ABB AnalyzeIT 8237 User manual

AnalyzeIT
Carbon Dioxide Monitor
8237
Instruction Manual
IM/8237_4

Health and Safety
To ensure that our products are safe and without risk to health, the following points must be noted:
1. The relevant sections of these instructions must be read carefully before proceeding.
2. Warning labels on containers and packages must be observed.
3. Installation, operation, maintenance and servicing must only be carried out by suitably trained personnel and in accordance with the
information given.
4. Normal safety precautions must be taken to avoid the possibility of an accident occurring when operating in conditions of high pressure
and/or temperature.
5. Chemicalsmustbestoredawayfromheat,protectedfromtemperatureextremesandpowderskeptdry.Normalsafehandlingprocedures
must be used.
6. When disposing of chemicals ensure that no two chemicals are mixed.
Safety advice concerning the use of the equipment described in this manual or any relevant hazard data sheets (where applicable) may be
obtained from the Company address on the back cover, together with servicing and spares information.
ABB
The Company
We are an established world force in the design and manufacture of instrumentation for
industrial process control, flow measurement, gas and liquid analysis and environmental
applications.
As a part of ABB, a world leader in process automation technology, we offer customers
application expertise, service and support worldwide.
We are committed to teamwork, high quality manufacturing, advanced technology and
unrivalled service and support.
The quality, accuracy and performance of the Company’s products result from over 100 years
experience, combined with a continuous program of innovative design and development to
incorporate the latest technology.
The UKAS Calibration Laboratory No. 0255 is just one of the ten flow calibration plants
operated by the Company and is indicative of our dedication to quality and accuracy.
EN ISO 9001:2000
Cert. No. Q 05907
R
E
G
I
S
T
E
R
E
D
EN 29001 (ISO 9001)
Lenno, Italy – Cert. No. 9/90A
0255
Stonehouse, U.K.
Warning – Refer to the manual for instructions
Caution – Risk of electric shock
Protective earth (ground) terminal
Earth (ground) terminal
Direct current supply only
Alternating current supply only
Both direct and alternating current supply
The equipment is protected
through double insulation
Electrical Safety
This equipment complies with the requirements of CEI/IEC 61010-1:1993 "Safety requirements for electrical equipment for
measurement, control, and laboratory use". If the instrument is used in a manner NOT specified by the Company, the protection
provided by the instrument may be impaired.
Symbols
One or more of the following symbols may appear on the equipment labelling:
Information in this manual is intended only to assist our customers in the efficient operation of our equipment. Use of this manual
for any other purpose is specifically prohibited and its contents are not to be reproduced in full or part without prior approval of the
Technical Publications Department.

