Book MAS-1.book
Contents
1. 4 Installing the MAS 1 When selecting a site for installation it is important to understand that the soil adjacent to the sensor surface has the strongest influence on the sensor reading and that the sensor measures the volumetric water content Therefore any air gaps or excessive soil compaction around the sensor can profoundly influence the readings Also do not install the sensors adjacent to large metal objects such as metal poles or stakes This can attenuate the sensor s electromagnetic field and adversely affect sensor readings Because the MAS I has gaps between its prongs it is also important to consider the size of the media you are inserting the sensor into It is possible to get sticks bark roots or other material stuck between the sensor prongs which will adversely affect readings Finally be careful when inserting the sensors into dense soil as the prongs will break if excessive sideways force is used when pushing them in Procedure 1 The MAS I sensor was designed for easy installation into the soil After digging a hole to the desired depth push the prongs on the sensor into undisturbed soil at the bottom of the hole or into the sidewall of the hole Make sure that the prongs are buried completely up to the black overmolding The sensor may be difficult to insert into extremely compact or dry soil If you have difficulty inserting the sensor try loosening the soil somewhat or wetting the soil Never pound it2. The MAS 1 requires only two conductors so long lines are both lower in noise and less expensive With the MAS Isensor the source impedance is small and a current loop is highly immune to noise on the line Measured voltage can be tailored to a particular data acquisition system simply by adjusting the value of Ryo A typical application might be to use a MAS 1 MAS 1 Soil Moisture Sensor 3 Integrating the MAS 1 with a 12 volt supply and a Ryo value of 100 ohms The output voltage range is the product of the current and the resistance Equation 1 so for 4 20 mA it would be 0 4 to 2 volts Testing the Sensor After integrating the MAS 1 into your PLC or other data acquisition system it is always a good idea to test the sensor output to verify that it is functioning correctly with your sys tem Two convenient test conditions are having the sensor surrounded by air and water To test in air suspend the sen sor from the cable making sure that it is at least 6 inches from any object To test in water place the sensor in a bucket of tap water do not use de ionized or distilled water The entire sensor prongs black plastic electronics portion should be immersed in water and should be at least 2 inches from any container surface Under these condi tions the sensor should transmit in the following ranges approximate Air 3 4 to 4 7 mA Tap water 18 1 to 22 4 mA MAS 1 Soil Moisture Sensor 4 Installing the MAS 1
3. AS 1 Soil Moisture Sensor 3 Integrating the MAS 1 3 Integrating the MAS 1 A 4 20mA system generally consists of a sensor a transmit ter a power supply and a device to read the current being transmitted through the current loop The MAS 1 is an inte grated sensor and 4 20mA transmitter When the MAS I is powered by the Power Supply it transmits a current though the loop that is proportional to the soil dielectric permittivity and therefore the soil volumetric water content In Figure 1 the current loop is shown by the dotted line labeled I 4 20mA The arrows indicate the direction of the current Power Supply 7 32V Logger Controller Figure 1 4 20mA current loop diagram The MAS I uses a microcontroller to regulate the interval at which it takes measurements It takes one second from the time it is powered up to take its first measurement and trans mit current though the loop The trasnmitted current will reach a stable value within four seconds of power up After the initial four second startup measurements are taken every one second while the current in the loop is continuously maintained Since the measurement intervals are controlled MAS 1 Soil Moisture Sensor 3 Integrating the MAS I by the MAS I itself there is no need to pulse the excitation voltage A constant supply voltage should be applied in order for the MAS 1 to function as it is designed Wiring Conventional PLC A Programmable Logi
4. MAS I 4 20 MA Soil Moisture Sensor User Manual Version 1 DECAGON DEVICES Decagon Devices Inc 2365 NE Hopkins Court Pullman WA 99163 509 332 2756 www decagon com support decagon com 2011 Decagon Devices Inc All rights reserved MAS 1 Soil Moisture Sensor Contents 1 Introduction 1 Customer Service and Tech Support 2 NIITAMO LS LA AA SA TR a 3 Sellers Liability dass ans saan b best 3 2 About the MAS 1 4 3 Integrating the MAS 1 5 WANS ica SEEVE tee a ae mare 6 Conventional PLC sec tsar 6 Non Conventional 6 Testing The SENSitivo oiei i Ao 9 4 Installing the MAS 1 10 Procedure sam te Takaa nsa cbse eile 10 Orlentationsass lt iamuua east Kies 11 Removing the Sensof movies ce wee 11 5 Calibration 12 Mineral Sols 5 bie Tm ass 12 Potting Soil Peat saas ones ao ouu 13 Rock WOO ihmis RS nes 13 6 Troubleshooting 14 TNO OX lt rotat se Sana AR ae A asa 15 MAS 1 Soil Moisture Sensor MAS 1 Soil Moisture Sensor 1 Introduction 1 Introduction Thank you for choosing the MAS 1 4 20 mA Soil Moisture Sensor These innovative sensors will enable you to monitor soil moisture accurately and affordably with a standard 2 wire 4 20 mA analog interface for use with many data acquisition and control systems The MAS 1 can not be used with the standard Decagon
