Decagon Devices Pawkit Operator's Manual
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Decagon Devices Pawkit Operator's Manual

Water activity meter
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Portable Water Activity
Measurement System
Operator' s Manual
Ver. 1.3

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  • Page 1 Portable Water Activity Measurement System Operator’ s Manual Ver. 1.3...
  • Page 2 Decagon Devices, Inc. 950 NE Nelson Court Pullman , WA 99163 tel: (509) 332-5158 fax: (509) 332-5158 www.decagon.com/pawkit pawkit@decagon.com Copyright 2001 Decagon Devices, Inc. All rights reserved...

  • Page 3: Table Of Contents

    2. About the Pawkit ....5 How Pawkit works..... 5 Accuracy .
  • Page 4 Pawkit Table of Contents Cleaning......26 Maintenance ......27 Disassembly .

  • Page 5: Introduction

    Customer Service If you ever need assistance with your Pawkit, or if you just have questions, there are several ways to contact us: Phone:...

  • Page 6: Warranty

    Again, please include as part of your message your Pawkit’s serial number, your name, address, phone, fax number, and return e-mail address. Warranty The Pawkit has a 30-day satisfaction guarantee and a one-year warranty on parts and labor.

  • Page 7: Seller's Liability

    Pawkit Introduction the content of this manual is correct and scientifi- cally sound. Seller’s Liability Seller warrants new equipment of its own manufac- ture against defective workmanship and materials for a period of one year from date of receipt of...
  • Page 8 Pawkit Introduction out limitation, the implied warranties of merchant- ability and fitness for a particular purpose), not expressly set forth herein.

  • Page 9: About The Pawkit

    Pawkit About the Pawkit 2. About the Pawkit The Pawkit is designed to be a simple, rapid and portable system for measurement of water activity. It is easy to use, durable, and requires little mainte- nance. How Pawkit works Pawkit uses a dielectric humidity sensor to measure of a sample.

  • Page 10: Getting Started

    , and measures based upon the chilled-mirror dewpoint method. Contact Decagon for more details. Getting Started Components of your Pawkit system: Your Pawkit should have been shipped to you with the following items: • Pawkit main unit • Durable carrying case •...

  • Page 11: Preparing For Operation

    Pawkit About the Pawkit Preparing for Operation To ensure that your Pawkit operates correctly and consistently, always place it on a level surface when measuring. This reduces the chance that sample material will spill inside the instrument. To avoid inaccurate readings, place your Pawkit in a location where the temperature remains fairly stable.

  • Page 12: Operation

    Pawkit Operation 3. Operation Operation of the Pawkit is very simple. Once you have ensured that you have a stable working envi- ronment, you are ready to begin sampling. Follow- ing is a description of the features and operation of the instrument.

  • Page 13: Sample Preparation And Insertion

    • Completely cover the bottom of the cup with the sample, if possible. Pawkit is able to accurately measure a sample that leave small spaces of the cup bottom exposed. For example, raisins only need to be placed in the cup and not flattened to cover the bottom.
  • Page 14 • Fill the cup no more than half-full of the sample. Pawkit does not require a large sample size to make its reading. As long as the bottom of the cup is covered by the sample and that the sam-...

  • Page 15: Sample Insertion And Chamber Movement

    Pawkit Operation Sample Insertion and chamber movement 1. Open the Pawkit chamber by holding the case near the LCD with one hand and pulling down on the metal tab with the other hand. Flex the base of the instrument until it snaps open, then lay it on a flat surface.
  • Page 16 Pawkit Operation Ensure cup is entirely within the chamber 3. Once the sample cup is properly inserted, press down on the front end of the case to secure the cup inside the instrument. You are now ready to take readings (see “Taking Measurements” sec-...
  • Page 17 Pawkit Operation 4. When you are finished with the sample, press on the back of the instrument above the LCD as illustrated to open the chamber and remove the cup.
  • Page 18 Pawkit Operation Do not press on the middle to close the instru- ment! 5. To close the instrument, turn it over, then press on the two points shown with your thumbs until it snaps closed.

