Eco Physics CLD 780 TR User manual

WARNING
The CLD 780 TR may only be switched on when it is connected to a vacuum pump and adequate
vacuum is achieved. In addition the vacuum tubing from the analyzer to the pump must be abso-
lutely light-tight and of adequate diameter (at least 16 mm). Ideally, the vacuum pump is switched
on, with dry air cartridges connected, 1 hour before the instrument itself and, after use, left running
30 – 60 minutes after the CLD 780 TR is switched off.
Similarly, it is extremely important that:
– the dry air inlet is always connected to an indicating dryer cartridge with unused drying capacity
(also, if possible, when the instrument is switched off).
–theO
2inlet is always connected to an adequate source of dry oxygen (at 750 to 1100 mbar
abs) or dry air (at atmospheric pressure).
– the sample is passed through a particle filter (pore size 5 µm or less).
When bringing the CLD 780 TR into operation for the first time, or after an extended shut-down with
the vacuum pump and/or dryer cartridges removed, run the vacuum pump, with dry air cartridges
connected, for several hours before switching the instrument on.
If these precautions are not observed then the consequences may be destruc-
tion or damage to the photomultiplier tube through exposure to daylight, or by
the formation of condensation.

E C O P H Y S I C S Table of Contents
CLD 780 TR / July 2000
1.1 Introduction 2
1.2 Safety precautions 3
2.1 CLD 780 TR Performance
data (O2operation) 10
2.2 CLD 780 TR Operating
data 11
2.3 Dimensions and weight of
the CLD 780 TR 12
3.1 Measurement principle 14
3.2 Description of the
CLD 780 TR analyzer 16
4.1 Unpacking 26
4.2 Installing the CLD 780 TR
and its peripherals 27
5.1 Start up 34
5.2 Operating the analyzer 35
5.3 Shutting the system down79
6.1 Introduction 82
6.2 Performing a calibration 84
7.1 Sampling 92
7.2 Quenching 93
7.3 Interferences 94
7.4 Observing the raw signal95
7.5 Influence of atmospheric
pressure fluctuations on the
measuring signal 97
OPERATING GUIDE
MEASUREMENT
PRINCIPLE
SPECIFICATIONS
TABLE OF CONTENTS
INTRODUCTION
INSTALLATION
CALIBRATION
PRACTICAL HINTS

E C O P H Y S I C S Table of Contents
CLD 780 TR / July 2000
8.1 Introduction 100
8.2 Interface hardware 101
8.3 Communications
protocol 103
8.4 Command set 108
9.1 Filtering the sample gas119
9.2 Dry air and O2inlet
filter 120
9.3 Silica gel drying
cartridges 122
9.4 Cleaning the analyzer
reaction chambers 124
9.5 Cleaning the instrument 131
10.1 Error messages and
correction procedure 134
10.2 Electrical test points 139
GAS PHASE TITRATION
QC/CONFORMITY
DISPOSAL
TROUBLESHOOTING
PERIODIC
MAINTENANCE
RS-232 INTERFACE
Read the safety rules first!
(Section 1.2)
!
OPTIONS
CONTINUOUS MEASURE
MODE
TABLE OF CONTENTS

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 1
1.1 Introduction 2
1.2 Safety precautions 3
1.2.1 Definitions, Personnel,
Definitions of terms 3
1.2.2 Symbols and safety hints
used in this manual 4
1.2.3 Intended use of the
analyzer 5
1.2.4 General dangers 5
1.2.5 General safety rules 7
1.2.6 Responsibilities and duties of
the supplier 8
INTRODUCTION
Read the safety rules first!
(Section 1.2)
!

