Campbell Scientific EC155 User Manual

INSTRUCTION MANUAL

EC155 CO2 and H2O Closed-Path

Copyright © 2010- 2014

Campbell Scientific, Inc.

Gas Analyzer

Revision: 6/14

Limited Warranty

“Products manufactured by CSI are warranted by CSI to be free from defects in
materials and workmanship under normal use and service for twelve months
from the date of shipment unless otherwise specified in the corresponding
product manual. (Product manuals are available for review online at

www.campbellsci.com.) Products not manufactured by CSI, but that are resold

by CSI, are warranted only to the limits extended by the original manufacturer.
Batteries, fine-wire thermocouples, desiccant, and other consumables have no
warranty. CSI’s obligation under this warranty is limited to repairing or
replacing (at CSI’s option) defective Products, which shall be the sole and
exclusive remedy under this warranty. The Customer assumes all costs of
removing, reinstalling, and shipping defective Products to CSI. CSI will return
such Products by surface carrier prepaid within the continental United States of
America. To all other locations, CSI will return such Products best way CIP
(port of entry) per Incoterms ® 2010. This warranty shall not apply to any
Products which have been subjected to modification, misuse, neglect, improper
service, accidents of nature, or shipping damage. This warranty is in lieu of all
other warranties, expressed or implied. The warranty for installation services
performed by CSI such as programming to customer specifications, electrical
connections to Products manufactured by CSI, and Product specific training, is
part of CSI's product warranty. CSI EXPRESSLY DISCLAIMS AND

EXCLUDES ANY IMPLIED WARRANTIES OF MERCHANTABILITY
OR FITNESS FOR A PARTICULAR PURPOSE. CSI hereby disclaims,
to the fullest extent allowed by applicable law, any and all warranties and
conditions with respect to the Products, whether express, implied or
statutory, other than those expressly provided herein.”

Assistance

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 [phone]. 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 "Statement of Product Cleanliness
and Decontamination" form and comply with the requirements specified in it.
The form is available from our web site at www.campbellsci.com/repair. A
completed form must be either emailed to [e-mail] or faxed to
[phone]. Campbell Scientific is unable to 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.

Precautions

DANGER — MANY HAZARDS ARE ASSOCIATED WITH INSTALLING, USING, MAINTAINING, AND WORKING ON OR AROUND

TRIPODS, TOWERS, AND ANY ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS, CROSSARMS, ENCLOSURES,
ANTENNAS, ETC. FAILURE TO PROPERLY AND COMPLETELY ASSEMBLE, INSTALL, OPERATE, USE, AND MAINTAIN TRIPODS,

TOWERS, AND ATTACHMENTS, AND FAILURE TO HEED WARNINGS, INCREASES THE RISK OF DEATH, ACCIDENT, SERIOUS
INJURY, PROPERTY DAMAGE, AND PRODUCT FAILURE. TAKE ALL REASONABLE PRECAUTIONS TO AVOID THESE HAZARDS.
CHECK WITH YOUR ORGANIZATION'S SAFETY COORDINATOR (OR POLICY) FOR PROCEDURES AND REQUIRED PROTECTIVE
EQUIPMENT PRIOR TO PERFORMING ANY WORK.

Use tripods, towers, and attachments to tripods and towers only for purposes for which they are designed. Do not exceed design
limits. Be familiar and comply with all instructions provided in product manuals. Manuals are available at www.campbellsci.com or
by telephoning 435-227-9000 (USA). You are responsible for conformance with governing codes and regulations, including safety
regulations, and the integrity and location of structures or land to which towers, tripods, and any attachments are attached. Installation
sites should be evaluated and approved by a qualified engineer. If questions or concerns arise regarding installation, use, or
maintenance of tripods, towers, attachments, or electrical connections, consult with a licensed and qualified engineer or electrician.

General

• Prior to performing site or installation work, obtain required approvals and permits. Comply

with all governing structure-height regulations, such as those of the FAA in the USA.

• Use only qualified personnel for installation, use, and maintenance of tripods and towers, and

any attachments to tripods and towers. The use of licensed and qualified contractors is highly
recommended.

• Read all applicable instructions carefully and understand procedures thoroughly before

beginning work.

• Wear a hardhat and eye protection, and take other appropriate safety precautions while

working on or around tripods and towers.

• Do not climb tripods or towers at any time, and prohibit climbing by other persons. Take

reasonable precautions to secure tripod and tower sites from trespassers.

• Use only manufacturer recommended parts, materials, and tools.

Utility and Electrical

• You can be killed or sustain serious bodily injury if the tripod, tower, or attachments you are

installing, constructing, using, or maintaining, or a tool, stake, or anchor, come in contact with
overhead or underground utility lines.

• Maintain a distance of at least one-and-one-half times structure height, or 20 feet, or the

distance required by applicable law, whichever is greater, between overhead utility lines and
the structure (tripod, tower, attachments, or tools).

• Prior to performing site or installation work, inform all utility companies and have all

underground utilities marked.

• Comply with all electrical codes. Electrical equipment and related grounding devices should

be installed by a licensed and qualified electrician.

Elevated Work and Weather

• Exercise extreme caution when performing elevated work.

• Use appropriate equipment and safety practices.

• During installation and maintenance, keep tower and tripod sites clear of un-trained or non-

essential personnel. Take precautions to prevent elevated tools and objects from dropping.

• Do not perform any work in inclement weather, including wind, rain, snow, lightning, etc.

Maintenance

• Periodically (at least yearly) check for wear and damage, including corrosion, stress cracks,

frayed cables, loose cable clamps, cable tightness, etc. and take necessary corrective actions.

• Periodically (at least yearly) check electrical ground connections.

WHILE EVERY ATTEMPT IS MADE TO EMBODY THE HIGHEST DEGREE OF SAFETY IN ALL CAMPBELL SCIENTIFIC PRODUCTS,
THE CUSTOMER ASSUMES ALL RISK FROM ANY INJURY RESULTING FROM IMPROPER INSTALLATION, USE, OR
MAINTENANCE OF TRIPODS, TOWERS, OR ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS, CROSSARMS,
ENCLOSURES, ANTENNAS, ETC.

Table of Contents

PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.

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

2. Cautionary Statements ............................................... 1

3. Initial Inspection ......................................................... 2

4. Overview ...................................................................... 2

5. Specifications ............................................................. 3

5.1 Measurements ...................................................................................... 3

5.2 Output Signals ...................................................................................... 5

5.3 Physical Description ............................................................................. 6

5.4 Power Requirements ............................................................................ 8

6. Installation ................................................................... 8

6.1 Mounting .............................................................................................. 8

6.2 Plumbing ............................................................................................ 11

6.2.1 Flow ............................................................................................ 11

6.2.2 Pressure ....................................................................................... 11

6.2.3 Filtration ...................................................................................... 12

6.2.4 Plumbing Connections ................................................................ 12

6.2.4.1 Sample Intake ................................................................... 13

6.2.4.2 Pump ................................................................................ 13

6.2.4.3 Zero and Span................................................................... 13

6.3 Wiring and Connections ..................................................................... 14

7. Settings ...................................................................... 17

7.1 Factory Defaults ................................................................................. 17

7.2 Details ................................................................................................ 18

7.2.1 SDM Address .............................................................................. 18

7.2.2 Bandwidth ................................................................................... 18

7.2.3 Unprompted Output .................................................................... 18

7.2.4 Unprompted Output Rate ............................................................ 18

7.2.5 RS-485 Baud Rate ....................................................................... 19

7.2.6 Analog Output ............................................................................. 19

7.2.7 ECMon Update Rate ................................................................... 19

7.2.8 Temperature Sensor .................................................................... 19

7.2.9 Fixed Temperature Value ............................................................ 19

7.2.10 Pressure Sensor ........................................................................... 19

7.2.10.1 Pressure Gain.................................................................... 20

7.2.10.2 Pressure Offset ................................................................. 20

7.2.10.3 Fixed Pressure Value ........................................................ 20

7.2.11 Differential Pressure ......................................................... 20

7.3 ECMon ............................................................................................... 20

i

Table of Contents

7.4 Device Configuration Utility ............................................................. 23

8. EC100 Outputs .......................................................... 23

8.1 SDM Output ...................................................................................... 23

8.2 USB or RS-485 Output ...................................................................... 24

8.3 Analog Outputs .................................................................................. 26

9. Maintenance .............................................................. 26

9.1 Routine Maintenance ......................................................................... 26

9.2 Intake Filter Replacement .................................................................. 27

9.3 Cleaning Analyzer Windows ............................................................. 28

9.4 Zero and Span .................................................................................... 31

9.5 Replacing the EC155 Desiccant/CO2 Scrubber Bottles ..................... 34

9.6 Factory Recalibration ........................................................................ 36

10. Datalogger Programming with CRBasic ................. 37

10.1 EC100() Instruction ........................................................................... 37

10.2 EC100Configure() Instruction ........................................................... 40

10.2.1 ConfigCmd 11 Zero-and-Span Control ...................................... 42

10.2.2 ConfigCmd 18 Heater Voltage ................................................... 42

10.3 Example CRBasic Program ............................................................... 43

11. Theory of Operation .................................................. 44

Appendices

Filter Bandwidth and Time Delay ........................... A-1

A.

B. Useful Equations ..................................................... B-1

C. EC155 Sample Cell and Intake Maintenance ........ C-1

C.1 Cleaning Sample Cell ...................................................................... C-1

C.2 Cleaning Intake Tube ...................................................................... C-1

Dust Blowout ........................................................................... C-1

C.2.1

C.2.2 Solvent Flush ............................................................................ C-2

D. Material Safety Data Sheets (MSDS) ..................... D-1

D.1 Magnesium Perchlorate MSDS ....................................................... D-1

D.2 Decarbite MSDS .............................................................................. D-2

E. EC155 Packing Information .................................... E-1

Figures

5-1. Dimensions of EC155 analyzer head with optional heated intake ....... 7

5-2. Dimensions of EC155 analyzer head without optional heated intake . 7
6-1. Exploded view of mounting the EC155 gas analyzer and the

CSAT3A sonic head ........................................................................ 9

ii

Table of Contents

6-2. EC100 enclosure mounting bracket mounted on a vertical mast

(left) and a tripod leg (right) ........................................................... 10

6-3. Exploded view of mounting the EC100 enclosure ............................. 11

6-4. End views of the analyzer showing the sample intake (optional

heated intake not shown), pump outlet, and zero-and-span

intake .............................................................................................. 13

6-5. EC100 electronics front panel. The picture on the left shows the

panel as it is shipped from the factory (enhanced barometer
shown). The picture on the right shows the panel after the user
has done all the wiring and made all connections (basic

barometer used). ............................................................................. 14

6-6. Bottom of EC100 enclosure ............................................................... 15

7-1. The Main window of ECMon ............................................................ 21

7-2. The Setup window in ECMon ............................................................ 22

7-3. The ECMon Status window ............................................................... 22

8-1. An example of USB data output in terminal mode ............................ 25

9-1. The underside of the optional heated intake ....................................... 28

9-2. The EC155 analyzer with the top shell open ...................................... 29

9-3. By loosening the thumbscrews above the sample cell, the latches

may be spun from position A to position B, thus freeing the

struts of the analyzer. ...................................................................... 29

9-4. The EC155 analyzer and sample cell with shell top open .................. 30

9-5. Analyzer removed from sample cell and shell ................................... 30

9-6. ECMon Zero/Span window ................................................................ 34

9-7. Replacing the source housing desiccant/scrubber bottle .................... 35

9-8. Replacing the detector housing desiccant/scrubber bottle .................. 36

A-1. Frequency and amplitude response of the EC100 filter at various

bandwidths ................................................................................... A-2

A-2. Frequency response comparison of the EC100 10-Hz bandwidth

and a 50-msec moving average .................................................... A-3

Tables

6-1. EC100 SDM output to a Campbell Scientific CR1000, CR3000,

or CR5000 Datalogger .................................................................... 16

7-1. Factory Default Settings ..................................................................... 17

8-1. USB and RS-485 Output Elements .................................................... 25

8-2. Multipliers and Offsets for Analog Outputs ....................................... 26

10-1. Output Modes for EC100 Instruction ................................................. 38

10-2. Bits in the Sonic Diagnostic Flag ....................................................... 38

10-3. Bits in the Gas Diagnostic Flag .......................................................... 39

10-4. ConfigCmd Values for Setting and Retrieving Settings ..................... 41

A-1. Filter Time Delays for Various Bandwidths ................................... A-3

iii

Table of Contents

iv

EC155 CO2 and H2O Closed-Path Gas
Analyzer

1. Introduction

The EC155 is an in-situ, closed-path, mid-infrared absorption gas analyzer that
measures molar mixing ratios of carbon dioxide and water vapor, along with
sample cell temperature and pressure. The EC155 may be used in conjunction
with the CSAT3 sonic anemometer, which measures orthogonal wind
components.