CONTENTS
1 INTRODUCTION .............................................................. 2
1.1 Description ........................................................... 2
1.2 Training ................................................................. 2
1.3 Location and Function of Main Components ........ 2
2 INSTALLATION ................................................................ 3
2.1 Accessories .......................................................... 3
2.2 Location ................................................................ 3
2.3 Mounting ............................................................... 3
2.4 Sampling Requirement ......................................... 3
2.5 Sample Connections ............................................ 3
2.6 Connections, General ........................................... 4
2.7 External Electrical Connections ............................ 5
2.8 Relay Contact Protection and Interference
Suppression ....................................................... 6
3SETTING UP .................................................................... 8
4LIQUID HANDLING SECTION ........................................ 8
4.1 Principle of Operation ........................................... 8
4.2 General Operation ................................................ 8
5ELECTRONICS SECTION ............................................. 10
5.1 Electronic Layout ................................................ 10
5.2 User Junction Box .............................................. 10
5.3 Microprocessor Unit ........................................... 10
5.4 Front Panel Controls .......................................... 10
5.5 Displays .............................................................. 11
5.6 L.E.D. Indication ................................................. 11
6 PROGRAMMING ........................................................... 12
6.1 Normal Operation ............................................... 13
6.2 Programming Pages ........................................... 13
6.2.1 Operating Page 1 ................................ 14
6.2.2 Operating Page 2 ................................ 15
6.2.3 Security Code Page ............................ 16
6.2.4 Set Up Input Page ............................... 17
6.2.5 Current Output Page ........................... 18
6.2.6 Set Up Alarms Page ............................ 21
6.2.7 Set Up Clock Page .............................. 23
6.2.8 Calibration User Code Page ............... 26
6.2.9 Set Up Temperature Control Page ...... 27
6.2.10 Electrical Calibration ......................... 27
6.2.11 Electrical Calibration Page ................ 28
7 CALIBRATION ............................................................... 31
7.1 Calibration Sequence ......................................... 31
8 MAINTENANCE................................................................ 32
8.1 Chemical Solutions ............................................. 32
8.1.1 Reagent Solution 0.75M
Sulphuric Acid .................................... 32
8.1.2 Standard Solutions .............................. 32
8.1.3 Probe Filling Solution .......................... 32
8.2 Scheduled Servicing ........................................... 33
8.2.1 Regular Visual Checks ........................ 33
8.2.2 Four Weekly......................................... 33
8.2.3 Twelve Monthly .................................... 33
8.2.4 Consumables Spares Kit ..................... 34
8.2.5 Probe Assembly ................................... 34
8.2.6 Fitting the Probe .................................. 35
8.2.7 Peristaltic Pump .................................. 36
8.2.8 Replacement of Plumbing Tubing ....... 36
8.3 Shutdown Procedure .......................................... 37
8.3.1 Short Term ........................................... 37
8.3.2 Long Term ............................................ 37
8.4 Unscheduled Servicing ....................................... 37
8.4.1 Malfunction of the Monitor ................... 37
8.4.2 Monitor Diagnostic Information ........... 37
8.4.3 Malfunction of the Probe ..................... 38
8.5 Microprocessor Unit Error Messages ................. 39
8.6 Procedure for Chloridising
the Reference Element .................................... 39
9 SPECIFICATION ............................................................ 40
10 SPARES ....................................................................... 41
APPENDIX A – REPLACING SOFTWARE EPROM ........... 43
A.1 Access the Transmitter Unit ............................... 43
A.2 Access the PCB ................................................. 43
A.3 Removing the PCB ............................................ 44
A.4 Changing the EPROM ....................................... 44
A.5 Completing the Procedure ................................. 44

2
Carbon Dioxide 8237
Standard
Solution
Containers
Constant Head Unit
(behind case)
with Sample Inlet and
Drain Connections
Peristaltic
Pump
Case Lock
Temperature
Controlled Block
Probe and Temperature
Sensors
(cover removed)
Cable Entry Glands
Case Lock
Microprocessor
Unit
Hinged Case
Solenoid Valves
(behind case) User Junction Box
(behind case)
Hinged Door
Push-to-Release
Latch
Guard Tubes
(behind case)
1INTRODUCTION
1.1 Description
The Model 8237 Carbon Dioxide Monitor is a microprocessor
based analyser using a gas sensing membrane probe to monitor
the level of CO2in cooling water samples in AGR Nuclear Power
Stations.
1.2 Training
Due to the specialised nature of the above instrument, it is
recommended that, where the end users personnel have had no
previous experience of maintaining this equipment, training be
provided by this Company.
Such training is available via the local Company in the UK, or
Overseas Agent elsewhere and may be carried out either on the
users premises or at the factory.
1.3 Location and Function of Main Components –
Fig. 1.1
Monitoring of carbon dioxide involves the addition of an acid
reagent to liberate bicarbonate ions in the sample as carbon
dioxide gas. The gas sensing probe responds to the partial
pressure and hence the concentration of carbon dioxide gas.
The 8237 carbon dioxide monitor has a liquid handling section in
the lower half of a moulded plastic enclosure, and the electronics
section in the upper portion.
Sample inlet and drain connections are at the base of the
instrument. A peristaltic pump, mounted centrally, proportions
sample and reagent through a mixing and reaction coil to a flow-
through cap at the end of a gas sensing probe where the
measurement takes place.
To maintain optimum measurement accuracy, it is necessary to
carry out two point calibration by introducing 'low' and 'high'
standard solutions of known concentration. The 8237 monitor
uses solenoid valves to introduce these solutions automatically at
programmable intervals under the control of the microprocessor.
Access to the probe, pump and calibration solution containers is
by means of a hinged acrylic door, which is held open or closed by
use of a push/push latch. The instrument case is also hinged to
allow access to the electronics section, guard tubes and solenoid
valves etc. for maintenance.
The electronics section consists of a microprocessor unit situated
at the top left which controls the instrument functions, and a user
junction box for all external electrical connections, at the top right
behind the hinged case.
Fig. 1.1 Location of Instrument Components

