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VP-4

9

REFERENCES

9

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 wa-
ter 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

, 7, 8, Geneva,

Switzerland.

21

Summary of Contents for VP-4

Page 1: ...Operator s Manual Decagon Devices Inc Version July 10 2017 12 32 13 ...

Page 2: ...VP 4 Decagon Devices 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 c 2017 Decagon Devices Inc ii ...

Page 3: ...Theory 8 4 RH Sensor 10 4 1 RH Sensor Conditioning 11 5 Connecting Sensors 12 5 1 Connecting to an Em50 Series Logger 12 5 2 Connecting to a Non Decagon Logger 13 5 3 Pigtail End Wiring 13 6 Communication 15 6 1 Digital Communication for Data Logger 15 7 Installation 18 8 Troubleshooting 20 9 References 21 10 Declaration of Conformity 22 iii ...

Page 4: ...them for assistance Email support decagon com or sales decagon com Phone 509 332 5600 Fax 509 332 5158 If contacting us by email or fax please include as part of your mes sage your instrument serial number your name address phone fax number and a description of your problem or question Please read these instructions before operating your sensor to en sure that it performs to its full potential 1 2...

Page 5: ... 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 instal lation operation use misuse nonuse repair or replacement of said material and equipment or out of the use of any method or process for whic...

Page 6: ...ine grade polyurethane encapsulant The RH T sensor chip is protected by a hydrophobic porous Teflon filter that is water and dust proof but has an extremely high vapor conductance allowing fast sensor equilibration with the surrounding atmosphere An additional stainless steel screen protects the Teflon filter and RH T sensor from impact and abrasion The rugged design allows the VP 4 to withstand l...

Page 7: ...e 1 Humidity Accuracy Chart Temperature Range 40 C to 80 C Resolution 0 1 C Accuracy Sensor measurement accuracy is variable across a range of temperatures Refer to the chart in Figure 2 to determine the accuracy specification for the VP 4 sensor Equilibration Time τ 63 400 s response time in 1 m s air stream Long term drift 0 04 C year typical 4 ...

Page 8: ...ccuracy Chart Vapor Pressure Range 0 to 47 kPa Resolution 0 001 kPa Accuracy Sensor measurement accuracy is variable across a range of temperatures and RH Refer to the chart below to determine the accuracy specification for the VP 4 sensor 5 ...

Page 9: ...ccuracy 0 4 kPa General Dimensions 1 96 cm dia x 5 4 cm h Power requirements 3 6 to 15 VDC 0 03 mA quiescent 4 mA dur ing 300 ms measurement Response Measurement Time 300 ms Output Decagon Digital or SDI 12 Operating Temperature 40 to 80 C Connector types 3 5 mm stereo plug or stripped tinned lead wires Pigtail 6 ...

Page 10: ...pon request Data Logger Compatibility not exclusive Decagon Em50 Em50R Em50G Firmware 2 19 Campbell Scientific Any logger with serial I O CR10X CR850 1000 3000 etc Handheld Reader Compatibility ProCheck rev 1 57 Software Compatibility ECH2O Utility rev 1 74 DataTrac rev 3 11 7 ...

Page 11: ...ure This is not as critical for non greenhouse indoor monitoring applications where radiation loading is small The VP 4 sensor provides a RH measurement that is referenced to saturation vapor pressure over liquid water even at temperatures be low 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 has the disadvantage ...

Page 12: ...mply the product of saturation vapor pressure and RH with RH expressed as a unitless ratio ranging from 0 to 1 Vapor Pressure es RH 2 Unlike relative humidity vapor pressure does not depend on temper ature and is relatively conservative over small spatial scales This means that the vapor pressure of the atmosphere near the VP 4 is the same as the vapor pressure at the VP 4 sensor even if the VP 4 ...

Page 13: ...easurements you can check the sensor accuracy using known RH conditions A convenient method for generating known RH conditions is through the use of salt solutions For an initial check we recommend prepar ing a saturated NaCl solution which has an equilibrium RH of 0 75 75 To prepare the salt solution start with lab grade NaCl and mix in enough water that there is a thin layer of liquid water pres...