Before using the EC155, please study

• Section 2, Cautionary Statements

• Section 3, Initial Inspection

• Section 6, Installation

More details are available in the remaining sections.

2. Cautionary Statements

• DANGER:

o The scrubber bottles (see Section 9.5, Replacing the EC155

Desiccant/CO

agents sodium hydroxide (caustic soda, NaOH) and anhydrous
magnesium perchlorate (Mg(ClO

• WARNING:

o Do not carry the EC155 or CSAT3A by the arms or carry the

EC155 by the strut between the arms. Always hold them by the
block, where the upper and lower arms connect.

o Handle the EC155 carefully. The optical source may be damaged

by rough handling, especially while the analyzer is powered.

o Over-tightening bolts will damage or deform the mounting

hardware.

Scrubber Bottles) contain the strong oxidizing

2

).

4)2

 Avoid direct contact with the chemicals.
 Ensure your work area is well ventilated and free of

reactive compounds, including liquid water.

 Store used chemical bottles in a sealed container until

disposal.

 Dispose of chemicals and bottles properly.
 Materials Safety Data Sheets (MSDS) are provided in

Appendix D. MSDS are updated periodically by
chemical manufacturers. Obtain current MSDS at

www.campbellsci.com.

1

EC155 CO2 and H2O Closed-Path Gas Analyzer

• CAUTION:

o Grounding the EC100 measurement electronics is critical. Proper

grounding to earth (chassis) will ensure maximum ESD
(electrostatic discharge) protection and improve measurement
accuracy.

o Do not connect or disconnect the gas analyzer or sonic connectors

while the EC100 is powered.

o The SDM, USB, and RS-485 output options include EC155

diagnostic data. Be aware that the absence of diagnostic data in
the analog output option could make troubleshooting difficult and
may lead to the user not being aware of potential problems with
the instrumentation (see Section 8, EC100 Outputs).

o Resting the analyzer on its side during the zero-and-span

procedure may result in measurement inaccuracy.

o When cleaning the gas-analyzer window, make sure the alcohol

and any residual water completely evaporate before proceeding
with the zero-and-span procedure (see Section 9.3, Cleaning
Analyzer Windows).

3. Initial Inspection

Upon receipt of your equipment, inspect the packaging and contents for
damage. File damage claims with the shipping company.

4. Overview

The EC155 is a closed-path, mid-infrared absorption analyzer that measures
molar mixing ratios of carbon dioxide and water vapor, along with sample cell
temperature and pressure. It has been designed specifically for eddy
covariance flux measurements and may be used in conjunction with the
CSAT3A 3D sonic anemometer head. The analyzer has a rugged, aerodynamic
design with low power requirements, making it suitable for field applications.

The EC155 gas analyzer connects directly to the EC100 electronics, which
computes real-time CO
sample cell of the analyzer. A CSAT3A sonic anemometer head may also be
connected to the EC100.

The EC155 has been designed specifically to address issues of aerodynamics,
power consumption, performance during precipitation events, ambient air
density fluctuations, temporal synchronicity, and system integration. Its unique
design enables it to operate with only 4.8 W power; it has minimal spatial
displacement from the sample volume of a CSAT3A sonic anemometer; the
EC100 electronics synchronize data from the EC155 and CSAT3A; and the
analyzer is easily integrated into the CPEC200 closed-path eddy covariance
system, a turn-key system containing data acquisition and control
instrumentation, a sample pump, and optional zero-and-span valve module.

and H2O molar mixing ratios of the air inside the

2

2

5. Specifications

5.1 Measurements

Features

• To compute carbon dioxide, water vapor, and sensible heat fluxes using

These measurements are required to compute carbon dioxide and water vapor
fluxes using the:

• Standard outputs:

EC155 CO2 and H2O Closed-Path Gas Analyzer

the eddy-covariance method, the EC155 measures:

o absolute carbon dioxide
o water vapor mixing ratios
o three-dimensional wind speed (requires CSAT3A)
o sonic air temperature (requires CSAT3A)
o sample-cell temperature
o barometric pressure

o CO

mixing ratio, H2O mixing ratio

2

o gas analyzer diagnostic flags
o cell temperature, cell pressure
o CO

signal strength, H2O signal strength

2

o differential pressure
o air temperature and air pressure are auxiliary sensor inputs

• Additional outputs:

o u

, uy, and uz orthogonal wind components

x

o sonic temperature (based on the measurement of c, the speed of

sound)

o sonic diagnostic flags

Compatibility: CR1000
CR3000
CR5000

Measurement

Rate: 100 Hz

2

Output bandwidth
Output rate

2

Operating temperature: -30

: 5, 10, 12.5, 20, or 25 Hz

: 10, 25 or 50 Hz

o

to 50oC

Gas analyzer

1

Measurement precision

density: 0.2 mg·m

CO

2

O density: 0.00350 g·m

H

2

-3

(0.15 µmol·mol-1)

-3

(0.006 mmol·mol-1)

3

EC155 CO2 and H2O Closed-Path Gas Analyzer

Factory calibrated range

: 0 to 1000 µmol·mol-1

CO

2

O: 0 mmol·mol

H

2

Analyzer temp: -30
Baro pressure: 70 to 106 kPa

performance

CO

2

Zero max drift
Gain Drift: ±0.1% of reading·°C
Sensitivity to H

O performance

H

2

Zero max drift
Gain Drift: ±0.3% of reading·°C
Sensitivity to CO

CSAT3A sonic measurement precision

: 1 mm·s-1

u

x

: 1 mm·s-1

u

y

: 0.5 mm·s-1

u

z

Sonic temperature: 0.025

-1

o

to 50oC

3

: ±0.55 mg·m-3·°C-1 (±0.3 μmol·mol·°C-1)

O: ±5.6 x 10-5 µmol CO2·mol-1 H2O (max)

2

3

: ±0.037 g·m-3·°C-1 (±0.05 mmol·mol-1·°C-1)

: ±0.05 mol H2O·mol-1 CO2 (maximum)

2

o

C

to 37oC dewpoint

4

-1

(maximum)

-1

(maximum)

5

CSAT3A sonic accuracy

Offset error

, uy: < ±8 cm·s-1

u

x

: < 4 cm·s-1

u

z

Gain error

Wind vector ±5° horizontal: < ±2% of reading
Wind vector ±10° horizontal: < ±3% of reading
Wind vector ±20° horizontal: < ±6% of reading

CSAT3A sonic reporting range

Full scale wind: ±65.553 m/s
Sonic temperature: -50° to +60°C

6

Sample cell sensors

Barometer

Basic barometer

Accuracy

-30 to 0°C: ±3.7 kPa at -30°C, falling linearly to ±1.5

0° to 50°C: ±1.5 kPa

Measurement rate: 10 Hz
Optional enhanced barometer:

Manufacturer: Vaisala
Model: PTB110
Accuracy

-30 to 0°C: ±0.15 kPa

Measurement rate: 1 Hz

Temperature sensor:

Manufacturer: BetaTherm
Model: 100K6A1A Thermistor
Accuracy: ±0.15

o

kPa at 0

o

C

C (-30o to 50oC)

4

1

noise rms, assumes:

o 25°C
o 85 kPa
o 19 mmol/mol H
o 326 mmol/mol CO
o 25 Hz bandwidth.

2

user selectable

3

-30° to 50°C

4

noise rms

5

assumes:

o -30° to +50°C
o wind speed <30 m·s
o azimuth angles between ±170°

6

refer to manufacturer’s product brochure or manual for details

5.2 Output Signals

Features

• EC100 electronics outputs data using:

O concentration

2

o CS SDM
o RS-485
o USB
o Analog out

EC155 CO2 and H2O Closed-Path Gas Analyzer

concentration

2

-1

Digital

1

SDM (Synchronous Device for Measurement)

Data type: FLOAT

RS-485

Data type: ASCII
Output Rate
Baud rate

2

: 5 to 50 Hz

2

: 1200 to 230400 bps

USB

Data type: ASCII

2

Output rate

Analog (two outputs for CO

: 10, 25 or 50 Hz

and H2O molar mixing ratios)

2

Voltage range: 0 mV to 5000 mV
Resolution: 76 µV (16 bit)
Update rate: 150 Hz

o

Accuracy (at 25

C): ±3 mV

mixing ratio equation: µmol/mol = 211.27 (V

CO

2

) – 56.34

out

Full scale range: -56 to 1000 µmol/mol

O mixing ratio equation: mmol/mol = 11.31 (V

H

2

) – 3.04

out

Full scale range: -3 to 53 mmol/mol

1

Synchronous Device for Measurement. A Campbell Scientific, Inc. proprietary serial interface

for datalogger to peripheral and sensor communication. See Section 8.1, SDM Output for details.

2

user selectable

5

EC155 CO2 and H2O Closed-Path Gas Analyzer

5.3 Physical Description

Sample cell volume: 5.9 cm3 (0.36 in3)

Sample cell length: 12.0 cm (4.72 in)

Sample cell diameter: 7.94 mm (0.313 in)

Spatial separation between
EC155 optional intake and
CSAT3A sample volume: 15.6 cm (6.1 in)

Length of tubing from tip
of optional heated intake
to sample cell: 58.4 cm (23 in)

Inside diameter of intake tubing: 2.67 mm (0.105 in)

Dimensions

Analyzer: 42.7 cm x 7.4 cm x 10.1 cm (16.8 in x 2.9
in x 4.0)
Length of optional intake: 38.1 cm (15.0 in)
EC100 electronics: 24.1 cm x 35.6 cm x 14 cm (9.5 in x 14 in
x 5.5 in)
Cable length: 3 m (9.8 ft) from analyzer to EC100
electronics

Weight

Analyzer: 3.9 kg (8.5 lbs)
Mounting hardware: 0.4 kg (0.9 lbs)
EC100 electronics and

enclosure: 3.2 kg (7 lbs)

Connections

Pump: 3/8 inch Swagelok
Zero/Span: 1/4 inch Swagelok
Sample Intake: 1/8 inch Swagelok or Optional Heated
Intake Assembly

6

EC155 CO2 and H2O Closed-Path Gas Analyzer

FIGURE 5-1. Dimensions of EC155 analyzer head with optional heated

intake

FIGURE 5-2. Dimensions of EC155 analyzer head without optional

heated intake

7

EC155 CO2 and H2O Closed-Path Gas Analyzer

WARNING

5.4 Power Requirements

Voltage supply: 10 to 16 Vdc

6. Installation

6.1 Mounting

Power at 25

Power at 25

Power at 25
mode (CSAT3A fully powered
and EC155 in stand-by): 3.0 W

Power for optional heated intake: set by user, 0 to 0.7 W.

The EC155 is supplied with mounting hardware to attach it to the end of a
horizontal pipe of 1.31 inch outer diameter, such as the CM202, CM204, or
CM206 crossarm (pn 1790x). The EC155 mounting hardware also
accommodates an optional CSAT3A sonic anemometer, placing it at the proper
position when the EC155 is configured with the optional heated intake
assembly. The following steps describe the normal mounting procedure with
the optional heated intake assembly and optional CSAT3A sonic head. Other
mounting arrangements are acceptable as long as the analyzer is upright. The
bottom of the analyzer has two #6-32 UNC-thread mounting holes for
applications that do not use the EC155 mounting platform.

o

C including CSAT3A: 4.8 W

o

C excluding CSAT3A: 4.0 W

o

C in power-down

Refer to FIGURE 6-1 throughout this section.

a. Mount a CM202, CM204, or CM206 crossarm (pn 1790X) to a tripod or

other vertical structure using a CM210 crossarm-to-pole bracket (pn

17767). The crossarm should be within ± 7 degrees of horizontal to allow
the CSAT3A sonic anemometer to be leveled.