3
All dimensions in mm
Junction
Box
60 Top of Case
30
Sample Inlet
& Drain
Tubes
110mm minimum clearance
required for accessto locks
Fixing Centres
Moulded Case
Shown in
Open Position
780
Fixing
Centres
278
482
220
Cable
Entry
Point
188
890
Open
Position
95Max.
angle of
opening
542
235
550
Closed
Position
8mm Keyhole
Slot
8mm Fixing
Holes
Top View
Edge of
Case
All dimensions in mm
2.1 Accessories
1 x reagent bottle
4 x calibration bottles
1 x 8237 probe kit
1 x spares kit
2.2 Location
The monitor should be installed in a clean, dry, well ventilated and
vibration-free location giving easy access, and where short
sample lines can be used. Rooms containing corrosive gases or
vapours (e.g., chlorination equipment or chlorine gas cylinders)
should be avoided. It is also advisable to have adjacent drains
near ground level, so that the waste outlet from the monitor can be
as short as possible, together with maximum fall. Power supplies
should also be adjacent. Ambient temperature: within the range 5
to 40°C.
2.3 Mounting – Fig. 2.1
The monitor has a moulded plastic case, mounted onto a flat
metal panel. To provide access, the case is hinged on the left
hand side and has two lockable catches on the right hand side to
hold the case in position in normal operation.
One keyhole slot is provided at the top of the flat panel to provide
easy mounting on a wall or framework. Two further fixing holes
are provided at the bottom of the flat panel. All holes are designed
to take 8mm bolts or studs.
Mains and signal cables are connected through cable glands in
the User Junction Box on the right hand side with the exception of
the optional serial interface which connects directly into the
Microprocessor Unit. Sample and drain pipework are brought in
through the bottom of the case.
2.4 Sampling Requirement
In addition to being as close as possible to the monitor, the
sampling point must provide a thoroughly mixed representative
sample. The sample must also conform to the following
conditions:
a) Sample flowrates must be between 5ml min–1 and
1250ml min–1.
b) Sample temperature should be within 20°C of the ambient
temperature and within the range 0 to 40°C.
c) Particles must be less than 10mgl–1 and the size must not
exceed 60 µm. Above these levels it is essential that the filter
supplied is fitted in both the sample and emergency inlets.
2.5 Sample Connections – Fig. 2.2
The inlet and outlet pipe connections are both located at the
bottom of the case. A 6mm (1/4in) hose adaptor is provided for the
sample inlet and a 9mm (3/8in) hose connection for the drain. The
inlet pipe must be of an inert, low gas permeability material such
as flexible p.v.c. (NOT silicone rubber), whereas the outlet pipes
may be of any flexible, inert material. The inlet pipe must
incorporate a shut-off valve at its upstream end, while the drain
outlet pipe should be short, venting to atmosphere as soon as
possible.
Fig. 2.1 Overall Dimensions and Mounting Details
2INSTALLATION

4
2.6 Connections, General
Warnings.
•Adisconnecting device such as a switch or circuit breaker conforming to local safety standards must be fitted to the final
installation. It must be fitted in close proximity to the instrument within easy reach of the operator and must be marked clearly
as the disconnection device for the instrument.
•Although certain instruments are fitted with internal fuse protection, a suitably rated external protection device, e.g. a 3A fuse
or miniature circuit breaker (m.c.b.), must also be fitted by the installer.
•Remove all power from supply, relay and any powered control circuits and high common mode voltages before accessing
or making any connections.
•The power supply earth (ground) must be connected to ensure safety to personnel, reduction of the effects of RFI
interference and correct operation of the power supply interference filter.
•The power supply earth (ground) must be connected to the earth (ground) stud on the junction box case – see Fig. 2.3.
•Use cable appropriate for the load currents. The terminals accept cables up to 14AWG (2.5mm2).
•The instrument conforms to Mains Power Input Insulation Category III. All other inputs and outputs conform to Category II.
•All connections to secondary circuits must have basic insulation.
•After installation, there must be no access to live parts, e.g. terminals.
•Terminals for external circuits are for use only with equipment with no accessible live parts.
•The relay contacts are voltage-free and must be appropriately connected in series with the power supply and the alarm/
control device which they are to actuate. Ensure that the contact rating is not exceeded. Refer also to Section 2.8 for relay
contact protection details when the relays are to be used for switching loads.
•Do not exceed the maximum load specification for the selected analog output range.
The analog output is isolated, therefore the –ve terminal must be connected to earth (ground) if connecting to the isolated
input of another device.
•If the instrument is used in a manner not specified by the Company, the protection provided by the equipment may be
impaired.
•All equipment connected to the instrument's terminals must comply with local safety standards (IEC 60950, EN61010-1).
Notes.
•An earthing (grounding) – stud terminal is fitted to the junction box case for bus-bar earth (ground) connection – see Fig. 2.3.
•Always route signal output and mains-carrying/relay cables separately, ideally in earthed (grounded) metal conduit. Use
twisted pair output leads or screened cable with the screen connected to the case earth (ground) stud.
Ensure that the cables enter the analyzer through the glands nearest the appropriate screw terminals and are short and
direct. Do not tuck excess cable into the terminal compartment.
•Ensure that the IP65 rating is not compromised when using cable glands, conduit fittings and blanking plugs/bungs (M20
holes). The M20 glands accept cable of between 5 and 9mm (0.2 and 0.35 in.) diameter.
…2 INSTALLATION

