Decagon Devices MPS-2 Operator'S Manual Download Page 17 | Manualshive

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4

RANGE AND ACCURACY

MPS-2 & MPS-6

most accurate as the soil dries. Measurements as the soil wets up
are slightly drier (more negative water potential) than the true water
potential of the soil. Our wetting and drying tests show the mag-
nitude of the hysteresis error is less than 10 kPa in the

−

20 kPa to

−

100 kPa range.

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Summary of Contents for MPS-2

Page 1: ...MPS 2 MPS 6 Dielectric Water Potential Sensors Operator s Manual Decagon Devices Inc Version December 1 2014 14 32 49 ...

Page 2: ...evices Inc 2365 NE Hopkins Court Pullman WA 99163 Phone 509 332 5600 Fax 509 332 5158 Website www decagon com Email support decagon com or sales decagon com Trademarks c 2011 2014 Decagon Devices Inc All Rights Reserved ii ...

Page 3: ...t Range 9 4 2 Measurement Accuracy 10 4 3 Calibration 12 4 4 Soil Type Dependence 13 4 5 Hysteresis 13 5 Connecting to a Logger 15 5 1 Connecting to Em50 Em50R Em50G logger 15 5 2 Connecting to a Non Decagon Logger 16 5 3 Using Non Decagon Loggers 18 5 4 Communication 18 5 5 Installing the Sensors 20 5 6 Campbell Scientific Programs 21 6 Maintenance and Troubleshooting 22 6 1 MPS 2 MPS 6 in Frozen...

Page 4: ...ughout this manual 1 1 Customer Support There are several ways to contact Decagon if you ever need assistance with your sensors or if you have questions or feedback We have cus tomer service representatives available to speak with you Monday thru Friday between 8am and 5pm Pacific time Note If you purchased your sensor through a distributor please con tact them for assistance E mail support decago...

Page 5: ...o water potential measure ment below 0 C Power Requirements 3 6 to 15 VDC 0 03 mA quiescent 10 mA max during 150 ms measurement Dimensions 9 6 cm L x 3 5 cm W x 1 5 cm D Sensor Diameter 3 2 cm Dielectric Measurement Frequency 70 MHz Measurement Time 150 ms milliseconds Output RS232 TTL with 3 6 volt levels or SDI 12 communication protocol 1 Please see Section 4 1 of this manual for more detailed i...

Page 6: ...ar antee and a one year warranty 1 4 Seller s Liability Seller warrants new equipment of its own manufacture against defec tive workmanship and materials for a period of one year from date of receipt of equipment the results of ordinary wear and tear ne glect misuse accident and excessive deterioration due to corrosion from any cause are not to be considered a defect but Seller s lia bility for de...

Page 7: ...process for which the same may be employed The use of this equipment constitutes Buyer s acceptance of the terms set forth in this warranty There are no understandings representations or warranties of any kind express implied statutory or otherwise including but with out limitation the implied warranties of merchantability and fitness for a particular purpose not expressly set forth herein 4 ...

Page 8: ...or permanent burial in the soil and continuous reading with a data logger or periodic reading with a handheld reader The only functional difference between the MPS 2 and MPS 6 is the amount of effort spent calibrating the sensor Each MPS 2 has a two point calibration that results in a fair degree of accuracy while the MPS 6 has a six point calibration that results in research grade accuracy Figure...

Page 9: ...evels move toward an equilibrium energy level When an ob ject comes into hydraulic contact with the soil the water potential of the object comes into equilibrium with the soil water potential For example tensiometers make use of this principal to measure the po tential energy of a liquid water reservoir in equilibrium with the soil water liquid equilibration and psychrometers dew point hygrome ter...

Page 10: ...e after measuring the water content of the ceramic Equation 1 represents the component variables for determining total soil water potential Ψt Ψt Ψp Ψg Ψo Ψm 1 The subscripts p g o and m are pressure gravitational osmotic and matric respectively Of these four components only Ψo and Ψm are significant and often measured in soil Ψo arises from dissolved salts in the soil and only becomes important i...

Page 11: ...2O Utility programs If the black plastic over mold of the sensor is in direct sunshine the temperature measure ment may read high Exposure of the overmold to solar radiation also drastically decreases the life expectancy of the sensor We do not recommend installing the sensor with the overmold in the sun 8 ...

Page 12: ...hey have a total pore vol ume that is weighted toward the larger pores which drain at water potentials within the plant available range However the MPS 2 and MPS 6 measurement range extends all the way to air dry 100 000 kPa As the sensor dries past the plant available range the total pore vol ume that drains at a given water potential decreases At these low water potentials the measured water pot...

Page 13: ...So in this scenario the air entry potential of the soil limits the wet end range rather than the ceramic discs themselves This is generally only an issue when using the sensor in poorly structured soils with high clay content 4 2 Measurement Accuracy Wet end The MPS 2 and MPS 6 sensors are identical in construction with the only difference between the two sensor types being the calibra tion method...

Page 14: ... good accuracy and low sensor to sensor variability to at least 1500 kPa plant permanent wilting point Field evaluations have shown low sensor to sensor variability to 4500 kPa See Figures 3 and 4 Good accuracy should theoretically be achievable to this level and well beyond but evaluation against accurate independent water potential measurements low water potential levels is problematic Figure 3 ...