Do not carry the EC155 by the intake or the CSAT3A by the
arms. Always hold the instruments by the body or base.

b. Mount the CM250 leveling mount (pn 26559) on the end of the crossarm.

Tighten the set screws on the leveling mount.

c. Bolt the mounting platform (pn 26570) to the CM250 leveling mount (pn

26559).

d. Place the EC155 gas analyzer on the mounting platform so the four rubber

feet fit into the platform holes, and tighten the captive screws located on
the bottom of the platform into the mounting holes on the bottom of the
analyzer.

e. If a CSAT3A is being used, mount it on the end of the mounting platform

using the captive CSAT3A mounting bolt.

8

EC155 CO2 and H2O Closed-Path Gas Analyzer

WARNING

WARNING

NOTE

CSAT3A Sonic

EC155 Gas

CM20X Crossarm

Mounting Platform

CM250 Leveling

f. Level the assembly by slightly loosening the bolt in the CM250 leveling

mount. Adjust the assembly until the leveling bubble on top of the
CSAT3A is in the bullseye. Retighten the bolt.

Over-tightening bolts will damage or deform the mounting
hardware.

Use caution when handling the EC155 gas analyzer. The
optical source may be damaged by rough handling,
especially when the EC155 is powered.

If the assembly is to be mounted on a high tower, it can be hoisted
using the handle on the front of the analyzer and the holes in the
mounting platform.

(pn 26570)

Mount (pn 26559)

Anemometer Head

Analyzer

(pn 1790X)

FIGURE 6-1. Exploded view of mounting the EC155 gas analyzer and

the CSAT3A sonic head

9

EC155 CO2 and H2O Closed-Path Gas Analyzer

NOTE

The CSAT3A sonic anemometer is an updated version of the
CSAT3, designed to work with the EC100 electronics. An
existing CSAT3 may be upgraded to a CSAT3A. Contact
Campbell Scientific for details.

g. Attach the EC100 electronic enclosure to the mast, tripod leg, or other part

of the mounting structure. To do this, attach the EC100 enclosure
mounting bracket (pn 26604) to the pipe by loosely tightening the u-bolts
around the pipe. The u-bolts are found in the mesh pocket inside the
EC100 enclosure. If the pipe does not run vertically up-and-down (e.g., if
you are attaching the enclosure to a leg of a tripod), rotate the bracket to
the side of the pipe. As the enclosure must hang up-right, angle
adjustments may need to be made by loosening the four nuts and rotating
the bracket plates relative to one another. If the necessary angle cannot be
reached in the given orientation, the four nuts may be removed and the top
plate indexed by 90 degrees to allow the bracket to travel in the other
direction (see FIGURE 6-2). Once adjusted, tighten all the nuts. Finally
attach the EC100 enclosure to the bracket by loosening the bolts on the
back of the enclosure, hanging the enclosure on the mounting bracket (it
should slide into place and be able to securely hang from the bracket), and
tightening the bolts (see FIGURE 6-3).

10

FIGURE 6-2. EC100 enclosure mounting bracket mounted on a vertical

mast (left) and a tripod leg (right)

EC155 CO2 and H2O Closed-Path Gas Analyzer

6.2 Plumbing

6.2.1 Flow

6.2.2 Pressure

FIGURE 6-3. Exploded view of mounting the EC100 enclosure

h. Remove the EC100 enclosure desiccant from the plastic bag and put it

back in the mesh pocket of the enclosure. Adhere the humidity indicator
card to the inside of the enclosure.

The EC155 has a small sample cell volume (5.9 cm3) to give good frequency
response at a relatively low flow rate. The sample cell residence time is 50 ms
for a nominal 7 LPM flow. The CPEC200 pump module is designed to provide
this flow for the EC155, but other user-supplied pumps may be used. There is
no specific limitation to the flow rate that may be used with the EC155, but the
sample cell pressure must be considered.

The EC155 is designed to be used near ambient pressure, but it will not be
damaged by operation under vacuum. The EC155 includes a differential
pressure sensor to measure the sample cell pressure relative to ambient
pressure, which has a range of ± 7 kPa. If the EC155 is operated less than
7 kPa from ambient pressure, the user must attach a separate, user-supplied
pressure sensor.

11

EC155 CO2 and H2O Closed-Path Gas Analyzer

The pressure drop in the optional heated intake assembly is approximately 2.5
kPa at 7 LPM flow with no filter. The filter adds approximately 1 kPa pressure
drop when it is clean. This pressure drop will increase as the filter clogs. The
filter should be replaced before the differential pressure reaches -7 kPa (unless
the user has supplied a pressure sensor with a wider range). See Section 9.2,
Intake Filter Replacement for details on replacing the filter.

If the EC155 is configured without the optional heated intake assembly, there
is tubing connecting the sample inlet fitting to the sample cell that will drop the
pressure approximately 4 kPa at 7 LPM.

6.2.3 Filtration

The EC155 will not be damaged by use without an inlet filter, although a
coarse screen (up to 1 mm hole size) is suggested to keep large debris out.
Over time particulates will collect on the optical windows, reducing the signal
levels until the windows must be cleaned (see Section 9.3, Cleaning Analyzer
Windows). Using a filter on the inlet will increase the time before the windows
must be cleaned. A finer pore size will keep the windows clean longer, but
will need to be replaced more frequently. The optional heated intake assembly
includes a 20 micron filter element, which gives a compromise between filter
replacement and window cleaning.

6.2.4 Plumbing Connections

There are three connections to the EC155 sample cell: the sample inlet, zero­and-span inlet, and pump outlet, as illustrated in FIGURE 6-4. In the normal
mode, a vacuum pump pulls an air sample from the sample inlet through the
sample cell. In zero-and-span mode the pump is turned off and a zero-and­span gas is pushed backwards through the sample cell, exhausted out through
the sample inlet.

12

EC155 CO2 and H2O Closed-Path Gas Analyzer

Sample Cell Cable

Analyzer Head Cable

6.2.4.1 Sample Intake

6.2.4.2 Pump

FIGURE 6-4. End views of the analyzer showing the sample intake

(optional heated intake not shown), pump outlet, and zero-and-span
intake

The EC155 can be ordered with a factory-installed intake assembly, or with a
Swagelok fitting to attach a user-supplied intake assembly. If the EC155 is
configured with the intake assembly, it is installed at the factory. No further
assembly is required.

If the EC155 is configured with no intake assembly, it has a 1/8 inch Swagelok
fitting at the front end for connection to the user-supplied intake assembly (see
FIGURE 6-4).

In normal mode the EC155 uses a vacuum pump to pull an air sample through
the sample cell. See the discussion on flow and pressure in the previous
section for pump requirements. The CPEC200 pump module (pn 26399-x) is
designed for use with the EC155. Connect the CPEC200 pump module or
user-supplied sample pump to the 3/8 inch Swagelok fitting at the back end of
the analyzer labeled Pump.

6.2.4.3 Zero and Span

The zero-and-span inlet connects to the pump connection passage near the
outlet of the sample cell. During normal operation the zero-and-span inlet
should be plugged, either with a Swagelok 1/4 inch plug, or with a tube
connecting to a closed valve or manifold system such as the CPEC200 valve

13

EC155 CO2 and H2O Closed-Path Gas Analyzer

NOTE

module. During zero and span the zero or span gas can be pushed into this
fitting to flow backward through the sample cell and exhausted through the
intake assembly.

The CPEC200 system includes a valve module controlled by a
CR3000 datalogger, which automates the zero gas and CO2 span
gas flows during the zero-and-span procedure.

6.3 Wiring and Connections

FIGURE 6-5 and FIGURE 6-6 below show EC100 electronics panel and the
bottom of the EC100 enclosure, respectively. Refer to these figures during
wiring and connecting.

14

FIGURE 6-5. EC100 electronics front panel. The picture on the left

shows the panel as it is shipped from the factory (enhanced
barometer shown). The picture on the right shows the panel after
the user has done all the wiring and made all connections (basic
barometer used).

EC155 CO2 and H2O Closed-Path Gas Analyzer

CAUTION

FIGURE 6-6. Bottom of EC100 enclosure

Do not connect or disconnect the EC155 gas analyzer head
or CSAT3 sonic head while the EC100 is powered.

a. Connect the EC155 gas analyzer head. Begin by removing the black

rubber cable entry plug (pn 26224) on the bottom right of the EC100
enclosure. (This plug can be stored in the mesh pocket of the enclosure).
Now insert the cable entry plug that is attached to the large cable of the
EC155 gas analyzer head into the vacant slot. Push the connector at the
end of the cable onto its mating connector (labeled Gas Analyzer) and
tighten the thumbscrews (see FIGURE 6-6). The EC155 gas analyzer
cable is approximately 3 meters in length.

b. Connect the EC155 sample cell cable. Unscrew the sample cell connector

cover, which is found on the bottom of the EC100 enclosure. Insert the
12-prong sample cell cable connector into the female connector on the
enclosure and screw it firmly in place. The EC155 sample cell cable is
approximately 3 meters in length.

c. Connect the CSAT3A sonic head (skip this step if not using the CSAT3A).

Similar to (a), begin by removing the black rubber cable entry plug found
on the bottom left of the EC100 enclosure. Insert the cable entry plug on
the CSAT3A cable into the slot and connect the male end to the female
connector labeled Sonic Anemometer on the EC100 electronics (see
FIGURE 6-5). Tighten the thumbscrews. The CSAT3A cable is
approximately 3 meters in length.

15

EC155 CO2 and H2O Closed-Path Gas Analyzer

TABLE 6-1. EC100 SDM output to a Campbell Scientific CR1000,

EC100 Channel

Description

Color

NOTE

CAUTION

Unlike previous models of the CSAT3 3D sonic anemometer, the
CSAT3A sonic head and the EC155 gas analyzer head have
embedded calibration information. This means that any CSAT3A
and any EC155 may be used with any EC100.

d. Ground the EC100 by attaching a thick wire (e.g., 12 AWG) to the

grounding lug found on the bottom of the EC100 enclosure. The other end
of the wire should be connected to earth (chassis) ground (i.e., grounding
rod). For more details on grounding, see the CR3000 datalogger manual,
grounding section.

Grounding the EC100 and other electrical components in
the measurement system is critical. Proper grounding to
earth (chassis) will ensure the maximum ESD (electrostatic
discharge) protection and higher measurement accuracy.

e. Connect a communications signal cable to the EC100. Loosen the nut on

one of the cable entry seals (Cable 1 or Cable 2) on the bottom of the
EC100, remove the plastic plug (the plug can be stored in the mesh pocket
in the enclosure), insert the cable, and retighten the nut by hand. Refer to
the sections below on SDM, USB, RS-485, and analog communications
for information on required signal cable types and connections to the
EC100 panel.

1. SDM Communications: Use cable CABLE4CBL-L (pn 21972). “L”

denotes the length of the cable, which is customer-specified at time of
order. TABLE 6-1 below details which color of wire in the cable
should be connected to each terminal found on the SDM connector of
the EC100 panel.

CR3000, or CR5000 Datalogger

SDM-C1 SDM Data Green

SDM-C2 SDM Clock White

SDM-C3 SDM Enable Red (or brown)

G Digital Ground Black

G Shield Clear

2. USB Communications: Use the EC100 USB cable (pn 26563) to

connect a PC to the on the bottom of the EC100 enclosure.

3. RS-485 Communications: Use cable CABLE3TP-L (pn 26987) for

lengths less than 500 ft. The connector on the EC100 panel labeled
RS-485 displays which terminals are for receiving and transmitting.

4. Analog Output: Use CABLE4CBL-L (pn 21972) or CABLE2TP-L

(26986-L). Once again, the customer specifies the length of this cable
at time of order. The connector labeled Analog Outputs on the EC100
panel indicates where each wire should be connected (CO
signal, H

16

O voltage signal, and two ground connections).