5
Sample Inlet Pipe
(6 mm i.d.)
Drain Tundish
Contaminated-Drain Pipe
(9 mm i.d.)
Tube wall fixing clips
150 mm
(approximate)
Monitor Case
Case Hinge Line
Push-on Hose Connectors
Constant-head Unit
250 mm (approximate) length
tubing
to allow the case
to open through 90
Overflow
Drain
Note. Sample pipework should
be of flexible PVC.
2INSTALLATION…
2.7 External Electrical Connections – Fig. 2.3
The external electrical connections are to be found in the User
Junction Box with the exception of the optional serial interface
which is connected directly into the Microprocessor Unit. The
cables are passed through the cable glands on the right hand side
of the junction box which are adjacent to the internal electrical
terminals.
Caution. Slacken the terminal screws fully before making
connections.
The connections are as follows:
a) Mains input 115V (110 to 120V) or 230V (220 to 240V). The
mains voltage is selected by means of the voltage selector –
see Fig. 2.3.
b) Current outputs 1 and 2 – two independent current outputs for
external recording or control. One output is supplied as
standard, the second is supplied as an optional extra – see
Fig. 2.4 for details regarding current output range.
Information. Because the current output is isolated, the
negative terminal must be connected to earth (ground) if
connecting to the isolated input of another device.
c) Relay 1 and 2 – two concentration alarms.
d) Relay 3 – calibration mode indication. This indicates when the
instrument is off line during a calibration.
e) Relay 4 – instrument 'OUT OF SERVICE' indication. This
indicates that the monitor readings are suspect and it is in
need of attention.
f) Relay 5 – 'OUT OF SAMPLE' – indication of loss of sample.
g) Optional serial interface – connected into the Micro-
processor Unit. See supplementary instruction manual for
details
Fig. 2.2 Sample Connections
Note. It is essential that all
sample pipework to the
monitor is kept as short as
possible to reduce the effects
on the sample due to the
presense of algæ which can
build up. This problem is
particularly acute in the
pipework between the filter
and the monitor because of
the small sample flow. Small
bore tubing is essential, e.g.
6 mm i.d.

6
L
N
N/C
C
N/O
N/C
C
N/O
N/C
C
N/O
N/C
C
N/O
N/C
C
N/O
+
-
+
-
RELAY
1
RELAY
2
CAL
OUT
OF
SERVICE
OUT
OF
SAMPLE
O/P 1
O/P 2
MAINS
INPUT
STD1 STD2
HEATER
230V
Mains Voltage Selector
110V to120V 220V to 240V
User
Cable
Entry
Glands
External
User
Connection
Terminals
Interconnection Cable from/to
Microprocessor Unit and Instrument
Components (wet section)
Internal
Interconnection
Cable Terminals
Solenoid Valves
and Heater
Indicators
Relay
Board
Mains
Transformer
Mains Fuse –
1A, 250V AC (T)
Cable Gland
MAINS
MAINS
F1 250V 1A (T)
PUMP
Mains 'ON'
Indicator
Mains
ON / OFF
Switch
Pump
ON / OFF
Switch
OFF
ON
OFF
ON
230V Position
220V min. to 240V max. AC
50/60Hz
115V Position
110V min. to 120V max. AC
50/60Hz
F2 5A 250V AC (F)
F3 0.5A 250V AC (T)
…2 INSTALLATION
2.8 Relay Contact Protection and Interference
Suppression – Fig. 2.5
If the relays are used to switch loads on or off the relay contacts
can become eroded due to arcing. Arcing also produces radio
frequency interference (r.f.i.) which can cause instrument
malfunctions and incorrect readings. To minimize the effects of
r.f.i., arc suppression components are required; these are
resistor/capacitor networks for a.c. applications, or diodes for d.c.
applications. These components can be connected either across
the load or directly across the relay contacts.
For a.c. applications the value of the resistor/capacitor network
depends on the load current and inductance that is switched.
Initially fit a 100R/0.022µF RC suppressor unit (part no. B9303)
as shown in Fig. 2.5A. If the instrument malfunctions the value of
the RC network is too low for suppression and an alternative
value must be used. If the correct RC suppressor unit cannot be
obtained, contact the manufacturer of the switched device for
details of the RC unit required.
For d.c. applications fit a diode as shown in Fig. 2.5B. For
general applications use an alternative IN5406 type (600V peak
inverse voltage at 3A – part no. B7363).
Note. For reliable switching the minimum voltage must be
greater than 12V and the minimum current greater than
100mA.
Fig. 2.3 Location of User Junction Box Components
Note. The mains and pump ON/OFF
switches are situated on the right
hand side of the junction box.
Caution. The AC power supply
ground cable must be connected to
the earth (ground) stud .
Caution. The protective
earth must be connected
to terminal 16.

