . . . . . . . . . 16
5.2 Configuration Tab . . . . . . . . . . . . . . . . . . . . 17
5.3 Admin Settings . . . . . . . . . . . . . . . . . . . . . . 23
5.4 DataTab ......................... 27
6 Cleaning and Maintenance 29
6.1 Cleaning the Block Sensors . . . . . . . . . . . . . . . 30
6.2 Cleaning an AquaLab TDL . . . . . . . . . . . . . . . 31
6.3 Cleaning Procedure: . . . . . . . . . . . . . . . . . . . 31
6.4 Verification of Calibration . . . . . . . . . . . . . . . . 33
7 Verification and Calibration 34
7.1 Water Activity Verification . . . . . . . . . . . . . . . 34
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CONTENTS AquaLab TDL
7.2 Verification of Calibration . . . . . . . . . . . . . . . . 35
8 Sample Preparation 47
8.1 Preparing the Sample . . . . . . . . . . . . . . . . . . 47
8.2 Samples Needing Special Preparation . . . . . . . . . . 48
8.3 Slow Water-Emitting Samples . . . . . . . . . . . . . . 49
8.4 Samples Not at Room Temperature . . . . . . . . . . . 49
9 Taking a Reading 51
9.1 Measurement Steps . . . . . . . . . . . . . . . . . . . . 51
9.2 How AquaLab Takes Readings . . . . . . . . . . . . . 51
10 Moisture Content Measurement 54
11 Computer Interface 55
11.1 AquaLink 4 Software . . . . . . . . . . . . . . . . . . . 55
11.2 AquaLink 4 Part 11 Compatible Software . . . . . . . 56
11.3 Using a Communication Program . . . . . . . . . . . . 56
12 Troubleshooting 58
13 Support and Repair 66
13.1RepairCosts ....................... 67
13.2 Loaner Service . . . . . . . . . . . . . . . . . . . . . . 67
14 Further Reading 68
14.1 Water Activity Theory & Measurement . . . . . . . . 68
15 Appendix A 90
15.1 Preparing Salt Solution . . . . . . . . . . . . . . . . . 90
16 Appendix B 92
17 Appendix C 93
18 Declaration of Conformity 98
19 Certificate of Traceability 99
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AquaLab TDL 1 INTRODUCTION
1 Introduction
Welcome to your AquaLab Tunable Diode Laser (TDL). AquaLab is
the quickest, most accurate, and most reliable instrument available
for measuring water activity. Whether you are researching or working
on the production line, the TDL suits your needs. It is easy to use
and provides accurate and timely results.
1.1 Customer Support
If you ever need assistance with your AquaLab, have any questions
or feedback, there are several ways to contact us. METER has Cus-
tomer Service Representatives available to speak with you Monday
through Friday, between 7 am and 5 pm Pacific time.
Note: If you purchased your AquaLab through a distributor, please
contact them for assistance.
Email:
support.foo[email protected] or sales.foo[email protected]
Phone:
1-509-332-5601
Fax:
1-509-332-5158
If contacting us by email or fax, please include as part of your mes-
sage your instrument serial number, your name, address, phone, fax
number, and a description of your problem or question.
1.2 About This Manual
This manual includes instructions for setting up your AquaLab, veri-
fying the calibration of the instrument, preparing samples, and main-
taining and caring for your instrument. Please read these instructions
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1 INTRODUCTION AquaLab TDL
before operating AquaLab to ensure that the instrument performs to
its full potential.
1.3 Warranty
AquaLab has a 30-day satisfaction guarantee and a one year warranty
on parts and labor. Your warranty is automatically validated upon
receipt of the instrument. We contact you within the first 90 days of
your purchase to see how the TDL is working for you.
1.4 Seller’s Liability
Seller warrants new equipment of its own manufacture against de-
fective workmanship and materials for a period of one year from the
date of receipt of equipment.
Note: We do not consider the results of ordinary wear and tear,
neglect, misuse, accident and excessive deterioration due to corro-
sion from any cause as defects.