2

voltage

2

EC155 CO2 and H2O Closed-Path Gas Analyzer

TABLE 7-1. Factory Default Settings

SDM Address

1

Bandwidth

20 Hz

Unprompted Output

Disabled

RS-485 Baud Rate

115200 bps

Unprompted Output Rate

10 Hz

Analog Output

Disabled

ECMon Update Rate

10 Hz

Temperature Sensor

Auto-Detect (EC155 Sample Cell
Thermocouple)

Pressure Sensor

EC100 Basic or EC100 Enhanced (depending
on order)

Pressure Differential Enable

Auto-Detect (Enabled for EC155)

Heater Control

Disabled

f. Wire power and ground (i.e., power reference) cable CABLEPCBL-L (pn

21969-L) to the EC100. Feed the cable through one of the cable port
openings in the bottom of the EC100 enclosure and attach the ends into the
green EC100 power connector (pn 3768). Plug the connector into the
female power connector on the EC100 panel. Ensure that the power and
ground ends are going to the appropriate terminals labeled 12V and
ground, respectively.

g. Connect the power cable to a power source. The power and ground ends

may be wired to the 12V and G ports, respectively, of a Campbell
Scientific datalogger or to another 12 Vdc source.

h. Once power is applied to the EC100, three LED status lights on the EC100

panel will illuminate. The power LED will be green and the sonic and gas
LEDs will be red until the unit has warmed up and is ready to make
measurements at which time the LEDs will be green. If after several
minutes the LED lights do not turn green, a diagnostic flag has been
detected. Check the individual diagnostic bits to determine the specific
fault. Diagnostics may be monitored using the Status window of ECMon,
the user interface software included with the EC155 (see Section 7,

Settings), or with a datalogger (see Section 10, Datalogger Programming
with CRBasic). The diagnostics may reveal that the unit needs to be

serviced (e.g., clean the optical windows of the sample cell, clear the
CSAT3A transducers of ice or debris, etc.).

7. Settings

7.1 Factory Defaults

Operation of the EC155 can be customized by changing the values of the
settings. Factory defaults will work well for most applications, but the user
may adjust the settings with a PC using either the ECMon software (see
Section 7.3, ECMon) or the Device Configuration Utility (see Section 7.4,
Device Configuration Utility), or with a datalogger using the

EC100Configure() instruction (see Section 10.2, EC100Configure()
Instruction).

TABLE 7-1 shows the default value for each of the settings.

17

EC155 CO2 and H2O Closed-Path Gas Analyzer

7.2 Details

This section gives an explanation for each setting.

7.2.1 SDM Address

This parameter must be set to use SDM output from the EC100. See Section

8.1, SDM Output for details on using SDM output.

Each SDM device on the SDM bus must have a unique address. The EC155
has a factory default SDM address of 1, but may be changed to any integer
value between 0 and 14. The value 15 is reserved as an SDM group trigger.

7.2.2 Bandwidth

The EC100 has a user-selectable low-pass filter to select the bandwith (5, 10,

12.5, 20, or 25 Hz). Setting the bandwith to a lower value will reduce noise.
However, it must be set high enough to retain the high-frequency fluctuations
in the CO
The factory default bandwidth of the EC100 is 20 Hz, which is sufficient for
most flux applications. Lower bandwith settings may be used for higher
measurement heights, which inherently have lower frequency content. Refer to
Appendix A for more information on the digital filter options.

and H2O, or the high frequency contributions to the flux will be lost.

2

If a spectral analysis is being done to evaluate the experimental setup, the
bandwidth should be set to the Nyquist frequency, which is half the datalogger
sample rate (for SDM output) or half the unprompted output rate (for USB and
RS-485 output). This ensures that the data will not be under-sampled and that
higher frequency variations will not be aliased to lower frequencies. Note that
if too small a bandwidth is selected, high frequency fluxes may be under­measured.

7.2.3 Unprompted Output

If the EC100 is to output data in one of the unprompted modes (USB or RS­485, see Section 8.2, USB or RS-485 Output), this setting must be set
accordingly. The factory default is to disable the unprompted output, assuming
data will be logged via SDM (see Section 8.1, SDM Output).

Only one unprompted output type (i.e., USB, RS-485) may be selected at a
given time. The rate at which the EC100 outputs these data is determined by
the Unprompted Output Rate setting.

7.2.4 Unprompted Output Rate

This setting determines the output rate for unprompted output (USB or RS-485,
see Section 8.2, USB or RS-485 Output). If the unprompted output is disabled,
this parameter is not used. The factory default output rate is 10 Hz, but it may
be set to 10, 25, or 50 Hz.

18

7.2.5 RS-485 Baud Rate

If the unprompted output mode is set to RS-485, this parameter determines the
baud rate. Otherwise this setting is not used. The RS-485 baud rate defaults to
115200 bps, although the user may enter another value.

7.2.6 Analog Output

The EC100 has two analog outputs for CO2 and H2O molar mixing ratios (see
Section 8.3, Analog Outputs for more information). These outputs may be
enabled/disabled with this setting. The default is for analog output to be
disabled.

7.2.7 ECMon Update Rate

This setting determines the rate at which data are sent over the USB connection
to the PC while running ECMon. The default setting of 10 Hz should be
adequate in most situations.

7.2.8 Temperature Sensor

The EC155 measures the temperature of the sample cell block with a
thermocouple embedded in the block. With the Auto-Select default setting,
the EC100 will automatically detect that an EC155 is connected to the
electronics and will report temperature measurements from the sample cell
thermocouple.

EC155 CO2 and H2O Closed-Path Gas Analyzer

To diagnose problems with the temperature measurement, a fixed temperature
value may be used, or the temperature sensor may be selected manually.

7.2.9 Fixed Temperature Value

If the Temperature Sensor setting is None, the EC155 will use the value of
this setting for the sample-cell temperature. This mode is intended for
troubleshooting only. In normal operation, the Temperature Sensor is set to
Auto-Select, and this setting is not used.

7.2.10 Pressure Sensor

This setting determines which pressure sensor will be used to measure the
barometric pressure. The EC100 always includes the EC100 basic barometer,
but it may be ordered with the optional EC100 enhanced barometer. This
setting is factory defaulted to the enhanced barometer if it is ordered, and to the
basic barometer otherwise.

There are two other possible settings for the Pressure Sensor. First, the user
may provide his or her own pressure sensor. In this case the setting should be
changed to User Supplied, with the appropriate values for gain and offset
entered (see below). This option may be used if the EC155 sample cell is to be
used outside the range of the differential pressure sensor (see Section 7.2.11)
For this mode the user-supplied pressure sensor must be plumbed to the EC155
sample cell, and the Differential Pressure sensor setting should be disabled.

19

EC155 CO2 and H2O Closed-Path Gas Analyzer

The final option is to select None for the Pressure Sensor setting. The EC100
will use a fixed (see below) value for pressure. This mode is intended for
troubleshooting only.

7.2.10.1 Pressure Gain

If the Pressure Sensor is set to User Supplied, this setting gives the gain
factor (kPa/V) used to convert measured voltage to pressure. Normally the
Pressure Sensor is set to EC100 Basic or EC100 Enhanced, and this setting
is not used.

7.2.10.2 Pressure Offset

If the Pressure Sensor is set to User Supplied, this setting gives the offset
(kPa) used to convert measured voltage to pressure. Normally the Pressure
Sensor is set to EC100 Basic or EC100 Enhanced, and this setting is not
used.

7.2.10.3 Fixed Pressure Value

If the Pressure Sensor setting is None, the EC155 will use the value of this
setting for the barometric pressure. This mode is intended for troubleshooting
only. In normal operation this setting is not used.

7.2.11 Differential Pressure

The EC155 includes a differential pressure sensor to measure the pressure
difference between the inside of the sample cell and barometric pressure. With
the Auto-Select default, the EC100 detects the presence of the EC155 and
automatically enables the differential pressure measurement. This pressure
difference is then added to the barometric pressure measurement to give the
pressure in the sample cell.

The EC155 sample cell differential pressure sensor has a range of ± 7 kPa,
which will accommodate most applications. If the sample cell is to be used
outside this range, the user must disable the Differential Pressure sensor and
connect a user-supplied pressure sensor (see Section 7.2.10, Pressure Sensor).

7.3 ECMon

Settings for the EC155 are easily verified and/or changed by using the
Windows PC support software ECMon (ECMon is short for Eddy Covariance
Monitor), which is found on the EC150 & EC155 Support CD (pn 27007) or
on the company website in the Support|Downloads section
(www.campbellsci.com/downloads).

Before installing ECMon, read the file titled Read.me.text found on the EC150
& EC155 Support CD. This will direct the user to install USB drivers (also
found on the Support CD), which are required for communications between the
PC and the EC100 via the EC100 USB cable (pn 26563). Once the drivers are
installed, download and run the ECMon.exe install file. Launch ECMon, and
connect the EC100 electronics to the PC with the included EC100 USB cable
(pn 26563). The USB connection for the EC100 electronics is found on the
bottom of the enclosure (see FIGURE 6-6). Once connected, select the
appropriate communications port in the ECMon Main Page and click Connect
(see FIGURE 7-1). Next click on the Setup button. All of the above settings
are now available for the user to change (see FIGURE 7-2).

20

EC155 CO2 and H2O Closed-Path Gas Analyzer

Besides changing settings, ECMon is also a useful tool for other common tasks
such as:

• Monitoring real-time data from the EC155 using the Display window

• Performing a manual zero and span of the instrument (see Section 9.4,

Zero and Span)

• Troubleshooting and monitoring diagnostics using the Status window (see

FIGURE 7-3).

FIGURE 7-1. The Main window of ECMon

21

EC155 CO2 and H2O Closed-Path Gas Analyzer

FIGURE 7-2. The Setup window in ECMon

22

FIGURE 7-3. The ECMon Status window

EC155 CO2 and H2O Closed-Path Gas Analyzer

NOTE

7.4 Device Configuration Utility

The Device Configuration Utility software may also be used to change settings,
although ECMon is generally preferred because of its more user-friendly
interface. Device Configuration may be downloaded from the EC150 &
EC155 Support CD (pn 27007), or may be downloaded free of charge from the
Campbell Scientific website in the Support|Downloads section
(www.campbellsci.com/downloads). Device Configuration requires a USB
driver to communicate with the EC100, similar to ECMon. See Section 7.3,
ECMon for notes on installing a USB driver.

After launching the Device Configuration Utility, the user should select
“EC100” from the list of device types. The EC100 electronics should be
connected to the PC with the EC100 USB cable (pn 26563) and the appropriate
USB port selected before connecting. Once connected, the settings tab
displays all the current settings. The Apply button must be clicked to save any
changes.

The Device Configuration Utility is also used to send an updated operating
system to the EC100 electronics. The Send OS tab gives directions on this
procedure.

8. EC100 Outputs

The EC100 outputs data in one of four types: SDM, USB, RS-485, or analog.
In general Campbell Scientific recommends that SDM be used if a Campbell
Scientific datalogger is responsible for data collection. However, RS-485
output is recommended over SDM if cable lengths exceed 100 meters. If a PC
is being used as the collection vehicle, USB and RS-485 are suitable outputs.
Analog output may also be used, however only CO
mixing ratio will be output. More information regarding each output type is
provided in the sections below.

The EC100 synchronously samples the gas in the EC155 sample
cell and the CSAT3A sonic head. However, a delay induced by
the intake assembly must be accounted for to ensure maximum
covariance. The exact delay will depend on the length and size of
the intake tubing and the pump flow rate. See
CPEC200 manual for details.

8.1 SDM Output

SDM (Synchronous Device for Measurement) is a Campbell Scientific
communication protocol that allows synchronized measurement and rapid
communication between a Campbell Scientific datalogger and multiple devices
including the EC155. Although nearly all of the Campbell Scientific
dataloggers support SDM, only the CR1000, CR3000, and CR5000 dataloggers
support the EC155.

mixing ratio and H2O

2

Appendix A or the

To use SDM data output, connect an SDM cable from the EC100 (see Section

6.3, Wiring and Connections) to a CR1000, CR3000, or CR5000 datalogger.
On CR1000 dataloggers, the SDM protocol uses ports C1, C2, and C3. These
are multipurpose control ports that are SDM-activated when an SDM
instruction is used in the datalogger’s program. On CR3000 and CR5000

23

EC155 CO2 and H2O Closed-Path Gas Analyzer

dataloggers, the SDM protocol uses SDM-dedicated ports SDM-C1, SDM-C2,
and SDM-C3.

