Decagon Devices VP-3 Operating Manual
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Decagon Devices VP-3 Operating Manual

Vapor pressure, temperature & relative humidity sensor
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VP-3
Vapor Pressure, Temperature &
Relative Humidity Sensor
Operator's Manual
Version 0

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Summary of Contents for Decagon Devices 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: Table Of Contents

    VP-3 User’s Manual Table of Contents 1. Introduction ....1 Customer Support ..... . .2 Specifications .
  • Page 4 VP-3 User’s Manual 6. Installation ... . . 22 Installation in a Radiation Shield... 22 7. Troubleshooting ..24 8.

  • Page 5: Introduction

    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 hydrophobic porous Teflon...

  • Page 6: Customer Support

    Customer Support If you ever need assistance 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.

  • Page 7: Specifications

    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 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 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-3 sensor: General Dimensions: 1.96 cm (dia) x 5.4 cm (h) Power requirements: 3.6 - 15 VDC, 0.03mA quiescent, 4mA...

  • Page 10: Warranty

    VP-3 User’s Manual 1. Introduction Operating Temperature: -40 to 80 °C Connector types: 3.5 mm (stereo) plug or stripped & tinned lead wires (Pigtail) Cable Length: 5m standard; custom cable length available upon request Datalogger Compatibility (not exclusive): Decagon: Em50, Em50R, Em50G (Firmware 2.11+) Campbell Scientific: Any logger with serial I/O (CR10X, CR850, 1000, 3000, etc.)
  • Page 11 VP-3 User’s Manual 1. Introduction but Seller’s liability for defective parts shall in no event exceed the furnishing of replacement parts F.O.B. the factory where originally manufactured. Material and equipment covered hereby which is not manufactured by Seller shall be covered only by the warranty of its manufacturer.

  • Page 12: Measurements

    2. Measurements 2. Measurements Relative Humidity The VP-3 utilizes a capacitance type RH sensor to measure the relative humidity of the surrounding air. Relative humidity is measured at the same location as the temperature sensor. For this to be an accurate representation of the atmospheric humidity, it is critical that the humidity sensor be at air temperature.
  • Page 13 VP-3 User’s Manual 2. Measurements Temperature The VP-3 has a band gap temperature sensor integrated into the sensor electronics. The temperature sensor is co-located with the RH sensor and will accurately measure the sensor temperature. If the VP-3 is adequately radiation shielded and aspirated, the sensor temperature will be very close to air temperature.
  • Page 14 This means that the vapor pressure of the atmosphere 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.

  • Page 15: Rh Sensor

    The VP-3 RH sensor typically drifts less than 0.5% RH per year. recommend that VP-3 sensors be re-calibrated every 1 to 2 years under normal use conditions to ensure best possible accuracy. To have your VP-3 fully calibrated or re-calibrate contact support@decagon.com and ask about our calibration service.
  • Page 16 VP-3 can be sealed into a small chamber that contains the salt solution. Whatever method is used, 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 occur.

  • Page 17: Rh Sensor Recalibration

    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 recalibration is recommended.

  • Page 18: Connecting Sensors

    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 meters (3200 ft).
  • Page 19 Data Power Figure 1: 3.5mm Stereo Plug Wiring The next step is to configure your logger port for the VP-3 and set the measurement interval, this may be done using either O Utility or DataTrac 3 (see respective manuals). Please check your software version to ensure it will support the VP-3.

  • Page 20: Connecting To A Non-Decagon Logger

    VP-3 User’s Manual 4. Connecting Sensors Connecting to a Non-Decagon Logger The VP-3 sensor may be purchased for use with non-Decagon data loggers. These sensors typically come pre-configured with stripped and tinned (pigtail) lead wires for use with screw terminals. Refer to your distinct logger manual for details on wiring.
  • Page 21 4. Connecting Sensors NOTE: The acceptable range of excitation voltages is from 3.6-15 VDC. If you wish to read the VP-3 with the Campbell Scientific Data Loggers, you will need to power the sensors off of a 12V or switched 12V port.

  • Page 22: Communication

    Decagon Serial String When excitation voltage is applied, the VP-3 sensor makes a measurement. Within about 140 ms of excitation two measurement values are transmitted to the data logger as a serial stream of ASCII characters.

  • Page 23: Sdi-12 Communication

    VP-3 User’s Manual 5. Communication SDI-12 Communication The VP-3 can also communicate using SDI-12 protocol, a three- wire interface where all sensors are powered (white wire), grounded (bare wire), and communicate (red wire) on shared nodes (for more information on the SDI-12 protocol, visit www.sdi-12.org).

  • Page 24: Sdi-12 Address

    SDI-12 Address The SDI-12 protocol requires that all sensors have a unique address. VP-3 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}.

  • Page 25: Power

    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...

  • Page 26: Installation

    For most outdoor and greenhouse measurement scenarios, the VP-3 should be housed in a radiation shield with adequate air flow to allow the sensor to come into equilibrium with air temperature.
  • Page 27 VP-3 User’s Manual 6. Installation 3. Insert the sensor into the 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: Troubleshooting

    VP-3 User’s Manual 7. Troubleshooting 7. Troubleshooting If you encounter problems with the VP-3 sensor, they most likely will manifest themselves in the form of no reading from communication problems or catastrophic sensor failure, or highly inaccurate measurements due to sensor poisoning by volatile chemicals.

  • Page 29: References

    VP-3 User’s Manual 8. References 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.

  • Page 30: Declaration Of Conformity

    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 pertinent testing documentation is freely available for verification.
  • Page 31 VP-3 User’s Manual Index Index CE compliance 26 Connecting sensors 14 non-Decagon logger 16 Customer support 6 Declaration of Conformity 26 Email 2 Fax 2 Installation 22 Measurements 8 Phone 2 Pigtail wiring 16 Power 20...

  • Page 32: Index

    VP-3 User’s Manual Index Radiation shield 22 References 25 RH sensor 11 recalibration 12, 13 reconditioning 12 SDI-12 communication 19 Seller’s liability 6 Serial string 18 Specifications 3 Stereo wiring, 3.5mm 15 Troubleshooting 24 Warranty 6 Wiring 3.5mm stereo 15...

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