Decagon Devices WP4C, Operator'S Manual

Page 1: ...WP4C Dewpoint PotentiaMeter Operator s Manual Version 1 ...

Page 2: ...NE Hopkins Court Pullman WA 99163 tel 509 332 2756 fax 509 332 5158 www decagon com support decagon com Trademarks WP4C PotentiaMeter is a registered trademark of Decagon Devices Inc 2010 Decagon Devices Inc All rights reserved ...

Page 3: ...bility 3 2 About the WP4C 4 Instrument Specifications 4 WP4C and Water Potential 5 How the WP4C works 5 WP4C and Temperature 6 3 Getting Started 7 Components of your WP4C 7 Choosing a Location 8 Features 8 Preparing the WP4C for Operation 9 Portability 10 4 The Menus 12 The Main Menu 12 Changing Languages 13 Reading Modes 13 System Configuration 15 Sample Equilibration Screen 20 ...

Page 4: ...aring the Sample 26 Dry Samples 27 Samples and Temperature 27 Measuring Plant Samples 29 7 Taking a Reading 30 How WP4C takes Readings 31 Cautions 31 8 Computer Interface 33 9 Theory Water Potential 35 Water Potential 35 Measuring Water Potential 35 Effect of Temperature on Water Potential 37 Estimating Osmotic Potential 38 10 Cleaning and Maintenance 39 Tools Needed 39 Accessing the Block 39 Clea...

Page 5: ...structions 45 Shipping Directions 45 Repair Costs 47 Loaner Service 47 12 Troubleshooting 48 Problems and Solutions 48 Sensor Performance Screen 54 13 Further Reading 56 References 56 Application Notes 57 Appendix A 58 Preparing Salt Solutions 58 Index 61 ...

Page 6: ...WP4C PotentiaMeter Table of Contents iv ...

Page 7: ...ccurate results We hope you find this manual informative and helpful in understanding how to maximize the capabilities of your WP4C About this Manual Included in this manual are instructions for setting up your WP4C calibration and maintaining and caring for your instrument Please read these instructions before operating WP4C to ensure that the instrument performs to its full potential Customer Se...

Page 8: ...r along with a description of your problem E mail If you need technical support or have questions about your application with WP4C you can send us messages via e mail at support decagon com Again please include as part of your message your WP4C s serial number your name address phone fax number and return e mail address Warranty WP4C has a 30 day satisfaction guarantee and a one year warranty on p...

Page 9: ... 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 installation operation use misuse nonuse repair or replacement of said mate...

Page 10: ... Type 1 Chilled mirror dewpoint sensor 2 Infrared temperature sensor Sample Cup Capacity 7 ml recommended 15 ml full Dimensions 24 1 x 22 9 x 8 9 cm 9 5 x 9 0 x 3 5 in Weight 3 2 Kg 7 1 lbs Case Material Powder Painted Aluminum Display 20 x 2 alphanumeric LCD with backlighting Data Communication RS232A compatible 8 data bit ASCII code 9600 baud no parity 1 stop bit Power 110VAC to 220 VAC 50 60 Hz...

Page 11: ... air in equilibrium with a sample in a sealed measure ment chamber For a more detailed description of water potential please refer to Chapter 9 titled Theory Water Potential of this manual How the WP4C works WP4C uses the chilled mirror dewpoint technique to mea sure the water potential of a sample In this type of instru ment the sample is equilibrated with the headspace of a sealed chamber that c...

Page 12: ...rculates the air within the sample chamber to reduce time to equilibrium Since both dewpoint and sample surface temperatures are simultaneously measured the need for complete thermal equilibrium is eliminated The WP4C controls the sample temperature by means of an internal thermo electrical module that monitors and stabilizes the sample block temperature according to how it is set WP4C and Tempera...

Page 13: ...WP4C Your WP4C should have been shipped with the following items WP4C main unit Quickstart guide Certificate of Calibration Power cord RS 232 interface cable 25 plastic sample cups and lids 10 Stainless Steel sample cups Operator s Manual 12 vials of 0 5 Molal KCl Cleaning Kit ...