Each SDM device on the SDM bus must have a unique address. The EC155
has a factory default SDM address of 1, but may be changed to any integer
value between 0 and 14 (see Section 7.2.1, SDM Address).

The sample rate for SDM output is determined by the inverse of the datalogger
scan interval, as set by the user in the datalogger program. Data are output from
the EC100 when a request is received from the logger, i.e. a prompted output
mode. The number of data values sent from the EC100 to the datalogger is
also set by the user in the datalogger program. CRBasic, the programming
language used by Campbell Scientific dataloggers, uses the EC100()
instruction to get data from an EC155. This instruction is explained in detail
under Section 10, Datalogger Programming with CRBasic of this manual.

8.2 USB or RS-485 Output

In contrast to the SDM output mode, which is prompted by a datalogger, data
can also be output from the EC100 via USB or RS485 in an unprompted mode.
In this case the EC100 sends out data without initiation from the receiving
device, at a rate determined by the EC100. Only one unprompted output type
(i.e., USB, RS-485) may be selected at a given time. RS-485 output is
recommended over SDM if cable lengths exceed 100 meters. If a Campbell
Scientific datalogger is not being used to collect the data from the EC155,
either unprompted mode is recommended.

To use USB or RS-485 output, connect a USB or RS-485 cable from the
EC100 to the receiving device (see Section 6.3, Wiring and Connections), and
configure the settings (see Section 7, Settings).

The Unprompted Output parameter must be set to USB or RS-485.

If RS-485 is selected, the RS-485 Baud Rate must be set.

The Unprompted Output Rate must be set to the desired output rate.

All output data will be in ASCII format, with each data element separated by a
comma. Each record will terminate with a carriage return and line feed.
TABLE 8-1 below lists the elements in each output array, and FIGURE 8-1
shows an example USB data feed in terminal mode.

24

EC155 CO2 and H2O Closed-Path Gas Analyzer

TABLE 8-1. USB and RS-485 Output Elements

Data
Element

1

Ux

m/s

3

Uz

m/s 4 Sonic Temperature

°C

6

CO2 Concentration

µmol/mol

7

H2O Concentration

mmol/mol

9

Air Temperature

°C

10

Air Pressure

kPa

12

H2O Signal Strength

Nominally 0.0 to 1.0

Sample Cell Pressure
Differential

14

Counter

Arbitrary

Arbitrary in

Description Units/comments

2 Uy m/s

5 Sonic Diagnostic Flag

8 Gas Diagnostic Flag

11 CO2 Signal Strength Nominally 0.0 to 1.0

13

15 Signature

kPa

hexadecimal

FIGURE 8-1. An example of USB data output in terminal mode

The final data element in each row or output array is the signature, a four
character hexadecimal value that is a function of the specific sequence and
number of bytes in the output array. The recording device (i.e., PC or
datalogger) calculates its own signature using each transmitted byte until
encountering the transmitted signature. The computed signature and the
transmitted signature are compared. If they match, the data were received
correctly. This is very similar to a Cyclic-Redundancy-Check (CRC).

In most situations, a PC begins by reading in the ASCII data and extracting the
last four ASCII characters, casting them as Long data type. The signature is
then calculated on the science data sent from the EC155, starting with CO

and

2

ending on the counter. All the characters after the counter are not part of the
signature. Once the signature is computed using the algorithm below, it is
compared to the transmitted signature. If signatures do not match, the data
should be disregarded.

25

EC155 CO2 and H2O Closed-Path Gas Analyzer

TABLE 8-2. Multipliers and Offsets for Analog Outputs

CO2

211.27

-56.34

H2O

11.31

-3.04

The following block of code is an example implementation of Campbell
Scientific’s signature algorithm in the programming language C. To generate
the signature of an output array of bytes, the seed needs to be initialized to
0xaaaa and a pointer passed to the first byte of the output array. The number of
bytes in the output array should be entered in as the swath. The returned value
is the computed signature.

//signature(), signature algorithm.
// Standard signature is initialized with a seed of 0xaaaa.
// Returns signature.
unsigned short signature( unsigned char* buf, int swath,
unsigned short seed ) {
unsigned char msb, lsb;
unsigned char b;
int i;
msb = seed >> 8;
lsb = seed;
for( i = 0; i < swath; i++ ) {
b = (lsb << 1) + msb + *buf++;
if( lsb & 0x80 ) b++;
msb = lsb;
lsb = b;
}
return (unsigned short)((msb << 8) + lsb);
}

8.3 Analog Outputs

If analog output is enabled, the EC100 will output two analog signals that
correspond to CO
Volts. TABLE 8-2 below gives the multipliers and offsets for the analog
outputs.

9. Maintenance

There are five basic types of maintenance for the EC155/EC100: intake filter
replacement (if EC155 was ordered with an intake), analyzer window cleaning,
zero and spanning, replacing analyzer desiccant/scrubber bottles, and factory
recalibration.

9.1 Routine Maintenance

The following items should be examined periodically:

Mixing Ratio
(µmol mol

-1

)

density and H2O density. These signals range from 0 to +5

2

Voltage Output Multiplier
(µmol mol-1 V-1)

Offset
(µmol mol-1)

• Check the humidity indicator card in the EC100 enclosure. If the highest

dot has turned pink, replace or recharge the desiccant bags. Replacement
desiccant bags may be purchased (pn 6714), or old ones may be recharged

26

by heating in an oven. See the manual ENC10/12, ENC12/14, ENC14/16,

NOTE

ENC16/18, available at www.campbellsci.com, for more details on
recharging desiccant bags.

• Make sure the Power and Gas LED status lights on the EC100 panel are

green. If not, verify that all sensors are connected securely and that the
instruments are powered. Also check the individual diagnostic bits for the
specific fault. See TABLE 10-2 and TABLE 10-3.

9.2 Intake Filter Replacement

This section only applies if your EC155 was ordered with the intake assembly.

The differential pressure between the sample cell and ambient pressure should
be monitored in the output data. (This can also be done using the display
screen of ECMon). If the differential pressure approaches the limit of the full
scale range (-7 kPa), it is likely that the intake filter is clogged and should be
replaced. To replace the filter, follow these steps:

a. Stop the air flow through the EC155.

b. Locate one of the EC155 intake filters (pn 26072) in the mesh pocket of

the EC100 enclosure.

EC155 CO2 and H2O Closed-Path Gas Analyzer

c. Remove the old filter by pulling on the small santoprene tab on the edge of

the filter (see FIGURE 9-1). Once removed, make sure the underlying
aluminum disk and intake hole are free from debris.

d. Place a new filter on the aluminum disk. Press along the santoprene edge

to make sure it is well-seated.

The standard intake filter has a sintered disk with 20 micron pore
size. For dusty sites, an intake filter with 40 micron pores may be
ordered (PN28698), which will increase the lifetime of the filter.
Ideally, the appropriate pore size will result in the filter needing
replacement at the same time the windows need cleaning (see
Section
rate through the analyzer will further increase the lifetime of the
filter, although this will also result in a decrease in frequency
response.

9.3). For extremely dusty conditions, lowering the flow

27

EC155 CO2 and H2O Closed-Path Gas Analyzer

Santoprene Tab

FIGURE 9-1. The underside of the optional heated intake

9.3 Cleaning Analyzer Windows

The windows of the analyzer should be cleaned if the signal strength of CO2 or

O drops below 80% of the original value. (These values may be monitored

H

2

in the output data, or they can be viewed with ECMon.) To clean the windows,
follow these steps:

a. Stop the air flow through the EC155.

b. Loosen the two captive thumbscrews (one on each end of the EC155), and

lift the top portion of the EC155 shell, leaning it back against the lower
shell. See FIGURE 9-2.

c. Loosen the thumbscrew on the cable clamp at the back of the analyzer to

release the cable, and loosen the two long thumbscrews found above the
sample cell. Rotate the latches so that the struts on the analyzer are free to
move upwards. See FIGURE 9-3.

d. Lift the analyzer head off the sample cell (see FIGURE 9-4), taking care

not to lose the O-rings (pn 26212) surrounding the optical windows (see
FIGURE 9-5). If an O-ring is lost, two replacement O-rings may be found
in the mesh pocket of the EC100 enclosure, or new ones may be ordered.

e. Wash the windows with isopropyl alcohol using cotton swabs or a non-

scratching tissue or cloth.

f. Put the analyzer back in place, making sure the O-rings are still intact.

The analyzer’s label should face out to the side.

g. Rotate the latches back in place to hold the analyzer’s struts down, and

tighten the long thumbscrews by hand. Also make sure the analyzer cable
is seated properly in the cable clamp and tighten the thumbscrew by hand.

28

h. Put the top portion of the EC155 shell back in place, and tighten the

thumbscrews.

EC155 CO2 and H2O Closed-Path Gas Analyzer

Thumbscrew

Thumbscrew

Thumbscrew

Cable Clamp

Top Shell

FIGURE 9-2. The EC155 analyzer with the top shell open

FIGURE 9-3. By loosening the thumbscrews above the sample cell, the

latches may be spun from position A to position B, thus freeing the
struts of the analyzer.

29

EC155 CO2 and H2O Closed-Path Gas Analyzer

O-ring

Optical Window

O-ring

Optical Window

FIGURE 9-4. The EC155 analyzer and sample cell with shell top open

30

FIGURE 9-5. Analyzer removed from sample cell and shell

9.4 Zero and Span

NOTE

As is the case with optical instrumentation, the EC155 may drift slightly with
exposure to natural elements. Thus, a zero-and-span procedure should be
performed occasionally. The first part of the procedure listed below simply
measures the CO
This allows the CO
quantify the state of the analyzer before the zero-and-span procedure, and in
theory could be used to correct recent measurements for drift. The last part of
the zero-and-span procedure adjusts internal processing parameters to correct
subsequent measurements.

If the EC155 was purchased as part of a CPEC200 closed-path
eddy covariance system, consult the CPEC200 manual. The
CPEC200 system has an optional valve module to allow the
datalogger to automate the zero-and-span procedure.

It is imperative that the zero-and-span procedure be done correctly and not
rushed; allocate plenty of time for the procedure. During a normal zero-and­span procedure a PC running the ECMon software is used to monitor and
control the EC155. However, the zero-and-span procedure can also be
performed using either the Device Configuration Utility software or a
datalogger running the EC100Configure() instruction (see Section 10.2,
EC100Configure() Instruction).

EC155 CO2 and H2O Closed-Path Gas Analyzer

and H2O span and zero, without making any adjustments.

2

and H2O gain factors to be calculated. These gain factors

2

To check and then set the EC155 zero and span, follow the steps below:

a. Connect the EC100 to a PC with the EC100 USB cable (pn 26563), and

launch ECMon on the PC. Select the appropriate USB port, and press
Connect. The main screen should now be reporting real-time CO

O concentrations.

H

2

and

2

b. Check the differential pressure and replace the intake filter as needed (see

Section 9.2, Intake Filter Replacement).

c. Check the signal strengths and clean the windows as needed (see Section

9.3, Cleaning Analyzer Windows).

d. Verify that the Gas LED status light on the EC100 panel is green. Also

make sure the analyzer is resting right-side-up. If the zero-and-span
procedure is being performed on-site, this should already be the case.

e. If the EC155 is configured with the heated intake assembly, connect the

zero-and-span gas to the Zero/Span inlet at the back of the analyzer. The
zero-and-span gas will be pushed backwards through the EC155 sample
cell and exhausted through the heated intake assembly. If the sample
pump is the CPEC200 pump module, it may be left connected and simply
shut off. A fraction of the zero-and-span gas will be pushed through the
pump, but not enough to affect the equilibration time. Alternatively, the
sample pump may be disconnected and the Pump connection plugged.

If the EC155 is configured with a sample inlet fitting to connect to the
user’s own intake assembly, there are two options for connecting the zero­and-span gas:

31

EC155 CO2 and H2O Closed-Path Gas Analyzer

NOTE

NOTE

1. Connect the zero-and-span gas to the Sample inlet, and disconnect the

pump, leaving the Pump connection open. The zero-and-span gas will
be pushed forward through the EC155 sample cell and exhausted out
the Pump fitting. In this case the Zero/Span connection may be left
plugged.

