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Decagon Devices VP-3 Operator's Manual

Vapor pressure, temperature & relative humidity sensor
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Operator's Manual
Decagon Devices, Inc.
Version: July 21, 2015 — 10:20:04

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Summary of Contents for Decagon Devices VP-3

  • Page 1 Operator’s Manual Decagon Devices, Inc. Version: July 21, 2015 — 10:20:04...
  • Page 2 VP-3 Decagon Devices, Inc. 2365 NE Hopkins Court Pullman WA 99163 Phone: 509-332-5601 Fax: 509-332-5158 Website: www.aqualab.com Email: support@aqualab.com or sales@aqualab.com c 2014 Decagon Devices, Inc.

  • Page 3: Table Of Contents

    1.3 Seller’s Liability ..... . 2 About VP-3 2.1 Specifications ..... . .

  • Page 4: Introduction

    1 INTRODUCTION Introduction Customer Support If you ever need assistance with your VP-3, or if you just have ques- tions or feedback, there are several ways to contact us. Customer ser- vice representatives are available to speak with you Monday through Friday, between 7am and 5pm Pacific time.

  • Page 5: Seller's Liability

    1 INTRODUCTION VP-3 Seller’s Liability Seller warrants new equipment of its own manufacture against de- fective workmanship and materials for a period of one year from the date of receipt of equipment. Note: We do not consider the results of ordinary wear and tear, neglect, misuse, accident as defects.

  • Page 6: About

    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 filter that is water and dust proof, but has an extremely high vapor...
  • Page 7 Long term Drift: <0.5% RH/year typical 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-3 sensor:...
  • Page 8 Long term drift: < 0.04 C/year typical Vapor Pressure Range: 0 to 47 kPa Resolution: 0.01 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-3 sensor:...
  • Page 9 2 ABOUT VP-3 VP-3 Figure 3: Vapor Pressure Accuracy 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 Output: RS232 (TTL) or SDI-12 Operating Temperature: 40 to 80 C Connector types: 3.5 mm (stereo) plug or stripped &...
  • Page 10 VP-3 2 ABOUT VP-3 Handheld Reader Compatibility: ProCheck (rev 1.5C+) Software Compatibility ECH2O Utility (rev 1.65+) DataTrac (rev 3.6+)

  • Page 11: Theory

    VP-3 Theory Relative Humidity The VP-3 utilizes a capacitance type RH sensor to measure the rela- tive humidity of the surrounding air. Relative humidity is measured at the same location as the temperature sensor. For this to be an ac- curate representation of the atmospheric humidity, it is critical that the humidity sensor be at air temperature.
  • Page 12 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 is not 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.

  • Page 13: Rh Sensor

    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 occur.

  • Page 14: Rh Sensor Conditioning

    VP-3 4 RH SENSOR that the VP-3 sensor be at the same temperature as the salt solution or large errors in the measured RH occur. Table 1: Salt Solutions Equilibrium RH Salt Molality (m) % Saturation (mol salt/kg water) LiCl 13.41 m...

  • Page 15: Connecting Sensors

    Simply plug the 3.5 mm “stereo plug” connector directly into one of the five sensor ports. Figure 5: 3.5 mm 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 ECH2O...

  • Page 16: Connecting To A Non-Decagon Logger

    ECH2O Utility, DataTrac 3 or a terminal program on your computer. Connecting to a Non-Decagon Logger The VP-3 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.
  • Page 17 Loggers, you must power the sensors off a 12 V or switched 12 V port. If your VP-3 has a standard 3.5 mm plug, and if you wish to connect it to a non-Decagon data logger, you have two options. First, you can clip off...

  • Page 18: Communication

    Decagon Serial String When excitation voltage is applied, the VP-3 sensor makes a mea- surement. Within about 140 ms of excitation two measurement val- ues transmit to the data logger as a serial stream of ASCII characters.
  • Page 19 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. The best and easiest way to change an address is to use Decagon’s ProCheck...
  • Page 20 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 temper- ature in Celsius, and the third number relative humidity in a unitless...

  • Page 21: Installation

    For most outdoor and greenhouse measurement scenarios, house the VP-3 in a radiation shield with adequate air flow to allow the sensor to come into equilibrium with air temperature. In general, tem- perature and humidity measurements become more accurate as wind speed increases.
  • Page 22 VP-3 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.

  • Page 23: Troubleshooting

    8 TROUBLESHOOTING VP-3 Troubleshooting If you encounter problems with the VP-3 sensor, they most likely manifest themselves in the form of no reading from communication problems, catastrophic sensor failure, or highly inaccurate measure- ments due to sensor poisoning by volatile chemicals. Before contact-...

  • Page 24: References

    VP-3 9 REFERENCES 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.

  • Page 25: 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 ex- ceeds the standards for CE compliance as per the Council Directives noted above. All instruments are built at the factory at Decagon and...
  • Page 26 Index CE Compliance, 22 Connection Em50 Logger, 12 Non-Decagon Logger, 13 Contact Information, ii, 1 Customer Support, 1 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...

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