Campbell KH20 Manuel utilisateur

KH20 Krypton Hygrometer

2/10

Campbell Scientific, Inc.

Warranty and Assistance

The KH20 KRYPTON HYGROMETER is warranted by CAMPBELL

SCIENTIFIC, INC. to be free from defects in materials and workmanship

under normal use and service for twelve (12) months from date of shipment

unless specified otherwise. Batteries have no warranty. CAMPBELL

SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or

replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.

The customer shall assume all costs of removing, reinstalling, and shipping

defective products to CAMPBELL SCIENTIFIC, INC. CAMPBELL

SCIENTIFIC, INC. will return such products by surface carrier prepaid. This

warranty shall not apply to any CAMPBELL SCIENTIFIC, INC. products

which have been subjected to modification, misuse, neglect, accidents of

nature, or shipping damage. This warranty is in lieu of all other warranties,

expressed or implied, including warranties of merchantability or fitness for a

particular purpose. CAMPBELL SCIENTIFIC, INC. is not liable for special,

indirect, incidental, or consequential damages.

Products may not be returned without prior authorization. The following

contact information is for US and International customers residing in countries

served by Campbell Scientific, Inc. directly. Affiliate companies handle

repairs for customers within their territories. Please visit

www.campbellsci.com to determine which Campbell Scientific company

serves your country.

To obtain a Returned Materials Authorization (RMA), contact CAMPBELL

SCIENTIFIC, INC., phone (435) 753-2342. After an applications engineer

determines the nature of the problem, an RMA number will be issued. Please

write this number clearly on the outside of the shipping container.

CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____

815 West 1800 North

Logan, Utah 84321-1784

For all returns, the customer must fill out a “Declaration of Hazardous Material

and Decontamination” form and comply with the requirements specified in it.

The form is available from our website at www.campbellsci.com/repair. A

completed form must be either emailed to repair@campbellsci.com or faxed to

435-750-9579. Campbell Scientific will not process any returns until we

receive this form. If the form is not received within three days of product

receipt or is incomplete, the product will be returned to the customer at the

customer’s expense. Campbell Scientific reserves the right to refuse service on

products that were exposed to contaminants that may cause health or safety

concerns for our employees.

KH20 Table of Contents

PDF viewers note: These page numbers refer to the printed version of this document. Use

the Adobe Acrobat® bookmarks tab for links to specific sections.

1. General Description.....................................................1

2. Specifications ..............................................................1

2.1 Measurements...........................................................................................1

2.2 Electrical...................................................................................................1

2.3 Physical.....................................................................................................2

3. Installation....................................................................2

3.1 Siting.........................................................................................................2

3.2 Mounting ..................................................................................................2

3.2.1 Parts and Tools Needed for Mounting............................................2

3.2.2 Mounting the KH20 Sensor............................................................3

3.2.3 Mounting the Electronics Box ........................................................3

4. Wiring............................................................................5

5. Datalogger Programming............................................6

5.1 KH20 Calibration .....................................................................................6

5.2 Example 1, CR3000 Program to Measure Water Vapor Fluctuations......7

6. Maintenance and Calibration......................................9

6.1 Visual Inspection......................................................................................9

6.2 Testing the Source Tube...........................................................................9

6.3 Testing the Detector Tube ........................................................................9

6.4 Managing the Scaling of KH20..............................................................10

6.5 Older KH20 ............................................................................................10

6.6 Calibration..............................................................................................10

Appendix

A. Calibrating KH20.....................................................A-1

A.1 Basic Measurement Theory ................................................................ A-1

A.2 Calibration of KH20 ........................................................................... A-1

Figures

1. Mounting KH20 onto a tripod ....................................................................3

2. Proper mounting position of the electronics box........................................4

3. Attaching cables to the electronics box ......................................................5

A-1. KH20 ln(mV) vs. Vapor Density....................................................... A-2

KH20 Table of Contents

Tables

1. Datalogger Connections for Differential Measurement............................. 5

2. KH20 Calibration Ranges.......................................................................... 6

A-1. Linear Regression Results for KH20 ln(mV) vs. Vapor Density ......A-2

A-2. Final Calibration Values for KH20....................................................A-3

KH20 Krypton Hygrometer

1. General Description

The KH20 is a krypton hygrometer for measuring water vapor fluctuations in

the air. The name KH20 (KH-twenty) was derived from KH2O (K-H2O), and

the sensor has been known with this name since 1985. It is typically used with

the CSAT3 3-D sonic anemometer for measuring latent heat flux (LE), using

Eddy Covariance technique. Please refer to the Open Path Eddy Covariance

System operator’s manual for details on flux measurements using the KH20

sensor.