2. Connect the zero-and-span gas to the Zero/Span inlet, and disconnect

the intake tube from the Sample connection. Disconnect the sample
pump and plug the Pump connection. The zero-and-span gas will be
pushed backwards through the EC155 sample cell and exhausted
through the Sample fitting.

f. Click on the Zero/Span button on the main screen of ECMon. A real-time

graph at the bottom of the window will appear that displays concentrations

and H2O (see FIGURE 9-6). Next allow CO2 span gas to flow

of CO

2

through the sample cell. The exact flow rate is not important since sample
cell pressure is being measured; however, a flow rate should be high
enough to flush the tubing and sample cell in a reasonable time. If the
tubing from the CO
equilibrate in several seconds even at relatively low flow rate (< 0.5 LPM).
However if the tubing is long (e.g. if the EC155 is left in place at the top of
the tower) it may take a few minutes to flush the tube, and a higher flow
rate (> 1 LPM) may be useful to reduce the equilibration time.

Once gas begins to flow through the sample cell, watch the graph on
ECMon for the measurement readings to stabilize. Once stable, write
down the reported CO

span tank to the EC155 is kept short, the CO2 will

2

concentration.

2

Optimally the concentration of span CO2 should be near the
concentration of CO2 being measured in the field. Also, the user
is advised to use CO
gas. The use of reference CO

mixtures in dry ambient air for the CO2 span

2

gas mixtures in pure nitrogen will

2

lead to errors due to a carrier gas effect on pressure-broadening of
the CO

absorption lines since oxygen gas has a smaller line-

2

broadening coefficient than nitrogen.

g. Stop the flow of CO2 span gas, and provide H2O span gas to the analyzer.

A dew point generator is often used for this. Allow a relatively high flow
rate for the first several minutes to more quickly stabilize the system, and
then decrease the flow to 0.2 to 0.4 L/min before making the measurement.
Higher flow rates should not be used when taking the measurement
because back-pressure on the dew point generator will cause errors. Write
down the reported H

O concentration.

2

As H2O may adsorb to surfaces inside the tubing and sample cell,
allow plenty of time for the system to reach equilibrium.

h. Stop the flow of H2O span gas, and allow zero air (no CO2 or H2O) to flow

through the analyzer. Dry nitrogen is often used as zero air. The exact
flow rate is not important since sample cell pressure is being measured,
however, a flow rate should be high enough to flush the tubing and sample
cell within a reasonable time period. Wait for the measurement readings
to stabilize and write down the reported values for CO

and H2O

2

concentrations.

32

EC155 CO2 and H2O Closed-Path Gas Analyzer

measmeas

actual

zerospan

span

gain−=

i. Examine the measurements that were written down for span CO2, span

O, and zero air. Compute the drift in instrument gain using the

H

2

following equation:

where,

• span

• span

• zero

Note that in the zero-and- span window of ECMon, span

= known concentration of the span gas

actual

= measured concentration of the span gas

meas

= measured concentration in zero gas.

meas

is reported to

actual

the right of the box where the user enters the span dew-point temperature.
The software calculates span

by taking into account the dew-point

actual

temperature and current ambient temperature and pressure. The equations
used for this calculation may be found in Appendix B. If drift (offset or
gain) for CO
and CO

or H2O is excessive, it may be time to replace the desiccant

2

scrubber bottles (see Section 9.5, Replacing Desiccant and

2

Scrubber Bottles).

j. With the zero air still flowing and measurements stabilized, click on the

Zero CO

analyzer to adjust the values of its CO
forcing the CO
H

2

k. Now, remove the zero air source and replace it with the CO

and H2O button in the Zero/Span window. This will cause the

2

and H2O concentrations to read zero. Verify the CO2 and

2

O concentrations now read zero.

Zero and H2O Zero parameters,

2

span gas.

2

Allow the gas to flow through the sample cell. Watch for readings to
stabilize.

33

EC155 CO2 and H2O Closed-Path Gas Analyzer

FIGURE 9-6. ECMon Zero/Span window

l. Enter the known concentration of CO

(in ppm) in the Span

2

Concentration box and press Span. This will cause the analyzer to adjust
the value of its CO
concentration to the value specified. Verify the CO

Span parameter, forcing the measured CO2

2

concentration reads

2

the correct value.

m. Replace the CO

span gas with an H2O span gas of known dew point.

2

Allow the gas to flow through the sample cell; as before, higher flows may
be desired for a couple minutes to more quickly establish equilibrium
before resuming a flow between 0.2 and 0.4 L/min. Wait for the readings
to stabilize.

n. Enter the known dew point (in °C) in the Span Dew Point box and press

Span. This will cause the analyzer to adjust the value of its H

O Span

2

parameter, forcing the measured dew point to the value specified. Verify
the dew point reads the correct value.

o. The zero-and-span procedure is now complete.

9.5 Replacing the EC155 Desiccant/CO2 Scrubber Bottles

34

If more than one year has passed since replacing the desiccant/scrubber, or if
zero-and-span readings have drifted excessively (see Section 9.4, Zero and
Span above), the desiccant/scrubber bottles (pn 26511) within the EC155
analyzer head should be replaced as follows:

a. Remove the analyzer in the same way as explained in Section 9.3,

Cleaning Analyzer Windows of this manual.

EC155 CO2 and H2O Closed-Path Gas Analyzer

CAUTION

CAUTION

b. Unscrew the large metal plug found at the base of the analyzer next to the

analyzer cable; it should only be hand-tight (see FIGURE 9-7). Once the
plug is removed, tip the analyzer up so the desiccant/scrubber bottle falls
out. Insert a new bottle lid-first into the analyzer. Firmly screw the plug
back in place.

c. On the other end of the analyzer, remove the two seal-screws from the

metal cap (see FIGURE 9-8). Carefully pull the cap off. Tip the analyzer
up so the desiccant/scrubber bottle falls out. Insert a new bottle lid-first.
Push the cap back on, and use two new seal-screws (included with
replacement desiccant/scrubber bottles) to hold the cap in place.

While the metal cap is removed, avoid touching the detector
and its electronics.

d. Insert the analyzer back into place, making sure to latch the analyzer’s

struts down. Do not operate the analyzer for at least 24 hours (longer if in
humid environments) to give the chemicals time to purge the air inside the
analyzer. A zero-and-span procedure should then be performed before
resuming measurements.

The scrubber bottles contain strong oxidizing agents. Avoid
direct contact with the chemicals inside the bottles. Also
ensure your work area is well ventilated and free of any
reactive compounds, including liquid water. Store used
chemical bottles in a sealed container until disposal.

The chemical bottles should be disposed of according to local and federal
regulations. For more information, MSDS (Material Safety Data Sheet) forms
for the chemicals are included in Appendix D.

FIGURE 9-7. Replacing the source housing desiccant/scrubber bottle

35

EC155 CO2 and H2O Closed-Path Gas Analyzer

FIGURE 9-8. Replacing the detector housing desiccant/scrubber bottle

9.6 Factory Recalibration

When the EC155 is manufactured, it goes through an extensive calibration
process, covering a wide range of temperatures, pressures, and gas
concentrations. All CO

in ambient air traceable to the WMO Mole Fraction Scale maintained by

CO

2

the Central Carbon Dioxide Laboratory and the Carbon Cycle Greenhouse
Gases Group of the Global Monitoring Division/National Oceanographic and
Atmospheric Administration in Boulder, CO, USA.

calibration gases used in this process are mixtures of

2

After an extended period of time in the field, the EC155 may need to undergo
this factory calibration again in order to ensure valid measurements. When
recalibration is deemed necessary, contact Campbell Scientific.

For the CSAT3A, refer to the CSAT3A instruction manual for information on
recalibration.

36

EC155 CO2 and H2O Closed-Path Gas Analyzer

Command

Input Variable Length

0 8 1

12 2 13

10. Datalogger Programming with CRBasic

CRBasic supports two instructions to communicate with the EC100 via SDM.
The first is the EC100() instruction, which reads measurement data from the
EC100. The second is the EC100Configure() instruction, which receives and
sends configuration settings.

10.1 EC100() Instruction

The EC100() instruction is used to retrieve data from the EC155 via SDM.
The instruction syntax is:

EC100(Dest,SDMAddress,EC100Cmd)

Dest is the input variable name in which to store the data from the EC155. The
length of the input variable array will depend on the selected value for the
EC100CMd. A value of -99999 will be loaded into Dest(1) if a signature error
on SDM data occurs.

SDMAddress defines the address of the EC155 with which to communicate.
Valid SDM addresses are 0 through 14. Address 15 is reserved for the
SDMTrigger() instruction.

EC100Cmd is a parameter that requests the data to be retrieved from the
analyzer. The results for the command will be returned in the array specified
by the Dest parameter. A numeric code is entered to request the data, as shown
in TABLE 10-1.

37

EC155 CO2 and H2O Closed-Path Gas Analyzer

TABLE 10-1. Output Modes for EC100 Instruction

1

Ux

m/s

4

Sonic Temperature

ºC

CO2

µmol/mol

TABLE 10-2. Bits in the Sonic Diagnostic Flag

Output
Mode

Data
Field

Description

Units

2 Uy m/s

3 Uz m/s

0, 1, 2,

5 Sonic Diagnostic Flag

6

7 H2O mmol/mol

8 Gas Diagnostic Flag

9 Air Temperature ºC

10 Air Pressure kPa

1, 2

11

12

2 13

CO

Signal Strength

2

H

O Signal Strength

2

Sample Cell Pressure
Differential

nominally 0.0 ≤ strength
≤1.0

nominally 0.0 ≤ strength
≤1.0

kPa

As shown, all output modes give two diagnostic values, the Sonic Diagnostic
Flag and the Gas Diagnostic Flag. The values contain a bit field, with each
bit representing a monitored condition. When a certain condition is detected,
the corresponding bit is set. The value remains set until the event that caused
the condition is no longer present. TABLE 10-2 and TABLE 10-3 below
describe the bits in the sonic diagnostic flag and the gas diagnostic flag,
respectively.

38

hex

bit

value decimal Name

Function

0 0x1 1 Low Amp Amplitude is too low

1 0x2 2 High Amp Amplitude is too high

2 0x4 4 Tracking Poor signal lock

3 0x8 8 Hi 3 Axis DC

Delta temperature exceeds
limits

4 0x10 16 Acquiring

Acquiring ultrasonic
signals

5 0x20 32 Cal Mem Err

Sonic head calibration
signature error

EC155 CO2 and H2O Closed-Path Gas Analyzer

TABLE 10-3. Bits in the Gas Diagnostic Flag

bit hex value decimal Name Function

0 0x1 1 Bad Data Data are suspect (there is

an active diagnostic flag)

1 0x2 2 Sys Fault General system fault

2 0x4 4 Sys Startup Gas analyzer is starting up

3 0x8 8 Motor Speed Motor speed outside of

limits

4 0x10 16 TEC Temp TEC temperature exceeds

limits

5 0x20 32 Light Power Source power exceeds

limits

6 0x40 64 Light Temp Invalid source temperature

7 0x80 128 Light I Source current exceeds

limits

8 0x100 256 Power Off Gas head not powered

9 0x200 512 Chan Err Gas input data out of sync

with home pulse

10 0x400 1024 Amb Temp Invalid ambient

temperature

11 0x800 2048 Amb Press Invalid ambient pressure

12 0x1000 4096 CO2 I CO2 I exceeds limits

13 0x2000 8192 CO2 Io CO2 Io exceeds limits

14 0x4000 16384 H2O I H2O I exceeds limits

15 0x8000 32768 H2O Io H2O Io exceeds limits

16 0x10000 65536 CO2 Io Var Moving variation in CO2 Io

exceeds limits

17 0x20000 131072 H2O Io Var Moving variation in H2O Io

exceeds limits

18 0x40000 262144 CO2 Io Ratio CO2 signal level too low

19 0x80000 524288 H2O Io Ratio H2O signal level too low

20 0x100000 1048576 Cal Mem Err Gas head calibration

signature error

21 0x200000 2097152 Heater Control Heater control error

22 0x400000 4194304 Diff Pressure Differential pressure

exceeds limits

39

EC155 CO2 and H2O Closed-Path Gas Analyzer

10.2 EC100Configure() Instruction

This instruction is another way, besides ECMon and Device Configuration, to
retrieve and modify settings. ECmon and Device Configuration are user­interactive, while the EC100Configure() instruction allows automated control
under CRBasic datalogger programming.