The Seller’s liability for defective parts shall in no event exceed the
furnishing of replacement parts Freight On Board the factory where
originally manufactured. Material and equipment covered hereby
which is not manufactured by Seller shall be covered only by the
warranty of its manufacturer. Seller shall not be liable to Buyer for
loss, damage or injuries to persons (including death), or to property
or things of whatsoever kind (including, but not without limitation,
loss of anticipated profits), occasioned by or arising out of the instal-
lation, operation, use, misuse, nonuse, repair, or replacement of said
material and equipment, or out of the use of any method or process
for which the same may be employed. The use of this equipment
constitutes the buyer’s acceptance of the terms set forth in this war-
ranty. There are no understandings, representations, or warranties
of any kind, express, implied, statutory or otherwise (including, but
without limitation, the implied warranties of merchantability and
fitness for a particular purpose), not expressly set forth herein.
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AquaLab TDL 1 INTRODUCTION
1.5 General Safety Information
Please read through this documentation carefully before putting the
instrument into operation. The documentation contains information
and warnings which the user must follow in order to ensure safe op-
eration. This instrument may only be operated in accordance with
the specifications in this documentation.
This instrument has left the factory in a flawless state in terms of
technical and electrical safety. To maintain this state and ensure
non-hazardous operation of the instrument, the following instruc-
tions must be observed carefully.
1. Only personnel qualified by METER are authorized to carry
out service work on the electrical components. When work is
required a Certificate of Calibration will be issued upon com-
pletion of the work.
2. Never remove the housing of the instrument. The instrument
could be damaged by this. There is also a risk of serious injury
if the live components are touched. There are no parts inside
the housing which can be serviced or replaced by the user.
3. An incorrect main power voltage can damage the instrument.
Only operate this instrument with a main power voltage spec-
ified for it (see rear label).
4. This product is grounded through the grounding conductor of
the power cord. To avoid electric shock, the grounding conduc-
tor must be connected to earth ground.
5. Should a fuse need to be replaced. Use only the fuse type and
rating specified for this instrument.
6. If the instrument is used in a manner not specified by the man-
ufacturer, the protection provided by the equipment may be
impaired.
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2 ABOUT AQUALAB AquaLab TDL
2 About AquaLab
AquaLab is the fastest and most accurate instrument for measuring
water activity, giving readings in five minutes or less. Its readings
are reliable, providing ±0.005 awaccuracy. The instrument is easy
to clean and checking calibration is simple.
Note: UL has listed this product to applicable UL Standards and
Requirements.
2.1 AquaLab TDL Instrument Specifications
Sensor Type: Tunable Diode Laser and Infrared Temperature
Water Activity Accuracy: ±0.005 @ 25 ◦C
Water Activity Resolution: 0.0001 aw
Water Activity Range: 0.000 to 1.000 aw
Water Activity Repeatability: ±0.001 aw
Read Time1:≤5 min.
Sample Temperature Control: 25 ◦C 15 to 50 ◦C (with calibration)
Sample Temperature Adjustment Increment: 1 ◦C
Sample Temperature Accuracy: ±0.2◦C
Sample Temperature Resolution: 0.01 ◦C
Sample Dish Capacity: 15 mL full
Operating Environment: 4 to 50 ◦C; 0 to 90% Humidity non-condensing
Case Dimensions: 26.7 x 17.8 x 12.7 cm
Weight: 3.1 kg
Case Material: POLYLAC PA-765 (ABS) with fire retardant
Display: 64 x 128 Graphical
1On samples with no significant impedance to vapor loss.
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AquaLab TDL 2 ABOUT AQUALAB
Data Communications: USB
Power: 110 to 220 VAC, 50/60 Hz
Warranty: One year parts and labor
2.2 AquaLab and Water Activity
Water activity (aw) is a measurement of the energy status of the
water in a system. The value indicates how tightly water is bound,
structurally or chemically, within a substance. Water activity is the
relative humidity of air in equilibrium with a sample in a sealed
measurement chamber. The concept of water activity is of partic-
ular importance in determining product quality and safety. Water
activity influences color, odor, flavor, texture and shelf-life of many
products. It predicts safety and stability with respect to microbial
growth, chemical and biochemical reaction rates, and physical prop-
erties. For a more detailed description of water activity as it pertains
to products, please refer to Section 3 of this manual, titled “Water
Activity Theory.”
