Decagon Devices VP-3 Operating Manual

VP-3

Vapor Pressure, Temperature &

Relative Humidity Sensor

Operator’s Manual

Version 0

Decagon Devices, Inc.

2365 NE Hopkins Court
Pullman WA 99163 USA

[e-mail]

tel: [phone]

fax:[phone]
www.decagon.com

VP-3 User’s Manual

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . 1

Customer Support . . . . . . . . . . . . . . . . . . . . . . .2

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Warranty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . . . . 6

2. 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

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

VP-3 User’s Manual

1. Introduction

1. Introduction

About the VP-3

Thank you for choosing Decagon’s VP-3 for measuring vapor
pressure, temperature and relative humidity (RH). This manual is
designed to help you understand the sensor’s features and how to
use this device successfully. The Decagon VP-3 sensor is an

accurate tool for monitoring vapor pressure, temperature and
relative humidity. The VP-3 utilizes a single sensor chip that
measures both temperature and RH. Each RH/T sensor chip is
individually calibrated with temperature and RH calibrations
stored on board and applied before data are output, ensuring best
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 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 resulting
ultra-rugged design allows the VP-3 to withstand permanent
exposure to hostile conditions, making it ideal for a wide range of

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VP-3 User’s Manual

1. Introduction

applications including standard meteorological/weather monitoring,
evapotranspiration measurement, micro-environment monitoring,
greenhouse monitoring and control, concrete moisture monitoring,
and building humidity monitoring for mold prevention/
remediation.

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.

NOTE: If you purchased your VP-3 through a distributor,

please contact them for assistance.

E-mail:
[e-mail] or [e-mail]

Phone:
1-509-332-5600

Fax:
1-509-332-5158

If contacting us by email or fax, please include as part of your
message the sensor’s name, your name, address, phone, and fax
number.

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VP-3 User’s Manual

1. Introduction

Specifications

Relative 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)

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VP-3 User’s Manual

1. Introduction

Hysteresis: < 1% RH typical
Long term Drift: < 0.5% RH/year typical

Temperature

Range: -40 oC to 80 oC

Resolution: 0.1 oC
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

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VP-3 User’s Manual

1. Introduction

Vapor P r essure

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:

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

General

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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.)

Handheld Reader Compatibility

ProCheck (rev 1.5C+)

Software Compatibility

ECH

O Utility (rev 1.65+), DataTrac (rev 3.6+)

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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 results of ordinary wear
and tear, neglect, misuse, accident and excessive deterioration due
to corrosion from any cause are not to be considered a defect);

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