The KH20 sensor uses a krypton lamp that emits two absorption lines: major

line at 123.58 nm and minor line at 116.49 nm. Both of these lines are

absorbed by water vapor, and a small amount of the minor line is absorbed by

oxygen. The KH20 is not suitable for absolute water vapor concentration

measurements due to its signal offset drift.

The KH20 heads are sealed and will not suffer damage should they get wet. In

addition, the electronics box and the connectors are housed inside a rain shield

(CSI p/n 14113) that protects them from moisture. The KH20 is suitable for

long-term continuous outdoor applications.

The KH20 sensor is comprised of two main parts: the sensor head and the

electronics box. The sensor head comes with cables with 6 ft of lead length

that connect the sensor to the electronics box. It is shipped with a rain shield

(CSI p/n 14113) to protect the electronics box and the connectors from

moisture, a 20 inch 3/4 IPS threaded aluminium pipe (CSI p/s 3874), a 3/4” x

3/4” Nu-Rail (CSI p/n 1017), and a 5/32 inch Allen wrench (CSI p/n 4697) for

mounting. The sensor comes with a signal/power cable which has 25 ft lead

length. If a longer cable is desired, the customer can order a replacement cable

(p/n KH20CBL-L) and specify the desired lead length after -L.

Discussion on the principles and theory of measurement is

included in Appendix A.

NOTE

2. Specifications

2.1 Measurements

Calibration Range: 1.7 to 19.5 g/m3(nominal)

Frequency Response: 100 Hz

Operating Temperature Range: -30 to +50°C

2.2 Electrical

Supply Voltage: 10 V to 16 Vdc

Current Consumption: 20 mA max at 12 Vdc

Power Consumption: 0.24 Watts

Output Signal Range: 0 to 5Vdc

KH20 Krypton Hygrometer

2.3 Physical

Dimensions

Sensor Head: 11.5” x 9” x 1.25” (29 cm x 23 cm x 3 cm)

Electronics Box: 7.5” x 5” x 2” (19 cm x 13 cm x 5 cm)

Rain Shield with Mount: 11.5” x 7” x 2.5” (29 cm x 18 cm x 6.5 cm)

Mounting Pipe: 20” (50 cm)

Carrying Case: 25” x 15” x 7” (64 cm x 38 cm x 18 cm)

Weight

Sensor Head: 3.55 lbs (1.61 kg)

Electronics Box: 1.4 lbs (6.4 kg)

Rain Shield with Mount: 4.75 lbs (2.2 kg)

Mounting Pipe with Nu-rail: 1.0 lbs (0.45 kg)

Carrying Case: 9.45 lbs (4.3 kg)

Shipping: 20.15 lbs (9.2 kg)

Package Includes:

KH20 sensor head with 5’ of cables

Power/Signal cable with 25’ lead length (CSI p/n KH20CBL-L)

Electronics Box

Rain Shield (CSI p/n 14113)

Horizontal Mounting Boom (20 inch 3/4” IPS threaded aluminium pipe)

(CSI p/n 3874)

Nu-rail (3/4” x 3/4”) (CSI p/n 1017)

Allen Wrench (5/32”) (CSI p/n 4697)

3. Installation

3.1 Siting

When installing the KH20 sensor for latent heat flux measurement in an eddy

covariance application, proper siting, sensor height, sensor orientation and

fetch are important. Please refer to Section 2 Installation and Mounting of the

Open Path Eddy Covariance System manual for more discussion on siting.

3.2 Mounting

3.2.1 Parts and Tools Needed for Mounting

You will need the following hardware to mount the KH20 sensor:

1. Tripod (CSI model CM115 standard) or tower

2. CM20x series crossarm (CSI model CM204 standard)

3. 3/4 inch IPS Aluminum Pipe, 12 inches long (CSI p/n 18048)

4. 3/4” x 1” Nu-rail (CSI p/n 1049)

5. Small Phillips and flat-head screw-drivers

6. 1/2 inch wrench

KH20 Krypton Hygrometer

3.2.2 Mounting the KH20 Sensor

Mount the KH20 sensor head as follows:

1. Attach the 20 inch long mounting boom to the KH20.

2. Mount a crossarm onto a tripod or tower.

3. Mount the 12 inch long pipe (CSI p/n 18048) to a crossarm via 1” x 3/4”

Nu-rail (CSI p/n 1049).