2.3 How TDL Works
The TDL uses a tunable diode laser to measure the water activity of
a sample. The sample is equilibrated with the head-space of a sealed
chamber containing a tunable laser that shines light of a controlled
wavelength at a detector that receives the light from the laser. At
equilibrium, the relative humidity of the air in the chamber is the
same as the water activity of the sample. In the TDL, the vapor
pressure of the headspace in equilibrium is determined by the loss of
signal strength from the laser caused by the presence of water vapor
in the headspace. This vapor pressure is divided by the saturated
vapor pressure at the sample temperature, which is measured us-
ing an IR sensor, to give water activity. AquaLab then signals you
by beeping and displays the final water activity. Since the sample
temperature is directly measured and no sensor is being used to de-
tect humidity, all that is needed to make a measurement is vapor
equilibrium, which can happen in as little as two to three minutes.
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2 ABOUT AQUALAB AquaLab TDL
2.4 AquaLab and Temperature
Samples not read at room temperature during the read cycle equi-
librate with the TDL temperature before the water activity is dis-
played. Large temperature differences cause longer reading times,
since TDL cannot make a complete and accurate reading until the
sample and the instrument equilibrate to within ±4◦C. There are
several advantages in having a temperature-controlled water activity
meter. A few major reasons are:
1. Research purposes. Researchers can use temperature con-
trol to study the effects of temperature on the water activity of
a sample, make a comparison of the water activity of different
samples independent of temperature, and conduct accelerated
shelf-life studies or other water activity studies where temper-
ature control is critical. There are many shelf-life, packaging,
and isotherm studies in which temperature control would be
very beneficial. (See Section 14. Further Reading for more
information)
2. Compliance with government or internal regulations for
specific products. Though the water activity of most products
varies by less than ±0.002 per ◦C, some regulations require
measurement at a specific temperature. The most common
specification is 25 ◦C, though 20 ◦C is sometimes indicated.
3. Minimization of extreme ambient temperature fluctu-
ations. If the environmental and AquaLab temperatures fluc-
tuate by as much as ±5◦C daily, water activity readings vary
by ±0.01 aw. Temperature control eliminates variations due to
changes in ambient conditions.
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AquaLab TDL 3 WATER ACTIVITY THEORY
3 Water Activity Theory
Water is a major component of foods, pharmaceuticals, and cosmet-
ics. Water influences the texture, appearance, taste and spoilage of
these products. There are two basic types of water analysis: moisture
content and water activity.
3.1 Moisture Content
The meaning of the term moisture content is familiar to most people.
It implies a quantitative analysis to determine the total amount of
water present in a sample. There are two primary methods for deter-
mining moisture content: loss on drying and Karl Fisher titration,
but you can also use secondary methods such as infrared and NMR.
Moisture content determination is essential in meeting product nu-
tritional labeling regulations, specifying recipes and monitoring pro-
cesses. However, moisture content alone is not a reliable indicator for
predicting microbial responses and chemical reactions in materials.
The limitations of moisture content measurement are attributed to
differences in the intensity with which water associates with other
components.
3.2 Water Activity
Water activity is a measure of the energy status of the water in a
system, and thus is a far better indicator of perishability than water
content. Figure 1 shows how the relative activity of microorganisms,
lipids and enzymes relate to water activity. While other factors, such
as nutrient availability and temperature, can affect the relationships,
water activity is the best single measure of how water affects these
processes. Researchers measure the water activity of a system by
equilibrating the liquid phase water in the sample with the vapor
phase water in the headspace and measuring the relative humidity
of the head-space. First place a sample in a sample cup that seals
inside the TDL sample chamber. Inside the sample chamber is a tun-
able diode laser and an infrared thermometer. The TDL determines
the vapor pressure in the headspace and the infrared thermometer
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3 WATER ACTIVITY THEORY AquaLab TDL
Figure 1: Water Activity Diagram adapted from Labuza
measures the sample temperature. From these measurements, the
relative humidity of the head-space is computed as the ratio of the
partial pressure measured by TDL to saturation vapor pressure at
the sample temperature. When the water activity of the sample and
the relative humidity of the air are in equilibrium, the measurement
of the head-space humidity gives the water activity of the sample.
In addition to equilibrium between the liquid phase water in the
sample and the vapor phase, the internal equilibrium of the sample
is important. If a system is not at internal equilibrium, one might
measure a steady vapor pressure (over the period of measurement)
which is not the true water activity of the system. An example of this
might be a baked good or a multi-component food. Initially out of
the oven, a baked good is not at internal equilibrium; the outer sur-
face is at a lower water activity than the center of the baked good.