5. arranties 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 MAS 1 Soil Moisture Sensor 2 About the MAS 1 2 About the MAS 1 The MAS 1 measures the dielectric constant of the soil in order to find its volumetric water content Since the dielec tric constant of water is much higher than that of air or soil minerals the dielectric constant of the soil is a sensitive measure of water content The MAS 1 supplies a 70 MHz oscillating wave to the sensor prongs that induces an electro magnetic field in the medium soil surrounding the sensor The charging and discharging of the sensor is controlled by the dielectric of the surrounding soil A microprocessor on the MAS 1 measures the charging of the sensor and therefore the dielectric constant of the soil which is related to the water content of the soil The micro processor makes a dielectric measurement and updates the trasnmitted current once per second The transmitted 4 20 mA current can be converted to the water content of the soil using a simple calibration function The MAS 1 was designed to be used with standard 4 20 mA controllers and monitoring systems It cannot be used with Decagon logging systems For more information about using Decagon logging systems please contact Decagon s customer support representatives M
6. ased your MAS 1 through a distributor please contact them for assistance MAS 1 Soil Moisture Sensor 1 Introduction Warranty The MAS 1 has a one year warranty on parts and labor It is activated upon the arrival of the instrument at your location Seller s Liability Seller warrants new equipment of its own manufacture against defective workmanship and materials for a period of one year from date of receipt of equipment the results of ordinary wear and tear neglect misuse accident and exces sive deterioration due to corrosion from any cause are not to be considered a defect but Seller s liability for defective parts shall in no event exceed the furnishing of replacement parts FO B the factory where originally manufactured Material and eguipment covered hereby which is not manu factured 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 prop erty or things of whatsoever kind including but not without limitation loss of anticipated profits occasioned by or aris ing out of the installation operation use misuse nonuse repair or replacement of said material and eguipment or out of the use of any method or process for which the same may be employed The use of this eguipment constitutes Buyer s acceptance of the terms set forth in this warranty There are no understandings representations or w
7. c Controller PLC is typically used to read the current transmitted from the MAS 1 The red wire see Figure 2 of the MAS 1 is connected to a voltage output terminal that is able to supply 7 32 VDC The black wire is connected to an input terminal that is capable of accepting a current input ranging from 4 mA to 20 mA 4 20mA Input Analog Current input Programmable Logic Controller PLC Water Content Sensor Supply Voltage Figure 2 Typical wiring connection Non Conventional When using a device such as a data logger that does not have an input capable of measuring current a pickoff resis tor can be used as shown in Figure 3 Assuming that the Sin gle Ended Input has an input impedance or resistance much larger that of Ryo then all of the current in the 4 20 mA loop passes through Ryo If the data logger can measure MAS 1 Soil Moisture Sensor 3 Integrating the MAS 1 the voltage drop over the Ryo then the current can be cal culated as I V measured Ryolt 1 Where I mA is the 4 20 mA current Ryo ohms is the resistance of the pickoff resistor and V mV is the measured voltage drop over Ryojt Single Ended Input Data Logger Water Content Sensor GND Supply Voltage Figure 3 Wiring connection for devices without current inputs The optional 100uF capacitor shown in parallel with the Rx reduces measurement noise It should have a voltage rating higher tha
8. data loggers Specifications Electrical Interface Standard 4 20 mA 2 wire analog transmitter Supply voltage 7 32 VDC continuous Output current 4 20 mA Overvoltage protection Yes Reverse polarity protection Yes Settling time 4 seconds Wiring Red wire supply Black wire output Shield Not connected Measurement Type Volumetric water content VWC Range 0 50 VWC typical Resolution Depends on current measurement data acquisition device Accuracy 4 VWC with factory mineral soil calibration in a typical mineral soil 1 2 VWC with medium specific calibration in most porous medium MAS 1 Soil Moisture Sensor 1 Introduction Output 4 20 mA current proportional to VWC Sensor measurement interval 1 second Operating Environment Temperature 40 to 50 C Physical Properties Dimensions 8 9 cm x 1 8 cm x 0 7 cm Cable 2 m 3 wire 22 AWG tinned Red and Black wire 24 AWG tinned bare wire Custom cable length available upon request Customer Service and Tech Support When contacting us via fax or email include the following information Your MAS 1 s serial number found on the white cable lable your name address phone and fax number and a description of your problem Phone Call Monday Friday between 8 a m and 5 p m PST US and Canada toll free 1 800 755 2751 Outside of the US and Canada 509 332 2756 Fax 509 332 5158 E mail support decagon com NOTE If you purch