7
Output
Module 1
Link for the Current
Output required
Output
Module 2
(if fitted)
Temperature Input
Module
Input Module
Protection
Plate
Captive
Screws
0 to 1mA 0 to 10mA 0 to 20mA 4 to 20mA
18181818
NC C NO
External
DC Supply
+–
Relay Contacts
Load
Diode
NC C NO
External
AC Supply
LN
Relay Contacts
C
R
Load
A – AC Applications
B – DC Applications
2INSTALLATION
Fig. 2.4 Selecting The Current Output Range
Fig. 2.5 Relay Contact Protection

8
Note. Before proceeding any further, ensure that all switches
are set to OFF on the right hand side of the electronics unit –
see Fig. 2.3.
a) Ensure that all external electrical and plumbing connections
have been made correctly.
b) Fill the guard tubes with soda lime crystals (self-indicating).
The guard tubes clip onto the rear face of the enclosure and
breather tubes pass through grommeted holes and then to
the standard solution bottles.
c) Fill reagent and standard solution bottles and connect them
the the monitor. (See Section 8.1 for details of these
solutions.)
d) Assemble and fit the probe according to the instructions in
Sections 8.2.5 and 8.2.6.
e) Connect the electrical supply and switch on.
Note. The temperature controlled block requires up to half an
hour to reach the normal control temperature. During this
time, 'Temp. Control Error' is indicated on the display. Any
calibrations are prevented by the microprocessor during this
time.
f) Verify that there is an adequate supply of sample to the
monitor constant head unit.
g) Fit the pump platen on the peristaltic pumps (see Section
8.2.7) and switch the pumps on with the switch on the side of
the monitor. Note that the peristaltic pumps rotate, and check
that sample and reagents are being drawn into the monitor by
observing the progress of any small bubbles present in the
inlet tubes.
h) Run the monitor for at least one hour to allow the temperature
to stabilize, solutions to be pumped into the system and to
purge the air from the pipework. Check for any leaks around
the pipe connections and rectify as necessary.
i) If the monitor exhibits good stability, i.e. ±2% of reading, carry
out a calibration – see Programming Page.
j) Check the condition of the sample filter and replace it if
necessary. Ensure that new filters are fitted correctly by taking
note of the flow directions indicated on the filter bodies.
4.1 Principle of Operation
Neither bicarbonate ion content nor total carbon dioxide can
be measured directly in an untreated sample, since the probe
can respond only to free carbon dioxide gas. The bicarbonate
ions must therefore be converted to free carbon dioxide by
adjusting the pH of the sample solution to a value less than
3.4. This is effected by addition of a sulphuric acid solution to
the sample before it is presented to the probe.
The gas sensing probe in the 8237 Monitor contains a glass
pH electrode whose pH sensitive glass membrane forms a
slightly convex tip and a robust long-life reference electrode.
The two electrodes are combined into a single assembly and
are connected as a pH measuring pair through an internal
reservoir of filling solution containing bicarbonate ions.
The filling solution is 0.05M sodium bicarbonate saturated with
sodium chloride and is separated from the sample by a
gas-permeable hydrophobic membrane fitted in the tip of the
probe. Sample is caused to flow past the probe membrane,
whereupon the partial pressures of carbon dioxide gas in the
two solutions on either side of the membrane equilibrate,
transferring gas across the membrane.
At equilibrium, the concentration of carbon dioxide in the thin
film of filling solution between the probe membrane and the
glass electrode membrane equals that in the sample. The
resultant change in pH value of the thin film is measured by the
pH electrode pair which thus develops an output potential
related to the carbon dioxide concentration in the sample. Like
most ion-selective electrodes, the 8237 Probe produces an
output which is logarithmic with respect to concentration.
Under typical circumstances, with appropriate standard
solutions and calibration frequencies, accuracies better than
±5% of reading or 0.1mgl–1 whichever is the greater, can be
achieved.
4.2 General Operation – Fig. 4.1
The sequence of events is:
a) The sample enters the constant head unit from below and any
excess is allowed to overflow to drain.
The constant head unit is fitted with a float switch to signal an
'Out of Sample' condition. This switch is used by the monitor to
initiate the 'Out of Sample' alarm.
b) From the bottom of the constant head unit the sample is
drawn through the normally open ports of the solenoid valves
SV1 and SV2 by one channel of the peristaltic pump.
c) The sulfuric acid reagent is drawn through another channel of
the peristaltic pump, and is then mixed with the sample. The
tube diameters are arranged so as to obtain the correct ratio
of sample and reagent.
d) The acidified sample is allowed to react under constant
temperature conditions to release free carbon dioxide gas.
e) The sample then enters a flow-through cap at the end of the
gas sensing probe where the measurement takes place.
3SETTING UP 4LIQUID HANDLING SECTION