  • Page 19: Taking Measurements

    Pawkit Operation Taking Measurements 1. Make sure the sample cup is inserted as described in the previous section. 2. Press the left button (I) to turn on the instru- ment. It will display the last reading taken. This allows you to begin a measurement and leave without having to attend the instrument through- out the measurement.
  • Page 20 Pawkit Operation 3. Press button I to begin the water activity mea- surement. The LCD display will be reset to 0.00 NOTE: Pressing button I any time during a measure- ment will restart the water activity measurement. 4. Once the measurement process has been...
  • Page 21 I again, or you can record the shown value and take the sample cup out. 6. To remove the sample, press on the back of the Pawkit to open the chamber, then remove the cup as shown:...

  • Page 22: Turning It Off

    Turning it off To turn off the Pawkit, leave it idle for more than 5 minutes, and it will shut off automatically. If the Pawkit has automatically shut itself off, pressing...

  • Page 23: Calibration

    (I) will wake up the instrument and display the last water activity measurement. Calibration As mentioned earlier, the Pawkit takes water activity measurements by measuring the change in electrical properties of a special polymer held between two electrodes. Due to the nature of the dielectric humidity sensor, there may be times when you may need to calibrate.

  • Page 24: Steps In Calibration

    1. Take a vial of the 0.760 NaCl standard and empty the entire contents of the vial into a sam- ple cup. Place the sample cup into the Pawkit, and close the chamber. 2. Press the left button (I) to take a reading. If it is reading the correct water activity ±0.02, your...
  • Page 25 Pawkit Operation the Pawkit shuts itself off. Press it once, and you will see the following screen: 0.76 u0.76 4. This screen shows that you are in the calibration mode. This one in particular shows that you are ready to adjust calibration upwards for the 0.76 standard.
  • Page 26 Note: If you do not press “Sto” no change will be made to the calibration of the Pawkit. 8. Repeat the above process with the 0.25 standard to set the calibration for the 0.25 water activity level.

  • Page 27: Sampling Precautions

    1.00 can shift the sensor calibration. Therefore, always remove samples as soon as the Pawkit is finished sampling (beeps) to avoid damage to the sensor. If a sample is accidentally left in the chamber for an extended period of time, be sure to check the calibration when the instrument is next used.

  • Page 28: Pawkit And Temperature

    Pawkit Operation Pawkit’s sensor can be damaged by long term expo- sure to high concentrations of ethyl alcohol. Read- samples with alcohol concentrations above about 10% can shift the calibration. If the instrument is used to read water activity of extracts and other...
  • Page 29 If your sample is colder than the ambient tempera- ture of the Pawkit, the accuracy of your reading after 5 minutes may be questionable. Wait until the sample’s temperature is similar to that of the Pawkit.

  • Page 30: Cleaning And Maintenance

    However, it is still important to keep it clean to ensure its proper working and func- tion. Here are some tips for keeping your Pawkit clean: • Use only a soft cotton cloth to clean the LCD.

  • Page 31: Maintenance

    1. With the Pawkit open, lift the back of the foot plate up until the tabs on the foot plate clear the notches in the retainer and it clicks. Next, pull the whole foot plate forward until the bottom disengages and the foot plate comes free.
  • Page 32 Pawkit Cleaning and Maintenance 2. Be careful not to kink or bend the cup tempera- ture sensor, which is in the blue Mylar tab. 3. To re-assemble, the springs in the foot plate must slid under the rod in the retainer and the tabs in the foot plate must be re-engaged in the notches in the retainer.
  • Page 33 Pawkit Cleaning and Maintenance Align the tabs with the rod. Press the contact points while lifting on the front tab of the foot plate. Push while pressing to click in place.

  • Page 34: Sensor Filter Cleaning/Replacement

    Pawkit Cleaning and Maintenance 4. When the foot plate is in place, open the Pawkit and carefully insert the blue Mylar sample tem- perature sensor tab between the front of the foot plate and the elastomer. Note: if the Pawkit does not open properly it means...

  • Page 35: Chamber Cleaning Instructions

    Pawkit Cleaning and Maintenance Note: The sensor is extremely fragile! Do not touch it. Chamber Cleaning Instructions ® 1. Use a moist cloth or Kimwipe to clean the sur- rounding chamber area. 2. Re-assemble the instrument as described in the...