Page 14: ...of the instrument To protect the internal electrical com ponents and to avoid inaccurate readings place your WP4C in a location where the temperature remains fairly stable This location should be well away from air condi tioner and heater vents open windows outside doors refrigerator exhausts or other items that may cause rapid temperature fluctuation Features Front view of WP4C LED indicator ligh...

Page 15: ...turn the knob to the OPEN LOAD position An empty disposable sample cup is usually placed upside down in the drawer to protect it during shipment Remove this sample cup and turn the instrument on The ON OFF switch is located on the lower right corner of the WP4C s back panel The follow ing screens will appear on the LCD RS 232 interface fuse well ON OFF Switch Power cord Plug Fan Lid thumb screw Mo...

Page 16: ...will begin the read cycle to measure the water potential of your sample Portability On occasion you may want to take water potential mea surements in the field where it is not feasible to take sam ples and return to the lab The following is a procedure for powering your WP4C using your vehicle as a power source at sites where AC power is not readily available 1 Purchase a portable power inverter t...

Page 17: ...ectly to the battery itself 4 Plug the WP4C to the inverter and turn it on When the instrument is on it draws up to 1 amp Check the rating of your battery if you want to know how long it will power the instrument for example if your battery is rated for 60 amp hours it will work for 60 hours when the vehicle isn t running 5 Allow the instrument to warm up for 15 30 minutes as you would in the lab ...

Page 18: ...ier the water potential and sample temperature are displayed on the screen On each side of the LCD there are buttons Each button performs a different function depending on which mode you want Following is a description of the modes and options you may use and the buttons used to set them 0 0 C 0 00 MPa pF 0 00 p sample temperature menu system setup language selection 0 0 C 0 00 MPa pF 0 00 p preci...

Page 19: ...one simply by pressing the upper right button of the instrument while it is not reading a sample You will see the following screen Press the upper right key again and the next language option German will appear Each time you press the right button the display will scroll to the next language option Select the desired language then press the lower left button to exit Reading Modes Precise Mode The ...

Page 20: ...with continuous mode enabled Here is a brief summary of the precise mode features Precise water potential value is insured by repeat ing measurements on a sample Read time is typically 10 15 minutes Green LED blinks until you turn the drawer knob to the OPEN LOAD position Continuous Mode Continuous mode measures the water potential of your sample continuously until you turn the drawer knob to the ...

Page 21: ...ome find it helpful to connect their WP4C to a computer while in continuous mode in order to log and store data over time For instructions on how to do this see Chapter 8 Fast Mode In fast mode the sample is measured only once Read time is typically 3 5 minutes Readings are less precise particu larly in the wet range However fast mode is recom mended for dry soil samples with water potential 40 MP...

Page 22: ...ng you that the water potential reading is completed for your sample the beeper and a flashing green LED located on the left front corner of the WP4C s case In fast and precise reading modes the LED will flash once when a sample is started When it is finished the LED will flash system configuration menu button 0 0 C pF 0 00 p 0 00 MPa Beeper Beeper Mode indicator Calibration menu Icon 4 beeps show...

Page 23: ...rned to the OPEN LOAD position After you have adjusted the beeper setting it will remain as you have set it until you change it again and will not be affected by turn ing the instrument on or off EXIT You may press the Exit button the lower left button to exit back to the main menu at any time Adjusting Calibration When you need to adjust calibration press the upper right button in the system conf...

Page 24: ...Holding down the button will rapidly increment the value The target setpoint temperature roughly corresponds to the temperature at which you wish the sample to read Therefore adjust the setpoint to the temperature that you want then begin measurements to see how close your WP4C comes to your desired temperature this works best by putting the WP4C in continuous mode After several samples it should ...