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 2
1.1 Introduction
The CLD 780 TR is the first commercially available NO analyzer which is
designed and developed specifically for airborne applications. It need
hardly be said that this new instrument delivers fast, continuous, highly
specific NO concentration data which is linear over all the measurement
ranges.
Analyzers using classical chemiluminescence techniques are not capable
of accurately measuring NO at concentrations of below a few ppb. Apart
from the inadequate detection limit of these instruments, they also suffer
from interferences caused by other components in the sample gas (e.g.
OH radicals, and a large number of hydrocarbons) which can produce
errors of several ppb. The design of the CLD 780 TR is based to a large
extent on the proven “fore-chamber” principle used by its predecessor in-
strument, the now legendary ECO PHYSICS CLD 770 AL ppt. The ad-
vanced fore-chamber construction in the CLD 780 TR ensures the elimina-
tion of interferences due to hydrocarbons and OH radicals.
The CLD 780 TR also achieves new levels of performance in terms of sig-
nal processing, instrument control, user-friendliness and problem diagnosis
thanks to the consistent use of leading-edge processor technology. The
serial interface allows the user not only to monitor the measurement data
and any error messages on an external display screen, but also permits
all instrument operating steps such as calibration, measurement range
switching and monitoring of diagnostics via computer.
Zero point compensation is performed automatically in the CLD 780 TR
without the need for a supply of zero air. The problems caused by con-
densation around the photomultiplier socket, which plague many chemi-
luminescence-base analyzers on the market, are avoided by the use of a
dry air flow around the cooled PMT housing.
The operation the CLD 780 TR is quickly grasped by the new user, the
menu-based control dialog between the keypad and the display being
self-explanatory. Despite this, we recommend that you read the following
chapters carefully to learn about the multifaceted capabilities of this
unique instrument.
As with the CLD 770 AL ppt, the CLD 780 TR is intended, if required, to
be used together with a photolytic converter. The combined operation of
CLD 780 TR and PLC 762 is therefore covered in Chapter 5 (Operating
Instructions), Chapter 6 (Calibration) and Appendix A3 (Gas Phase Titra-
tion etc.). Detailed information regarding the PLC 762 itself can be found
in the PLC 762 Operator’s Manual.

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 3
1.2 Safety precautions
This section summarizes the safety precautions, which are to be observed
without exception when using the CLD 780 TR analyzer (in the following
sections called “analyzer“).
For all persons working with the analyzer, reading and comprehending
the sections relevant to their work is obligatory. This is especially valid for
this section, the reading of which is binding for all persons operating the
analyzer, including those using it only temporarily or occasionally, e.g.
for service purposes.
1.2.1 Definitions, Personnel, Definitions of terms
– Supplier
The supplier is ECO PHYSICS AG in CH-8635 Duernten, Switzerland
and all other persons who claim to be the supplier by marking the ana-
lyzer with their name, their logo or any other distinguishing label.
Furthermore the representative or the importer of the analyzer or other
commercial businesses in the distribution channel acts as supplier, as
far as their activities influence the safety conditions of the analyzer.
–Enduser
The end user is the local owner of the analyzer. He is responsible for
the intended use (see below).
Qualifications of the operating personnel
(I.e. all persons involved with the analyzer)
– General operation:
Installation, operation, calibration and periodic maintenance must be
performed by personnel who have attended technical courses and
have adequate instrument-related skills. This basic knowledge allows
them to estimate potential risks and hazards in the use of the analyzer
and its accessories. Alternatively, these persons have been specifically
trained in order to comply with these requirements.

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 4
–Service:
Repair, exchange of modules, printed circuit boards etc. must be per-
formed only by trained service personnel, instructed and authorized by
ECO PHYSICS.
– Programming, communication and electronics:
Programming of the serial interface in order to operate the analyzer
by a computer system and to install the communication interface shall
be performed by appropriately skilled and qualified software engi-
neers.
Significance of the safety precautions
The goal of these safety precautions is to draw attention to the remaining
risks in order to allow a safe and economical operation.
1.2.2 Symbols and safety hints used in this manual
Safety symbols similar to the following are used in this manual to draw at-
tention to potential risks when the analyzer is used according to its in-
tended use:
WARNING
Toxic gases!
Safety warnings in and at the analyzer
Warning labels inside the analyzer:
– Danger - High Voltage
Gefahr - hohe Spannung
– Disconnect power before opening
Vor dem Öffnen Netzstecker ziehen
Warning labels on the back panel (outside):
– Servicing to be performed by qualified personnel only. Disconnect
power before undertaking repair or maintenance
Servicearbeiten dürfen nur durch qualifiziertes Personal durchgeführt
werden. Netzstecker ziehen vor Reparaturen oder Instandstellungsar-
beiten.
!