  • Page 36: Battery Replacement

    1. Remove the Pawkit bottom completely as described in the “Disassembly” section above. 2. Turn the top portion of the Pawkit over so you are looking at the underside. Four tabs on the retainer engage the rim of the Pawkit case top.
  • Page 37 Pawkit Cleaning and Maintenance underneath the case rim, then pull the retainer forward to disengage the rear tabs. 3. Separate the elastomer, circuit board and retainer from the stainless steel case. Next remove the retainer and circuit board from the elastomer, being careful not to kink the tempera- ture sensor flex.
  • Page 38 Pawkit Cleaning and Maintenance 4. Replace both batteries in the elastomer pocket with new CR1632 or equivalent 3V lithium coin cells. Make sure to orient the batteries so the positive (+) contact is facing down into the elas- tomer pocket. Make sure the two small springs which make contact between the (+) battery ter- minal and the circuit board are in place.
  • Page 39 Pawkit Cleaning and Maintenance 7. Attach the bottom of the Pawkit as described in the “Disassembly” section above.

  • Page 40: Repair Instructions

    Pawkit Repair Instructions 5. Repair Instructions If your Pawkit ever needs to be sent in for service or repair*, call Decagon at 1-800-755-2751 (US and Canada) or (509) 332-2756, or fax us at (509) 332- 5158. We will ask you for your address, phone...

  • Page 41: Repair Costs

    To safely ship your instrument back to us, pack the Pawkit in its carrying case, securely in a box that has styrofoam peanuts or other packing material to prevent damage in shipment.

  • Page 42: Theory: Water Activity

    Pawkit Theory 6. Theory: Water Activity in Products Water is a major component of foods, pharmaceuti- cals, and cosmetics. Water influences the texture, appearance, taste and spoilage of these products. There are two basic types of water analysis: water content and water activity.

  • Page 43: Water Activity

    Pawkit Theory Water activity Water activity ( ) is a measurement of the energy status of the water in a system. It 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.
  • Page 44 Pawkit Theory Figure 1. Water Activity Diagram—adapted from Labuza Water activity of a system is measured by equilibrat- ing the liquid phase water in the sample with the vapor phase water in the headspace and measuring the relative humidity of the headspace. In the Paw- kit, a sample is placed in a sample cup which is sealed inside a chamber.

  • Page 45: Effect Of Temperature On Water Activity

    Pawkit Theory ment of the headspace 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 inter- nal equilibrium of the sample is important. If a sys-...

  • Page 46: Water Potential

    Pawkit Theory 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 prod- ucts. Water activity is closely related to a thermody- namic property...
  • Page 47 Pawkit Theory 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...

  • Page 48: Sorption Isotherms-Relating Aw To Water Content

    Pawkit Theory cohesive forces that hold water in pores and capil- laries, and to particle surfaces. If cellulose or protein were added to water, the energy status of the water would be reduced. Work would need to be done to extract the water from this matrix.
  • Page 49 Pawkit Theory safety margins are built in to water content specifi- cations 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.
  • Page 50 Pawkit Theory tion to microbial growth, chemical reactivity, and stability over water content has been shown.

  • Page 51: Further Reading

    Pawkit Further Reading 7. Further Reading Water Activity Theory and Measurement Duckworth, R. (1975). Water Relations of Foods. Academic Press, New York. Gomez-Diaz, R. (1992). Water activity in foods: Determination methods. Alimentaria. 29:77- Greenspan, L. (1977). Humidity fixed points of binary saturated aqueous solutions.

  • Page 52: Food Quality And Safety

    Pawkit Further Reading van den Berg, C. (1985). Water activity. In: Concen- tration and Drying of Foods. MacCarthy, D. (ed.) Elsevier, London. pp. 11-35. Food Quality and Safety Brandt, L. (1996). Bound for success. Controlling water activity gives technologists the edge in...

  • Page 53: Water Activity And Microbiology

    Pawkit Further Reading Water Activity and Microbiology Beuchat, L.R. (1981). Microbial stability as affected water activity. Cereal Foods World. 26(7):345-349. Chen, H.C. (1995). Seafood microorganisms and seafood safety. Journal of Food and Drug Analysis. 3:133-144. Farber, J.M., F. Coates, and E. Daley. (1992). Mini- mum water activity requirements for the growth of Listeria monocytogenes.