Page 25: ...below chamber temperature before starting a reading For slow equilibration samples such as plant and moist soil samples 0 5 MPa precise reading mode may yield small errors For these types of samples it is recommended to use continuous mode and log data over time See Chapter 8 to determine when equilibrium conditions are reached For samples with very little water holding capac ity i e dry sand samp...

Page 26: ...our sample and the WP4C press the lower right button at the main menu This screen can only be accessed when the drawer knob is in the OPEN LOAD position The following screen will appear This screen shows the temperature difference between the sample Ts and the chamber block Tb allowing you to quickly check if the sample is too hot which may cause condensation inside the chamber Press the lower rig...

Page 27: ...gon Verification Standards Verification standards are specially prepared salt solutions that have a specific molality and water potential The potassium chloride KCl verification standards are accu rate easy to use and readily available from Decagon Devices Most importantly they greatly reduce prepara tion errors We therefore recommend using Decagon s KCl Performance Verification Standard for the m...

Page 28: ...amber For batch processing the instrument should be checked regularly against the KCl standard This will alert you to the possibility of contami nation of the unit or shifts in the calibration from other causes How to Verify and Calibrate the WP4C Since errors in the calibration value result in errors in all values subsequently measured care should be taken to do it right Checking and Adjusting Ca...

Page 29: ...plash or spill and con taminate the chamber Check to be sure the sample temperature is below chamber temperature lower right button 4 Turn the drawer knob to the READ position to make a reading When the reading is complete the following screen will appear NOTE The WP4C will automatically shift to precise sam pling mode for the verification calibration The reading should be within 0 05 MPa of the c...

Page 30: ...bration has probably occurred Press the upper right button to move the value up the lower right button to move it down When it is at the correct value for the verifica tion standard press the Exit button The value will be stored Note This is the only menu where these buttons can change the cali bration so you won t hurt anything by pressing these buttons in other menus 7 Read the KCl standard agai...

Page 31: ...r samples in the wet end If you are measuring samples with water potential wetter than 1 MPa you should use the stainless steel sample cups You can also oven dry soil samples directly in the stainless steel cups to determine water content gravimetrically which is conve nient if you are generating soil moisture characteristic curves It is important to note that you must thoroughly clean the stainle...

Page 32: ...sample cup more than half full Overfilled cups may contaminate the sensors in the chamber more is not necessarily better 3 Make sure that the rim and outside of the sample cup are clean Wipe any excess sample material from the rim of the cup with a clean tissue Material left on the rim or the outside of the cup will contaminate the sensor chamber and will be transferred to subsequent samples The r...

Page 33: ...al value is drier than about 300 MPa WP4C will display an error message indi cating the lowest reading it could make on that particular sample For example if you were measuring a dry sample and the following screen appeared this screen indicates that the last water potential reading the WP4C measured on this sample was 301 8 Megapas cals Therefore the actual water potential of the sample is lower ...

Page 34: ...and note the temperature difference If it is close enough to the block temperature turn the knob to the READ position to begin reading There is a linear relationship between the sample s dewpoint temperature and its water potential The dewpoint decreases 0 12 C per MPa For example a very dry sample at 40MPa can be 4 8 C 12 x 40 above the chamber temperature without condensing A sample at 1 MPa fai...

Page 35: ...ample temperature is just a little below chamber temperature Measuring Plant Samples The WP4C can be used to measure the water potential of leaves and plant material Please refer to the application note Measurement of Leaf Water Potential Using the WP4 which can be found at www decagon com ...

Page 36: ...inate the chamber s sensors 3 Carefully slide the drawer closed being especially care ful if you have a liquid sample that may splash or spill and contaminate the chamber 4 Access the sample temperature menu press lower right button to watch the temperature difference between the sample and the instrument 5 Turn the sample drawer knob to the READ position to seal the sample cup with the chamber Th...

Page 37: ...ontaminate the instrument s chamber if the instrument is accidentally moved or jolted Never try to move your instrument after a sample has been loaded Movement may cause the sample mate rial to spill and contaminate the sample chamber Take special care not to move the sample drawer too quickly when loading or unloading liquid samples in order to avoid spilling If a sample has a temperature that is...