9
Sample
Inlet
Two Channel
Peristaltic Pump
To Electronics Section
Drain via
Constant
Head Unit
Heat Exchanger
Block
Sample
Heater Coil
Probe
Sample / Calibrate
Solenoid Valves
Standard
Solution 1
(Low)
Reaction
Coil
Constant Head Unit Heater
Mat
Standard
Solution 2
(High)
Reagent
Solution
Red
Channel
Red
Channel
SV1 SV2
Overflow
Drain
Contaminated
Drain
Out of Sample
Float Switch
From
Flowcell
Guard
Tubes
4LIQUID HANDLING SECTION
f) The sample then flows to waste via the contaminated drain connection.
g) During a calibration, the monitor introduces two calibration solutions sequentially in place of the sample by means of the solenoid
valves SV1 and SV2.
To provide remote indication of a calibration in progress, the calibration relay is activated.
Fig. 4.1 Flow Schematic

10
Flow Cell
Heater Block
Heater
Control
Microprocessor Unit User Junction
Box
Mains Supply – see Fig. 2.3
Concentration Alarm Relays
Calibration Mode Relay
Out of Service Relay
Current Outputs
Out of Sample Relay
External
User
Connections
External
Serial
Interface
Connections
Reference
Electrode
Ion-Selective
Electrode Sample/Calibrate
Soleniod Valves
Interconnection
Cables
Out of Sample
Float Switch
Pump and
Stirrer Motors
Liquid Handling
Section
Protective Earth
5ELECTRONICS SECTION
5.1 Electronic Layout – Fig. 5.1
The electronic section comprises two separate sections:
•The User Junction Box at the top right hand side.
•The Microprocessor Unit at the top left hand side.
5.2 User Junction Box
The User Junction Box contains the relays for the heater, solenoid
valves and alarms, and all the user external connection terminals,
with the exception of the serial interface (if fitted).
Once installed there should be no need to remove the junction
box cover on a regular basis. However, to assist in any fault
finding procedure, there are l.e.d.s on the p.c.b. to indicate if the
relays and heater are being energised.
Switches for the mains and pump/heater are situated on the right
hand side of the junction box, together with a mains indication
lamp and mains fuse – see Fig. 2.3.
Two additional fuses (F2 and F3) are located within the junction
box. These are connected in the 24V AC circuits.
5.3 Microprocessor Unit
The Microprocessor Unit contains the analogue input processing,
microprocessor, alarm and current output generation, and (if
fitted) the serial interface output.
The programme controls, digital and dot-matrix displays, alarm
indication and status l.e.d.s are all mounted on the front panel of
the microprocessor unit.
5.4 Front Panel Controls – Fig. 5.2
The programme controls comprise eight tactile membrane
switches. These switches are situated behind a hinged door
below the display, access is via a screwdriver-operated catch. In
normal operation the switches are used to view the measured ion
concentration value, initiate a manual calibration, or to activate
the 'alarm hold' facility.
When programming, the switches are used to sequence through
a programming procedure as detailed. The procedure is set out in
programming pages for Input, Current Output, Alarms, Real Time
Clock and Monitor Calibration. Each programme page contains
the programme functions, the values or parameters of which are
programmable.
Switch functions are as follows:
Mode
Used for viewing the CO2-concentration, electrode
mV output, block control temperature, sensor slope,
date, time, the day of the next calibration and the date
of the last calibration.
Cal
Used to enable or disable the automatic calibrations,
enter the standard solution values and manually
initiate a calibration sequence. Operating 'Cal' during
a calibration aborts the sequence and returns to
normal operation.
Hold
Used to inhibit any change in the alarm relay/l.e.d.
status and the start of any auto calibration. The feature
is used during maintenance ('Hold' l.e.d. illuminated).
Fig. 5.1 Electrical Connections Layout