Page 15: ...d state at Decagon Devices This two point calibration results in the accuracy stated above Although better wet end accu racy can be achieved through user calibration of the MPS 2 sensor it is more cost effective and convenient to simply order MPS 6 sensors that are fully calibrated in the wet end at Decagon 3 Figures 3 and 4 reproduced with permission from Walthert L 2013 Soil as a site factor in ...

Page 16: ...cs in equilibrium with the soil The MPS 2 and MPS 6 work in any soil type or other porous media as long as you install them correctly with adequate hydraulic contact to ensure timely water potential equilibrium between the sensor and the medium of interest 4 5 Hysteresis The amount of water that a soil holds at a given water potential is greater if the material is dried to that water potential tha...

Page 17: ...l dries Measurements as the soil wets up are slightly drier more negative water potential than the true water potential of the soil Our wetting and drying tests show the mag nitude of the hysteresis error is less than 10 kPa in the 20 kPa to 100 kPa range 14 ...

Page 18: ...he need for splicing the cable If you do need to extend the cable please be sure to ad equately waterproof the cable splices as inadequately waterproofed cable splices are a major failure point Visit our website for detailed suggestions on waterproofing cable splices 5 1 Connecting to Em50 Em50R Em50G logger The MPS 2 and MPS 6 work best with the Em50 data logger se ries Simply plug the 3 5 mm ste...

Page 19: ...ypically come pre configured with stripped and tinned pigtail lead wires for use with screw termi nals Refer to your distinct logger manual for details on wiring See Section 5 3 for more information on connecting the MPS 2 and MPS 6 sensors to non Decagon loggers or visit http www decagon com su pport mps 2 and mps 6 integrator s guide for the complete Integra tor s guide Figure 6 Pigtail End Wiri...

Page 20: ...ip and tin the wires and wire it directly into the data logger This has the advantage of creating a direct connection with no chance of the sen sor becoming unplugged however you cannot easily use it in the future with a Decagon readout unit or data logger The other op tion is to obtain an adapter cable from Decagon The 3 wire sensor adapter cable has a connector for the sensor jack on one end and...

Page 21: ...e power must be removed and reapplied to transmit a new set of values The ASCII stream contains two numbers separated by spaces The stream terminates with the carriage return character The first num ber output is water potential in kilopascals The second number is the temperature in degrees Celsius SDI 12 Communication The sensor can also communicate using the SDI 12 protocol a three wire interfac...

Page 22: ...to a bus the sensor address must be changed Address options include 0 9 A Z a z The best and easiest way to change an address is to use Decagon s ProCheck if the ProCheck does not have this option please up grade your firmware to the latest version SDI 12 addressing can be accessed in the CONFIG menu by selecting SDI 12 Address Addresses may then be changed by simply pressing the up or down arrows...

Page 23: ...g the sensor is to take some native soil wet it and pack it in a ball around the entire sesnor making sure that the moist soil is in contact with all surfaces of the ceramic The sensor and moist soil are then packed into the soil at the desired depth In sandy soils the soil may not adhere to the sensor even when wet In this case the sensor can be packed into soil at the bottom of a hole dug to the...

Page 24: ...ograms Because the sensors use digital rather than analog communication they require special considerations when connecting to a Campbell Scientific data logger Please visit our website at http www decagon com support to view sample Campbell Scientific programs 21 ...

Page 25: ...ecommend you minimize exposure of the ceramic material to skin oils and that you do not handle the discs with greasy hands or expose the discs to synthetic oils or other hydrophobic compounds 6 1 MPS 2 MPS 6 in Frozen Soils The MPS 2 and MPS 6 measure the dielectric permittivity of two ceramic discs to measure their water content and then derive their water potential The dielectric permittivity of...

Page 26: ...he sensors showed any significant change in output due to the freezing tests 6 2 Troubleshooting If you encounter problems with the MPS 2 or MPS 6 sensor they most likely manifest themselves in the form of incorrect or erroneous readings Review these troubleshooting suggestions before contact ing Decagon about the sensor Data Logger 1 Check to make sure the connections to the data logger are both ...

Page 27: ...6 MAINTENANCE AND TROUBLE MPS 2 MPS 6 3 Check the ceramic disc for damage or contamination 24 ...

Page 28: ...sed on Adsorption Cavitation and a Double Porocity Model International Journal of Geomechanics 9 6 250 257 Gee G W A L Ward Z F Zhang G S Campbell and J Math ison 2002 The influence of hydraulic nonequilibrium on pressure plate data Vadose Zone Journal 1 172 178 Koopmans R W R and R D Miller 1966 Soil freezing and soil water characteristic curves Soil Sci Soc Am Proc 30 1966 680 685 Spaans E J A a...

Page 29: ...Equipment Water Potential and Tempera ture Sensors Model Number MPS 2 MPS 6 Year of First Manufacture 2011 This is to certify that the MPS 2 and MPS 6 dielectric water poten tial sensors manufactured by Decagon Devices Inc a corporation based in Pullman Washington USA meet or exceeds the standards for CE compliance as per the the aforementioned Council Directives All instruments are built at the f...

Page 30: ...nergy of Water 6 Fax ii 1 Frozen Soils 22 Hydraulic Contact 6 20 Hysteresis 13 Liability 3 Maintenace 22 Manufacturer 26 Measurement Accuracy Dry End 11 Wet End 10 Model Number 26 Moisture Characteristic Curve 7 Range 9 References 25 Sandy Soil 20 Sensor Installation 20 Soil Water Content 6 Soil Water Potential 6 Telephone ii 1 Temperature Range 2 Tensiometers 6 Thermodynamics Second Law 6 Trouble...

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