Page 38: ...accurately If you are reading and a triangular warning symbol appears in the top right corner of the display this indi cates that the mirror has become too dirty to give accurate measurements You will need to clean the mirror and chamber before continuing to sample For more details about this symbol please refer to Chapter 12 For cleaning instructions refer to Chapter 10 C pF 7 38 24 9 C 1 84 MPa ...

Page 39: ...Select the COM Port your RS 232 cable is connected to 2 Settings are the following Bits per second 9600 8 databits no parity 1 stop bit and flow control set to hardware Click OK 3 Plug your RS 232 cable to the COM port you selected and connect it to your WP4C Begin reading Your WP4C s data will be displayed on screen as it samples It will be output in the following format 4 When you are finished r...

Page 40: ...WP4C PotentiaMeter 8 Computer Interface 34 in the terminal session or cut and paste it to a spread sheet or text editor 1 A good free terminal program can be found at http ttssh2 sourceforge jp ...

Page 41: ...centration of dissolved substance in the water Pressure potential depends on the hydrostatic or pneu matic pressure on the water The WP4C measures the sum of the osmotic and matric potentials in a sample Often one or the other of these potentials will be the dominant factor in determining the total potential For example solutions like the KCl calibra tion standard have only an osmotic component So...

Page 42: ... potential by equilibrating the liquid phase water of the sample with the vapor phase water in the headspace of a closed chamber then measur ing the vapor pressure of that headspace In the WP4C a sample is placed in a sample cup which is sealed against a sensor block Inside the sensor block is a fan a dew point sensor a temperature sensor and an infrared thermome ter The dew point sensor measures ...

Page 43: ...ch is not the true water potential of the sample Effect of Temperature on Water Potential Temperature plays a critical role in water potential deter minations Most critical is the measurement of the differ ence between sample and dew point temperature If this temperature difference were in error by 1 C an error of 8 MPa would result In order for water potential measure ments to be accurate to 0 05...

Page 44: ... user ensure that the sample won t condense on the sensor block Estimating Osmotic Potential The WP4C measures the sum of osmotic and matric potential An approximate value for the osmotic potential can be found by measuring the electrical conductivity EC of the saturation extract of the soil The osmotic potential of the saturation extract is computed from Ψos MPa 0 036EC dS m The osmotic component...

Page 45: ...ncluded in the WP4C Cleaning Kit They are ideal for cleaning because they don t leave much of a lint residue like most tissues They also don t have any other compounds in the tissue that may contaminate the sensors in the WP4C s block Never use cotton swabs to clean the block sensors Most cotton swabs con tain adhesives and other compounds that are released and transferred to the mirror and other ...

Page 46: ...r block 4 Unplug the cable with the 20 pin socket that attaches the block to the main circuit board by releasing the two locking levers that are on either side of the socket 5 Carefully lift the block straight up from its mount Turn the block over to expose the chamber cavity as shown in the illustration View of inside block chamber thermopile mirror optical sensor chamber fan ...

Page 47: ...ed within or around the sample chamber b Wrap a NEW Kimwipe around the end of the thin plastic rod spatula and moisten it with isopropyl alcohol or Decagon Cleaning Solution Note Do NOT dip a used Kimwipe into your container of IPA or cleaning solution the IPA or cleaning solution will become contaminated c WASH Clean all surface edges of the samples cham ber including the edge where the sample cu...

Page 48: ... isopropyl alcohol or Decagon Cleaning Solution b WASH Carefully clean the mirror with the moist Kimwipe c RINSE Repeat steps b and c using new Kimwipes with distilled water d DRY Repeat steps b and c using new dry Kimwipes to help remove any moisture remaining from the cleaning e Visually inspect the mirror for cleanliness Re clean if necessary Note Do not reuse Kimwipes 3 Cleaning the Optical Se...