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 5
1.2.3 Intended use of the analyzer
The analyzer is exclusively designed for monitoring of nitrogen oxides in
gases.
The intended use implies:
– operating the instrument within the technical specifications described in
section 2
– following this operating manual and observing all the hints, warnings
and recommendations it contains
Non-intentional use (misuse)
All other types of use beyond the description above are considered as
non-intentional. Damages resulting from such misuse cannot be claimed
from the supplier. He assumes no responsibility. The whole risk remains
with the end-user.
1.2.4 General dangers
WARNING Exhaust gas!
The vacuum pump exhaust must be allowed to vent either above roof level
or to a special-purpose ventilation system using a tube with a minimum in-
ner diameter of sixteen millimeters. Neglecting to observe this safety pre-
caution may cause severe health problems (e.g. the inhalation of NO2
may cause irritation of the respiratory tract or in severe cases to lung
damage.)
WARNING
High pressure gas!
All relevant safety precautions must be observed without exception:
– Pressurized gas cylinders must be secured against falling. Horizontally
stored cylinders must be prevented from rolling.
– The pressure reduction valves and all tubing from gas cylinder to vent
must be regularly checked for leaktightness.
–etc.
WARNING Toxic gases!
!
!
!

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 6
Nitrogen-monoxide (NO), Ozone (O3) and especially nitrogen dioxide
(NO2) are toxic! Following the recommendations and instructions in this
manual assures safe operation when the analyzer is correctly used
(”intentional use” condition).
Specific dangers with the analyzer
NO
Nitrogen monoxide is used only for calibration. This should be performed
at a similar concentration as the expected concentration of the sample
gas.
NO2
We recommend that for the determination of NO2the converter shall be
checked by the principle of gas-phase-titration (GPT; refer to section
6.2.4). However, when using bottled NO2extreme care shall be observed
on account of the high toxicity to avoid any leakage of the gas.
O3
Ozone is produced inside the analyzer in the ozone generator using
dried ambient air. In a correctly installed and operated system this ozone
will be destroyed in the ozone scrubber located on and immediately up-
stream of the vacuum pump. Furthermore, the actual concentration of
ozone is low, and under fault conditions the ozone generator is automati-
cally shut down by the analyzer control system.
Dangers involving peripherals
A complete description of precautions to eliminate the dangers associated
with peripheral devices, which are application-specific, is beyond the
scope of this manual. As an example (relating to the sampling system)
special care should be observed when handling hot and aggressive
gases, and the appropriate safety precautions applied.

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 7
1.2.5 General safety rules
Legally-binding regulations
In addition to the instructions in this manual, all current environmental,
safety and technical regulations must be respected.
General inspection requirements
To be met after each maintenance, repair or service operation.
Power connections
The analyzer may only be installed and connected to the mains power-
supply according to the installation guide in section 4.2 of this manual. All
power lines must be switched to cut off the electrical supply at source.
Accessories and spare parts
For maintenance and repair the options and spare parts originally manu-
factured by ECO PHYSICS and included in this manual should be used
exclusively.
Modifications and alterations
Modifications of the analyzer or options and parts, which affect safety
aspects, are only permissible with the written consent and prior agreement
of ECO PHYSICS AG.