Page 14: ...urs A 75 RH environment can be conveniently established by sealing the sensor in a headspace over saturated NaCl prepared as described above RH Sensor Calibration Decagon offers a service to calibrate VP 4 sensors contact Decagon Support at support decagon com for more information Prior to shipping the RH sensors are verified over salt solutions at 25 50 and 76 RH to ensure that they are properly ...

Page 15: ...tensive directions on how to integrate the VP 4 sensor into third party loggers The VP 4 sensor comes standard with a five meter cable Sensors may be purchased with custom cable lengths for an additional fee on a per meter fee basis Decagon has tested its digital sensor suc cessfully up to 1 000 meters 3 200 ft This option eliminates the need for splicing the cable a possible failure point 5 1 Con...

Page 16: ...r to your computer you need to use the ECH2O Utility DataTrac 3 or a terminal program on your computer 5 2 Connecting to a Non Decagon Logger The VP 4 sensor may be purchased for use with non Decagon data loggers These sensors typically come configured with stripped and tinned pigtail lead wires for use with screw terminals Refer to your distinct logger manual for details on wiring Our Integrator ...

Page 17: ... strip 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 sensor becoming unplugged however it then cannot be easily used in the future with a Decagon readout unit or data logger 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 ...

Page 18: ...he Decagon logger is automatic and only requires you to select the correct sensor configu ration for the sensor port When a Decagon logger applies excitation voltage the VP 4 sensor makes a measurement Within about 550 ms of excitation three measurement values transmit to the data logger as a serial stream of ASCII characters complete with checksum and sensor identification Please see the VP 4 Int...

Page 19: ...an be disconnected individually if a problem arises A single three wire cable can be run from the junction box to the data logger SDI 12 Address The SDI 12 protocol requires that all sensors have a unique address VP 4 sensors come from the factory with an SDI 12 address of 0 To add more than one SDI 12 sensor to a system the sensor address must be changed Address options include 0 9 A Z a z The be...

Page 20: ...ered but not making a measurement or communicating it uses 30µA When using the sensor as part of an SDI 12 bus it is recom mended that the sensors be excited continuously to avoid issues with initial sensor startup interfering with the SDI 12 communications Reading When reading the VP 4 in SDI 12 mode the first number output by the sensor is vapor pressure in kPa the second number is temper ature ...

Page 21: ...ield is not critical for non greenhouse indoor monitoring applications where radiation loading is small Decagons 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 prevents false readings of elevated temperatures allowing for accurate measure ment of ambient air temperature ...

Page 22: ...VP 4 7 INSTALLATION 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 19 ...

Page 23: ...ns to the data logger are both correct and secure 2 Ensure that your data logger batteries are not dead or weak ened 3 Check the configuration of your data logger in ECH2O Utility or ECH2O DataTrac to make sure you have selected VP 4 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 con taminated or blocked...

Page 24: ...1946 Low pressure properties of wa ter 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 7 8 Geneva Switzerland 21 ...

Page 25: ...Pullman WA 99163 USA Type of Equipment Temperature Humidity Pressure Sensor Model Number VP 4 Year of First Manufacture 2015 This is to certify that the VP 4 manufactured by Decagon Devices Inc a corporation based in Pullman Washington USA meets or ex ceeds the standards for CE compliance as per the Council Directives noted above All instruments are built at the factory at Decagon and pertinent te...

Page 26: ...ication 15 Declaration of Conformity 22 Email 1 Fax 1 Installation with Radiation Shield 18 Phone 1 Power Requirements 14 Radiation Shield 18 References 21 RH Sensor 8 Calibration 11 Conditioning 11 Stability 10 SDI 12 Communication 15 Seller s Liability 2 Specifications 3 Theory 8 Troubleshooting 20 Warranty 1 Wiring 3 5 mm 12 Pigtail 12 23 ...

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