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VP-3

 User’s Manual

8. References

25

8. References

Buck, A.L., 1981.  New equations for computing vapor pressure 
and enhancement factor.  Journal of Applied Meteorology, 20: 
1527-1532

Goff, J.A. and S. Gratch, 1946.  Low-pressure properties of water 
from -160

°

 to 212

°

F.  Transactions of the American society of 

heating and ventilating engineers, 51: 125-164

Murray,  F.W., 1967.  On the computation of saturation vapor 
pressure.  Journal of Applied Meteorology, 6: 203-204.

WMO, 2008.  Guide to meteorological instruments and methods 
of observation.  World Meteorological Organization No. 8, 7

th

edition, Geneva, Switzerland.

Summary of Contents for VP-3

Page 1: ...VP 3 Vapor Pressure Temperature Relative Humidity Sensor Operator s Manual Version 0 ...

Page 2: ...Decagon Devices Inc 2365 NE Hopkins Court Pullman WA 99163 USA support decagon com tel 1 509 332 5600 fax 509 332 5158 www decagon com ...

Page 3: ...Measurements 8 3 RH Sensor 11 RH Sensor Stability 11 RH Sensor Recalibration 13 4 Connecting Sensors 14 Connecting to an Em50 Series logger 14 Connecting to a Non Decagon Logger 16 5 Communication 18 Decagon Serial String 18 SDI 12 Communication 19 SDI 12 Commands 19 SDI 12 Sensor Bus 19 SDI 12 Address 20 Power 21 Reading 21 ...

Page 4: ...VP 3 User s Manual 6 Installation 22 Installation in a Radiation Shield 22 7 Troubleshooting 24 8 References 25 Declaration of Conformity 26 Index 28 ...

Page 5: ...st possible accuracy A micro processor within the VP 3 calculates vapor pressure from the RH and temperature measurements and outputs all three parameters using an RS232 TTL string and the common SDI 12 communication protocol The VP 3 sensor is packaged in a rugged Delrin housing with the sensor electronics potted in marine grade polyurethane encapsulant The RH T sensor chip is protected by a hydr...

Page 6: ...sistance with your VP 3 or if you just have questions or feedback there are several ways to contact us Customer service representatives are available to speak with you Monday through Friday between 7am and 5pm Pacific time NOTE If you purchased your VP 3 through a distributor please contact them for assistance E mail support decagon com or sales decagon com Phone 1 509 332 5600 Fax 1 509 332 5158 ...

Page 7: ...e Humidity Range 0 to 100 RH Resolution 0 1 RH Accuracy Sensor measurement accuracy is variable across a range of RH Refer to the chart below to determine the accuracy specification for the VP 3 sensor Response time τ 63 40 s response time in 1 m s air stream ...

Page 8: ...ure Range 40 o C to 80 o C Resolution 0 1 o C Accuracy Sensor measurement accuracy is variable across a range of temperatures Refer to the chart below to determine the accuracy specification for the VP 3 sensor Response time τ 63 400 s response time in 1 m s air stream Long term drift 0 04 C year typical ...

Page 9: ...or measurement accuracy is variable across a range of temperatures and RH Refer to the chart below to determine the accuracy specification for the VP 3 sensor General Dimensions 1 96 cm dia x 5 4 cm h Power requirements 3 6 15 VDC 0 03mA quiescent 4mA during 300ms measurement Output RS232 TTL or SDI 12 ...

Page 10: ...0 3000 etc Handheld Reader Compatibility ProCheck rev 1 5C Software Compatibility ECH2O Utility rev 1 65 DataTrac rev 3 6 Warranty All Decagon products have a 30 day satisfaction guarantee and a one year warranty on parts 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...

Page 11: ...f 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 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 Buyer s acceptance of the terms set forth in this warranty There are no...

Page 12: ...ium with air temperature This is not as critical for non greenhouse indoor monitoring applications where radiation loading is small The VP 3 sensor provides a RH measurement that is referenced to saturation vapor pressure over liquid water even at temperatures below freezing where ice is likely to be present instead of super cooled water Although this is the standard way to define RH WMO 2008 it h...

Page 13: ...the VP 3 is adequately radiation shielded and aspirated the sensor temperature will be very close to air temperature Vapor Pressure Vapor pressure is calculated from the primary measurements of sensor RH and sensor temperature The saturation vapor pressure es is calculated from the sensor temperature using the Magnus Tetens equation for calculating saturation vapor pressure over liquid water formu...

Page 14: ...near the VP 3 is the same as the vapor pressure at the VP 3 sensor even if the VP 3 isn t at the same temperature as the atmosphere Additionally it is the vapor pressure of the atmosphere not RH that controls the rate of vapor phase water transport e g evaporation transpiration and re distribution of water vapor As discussed above RH measurements below a temperature of 0 C will have error introduc...

Page 15: ...ur calibration service The polymer RH sensing element in the VP 3 can also be poisoned by exposure to volatile organic compounds solvents and other chemicals The effects of exposure to these chemicals can range from subtle loss of accuracy to catastrophic failure If you suspect that your VP 3 has suffered chemical exposure or notice questionable RH measurements you can check the sensor accuracy us...

Page 16: ...repare your own solutions using the mixing ratios shown below but great care and precision are required to obtain accurate results It is especially important that the salt used be pure and dry Decagon s salt solutions are specified accurate to within 0 3 RH As mentioned above it is critical that the VP 3 sensor be at the same temperature as the salt solution or large errors in the measured RH will...