One must wait a period of time in order for the water to migrate
and the system to come to internal equilibrium. It is important to
remember the restriction of the definition of water activity to equi-
librium.
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AquaLab TDL 3 WATER ACTIVITY THEORY
Temperature Effects
Temperature plays a critical role in water activity determination.
The AquaLab infrared thermometer measures the difference in tem-
perature between the sample and the block. It is carefully calibrated
to minimize temperature errors, but when temperature differences
are large water activity can change during testing. Best accuracy is
therefore obtained when the sample is near chamber temperature.
Another effect of temperature on water activity occurs when sam-
ples are near saturation. A sample that is close to 1.0 awand is
only slightly warmer than the sensor block condenses water within
the block. Condensation causes errors in the measurement, and in
subsequent measurements until it evaporates. A sample at 0.75 aw
needs to be approximately 4 ◦C above the chamber temperature to
cause condensation. The AquaLab warns the user if a sample is more
than 4 ◦C above the chamber temperature, but for high water ac-
tivity samples the operator needs to be aware that condensation can
occur if a sample that is warmer than the block is put in the TDL.
3.3 Water Potential
Some additional information may be useful for understanding what
water activity is and why it is such a useful measure of moisture
status in products. Water activity is closely related to a thermody-
namic property called the water potential, or chemical potential (µ)
of water, which is the change in Gibbs free energy (∆G) when water
concentration changes. Equilibrium occurs in a system when (µ) is
the same everywhere in the system. Equilibrium between the liquid
and the vapor phases implies that (µ) is the same in both phases. It
is this fact that allows us to measure the water potential of the va-
por phase and use that to determine the water potential of the liquid
phase. Gradients in (µ) are driving forces for moisture movement.
Thus, in an isothermal system, water tends to move from regions of
high water potential (high aw) to regions of low water potential (low
aw). Water content is not a driving force for water movement, and
therefore can not be used to predict the direction of water movement,
except in homogeneous materials.
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3 WATER ACTIVITY THEORY AquaLab TDL
10

AquaLab TDL 3 WATER ACTIVITY THEORY
Factors In Determining Water Activity
The water activity of the water in a system is influenced by factors
that effect the binding of water. They include osmotic, matric, and
pressure effects. Typically water activity is measured at atmospheric
pressure, so only the osmotic and matric effects are important.
Osmotic Effects: Osmotic effects are well known from biology and
physical chemistry. Water is diluted when a solute is added. If
this diluted water is separated from pure water by a semi-permeable
membrane, water tends to move from the pure water side through
the membrane to the side with the added solute. If sufficient pressure
is applied to the solute-water mixture to just stop the flow, this pres-
sure is a measure of the osmotic potential of the solution. Addition
of one mole of an ideal solute to a kilogram of water produces an
osmotic pressure of 22.4 atm. This lowers the water activity of the
solution from 1.0 to 0.98 aw. For a given amount of solute, increasing
the water content of the systems dilutes the solute, decreasing the
osmotic pressure, and increasing the water activity. Since microbial
cells are high concentrations of solute surrounded by semi-permeable
membranes, the osmotic effect on the free energy of the water is im-
portant for determining microbial water relations and therefore their
activity.
Matric Effects: The sample matrix affects water activity by phys-
ically binding water within its structure through adhesive and cohe-
sive forces that hold water in pores and capillaries, and to particle
surfaces. If cellulose or protein were added to water, the energy sta-
tus of the water would be reduced. Work would need to be done to
extract the water from this matrix. This reduction in energy status
of the water is not osmotic, because the cellulose or protein concen-
trations are far too low to produce any significant dilution of water.
The reduction in energy is the result of direct physical binding of
water to the cellulose or protein matrix by hydrogen bonding and
van der Waals forces. At higher water activity levels, capillary forces
and surface tension can also play a role.