EC100Configure() is a processing instruction. Whether running in pipeline
mode or sequential mode the datalogger will execute the instruction from
processing. This functionality allows the instruction to be placed in conditional
statements. Running from processing also introduces ramifications when
attempting to execute the EC100Configure() instruction while other SDM
instructions are executing in pipeline mode. This instruction locks the SDM
port during the duration of its execution. If the pipelined SDM task sequencer
needs to run while the SDM is locked, it will be held off until the instruction
completes. This locking will likely result in skipped scans when reconfiguring
an EC155.

For the EC155 to save settings, it must go through a lengthy write-read-verify
process. To avoid saving the settings after each set command, the result code
can be used to determine if any settings were modified from their original
value. When a change is detected the save settings command (command code

99) can then be sent to the EC155. The DestSource parameter variable should
be set to 2718 to save the settings. The reception of this command is
acknowledged but since it takes up to a second to complete, a successful return
code does not mean that all of the data was successfully written to the
appropriate non-volatile memory.

The instruction syntax is:

EC100Configure(Result,SDMAddress,ConfigCmd,DestSource)

Result is a variable that contains a value indicating the success or failure of the
command. A result code of 0 means that the command was successfully
executed. If reading a setting, 0 in the result code means that the value in the
DestSource variable is the value the desired setting has in the EC155. When
writing a setting, if the result code is 0, the value and setting were compatible,
but the value was not changed because it contained the same value that was
sent. A return code of 1 from the set operation means that the value was valid,
different, set and acknowledged. This allows CRBasic code to control whether
or not to save the settings. NAN (i.e., not a number) indicates that the setting
was not changed or acknowledged or a signature failure occurred.

SDMAddress defines the address of the EC155 to configure. Valid SDM
addresses are 0 through 14. Address 15 is reserved for the SDMTrigger()
instruction.

ConfigCmd is a variable that indicates whether to get or set a setting. The
options are listed in TABLE 10-4.

DestSource is a variable that will contain the value to read when getting a
setting, or that will contain the value to send when writing a setting to the
EC155.

40

EC155 CO2 and H2O Closed-Path Gas Analyzer

TABLE 10-4. ConfigCmd Values for Setting and Retrieving Settings

Set

Retrieve

Pressure Sensor: 0 = EC100 Basic, 1 = User-

6

106

Pressure Gain

10

110

RS-485 Baud Rate

ConfigCmd
Variable

Setting Description
(some settings list possible values for the
DestSource variable)

0 100

1 101

2 102

Bandwidth: 5 = 5 Hz, 10 = 10 Hz, 12 = 12.5 Hz, 20 =

20 Hz, 25 = 25 Hz

Unprompted Output: 10 = 10 Hz, 25 = 25 Hz, 50 =

50 Hz

Supplied, 2 = EC100 Enhanced, 3 = None (use fixed
value)

3 103 Differential Pressure: 0 = Disable, 1 = Enable

4 104 Fixed Pressure Value

5 105 Pressure Offset

Temperature Sensor:
0 = EC150 Temperature Probe

7 107

1 = EC155 Sample Cell Thermistor
2 = EC155 Sample Cell Thermocouple
3 = None (use fixed value)

4 = Auto-Select

8 108 Fixed Temperature Value

9 109

Unprompted Output Mode: 0 = Disable, 1 =USB, 2 =
RS-485

Span/Zero Control: 0 = Inactive, 1 = Zero, 2 = Span
CO

11 111

, 3 = Span H2O (see Section 10.2.1, ConfigCmd

2

11 Zero-and-Span Control

12 112 CO2 Span Concentration

13 113 H2O Span Dew Point Temperature

14 114 CO2 Zero

15 115 CO2 Span

16 116 H2O Zero

17 117 H2O Span

18 or

218**

118

Heater Voltage (0 to 4.5375V, −1 = Off) (see Section

10.2.2, ConfigCmd 18 Heater Voltage)

19 119 Reserved

20 120 Analog Output Enable: 0 = Disable, 1 = Enable

21 121 PowerDown: 0 = Gas Head On, 1 = Gas Head Off

99 N/A Save Settings to EEPROM memory

41

EC155 CO2 and H2O Closed-Path Gas Analyzer

30

2

V

PH=

10.2.1 ConfigCmd 11 Zero-and-Span Control

To perform zeroing of CO2 and H2O, ConfigCmd 11 is set to 1. After the
EC155 completes the zero, it will write the value to -1. The datalogger can
poll this value or simply wait for a period of time to allow the zeroing to
complete. To perform CO
(ConfigCmd 12) must be written to the proper value in ppm CO
setting the Span/Zero Control setting (ConfigCmd 11) to 2. After the CO
is completed, the value of the Span/Zero Control setting will change to -2.

O span is similar to CO2. First the H2O dew point value (ConfigCmd 13)

H

2

must be written to the desired value. Then the Span/Zero Control setting is set
to 3. After the EC155 completes the span, the span control setting is written as

-3. ConfigCmd’s 14 through 17 automatically store the results of the zero-and-
span procedure. Each result is a coefficient used in the gas analyzer’s
algorithms for calculating gas concentrations.

10.2.2 ConfigCmd 18 Heater Voltage

Normally the EC100Configure() instruction is run in the datalogger’s
processing task. Skipped scans can occur when the EC100Configure()
instruction executes. When changing operational parameters, these skipped
scans are acceptable. However, it may not be acceptable when changing the
heater voltage. ConfigCmd 218 allows the EC100Configure() instruction to
operate in the SDM task, thus avoiding skipped scans. When using ConfigCmd
218, the command must be a constant and the instruction cannot be placed in a
conditional statement.

span, the CO2 Span Concentration setting

2

prior to

2

span

2

If the EC155 includes the optional heated intake assembly, this setting gives
the voltage applied to the heater. It can be set to -1 to disable the heater, or set
it to any voltage between 0 and 4.5375 V. The heater prevents condensation in
the intake tube.

The resistance of the heater in the intake assembly is 30 ohms, so the heater
power will be given by:

(W)

The maximum power (at 4.5 V) is 0.7 (W). The heater may be operated
continuously at full power, over the full range of operating temperatures. If
ambient conditions are dry enough to prevent condensation without heating the
intake, the power may be turned down to conserve power. Note that the
CPEC200 system automatically controls the intake heater power as needed to
prevent condensation.

42

EC155 CO2 and H2O Closed-Path Gas Analyzer

10.3 Example CRBasic Program

'CR3000 Series Datalogger

'CR3000 Series Datalogger

Public sonic_irga(13)
Alias sonic_irga(1) = Ux
Alias sonic_irga(2) = Uy
Alias sonic_irga(3) = Uz
Alias sonic_irga(4) = Ts
Alias sonic_irga(5) = diag_sonic
Alias sonic_irga(6) = CO2
Alias sonic_irga(7) = H2O
Alias sonic_irga(8) = diag_irga
Alias sonic_irga(9) = cell_tmpr
Alias sonic_irga(10) = cell_press
Alias sonic_irga(11) = CO2_sig_strgth
Alias sonic_irga(12) = H2O_sig_strgth
Alias sonic_irga(13) = diff_press
Units Ux = m/s
Units Uy = m/s
Units Uz = m/s
Units Ts = C
Units diag_sonic = arb
Units CO2 = umol/mol
Units H2O = mmol/mol
Units diag_irga = arb
Units cell_tmpr = C
Units cell_press = kPa
Units CO2_sig_strgth = arb
Units H2O_sig_strgth = arb
Units diff_press = kPa

DataTable (ts_data,TRUE,-1)
DataInterval (0,0,mSec,10)

Sample (13,Ux,IEEE4)
EndTable

BeginProg
Scan (100,mSec,0,0)
EC100 (Ux,1,2)
CallTable ts_data
NextScan
EndProg

43

EC155 CO2 and H2O Closed-Path Gas Analyzer

cl

o

ePP

ε

−

=

11. Theory of Operation

The EC155 is a non-dispersive mid-infrared absorption analyzer. Infrared
radiation is generated in the larger block of the analyzer before propagating
through a 12 cm sample cell. Chemical species located within the sample cell
will absorb radiation at characteristic frequencies. A mercury cadmium
telluride (MCT) detector in the smaller block of the gas analyzer measures the
decrease in radiation intensity due to absorption, which can then be related to
analyte concentration using the Beer-Lambert Law:

where P is irradiance after passing through the optical path, P

is initial

o

irradiance, ε is molar absorptivity, c is analyte concentration, and l is
pathlength.

In the EC155, radiation is generated by applying constant power to a tungsten
lamp, which acts as a 2200 K broadband radiation source. Specific
wavelengths are then selected using interference filters located on a spinning
chopper wheel. For CO

, radiation with a wavelength of 4.3 µm is selected, as

2

it corresponds to the molecule’s asymmetric stretching vibrational band. For

O, radiation at 2.7 µm, corresponding to water’s symmetric stretching

H

2

vibrational band, is used.

The EC155 is a dual wavelength single beam analyzer; thus, rather than using a
separate reference cell and detector, the initial intensity of the radiation is
calculated by measuring the intensity of nearby, non-absorbing wavelengths
(4 µm for CO

and 2.3 µm for H2O). These measurements account for any

2

source and detector aging and window contamination.

The chopper wheel spins at a rate of 100 revolutions per second, and the
detector is measured 512 times per revolution, resulting in a detector sampling

o

rate of 512 kHz. The detector is maintained at -40

C using a 3-stage

thermoelectric cooler and is coupled to a low noise pre-amp module.

The EC100 electronics digitize and process the detector data (along with
ancillary data such as sample-cell temperature and pressure) to give the CO

O concentration for each chopper wheel revolution (100 Hz), filtered to

and H

2

2

the user-specified bandwidth. The EC100 also synchronously measures and
processes data from an optional CSAT3A 3D sonic anemometer head.

44

Appendix A. Filter Bandwidth and Time Delay

The EC100 measures CO2 and H2O from the EC155 gas analyzer head (as well
as wind velocity and sonic temperature from the optional CSAT3A sonic head)
at 100 Hz and then applies a user-selectable low-pass filter. The available filter
bandwidths are 5, 10, 12.5, 20, and 25 Hz. FIGURE A-1 shows the amplitude
response of these filters. The EC100 filters provide a flat pass band, a steep
transition from pass band to stop band, and a well-attenuated stop band.
FIGURE A-2 compares the EC100 10-Hz filter to a 50-msec moving average
filter with approximately the same bandwidth.

The ideal eddy-covariance filter is one that is wide enough to preserve the low­frequency signal variations that transport flux and narrow enough to attenuate
high-frequency noise. In addition, to minimize aliasing (the misinterpretation
of high-frequency variation as lower-frequency variation) the measurement
bandwidth must be less than half of the sample rate, or the datalogger scan rate.
Two factors complicate choosing the ideal eddy-covariance bandwidth. First,
the flux signal bandwidth varies from one installation to another, and the flux
signal bandwidth varies with mean wind speed at a given installation. Second,
the fast sample rate required to anti-alias a desired signal bandwidth may result
in large, unwieldy data sets.

Fortunately, the covariance calculation itself relaxes the need for the ideal
bandwidth. First, the time-averaged (typically thirty-minute) covariance
calculations inherently reduce noise, and second, aliasing does not degrade the
accuracy of covariance calculations. Therefore, the factory default for the
EC100 bandwidth (20 Hz) is rather wide to preserve the signal variations that
transport flux, and that bandwidth is suitable for most flux applications.
Additional bandwidths are available for experimenters desiring to match the
EC100 filter bandwidth to their data acquisition sample rate to avoid aliasing.
In this case, the selected bandwidth should be one-half of the sample rate (or
datalogger scan rate), and experimenters should be careful to avoid attenuation
of flux-carrying signals.