Page 17: ... at 25 50 and 76 RH The calibration values are stored onboard the VP 3 sensor allowing the data to be corrected before being output thus eliminating the need for calibration during post processing We recommend that VP 3 sensors be re calibrated every 1 to 2 years under normal use conditions to ensure best possible accuracy For safety critical or especially high accuracy applications more frequent ...

Page 18: ...nned wires pigtail for terminal connections Visit our website at www decagon com support literature to get extensive directions on how to integrate the VP 3 sensor into third party loggers The VP 3 sensor comes standard with a 5 meter cable Sensors may be purchased with custom cable lengths for an additional fee on a per foot fee basis Decagon has tested its digital sensor successfully up to 1000 ...

Page 19: ...rt the VP 3 To update your software to the latest version please visit Decagon s free software download site www decagon com support downloads The following firmware and software support the VP 3 sensor Em50 Em50R Em50G Firmware version 2 11 or greater ProCheck Firmware version 1 5C or greater ECH2O Utility 1 65 or greater ECH2O DataTrac 3 6 or greater To download data from the logger to your comp...

Page 20: ...on wiring Our integrator s guide gives detailed instructions on connecting the VP 3 sensor to non Decagon loggers Please visit www decagon com support literature to reference the complete integrator s guide Pigtail End Wiring Connect the wires to the data logger as shown with the supply wire white connected to the excitation the digital out wire red to a digital input the bare ground wire to groun...

Page 21: ...nd wire it directly into the datalogger This has the advantage of creating a direct connection with no chance of the sensor becoming unplugged however it then cannot be easily used in the future with a Decagon readout unit or datalogger The other option 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 three wires on the o...

Page 22: ...0 ms of excitation two measurement values are transmitted to the data logger as a serial stream of ASCII characters The serial out is 1200 baud asynchronous with 8 data bits no parity and one stop bit The voltage levels are 0 3 6V and the logic levels are TTL active low The power must be removed and reapplied for a new set of values to be transmitted The ASCII stream contains 2 numbers separated b...

Page 23: ...ecagon com support literature for detailed instructions SDI 12 Commands Following are SDI 12 commands that the VP 3 Sensor responds to The sensor address is shown as a If a is substituted for a all addresses respond SDI 12 Sensor Bus Up to 62 sensors can be connected to the same 12 V supply and communication port on a datalogger This simplifies wiring because no multiplexer is necessary However on...

Page 24: ... 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 option is not available on your ProCheck please upgrade to the latest version of firmware 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 until you see the desired address and p...

Page 25: ... part of an SDI 12 bus it is recommended that the sensors be excited continuously to avoid issues with initial sensor startup interfering with the SDI 12 communications Reading When reading the VP 3 in SDI 12 mode the first number output by the sensor is vapor pressure in kPa the second number is temperature in Celsius and the third number relative humidity in a unitless ratio from 0 to 1 0 100 ...

Page 26: ...e wind speed the more accurate the temperature and relative humidity measurements will be A radiation shield is not critical for non greenhouse indoor monitoring applications where radiation loading is small Decagon s radiation shield comes with a mounting bracket and seven discs that prevent direct sunlight from coming into coming contact with the sensor This isolation from solar radiation preven...

Page 27: ...bottom of the shield and snap the cap back into place 4 The unit can then be mounted on the desired surface for your study NOTE Be sure to fasten the sensor cord to your mounting post to help support the weight of the cable in order to prevent it from being pulled out ...

Page 28: ...the connections to the data logger are both correct and secure 2 Ensure that your data logger s batteries are not dead or weakened 3 Check the configuration of your data logger in ECH2O Utility or ECH2O DataTrac to make sure you have selected VP 3 Sensors 1 Check sensor cables for nicks or cuts that could cause a mal function 2 Check your screen and filter to make sure that they are not contaminat...

Page 29: ...tch 1946 Low pressure properties of water from 160 to 212 F Transactions of the American society of heating and ventilating engineers 51 125 164 Murray F W 1967 On the computation of saturation vapor pressure Journal of Applied Meteorology 6 203 204 WMO 2008 Guide to meteorological instruments and methods of observation World Meteorological Organization No 8 7th edition Geneva Switzerland ...

Page 30: ...9163 USA Type of Equipment Temperature Relative Humidity and Vapor Pressure Sensor Model Number VP 3 Year of First Manufacture 2012 This is to certify that the VP 3 manufactured by Decagon Devices Inc a corporation based in Pullman Washington USA meets or exceeds the standards for CE compliance as per the Council Directives noted above All instruments are built at the factory at Decagon and pertin...

Page 31: ...l Index 29 Index C CE compliance 26 Connecting sensors 14 non Decagon logger 16 Customer support 6 D Declaration of Conformity 26 E Email 2 F Fax 2 I Installation 22 M Measurements 8 P Phone 2 Pigtail wiring 16 Power 20 ...

Page 32: ...ield 22 References 25 RH sensor 11 recalibration 12 13 reconditioning 12 S SDI 12 communication 19 Seller s liability 6 Serial string 18 Specifications 3 Stereo wiring 3 5mm 15 T Troubleshooting 24 W Warranty 6 Wiring 3 5mm stereo 15 pigtail 16 ...

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