9. encounter problems with the MAS 1 they will usu ally be caused by one of two situations If the MAS 1 readings in air and or water are outside the ranges given in the Testing the Sensor section then there is likely a problem with the connection to the PLC or other data acquisition system Check the wiring and check to make sure that the supply voltage is in the specified range If the MAS 1 is reading a negative value for VWC while it is inserted into the soil make sure that you have good sensor to soil contact When inserted the MAS 1 should be completely covered up past the black over molding Removing and re installing the full length of the sensor with good sensor to soil contact should rem edy this problem If problems persist contact Decagon for assistance 14 MAS 1 Soil Moisture Sensor Index Index C Calibration 12 Contact information 2 D Dielectric constant 4 E E mail 2 F Fax Number 2 Functional testing 9 Installation 10 Integration 5 O Orientation 11 S Seller s liability 3 Specifications 1 T Telephone number 2 Troubleshooting 14 15 MAS 1 Soil Moisture Sensor Index W Warranty 3 Wiring 6 16
10. in 10 MAS 1 Soil Moisture Sensor 4 Installing the MAS 1 2 Carefully backfill the hole to match the bulk density of the surrounding soil Be careful to not over stress the cable or overmold by bending when installing the sensor Orientation The sensor can be oriented in any direction However ori enting the flat side perpendicular to the surface of the soil will minimize effects on downward water movement Removing the Sensor When removing the sensor from the soil do not pull it out of the soil by the cable Doing so may break internal connec tions and make the sensor unusable 11 MAS 1 Soil Moisture Sensor 5 Calibration 5 Calibration The current transmitted by the MAS 1 is proportional to the dielectric permittivity of the medium surrounding the sen sor and therefore its volumetric water content VWC of the medium The VWC is calculated by applying a calibration equation to the current transmitted by the MAS 1 The fol lowing are generic calibration eguations for common growth media Applying these eguations will generally result in accuracy of 4 VWC as long as the electrical conductiv ity of the medium is less than 8 dS m If you wish to use the MAS 1 in a medium that isn t listed below if you need bet ter than 4 accuracy or if you are working in a high salin ity material then you should develop a custom calibration for your particular medium See www decagon com for step by step instr
11. n the largest supply voltage and be sure to observe correct polarity The value of Ryo is limited by the amount of impedance that the MAS 1 circuitry can drive current through The val ues in Table 1 represent the maximum load that the MAS 1 can drive at the given supply voltage Equation 2 was derived from the values in Table 1 which were obtained through direct measurement V represents the supply volt age to the MAS 1 which ranges from 7 32 VDC Ryoit Max MAS 1 Soil Moisture Sensor 3 Integrating the MAS I is the maximum resistor value that can be used to convert the current to a voltage If Ryo is greater than Ryo Max the output current will decrease which will cause the MAS I to output incorrect readings Equation 2 can be used to deter mine the maximum value for Ryo Ryolt Max 58 65 1 Vin 355 76 2 Supply Voltage Load 12 V 340 24 V 1 072 K 32 V 1 509 K Table 1 Maximum resistance values for Ryo at specified voltages The MAS 1 sensor has several advantages over voltage out put sensors even for voltage input data loggers The MAS 1 supply voltage doesn t need to be regulated for the sensor to work properly it can be any value between 7 and 32 volts without affecting sensor output When using a current based sensor like the MAS 1 the signal is not affected by electrical resistance in the cable so the sensor output is not affected by cable length or wire gauge
12. uctions on developing a custom calibra tion Decagon can also develop a custom calibration for your medium contact Decagon for more details on the cali bration service Mineral Soils A single calibration equation will generally result in good accuracy for all mineral soil types with electrical conductiv ity lt 8 dS m VWC is given by VWC 0 00328 mA 0 0244 mA 0 00565 If your data aquisition system isn t capable of higher order mathematical operations the mineral soil calibration can be 12 MAS 1 Soil Moisture Sensor 5 Calibration approximated by the following linear model This will result in slightly worse accuracy at low VWC with errors becoming large above 35 VWC VWC 0 0479 mA 0 391 Potting Soil Peat The following equation can be used to convert MAS I trans mitted current into VWC in potting soil and peat potting mixes Please note that different potting soil types are quite variable so this calibration equation may not result in good accuracy in your particular mix although precision should still be good We recommend a custom calibration for best accuracy when using the MAS 1 in potting soils VWC 0 00531 e 0 29 mA4 Rock Wool The MAS 1 was calibrated in Groden Expert rockwool at several eletrical conductivities VWC can be calculated as VWC 0 00446 mA 0 0359 mA 0 0741 13 MAS 1 Soil Moisture Sensor 6 Troubleshooting 6 Troubleshooting If you
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