E C O P H Y S I C S Introduction
CLD 780 TR / July 2000 8
1.2.6 Responsibilities and duties of the supplier
The supplier is responsible for the safety of the product; this can only be
guaranteed if the end user undertakes to follow fully the requirements and
suggestions contained in this handbook. The end-user has a duty of care
to ensure that this is done.
The supplier observes his product beyond the time of delivery. He is enti-
tled to request information especially related to safety from the end user.
Duties of the end user: Training, personnel competence
The end user makes sure that only trained and authorized personnel can
work with the analyzer. He is responsible for comprehensive training fol-
lowing the instructions of this manual. He designates the responsible per-
sons and delegates competencies.
Instruction on the dangers to personnel
The end user makes sure, that his personnel install and operates this ana-
lyzer only in compliance with this manual. He is responsible for the neces-
sary supply of safety-relevant tools and support materials.
Duty of care and maintenance
The analyzer must be maintained in operational condition; full periodic
maintenance shall be performed.
Duty to observe and inform
In case of any (remaining) risks or dangers, which have not been covered
in this manual, the end user of the analyzer is requested to inform the
supplier immediately.

E C O P H Y S I C S Specifications
CLD 780 TR / July 2000 9
2.1 CLD 780 TR Performance
data (O2operation) 10
2.2 CLD 780 TR Operating
data 11
2.3 Dimensions and weight of
the CLD 780 TR 12
SPECIFICATIONS
Read the safety rules first!
(Section 1.2)
!

E C O P H Y S I C S Specifications
CLD 780 TR / July 2000 10
2.1 CLD 780 TR Performance data (O2operation)
Measurement range 0.005 - 5 ppb
0.01 - 10 ppb
0.05 - 50 ppb
0.1 - 100 ppb
0.5 - 500 ppb
In each range the signal integration in-
terval can be varied in 0.1 sec steps
from 0.1 to 999 sec.
Zero-point noise, 1 σ< 0.025 ppb 1)
Signal noise, 1 σ< 0.5 % of signal or zero-point
noise whichever is greater 1)
Detection limit, ± 1 σ< 0.05 ppb 1)
< 0.01 ppb 2)
Interference NH3: < 1
(in % NO equivalent) SO2: below detection limit
water vapor: 1 vol% water vapor
in sample reduces measured NO
value by at most 8 %
Zero-point drift negligible
Rise time < 1 sec (combined pneumatic and
electronic response times for signal
to reach 95 % of end value after a
step change in NO concentration)
Fall time < 1 sec (see Rise time)
Delay time < 1 sec in “Continuous” mode
(see Section 5.2.2.2 Window 3)
≈4 sec in “NO” or “NO.c” mode,
with signal integration interval of 1
sec (see Section 5.2.2.2 Window
3)
Linearity within range ± 1 % of full scale
1) signal integration interval 3 sec and O2operation
2) signal integration interval 60 sec and O2operation

E C O P H Y S I C S Specifications
CLD 780 TR / July 2000 11
2.2 CLD 780 TR Operating data
Analog outputs 0 to 1 V
(galvanically isolated) 0.2 to 1 V
0 to 10 V (into 500 kΩmin)
2 to 10 V
0 to 20 mA
4 to 20 mA (into 500 Ωmax)
Interface (programmable) RS-232
Permitted ambient temperature 5 to 50 °C
Permitted humidity range 5 to 95 % RH (non condensing)
Reaction chamber temperature 40 °C, regulated
Photomultiplier temp. < -15 °C
Reaction chamber pressure 14 ± 4 mbar abs.
Inlet pressure range
– Sample and /or calibration gas 800 to 1050 mbar abs. (ambient)
(170 to 1050 with Option 2)
– O2/Dry air 750 to 1100 mbar abs.
(not true with Options 1&2. See
section 3.3 in Appendix A4)
Sample/Cal gas flow 3150 ml/min
Ozone flow (O2or dry air) 330 ml/min
PMT purge flow (dry air) < 50 ml/min
Electrical data
– Power uptake 200 VA
– Supply voltage 28 VDC ± 10 %
(24 VDC + 10/- 15 % optional)

E C O P H Y S I C S Specifications
CLD 780 TR / July 2000 12
2.3 Dimensions and weight of the CLD 780 TR
Dimensions
– Housing width 440 mm
height 255 mm
depth 420 mm
– Front panel width 483 mm
height 264 mm
depth 4 mm
Weight 35 kg
Materials of construction
– Housing Aluminium
– Front panel Aircraft-grade aluminium
Connections all located on front panel
(electrical & pneumatic)

E C O P H Y S I C S Measurement principle
CLD 780 TR / July 2000 13
3.1 Measurement principle 14
3.2 Description of the
CLD 780 TR analyzer 16
3.2.1 Introduction 16
3.2.2 Detector unit 16
3.2.3 Ozone generator 17
3.2.4 Gas flow 19
3.2.5 CLD 780 TR Electronics 22
MEASUREMENT PRINCIPLE
Read the safety rules first!
(Section 1.2)
!