4. Mount the KH20 onto the 12” long pipe using a 3/4” x 3/4” Nu-rail (CSI

p/n 1017). Mount the KH20 such that the source tube, the longer of the

two tubes, is positioned on top, as shown in Figure 1. Gather any loose

cables and tie them up, using cable ties, onto the tripod or tower mast.

FIGURE 1. Mounting KH20 onto a tripod.

3.2.3 Mounting the Electronics Box

Mount the electronics box as follows:

1. First, remove the front cover of the rain shield by loosening the two pan-

head screws on the bottom front of the rain shield, and then pushing the

cover all the way up, and sliding it out.

It will be difficult to mount the rain shield to a mast with the

front cover on, since the 1/2 inch nut holding the bottom U-bolt

is located inside the rain shield.

NOTE

KH20 Krypton Hygrometer

2. Before mounting the rain shield onto a tripod, first mount the electronics

box inside the rain shield. Remove the four pan-head screws from the

back panel of the rain shield. Align the electronics box, and use the four

pan-head screws to secure the electronics box onto the back panel. Make

sure the electronics box is pushed all the way up, and the screws are

positioned at the bottom of the mounting slot on the electronics box (see

Figure 2). This will provide enough room to attach the connectors to the

bottom of the electronics box later on.

FIGURE 2. Proper mounting position of the electronics box.

If the electronics box is not pushed all the way up during

mounting, you will not have enough room to attach the

connectors to the bottom of the electronics box, as the U-bolt for

the rain shield will block the position of the connectors.

NOTE

3. Mount the rain shield onto the tripod or tower mast using the U-bolt

provided. Make sure that the distance between the KH20 sensor head and

the rain shield is within 5 feet so that the cables from the sensor head will

be within reach of the electronics box. Also make sure that the rain shield

is mounted vertically with an opening pointing downward so that the rain

will effectively run down the rain shield and not penetrate inside.

KH20 Krypton Hygrometer

4. Connect the three cables to the bottom of the electronics box around the

U-bolt on the rain shield (see Figure 3). If there is not enough room for

the connectors around the U-bolt, make sure the electronics box is

mounted at a highest possible position (see step 2).

FIGURE 3. Attaching cables to the electronics box.

5. Place the front cover back on the rain shield and tighten the two pan-head

screws to secure it in place.

6. Gather any loose cables and tie them up, using cable ties, onto the tripod

or tower mast.

4. Wiring

The KH20 sensor is shipped with a power/signal cable with a 25 ft standard

lead length. Table 1 shows the connections for the KH20 to the CR1000,

CR3000, and CR5000.

TABLE 1. Datalogger Connections for Differential Measurement

Function Wire Color CR1000/CR3000/CR5000

KH20 Signal + White Differential Input (H)

KH20 Signal - *Black Differential Input (L)

KH20 Power + Red 12V

KH20 Power - Black (from Red/Black set) G

Shield Clear

*Jumper to with user supplied wire

KH20 Krypton Hygrometer

5. Datalogger Programming

The KH20 sensor outputs 0 to 5 Vdc analog signal. These signals can be

measured using the VoltDiff instruction on the CRBasic dataloggers or the

Volt (Diff) (P2) instruction on the traditional Edlog dataloggers.

5.1 KH20 Calibration

Each KH20 is calibrated over a vapor range of approximately 2 to 19 g/m3.

The calibration is performed twice under the following two conditions:

window clean, and scaled. The water vapor absorption coefficient for three

different vapor ranges are calculated from the collected calibration data: full

range, dry range, and wet range. Table 2 shows a sample of the KH20 vapor

ranges over which three different water vapor absorption coefficients are

calculated. See Appendix A for more information on KH20 calibration.

TABLE 2. KH20 Calibration Ranges

Ranges Vapor Density (g/m3)

Full Vapor Range 2 – 19

Dry Vapor Range 2 – 9.5

Wet Vapor Range 8.25 – 19

Before the water vapor absorption coefficient, kw, is entered into the datalogger

program for the KH20, the following decisions must be made:

•Will the windows be allowed to scale?

•What vapor range is appropriate for the site?

Once the decision is made, the appropriate kwcan be chosen from the

calibrations sheet. The calibration sheet also contains the path length, x, for a

specific KH20. Using the water vapor absorption coefficient for either the dry

or the wet vapor range will produce more accurate measurements than using

that for the full range. If the vapor range of the site is unknown, or if the vapor

range is on the border line between the dry and the wet vapor ranges, the full

range should be used.

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