  • Page 54: Water Activity In Foods

    Pawkit Further Reading Water Activity in Foods Meat and Seafood Chen, N. and L.A. Shelef. (1992). Relationship between water activity, salts of lactic acid, and growth of Listeria monocytogenes in a meat model system. Journal of Food Protec- tion. 55:574-578.
  • Page 55 Pawkit Further Reading Shimasaki, T., K. Miake, Y. Tsukamasa, M.A. Sug- iyama, Y. Minegishi, and H. Shinano. (1994). Effect of Water Activity and Storage Temper- ature on the Quality and Microflora of Smoked Salmon. Nippon Suisan Gakkaishi. 60:569-576. Dairy Products Fresno, J.M., M.E.
  • Page 56 Pawkit Further Reading of apple slices at various water activities. Food Research International. 28:83-86. Kiranoudis, C.T., Z.B. Maroulis, E. Tsami, and K.D. Marinos. (1993). Equilibrium moisture con- tent and heat of desorption of some vegeta- bles. Journal of Food Engineering. 20:55-74.
  • Page 57 Pawkit Further Reading Gómez, R., Fernandez-Salguero J., M.A. Carmona, and D. Sanchez. (1993). Water activity in foods with intermediate moisture levels: Bak- ery and confectionery products: Miscellany. Alimentaria. 30:55-57. Michniewicz, J., C.G. Biliaderis, and W. Bushuk. (1992). Effect of added pentosans on some properties of wheat bread.

  • Page 58: Pharmaceuticals/Cosmetics

    Pawkit Further Reading Kusumegi, K., T. Takahashi, and M. Miyagi. (1996). Effects of addition of sodium citrate on the pasteurizing conditions in "Tuyu", Japanese noodle soup. Journal of the Japanese Society for Food Science and Technology. 43:740- 747. Sa, M.M. and A.M. Sereno. (1993). Effect of tempera- ture on sorption isotherms and heats of sorp- tion of quince jam.

  • Page 59: Miscellaneous

    Pawkit Further Reading solid dosage forms. Pharmaceutical Research. 8(3):292-297. Friedel, R.R. and A.M. Cundell. (1998). The applica- tion of water activity measurement to the microbiological attributes testing of nonster- ile over-the-counter drug products. Pharma- copeial Forum. 24(2):6087-6090. Kontny, M.J. (1988). Distribution of water in solid pharmaceutical systems.
  • Page 60 Pawkit Further Reading Brake, N.C. and O.R. Fennema. (1993). Edible coat- ings to inhibit lipid migration in a confec- tionery product. Journal of Food Science. 58:1422-1425. Fernandez-Salguero J., R. Gómez, and M.A. Car- mona. (1993). Water activity in selected high- moisture foods.

  • Page 61: Declaration Of Conformity

    Model Number: Year of First Manufacture: 2000 This is to certify that the Pawkit water activity meter, manufactured by Decagon Devices, Inc., a corpora- tion based in Pullman, Washington, USA meets or exceeds the standards for CE compliance as per the Council Directives noted above.
  • Page 62 Pawkit Declaration of Conformity...
  • Page 63 17, 23 buttons 15 to begin measurement 16 calibration 19 steps 20 calibration standards 6, 19 LiCl 19 NaCl 19 cautions with sampling 23 CE compliance 57 chamber cleaning 31 contamination 18 cleaning 26 sensor filter 30 closing the Pawkit 14...
  • Page 64 Pawkit Index closing the chamber 11 cold samples 24, 25 customer service 1 d25 21 d76 21 Declaration of Conformity 57 disassembling 27 display 16 e-mail address 2 email address 2 environment for sampling 6 enzymes and water activity 39...
  • Page 65 Pawkit Index high temperature 24 hot samples 24 humidity related to water activity 5 inserting samples 11 isotherms 44 cleaning 26 display 16 liability seller’s 3 LiCl standards 19 lids for sample cups 10 lipids and water activity 39 liquid phase water 40...
  • Page 66 Pawkit Index moisture content 38 molality of calibration standards 19 NaCl standards 19 turning off 18 opening the chamber 11 operation environment 6 osmotic effects 43 Pawkit accessories 6 closing 14 disassembly and re-assembly 27 features 8 measurement technique 5...
  • Page 67 Pawkit Index dairy products 51 food quality and safety 48 meat and seafood 50 microbiology 49 pharmaceuticals 54 water activity theory 47 relative humidity 39, 40 removing the sample 17 repair costs 37 shipping 36 repair instructions 36 sample insertion 11...
  • Page 68 Pawkit Index telephone number 2 temperature 24 effects on water activity 41 equilibrium 41 theory 38 water activity 39 time for measurement 17 toll-free number 2 u25 21 u76 21 vapor phase water 40 volatiles 23 warranty 2 water activity...
  • Page 69 Pawkit Index relation to water activity 42 wet samples cautions with 23...

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