11
Note. If the 'Hold' facility is inadvertently left
switched-in, it is automatically cancelled after a
period of approximately 3 hours has elapsed.
Enter
Used for storing the programmed function parameters
and values in the instrument's nonvolatile memory.
Note. The instrument responds instantly to any
programme change but the new value is lost in
the event of a power interruption if it has not
been 'Entered'.
Parameter Advance – used for selecting a particular
parameter from a programme page.
Used for increasing or decreasing a parameter value
or stepping up or down through a selection of
parameters applicable to a particular function.
Note. Continued pressure on the 'Raise' or
'Lower' switches causes the rate of change of
the displayed value to increase. To make small
adjustments, operate the switches momentarily.
Page Advance – used, via the security code, for
selection of individual programme pages.
5.5 Displays – Fig. 5.2
Two blue vacuum fluorescent displays are provided:
a) The upper is a 5-digit 7-segment type display which indicates
the measured variable.
b) The lower is a 20-character dot matrix type which provides
user information during setting up and in normal operation.
5.6 L.E.D. Indication – Fig. 5.2
There are 5 l.e.d.s (indicators situated between the two displays)
which provide information on the current status of the monitor.
From left to right the indicators are as follows:
A1 or A2
Used to indicate a concentration alarm state (either
high or low). This indicator is used in association with
an external alarm relay output.
Hold
Used to indicate that the 'Hold' button has been
operated.
Cal
Indicates when a calibration sequence is taking place.
Fail
Indicates that the monitor was unable to carry out a
successful calibration.
5-digit Display
(Concentration)
Alarms Hold Cal Fail
12
Hold
Cal EnterMode
20-character
Dot-Matrix Display
Alarm and Status
L.E.D.s
Connections
Cover
5 ELECTRONICS SECTION
Fig. 5.2 Location of Controls, Displays and L.E.D.s

12
Note 1. 'Cal Date' is the date when the first calibration is due and is updated every time an automatic calibration is carried out, i.e 'Cal Date' = autocal date + 'Cal Interval' Note 2. 'Cal Time' is the time of the day when the autocalibration is required. Note 3. Operating during a calibration aborts the sequence and returns the system to normal operation. 'Next AutCal' is the date of the last automatic calibration + the calibration interval 'Cal interval'. If the instrument has been switched off, the next 'AutCal' is the present date + the 'Cal interval'. If the 'AutCal' is switched off, 'OFF' is displayed on the 20-character display. Note 4.
'Last Cal' is the date of the last automatic or manual calibration.
Carbon dioxide <unit> Millivolts Control Temp Slope Date Time Next AutCal Last Cal
SECURITY CODE 0 SET UP INPUT
Control Temp.
Ion Units
SET UP TEMP. CONTROL Cycle Time Prop. Band Integral Time
CAL USER CODE 0
CURRENT OUTPUT OP1 Cal Hold Op1 Law. OP1 FSD OP1 Zero OP2 Cal Hold OP2 Law OP2 FSD OP2 Zero Test Output Zeros
Test Output FSD
Alter Sec. Code % Output
SET UP ALARMS A1 Enabled A1 Action A1 Failsafe A1 Hysteresis A1 Delay A1 Setpoint A2 Enabled A2 Action A2 Failsafe A2 Hysteresis A2 Delay A2 Setpoint
SET UP CLOCK Set Clock? Set Year Set Month Set Day of Month Set Hours Set Minutes Cal Date Cal Time Cal Interval
CALIBRATION mV Zero mV FSD Temp. Zero Temp. FSD Adjust Output 1 Zero Adjust Output 1 FSD Adjust Output 2 Zero Adjust Output 2 FSD Cal Time 1 Cal Time 2 Cal Time 3
Cal User Code
or
Note 4
Note 5
Lin
Lin
No
Incorrect
Code
Note 1 Note 2
Enable Auto Cals
MANUAL CAL SEQUENCE
Ion Std 1 Ion Std 2 Initiate Cal.
Calibrating Std 1 Calibrating Std 2
CALIBRATION PASSED CAL. FAILED (SLOPE) CAL. FAILED (SLOW)
Electrode mV Electrode mV
No
or or
xx.xC
DD:MM:YY HH:MM:SS
xxx.x%
(Units)
– –
•
–C(Yes/No)
(Log/Lin)
•
–
•
– –
(Yes/No)
(Log/Lin)
–
•
– –
0
– – –
•
–
(Yes/No) (Yes/No)
(High/Low)
– %
– – m
(Yes/No) (Yes/No)
– –
•
– –
(High/Low)
– %
– – m
(Yes/No)
– – – – – – – – – – – – – –
– Days
(Y/N)
(Yes/No)
– –
– – –
– – – –
– –
•
–
– –
•
–C
– – –C
– –m – –m – –m
0
DD:MM:YY DD:MM:YY
No No
Operating Page 1
Operating Page 2
Mode
Cal
– – – –
•
– – – –
– – – –
•
– –
•
–
•
–
•
– –
– – – –
•
– – –
•
– – –
•
Incorrect Code
Note 5.
Cal
xx.xmV
Calibration Std 1
Calibrating Std 2
Cal
Cal
*
*
See Note 3
6PROGRAMMING
Fig. 6.1 Overall Programming Chart