E C O P H Y S I C S Measurement principle
CLD 780 TR / July 2000 14
3.1 Measurement principle
The reference measurement principle specified by the U.S. Environmental
Protection Agency (EPA) for nitrogen dioxide (NO2) is the gas phase
chemiluminescent reaction of nitric oxide (NO) with ozone (O3). NO is
measured directly, NO2indirectly. The NO2-to-NO reduction is achieved
by the use of a converter. The reactions between NO and an excess
amount of O3are detailed in the following formulae:
NO + O3NO2+O
2[1]
NO + O3NO2*+O
2[2]
NO2*NO2+h
ν[3]
NO2*+M NO
2+M [4]
NO2*denotes the excited nitrogen dioxide molecule, M for deactivating
collision partners such as N2, O2and H2O. The spontaneous deactivation
of NO2occurs with emission of light [3]. By far the larger fraction of NO2*
loses its excitation energy without light emission by colliding with other
molecules [M) [4]. In order to achieve a high yield of light the reaction of
NO with O3must take place under low pressure.
The light intensity generated by the chemiluminescent reaction [3] is pro-
portional to the mixing ratio of NO. A photomultiplier tube [PMT) is used
to convert the light energy emitted from [3] into electrical impulses. A
counter counts the electrical impulses over a chosen integration time inter-
val (ITI) and a microprocessor calculates the signal (SNO) in ppbv.
For the correct measurement of low levels of NO (pptv) it is important to
recognize that there are other sources of the signal (S1). The instrument’s
measured signal (S1) contains, beside SNO, also the dark current signal of
the PMT (SD). Since the detector registers the chemiluminescent emission of
other reactions than that between NO and O3, S1also contains SIn (signal
from interfering reactions). This can be significant, for example in rural ar-
eas at night where SIn can be higher than SNO.
The total signal S1therefore is:
S1= SNO + SIn + SD
where: SD= dark current
SIn = chemical interferences
SNO = the NO concentration.
If SIn = 0 and SDis known for a specific ITI ∆t, the dark current SDgives the
detection limit of the NO concentration. The interference signal SIn can be
very simply determined by use of a pre-chamber. This is possible because
most of the interference reactions that produce the signal SIn are signifi-
cantly slower than reactions [1] to [3].

E C O P H Y S I C S Measurement principle
CLD 780 TR / July 2000 15
For this reason the CLD 780 TR employs a pre-chamber where NO com-
pletely reacts with ozone. If the residence time of the sample gas in the
pre-chamber allows the complete deactivation of the excited NO2*, the
signal SNO detected by the PMT in the main reaction chamber is zero. Al-
ternating measurements with and without the pre-chamber allow the calcu-
lation of the correct NO concentration in the sample gas:
S1=S
NO +S In +S D
S2≈SIn +S
D
--------------------------------------------------------------------------------------------------------
SNO ≈S1-S
2
One measuring cycle consists of two steps:
Step 1 (measuring mode) producing the signal S1.
Step 2 (zero mode) producing signal S2.
In both modes the sample gas flows first through the pre-chamber and
then through the main chamber. In Step 1 the sample gas is mixed with
high-concentration ozone in the main chamber. During Step 2 (zero
mode) the ozone is added to the sample gas in the pre-chamber. The
PMT, of course, always measures the optical emission from the main
chamber only.
Thus the duration of a complete measurement cycle is twice the integration
time ∆t plus a few seconds of purging time. In NO measurement mode,
with an integration time ∆t = 30 s, the instrument displays a new NO con-
centration value in ppb every 62 s. See also section 5.2.2.2 (3).

