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Decagon Devices VP-4 Operator's Manual

Vapor pressure, temperature, barometric pressure & relative humidity sensor
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Operator's Manual
Decagon Devices, Inc.
Version: July 10, 2017 — 12:32:13

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Summary of Contents for Decagon Devices 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.

  • Page 3: Table Of Contents

    1.3 Seller’s Liability ..... . 2 About VP-4 2.1 Specifications ..... . .

  • Page 4: Introduction

    1 INTRODUCTION Introduction Customer Support If you ever need assistance with your VP-4, 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-4 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

    A microprocessor within the VP- 4 calculates vapor pressure from the RH and temperature measure- ments. The VP-4 uses a sensor chip to measure both air temperature and RH and a secondary chip to measure barometric pressure. Each VP-4 has calibrations coefficients stored on board.
  • Page 7 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: <...
  • Page 8 Figure 2: Temperature Accuracy 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:...
  • Page 9 2 ABOUT VP-4 VP-4 Figure 3: Vapor Pressure Accuracy Barometric Pressure Range: 49 to 109 kPa Resolution: 0.01 kPa Accuracy: 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-...
  • Page 10 VP-4 2 ABOUT VP-4 Cable Length: 5 m standard; custom cable length available upon 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+)

  • Page 11: Theory

    VP-4 Theory Relative Humidity The VP-4 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-4 is the same as the vapor pressure at the VP-4 sensor, even if the VP-4 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-4 can be sealed into a small chamber that contains the salt solution. Whatever method is used, it is critical that the VP-4 sensor be at the same temperature as the salt solution or large errors in the measured RH occur.

  • Page 14: Rh Sensor Conditioning

    4 RH SENSOR fied accurate to within 0.3% RH. As mentioned above, it is critical that the VP-4 sensor be at the same temperature as the salt solution or large errors in the measured RH occur. Table 1: Salt Solutions...

  • Page 15: Connecting Sensors

    (pigtail) for terminal con- nections. Visit our website at www.decagon.com/support/literature to get extensive 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).

  • Page 16: Connecting To A Non-Decagon Logger

    Logger configuration may be done using either ECH2O Utility or DataTrac 3 (see respective manuals). Please check your software version to ensure it supports the VP-4. To update your software to the latest version, please visit Decagons free software download site: www.decagon.com/support/downloads.
  • Page 17 Loggers, you must power the sensors off a 12 V or switched 12 V port. If your VP-4 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

    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.
  • Page 19 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 best and easiest way to change an address is to use Decagon’s ProCheck...
  • Page 20 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 in Celsius, the third number is relative humidity in a unitless ratio from 0 to 1 (0 to 100%), and the fourth number is barometric pressure in kPa.

  • Page 21: Installation

    For most outdoor and greenhouse measurement scenarios, house the VP-4 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-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.

  • Page 23: Troubleshooting

    8 TROUBLESHOOTING VP-4 Troubleshooting If you encounter problems with the VP-4 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-4 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-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...
  • Page 26 Index CE Compliance, 22 Connection Em50 Logger, 12 Non-Decagon Logger, 13 Contact Information, ii, 1 Customer Support, 1 Data Logger Digital Communication, 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...

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