The EC100 electronics synchronously sample the gas in the EC155 sample cell
and the CSAT3A sonic head. However, delays induced by the intake assembly
must be accounted for. The exact delay will depend on the length and size of
the intake tubing and the pump flow rate. This delay needs to be
experimentally determined by shifting the time delay until the covariance of
the vertical wind and the gas concentrations are maximized.

Experimenters wishing to synchronize their EC100 data with other
measurements in the data acquisition system must account for the time delay of
the EC100 filter. TABLE A-1 shows the delay for each of the filter
bandwidths. The EC100 provides a constant time delay for all spectral
components within each filter’s pass band.

The following examples show how to use TABLE A-1. To synchronize
EC100 data to other datalogger measurements when the datalogger scan rate is
25 Hz and the EC100 bandwidth is set to 20 Hz (a 200-msec time delay from
TABLE A-1), delay the non-EC100 data by five datalogger scans. Similarly,
for a 10-Hz datalogger scan rate and the same 20-Hz EC100 bandwidth, delay

A-1

Appendix A. Filter Bandwidth and Time Delay

1 10 70

Hertz

0.0001

0.001

0.01

0.1

1

10

No Units

5 Hz

10 Hz

12.5 Hz

20 Hz

25 Hz

EC100 Bandwidths (Amplitude Responses)

the non-EC100 data by two datalogger scans to match the EC100 data. For the
best synchronicity, choose a datalogger scan interval that is an integer multiple
of the EC100 filter delay.

The EC100 measures the gas and wind data at 100 Hz, and the 100-Hz data are
down-sampled to the datalogger’s scan rate through SDM communications (see
Section 8, EC100 Outputs). This process synchronizes the EC100 gas and
wind data with other signals measured by the datalogger to within ±3.333 ms
(plus or minus one-half of the inverse of 100 Hz). Alternatively, when sending
data to a non-Campbell data acquisition system, the EC100 down-samples its
USB and RS-485 outputs to a user-selectable rate of 10, 25, or 50 Hz.
Although the gas and wind data from the EC100 remain synchronized with one
another, the user must consider the down-sampled output interval when
synchronizing the EC100 data with other measurements in their system. These
slower output intervals will increase the asynchronicity of EC100 data with
other system measurements.

FIGURE A-1. Frequency and amplitude response of the EC100 filter at

various bandwidths

A-2

Appendix A. Filter Bandwidth and Time Delay

TABLE A-1. Filter Time Delays for Various Bandwidths

1 10 70

Hertz

0.0001

0.001

0.01

0.1

1

10

No Units

EC100 10-Hz Bandwidth Filter

10-Hz Bandwidth from a 50-msec Moving Average

EC100 10-Hz Filter Compared to 20-msec Moving Average (Amplitude Responses)

FIGURE A-2. Frequency response comparison of the EC100 10-Hz

bandwidth and a 50-msec moving average

Bandwidth (Hz) Time Delay (ms)

5 800

10 400

12.5 320

20 200

25 160

A-3

Appendix A. Filter Bandwidth and Time Delay

A-4

Variable or Constant

Description

Units

c

ρ

v

ρ

d

ρ

c

X

CO2 Molar Mixing Ratio
(concentration relative to dry air)

v

X

H2O Molar Mixing Ratio
(concentration relative to dry air)

c

M

d

M

v

M

P

Ambient Pressure

kPa

R

Universal Gas Constant

8.3143×10–6 kPa m3 K–1 mmol–1

T

Ambient Temperature

C

e

Vapor Pressure

kPa

f

d

T

tmpdT_

Temporary variable for dew point
calculation

( )















−

+

=

v

vcc

c

MTR

P

MX

ρ

ρ

15.273

10

6

( )( )

v

vv

v

XTR

PMX

++

=

100015.

273

ρ

( )
( )

15.273+

−

=

TR

MeP

d

d

ρ

( )

15.273

1000

+















+

−

=

TR

M

X

PX

P

d

v

v

d

ρ

Appendix B. Useful Equations

The following table lists all the variables and constants used in the equations
below:

Table of Variables and Constants

Mass Density mg m-3

CO

2

O Mass Density g m-3

H

2

-3

Mass Density of Dry Air g m

Molecular Weight of CO

Molecular Weight of dry air 0.029 g mmol

Molecular weight of H

Enhancement Factor Arbitrary

Dew Point Temperature

44 mg mmol-1

2

O 0.018 g mmol-1

2

µmol mol-1

mmol mol-1

o

o

C

Arbitrary

-1

Mass Density from Molar Mixing Ratios

(B-1)

(B-2)

(B-3)

(B-4)

B-1

Appendix B. Useful Equations

( )















+

−















+

=

v

vd

d

X

X

TR

PM

1000

1

15.273

ρ

tmpd

tmpd

d

T

T

T

_

_

502.17

97.240

−

=

( )















+⋅

=

v

v

tmpd

Xf

PX

lnT

100061121.0

_

( ) ( )

295

109.5102.300072.1 PTPf

−−

×+×+=

1000

eP

e

X

v

−

=















+

⋅⋅=

d

d

T

T

EXPfe

97.240

502.17

61121.0

( )(

)

( )















++

=

d

d

v

T

T

EXP

TR

f

97.

240

502.17

15.273

61121.0

018.0

ρ

v

v

X

PX

e+=

1000

( )

v

v

M

TR

e

15.273+

=

ρ

(B-5)

Dew Point from Molar Mixing Ratio

(B-6)

(B-7)

(B-8)

Water Vapor Molar Mixing Ratio from Dew Point

(B-9)

(B-10)

Water Vapor Mass Density from Dew Point

(B-11)

Vapor Pressure from Molar Mixing Ratio and Water Vapor Density

(B-12)

(B-13)

B-2

Equations (1) and (2) were derived from Leuning, 2004; Eq. 6.23.

Equations (6) - (8) and (10) - (11) were derived from Buck, 1981; Eq. 2a, 3a,
and 6.

NOTE

CAUTION

Appendix C. EC155 Sample Cell and Intake Maintenance

The following steps can be undertaken when the sample cell and intake tube
becomes dirty, or as part of routine maintenance of the EC155. Refer to
Section 9.3, Cleaning Analyzer Windows, for figures and instructions for
accessing and removing the analyzer from the sample cell.

C.1 Cleaning Sample Cell

1. Turn off the pump.

2. Power down the analyzer.

3. Remove the analyzer from the sample cell.

4. Use water or alcohol on a soft cotton swab to clean the inside of the

sample cell.

Take care not to let the water or alcohol drip down into the holes
at ends of the sample cell. Each end has a small passage that
connects to the pressure sensor. These passages can become
plugged by residue carried by the water or alcohol. This problem
can be avoided by using cotton swabs that are slightly moist, not
saturated. However, if more aggressive cleaning is needed, invert
the sample-cell assembly during cleaning so any liquid drains
away from these passages.

C.2 Cleaning Intake Tube

The EC155 intake tube is not designed to be removed by the user. If it
becomes dirty, it may be cleaned while attached to the sample cell assembly.
The appropriate cleaning procedure depends on whether the contamination is
particulate matter that has collected during dry, dusty conditions, or if it is an
accumulation of soluble material such as salt deposits. Guidance for cleaning
either type of contamination is found in the following sections.

C.2.1 Dust Blowout

If the intake tube is dusty, the procedure can easily be performed in the field.
Campbell Scientific recommends that the procedure is performed any time the
windows are cleaned.

Do not blow the dust out of the intake assembly using
compressed gas as this may damage the differential
pressure sensor in the sample cell assembly. The maximum
pressure allowed on the pressure sensor is 75kPa
(differential).

1. Run the system normally, with the analyzer in place and the pump on.

2. Remove the filter at the inlet of the intake.

C-1

Appendix C. EC155 Sample Cell and Intake Maintenance

NOTE

NOTE

3. Plug the hole in the inlet with your finger. The pump will pull a

vacuum on its internal filter/buffer volume, the pump tube, analyzer,
and intake tube.

4. After approximately one minute, unplug the hole.

During these steps, ambient air will rush in and blow dust from
the inner walls of the intake tube, which is likely be deposited on
the analyzer windows. For this reason, Campbell Scientific
recommends performing the dust blowout prior to cleaning
windows.

5. Repeat this procedure as needed.

When the windows no longer become dirty (CO
change) this indicates no more dust is being removed from the intake tube.

C.2.2 Solvent Flush

If the intake tube has other contamination, such as salt deposits, it may be
flushed with water or alcohol, but be careful to keep the solvent out of the
pressure sensor passages (see earlier note on cleaning the sample cell).
Following the steps in the following procedure, will help keep the pressure
sensor passages clear.

1. Power the system down.

2. Remove the sensor head from the sample cell.

3. Close the lid of the sample cell assembly.

4. Position sample cell assembly upside down. This allows the solvent

5. Tilt slightly so that the intake is higher than the sample cell.

6. Remove the intake filter.

7. Fill a syringe with solvent (generally, tap water will be sufficient) and

8. Depress the plunger to let the solvent flow through the intake tube.

and H2O signal levels do not

2

to flow away from the pressure sensor passage.

press it against the hole in the end of the intake tube.

The waste solvent will collect in the lid of the sample cell assembly.

C-2

9. Fill the syringe with air and push the air through the intake tube to

force most of the solvent out of the tube.

10. Dump the solvent out of the sample cell assembly and wipe the

assembly dry.

11. Clean the analyzer windows and the sample cell as described in

Section 9.3, Cleaning Analyzer Windows, and C.1, Cleaning Sample
Cell, in the section above.

This procedure is likely to leave some of the solvent in the system.
Make sure it is completely dry before attempting a zero/span.

Appendix D. Material Safety Data Sheets (MSDS)

D.1 Magnesium Perchlorate MSDS

D-1

Appendix D. Material Safety Data Sheets (MSDS)

D.2 Decarbite MSDS

D-2

Appendix D. Material Safety Data Sheets (MSDS)

D-3

Appendix D. Material Safety Data Sheets (MSDS)

D-4

Appendix E. EC155 Packing Information

E-1

Appendix E. EC155 Packing Information

E-2

Campbell Scientific Companies

Campbell Scientific, Inc. (CSI)

815 West 1800 North

Logan, Utah 84321

UNITED STATES

www.campbellsci.com • [e-mail]

Campbell Scientific Africa Pty. Ltd. (CSAf)

PO Box 2450

Somerset West 7129

SOUTH AFRICA

www.csafrica.co.za • [e-mail]

Campbell Scientific Australia Pty. Ltd. (CSA)

PO Box 8108

Garbutt Post Shop QLD 4814

AUSTRALIA

www.campbellsci.com.au • [e-mail]

Campbell Scientific (Beijing) Co., Ltd.

8B16, Floor 8 Tower B, Hanwei Plaza

7 Guanghua Road

Chaoyang, Beijing 100004

P.R. CHINA

www.campbellsci.com • [e-mail]

Campbell Scientific do Brasil Ltda. (CSB)

Rua Apinagés, nbr. 2018 ─ Perdizes

CEP: 01258-00 ─ São Paulo ─ SP

BRASIL

www.campbellsci.com.br • [e-mail]

Campbell Scientific Canada Corp. (CSC)

14532 – 131 Avenue NW

Edmonton AB T5L 4X4

CANADA

www.campbellsci.ca • [e-mail]

Please visit www.campbellsci.com to obtain contact information for your local US or international representative.

Campbell Scientific Centro Caribe S.A. (CSCC)

300 N Cementerio, Edificio Breller

Santo Domingo, Heredia 40305

COSTA RICA

www.campbellsci.cc • [e-mail]

Campbell Scientific Ltd. (CSL)

Campbell Park

80 Hathern Road

Shepshed, Loughborough LE12 9GX

UNITED KINGDOM

www.campbellsci.co.uk • [e-mail]

Campbell Scientific Ltd. (CSL France)

3 Avenue de la Division Leclerc

92160 ANTONY

FRANCE

www.campbellsci.fr • [e-mail]

Campbell Scientific Ltd. (CSL Germany)

Fahrenheitstraße 13

28359 Bremen

GERMANY

www.campbellsci.de • [e-mail]

Campbell Scientific Spain, S. L. (CSL Spain)

Avda. Pompeu Fabra 7-9, local 1

08024 Barcelona

SPAIN

www.campbellsci.es • [e-mail]