E C O P H Y S I C S Measurement principle
CLD 780 TR / July 2000 16
3.2 Description of the CLD 780 TR analyzer
3.2.1 Introduction
Great effort has been made during the design phase of the CLD 780 TR to
achieve a modular construction. A further characteristic of the instrument,
essential for airborne installations, is the location of all external connec-
tion points (both electrical and pneumatic) on the front panel. In addition
to this, the depth of the housing has been minimized to reduce the prob-
lem of lack of space which must often be overcome in aircraft. The main
electronic boards (power supply, microprocessor controller and pressure
sensor) are mounted on a supporting plate which can be folded upwards
for ease of access.
The arrangement of the individual modules in the instrument is shown in
Fig. 3.1.
The construction and operation of the most important components, to-
gether with the flow diagram and electronics system, is described below.
3.2.2 Detector unit
(see Fig. 3.1)
Despite the fact that the CLD 780 TR analyzer contains two reaction
chambers (pre-chamber and main chamber), the instrument is in principle
a single-channel analyzer. When combined with a photolytic converter
the analyzer is able to measure NO and NOx(NO.c). The detection of
both components in the sample gas is accomplished through automatic
switching of the gas flow in a two step cycle. The measurement of NO is
achieved in a first step, that of NO.c in a second step (see “MODE“-
window (3), paragraph 5.2.2.2). Referring to fig. 3.1, the pre-chamber
[7] serves to determine the interference signal and the chemical zero
point. The actual chemiluminescence reaction that produces the measure-
ment signal takes place in the main reaction chamber [8]. A 3/2-way tef-
lon solenoid valve [6] switches the ozone flow to either the fore-chamber
or main chamber. When a main chamber measurement occurs the sample-
gas and the ozone-flow are concentrically guided into the main chamber
where the two streams are mixed. The main chamber is viewed by the
photomultiplier (PMT) unit [14].
The photomultiplier (PMT) is a “head-on“ type which collects the light di-
rectly, not reflected by a mirror. The photons emitted by the chemilumin-
scent reaction in the main chamber are converted by the PMT into current
pulses and amplified. The cooled PMT is thermally insulated against heat
flow from outside and from the reaction chamber. The inside of the PMT
housing is flushed with dry air in order to prevent condensation. The cool-
ing to below –15 °C greatly reduce fluctuations in the dark current, so

E C O P H Y S I C S Measurement principle
CLD 780 TR / July 2000 17
that the detector sensitivity remains stable and the signal noise minimized.
All other parameters that influence the reaction rate (chamber pressure,
ozone generator voltage and chamber inlet temperature) are constantly
monitored. To insure optimal NO selectivity a red filter is positioned be-
tween the main chamber and the PMT.
3.2.3 Ozone generator
(see Fig. 3.1)
The integrated ozone generators [5] operate on the “silent electrical dis-
charge“ principle. Oxygen or dry air is passed through an alternating
current electrical field, and ozone is generated through ionization. A sta-
bilized, constant-frequency high voltage is used to create the discharge.
The high ozone yield from the generator assures measurement linearity
over five concentration decades. For maximum sensitivity and accuracy
supply the ozone generators with pure oxygen (O2) instead of dry air. The
analyzer is optimized for operating under this condition (see 4.2.3, pt. 3).
The basic version of the CLD 780 TR does not include an internal pressure
regulator for the ozone generator oxygen supply. This option is however
recommended for optimal performance (see section 3.3 in Appendix 4).
It is of course still perfectly feasible to operate the ozone generator with
ambient air. However, the supply air must be dry. For stable ozone pro-
duction the dew point should be -20 °C (corresponding to < 1000 ppmv
H2O). Each CLD 780 TR is shipped with three silica gel cartridges as stan-
dard, one of which is for drying the ozone generator supply air (see Fig.
4.2). The cartridge contents must be renewed or regenerated periodically
(see chap. 9).