Page 49: ... cleaning solution d DRY Repeat steps a b but use a new dry Kimwipe to help remove any moisture remaining from the cleaning e Visually inspect the thermopile for cleanliness This sensor must be free of all dirt and lint Re clean if nec essary 5 Inside Case 1 Clean the sample drawer and drawer base as described above for the thermopile Remove any debris that may have collected inside the case 2 Che...

Page 50: ...parts of your WP4C it is important to check the instrument s per formance in order to correct for any calibration change that may have occurred during cleaning procedures Check the calibration of your instrument by measuring the water potential of the KCl standard If a change has occurred refer to chapter 5 for directions on how to reca librate If after adjusting calibration your instrument is sti...

Page 51: ... international distributors please contact them before contacting Decagon They may be able to provide you with local service and help you remedy the problem Shipping Directions When you ship your instrument back to us please include with it a document with the complete shipping address name and department of the person responsible for the instrument and most importantly a description of the proble...

Page 52: ...the box If you aren t using the foam inserts pack the box moderately tight with packing material like styrofoam peanuts 2 Put your instrument in a plastic bag to avoid disfigur ing marks from the packaging 3 Don t ship your WP4C to us with the power cord we have plenty here to use with your instrument and it may damage the instrument in shipment 4 Please review the RMA form and verify the ship to ...

Page 53: ... their warranty period costs for parts labor and shipping will be billed to you We have a minimum repair charge and an extra fee will be charged for rush work Decagon will pro vide an estimated repair cost if requested Loaner Service We have loaner instruments that can be provided while your instrument is being serviced There is however a limited number of loaner instruments They are granted on a ...

Page 54: ...n t addressed here or if these remedies still don t resolve your problem contact Decagon at 1 800 755 2751 US only or 509 332 2756 for those outside the US If purchased from a distribu tor please contact the distributor for assistance first Problems and Solutions The following table is a brief guide to help you quickly define solutions to your problems For more detailed descriptions of these probl...

Page 55: ... equilibrium 4 301 8 MPa Sample too dry to accu rately measure Dirty chamber or mirror 5 Triangle appears in upper right corner Mirror is dirty 6 block failure appearsonscreenafter turning on WP4C Block is disconnected from motherboard Block memory compo nent has failed 7 7 7 7 set T option no longer appears on sy s tem config screen Temperature control mod ule in WP4C is broken or not functioning...

Page 56: ...om the wall and the instru ment 2 Locate the panel where the power cord plugs in The fuse box is on the right side of that panel Press in on the release tab and pull the fuse holder out 3 Pull the broken fuse s out and replace with a 2 0 Amp 250V fuse Caution Do not use any other kind of fuse or you will risk damage to your instrument and void your warranty 4 Replace the fuse holder and push it in...

Page 57: ...measurements to take longer than usual and nothing can be done to speed up the pro cess Refer to Chapter 6 for further explanation The fan blade inside the block chamber may be bro ken If even the KCl standard takes a long time to read and the sample chamber is clean you may have a broken or bent chamber fan blade This is especially likely if you have just cleaned the chamber If you suspect this m...

Page 58: ...ution you are using is not in equilibrium 4 PROBLEM Message on screen displays the following example SOLUTION The sample is too dry for the instrument to read accurately If your sample has a water potential that is above the detection limits of the instrument this mes sage will come up Essentially it means that there is not enough sample moisture to condense on the mir ror and provide a reading Th...

Page 59: ...C senses that the mirror performance has dropped to unacceptable levels it will display the triangular warning sign after the sample has been measured When this appears you should stop sam pling and clean the chamber If the triangle is still on the screen after cleaning the mirror is most likely still dirty and you will need to clean it until the triangle disappears 6 PROBLEM The following screen ...

Page 60: ... have failed on the block s circuit board Sensor Performance Screen If after cleaning your instrument and reading the other troubleshooting hints you have reason to believe that one of the components of your WP4C may be causing mea surement error you can access a screen that will display values for component performance This is done by hold ing down the lower right button while turning on the inst...