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3 WATER ACTIVITY THEORY AquaLab TDL
3.4 Sorption Isotherms
Relating Water Activity to Water Content
Changes in water content affect both the osmotic and matric binding
of water in a product. Thus a relationship exists between the water
activity and water content of a product. This relationship is called
the sorption isotherm, and is unique for each product. Besides being
unique to each product, the isotherm changes depending on whether
it was obtained by drying or wetting the sample. These factors need
to be kept in mind if one tries to use water content to infer the
stability or safety of a product. Typically, large safety margins are
built into water content specifications to allow for these uncertainties.
While the sorption isotherm is often used to infer water activity
from water content, one could easily go the other direction and use
the water activity to infer the water content. This is particularly at-
tractive because water activity is much more quickly measured than
water content. This method gives particularly good precision in the
center of the isotherm. In order to infer water content from water
activity, one needs an isotherm for the particular product. METER
sells an Isotherm Generator called the AquaLab Vapor Sorption Ana-
lyzer (VSA) or you can also have METER run the isotherm for a fee.
For example, if you were using the AquaLab to monitor the water
content of dried potato flakes, you would measure the water activity
and water content of potato flakes dried to varying degrees using the
standard drying process for those flakes. You could then use that
data to construct an isotherm and infer the water content using the
measured water activity of samples and that isotherm.
We cannot overemphasize the importance of the concept of water
activity for foods, pharmaceuticals, and cosmetics. Water activity
is a measure of the energy status of the water in a system. More
importantly, the usefulness of water activity in relation to microbial
growth, chemical reactivity, and stability over water content has been
shown.
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AquaLab TDL 4 GETTING STARTED
4 Getting Started
4.1 Components of your AquaLab
Your AquaLab should have been shipped with the following items:
•AquaLab water activity meter
•Calibration certificate
•Power cord
•USB interface cable
•50 disposable sample cups
•Operator’s Manual
•Quick Start Guide
•Cleaning kit
•Two vials each of the following verification solutions:
1.00 awUSP Purified Water
0.984 aw0.50 mol/kg KCL
0.920 aw2.33 mol/kg NaCl
0.760 aw6.00 mol/kg NaCl
0.500 aw8.57 mol/kg LiCl
0.250 aw13.41 mol/kg LiCl
•AquaLink 4 Software Package
4.2 Choosing a Location
To ensure that your AquaLab operates correctly and consistently,
place it on a level surface. This reduces the chance of sample mate-
rial spillage or sample chamber contaminate. Also select a location
where the temperature remains fairly stable to avoid temperature
changes that can affect accuracy. This location should be well away
from air conditioner and heater vents, open windows, etc. Place
the AquaLab in a location where cleanliness can be maintained to
prevent contamination of the sample chamber.
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4 GETTING STARTED AquaLab TDL
4.3 Preparing AquaLab for Operation
After finding a good location for your AquaLab, plug the power cord
into the back of the unit. The ON/OFF switch is located on the
lower left corner of the AquaLab back panel. When the AquaLab
is turned on, you should see a model name/number screen and then
the main Measurement screen.
Warning: Only use the supplied power cord or one rated for your
AquaLab 4 and certified for the country of use. The cord must be
minimum of 18 AWG and have a rating for 10 Amps or greater.
The Measurement screen shows the water activity (aw) in the middle
of the screen, directly above the sample temperature.
Note: Allow your AquaLab a 15 minute warm-up period to ensure
the most accurate readings.
If you have users set up, the User screen appears instead of the
Measurement screen. (See Section 5 for more information on ad-
ministrative settings and user setup.) Select the appropriate user to
begin.
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AquaLab TDL 4 GETTING STARTED
15

5 MENUS AquaLab TDL
5 Menus
At the top of the display screen there are three tabs: Measurement,
Configuration, and Data. These tabs indicate the three menus you
can access. To change between the tabs press the right most button
below the document icon.
The enter icon is the Read or Enter button. Once the latch is set
to the Read position, the document icon switches to an “X” icon,
which allows the user to stop the current reading. During a reading,
pressing Enter again restarts the reading.
5.1 Measurement Tab
The Measurement tab, as seen above, is the main screen which dis-
plays each time you turn on your AquaLab. If this screen does not
appear, refer to Section 12 for troubleshooting instructions. As men-
tioned earlier, the water activity and sample temperature are dis-
played on the screen.
Pushing the right or left arrow keys changes the display to a tem-
perature Equilibrating screen. This screen shows the temperature
difference between the sample temperature and the lid temperature.
16