Page 61: ...The bottom left value is the block temperature This value should be around ambient temperature The bottom right value is the mirror reflectance voltage in units of volts This value should normally be around 0 5 or above but if it drops below 0 3 there is something wrong You can t change anything in this screen but it is here to give you an indication of the component performance If you notice that...

Page 62: ...mpbell and W K Barlow 1973 A dewpoint hygrometer for water potential measure ment Agric Meteor 12 113 121 G W Gee M D Campbell G S Campbell and J H Camp bell 1992 Rapid measurement of low soil water potentials using a water activity meter Soil Science Society of America 56 4 1068 1070 Papendick R I and G S Campbell 1980 Theory and measurement of water potential in Water Potential Relations in Soil...

Page 63: ... educa tion tab choose WP4C Generating a Soil Moisture Characteristic with the WP4C Measuring Leaf Water Potential using the WP4C Field Portability Instructions for the WP4C Water Potential The Key to Successful Seed Priming Seed Longevity in Storage is Enhanced by Controlling Water Activity Classification of Expansive Soils using the WP4C Dewpoint PotentiaMeter ...

Page 64: ...given concentrations of NaCl and KCl at 20 C Table 2 Water Potential of NaCl and KCl in Megapascals MPa Concentration Moles kg NaCl KCl 0 05 0 232 0 232 0 10 0 454 0 452 0 20 0 901 0 888 0 30 1 349 1 326 0 40 1 793 1 760 0 50 2 242 2 190 0 60 2 699 2 622 0 70 3 159 3 061 0 80 3 618 3 501 0 90 4 087 3 931 1 00 4 558 4 372 ...

Page 65: ...WP4C PotentiaMeter Appendix A 59 ...

Page 66: ...WP4C PotentiaMeter Appendix A 60 ...

Page 67: ...for menu selection 12 C c for continuous mode 14 Calibration changes in 21 menu 17 steps 22 24 when to check 22 Calibration drift 21 Cautions 31 Checking calibration 44 Chilled mirror technique 5 Cleaning 39 inside case 43 optical sensor 42 sensor block 39 Components 7 Computer interface 33 Continuous mode 14 ...

Page 68: ...r 32 Distilled water 22 Dry samples 52 Dry water potential 27 E E mail address 2 Error messages 48 52 Exit 17 F Fan inside sample chamber 6 Fast mode 15 Fax number 2 Features 8 Field measurements 10 Flashing See LED French 13 Further reading 56 Fuse changing 50 G German 13 Gravitational potential 35 ...

Page 69: ...suring water potential in continuous mode 15 LED 16 Linear offset how to adjust for 22 Loaners 47 Location for reading 8 M Main menu 10 12 Maintenance 39 Manual 1 Matric potential 35 Menus main menu 12 system configuration 15 Molality of verification standards 21 N Norwegian 13 ...

Page 70: ...ng salt solutions 58 Pressure potential 35 R Read time affected by sample temp 27 long read time 49 51 Reading modes 13 Continuous 14 Fast 15 Precise 13 Readings cautions 31 how WP4C takes 31 taking readings 30 References 56 Repair costs 47 instructions for 45 shipping 45 S Salt standards See verification standards Sample ...

Page 71: ...ion screen 6 20 Saturated salts 58 Seller s liability 3 Sensor performance screen 54 Shipping for repair 45 Spanish 13 Spilling the sample 31 Swedish 13 T TE set 18 Technical support 1 Telephone number 2 Temperature effects on reading 6 effects on water potential 37 hot samples 31 of instrument 31 samples not at room temp 27 Time long read times 51 Toll free number 2 Triangle 32 ...

Page 72: ...ings too high low for 51 W Warm up 10 Warranty 2 Water content definition 35 vs water potential 35 Water potential 58 definition 5 35 displayed 10 equation 36 measuring 35 theory 35 WP4C and temperature 6 Chilled mirror dewpoint technique 5 important tips 19 measuring water potential 36 preparing for operation 9 theory 35 ...