13
6PROGRAMMING…
6.1 Normal Operation
In normal operation (Operating Page 1) the lower, dot matrix,
display gives indication of the units of measurement, millivolt
value, sensor slope and time. Selection is made using the
switch. Operation of the
Cal
switch gives access to a second
Operating Page (Operating Page 2) in which the standard
solution values can be set and a manual calibration can be
initiated. Either page can be selected at any time by using the
Mode
or
Cal
switches.
6.2 Programming Pages
Operation of the switch enables a series of 'programming'
pages to be displayed. Unauthorised entries to this page are
inhibited by a 5-digit security code which is displayed immediately
after the page header.
In the programming pages, displayed values indicated 'xxxxx' are
for viewing only and cannot be altered by the operator. Displayed
values indicated '– – –' can be altered using the and
switches. When the desired reading is displayed, operate the
Enter
switch. The l.e.d.s flash momentarily, to indicate that the value
has been stored in the nonvolatile memory. Although the
instrument operates satisfactorily if the
Enter
switch is not
operated, in the event of power interruption, the new values are
lost. When power is reapplied, the previously 'entered' values are
restored. If previously programmed values are to be viewed only,
it is unnecessary to operate the
Enter
switch.

14
Advance to next parameter.
The heater block control temperature is displayed in degrees Celsius.
Control Temperature
Carbon Dioxide <Unit>
The values displayed in Operating Page 1 are for viewing only and cannot be altered in this page.
Millivolts
Control Temp
The sensor output is displayed in millivolts.
Measurement Units
The measurement units are displayed, e.g. Carbon dioxide mgl
-1
.
Sensor Output
Advance to next parameter.
The slope value should be between 70 and 110%. If the value is outside these limits
check the electrode.
Slope Check ValueSlope
Advance to next parameter.
The date is displayed.
DateDate
Advance to next parameter.
The time is displayed.
Time
Advance to next parameter.
Time
The date when the next automatic calibration is to be carried out is displayed. If the
automatic calibration is disabled, 'OFF' is displayed in place of the date.
Next Calibration Date
Advance to next parameter.
Next AutCal
The date of the last automatic or manual calibration is displayed.
Last Calibration Date
Advance to next parameter.
Last Cal
Return to top of Operating Page.
Advance to Security Page (Section 6.2.3).
SECURITY CODE -----
or or
x x • xmV
x x
•
x C
x x x
•
x %
DD: MM:YY
HH :MM:SS
DD: MM:YY
DD: MM:YY
or
Mode
or
Mode
or
Mode
or
Mode
or
Mode
or
Mode
or
Mode
or
Mode
…6 PROGRAMMING
6.2.1 Operating Page 1

15
Set the value of the 'Low' standard solution (Std 1).
Because of the instability of such solutions, low value carbon dioxide standard
solutions should be avoided. It is not possible to programme a carbon dioxide
standard solution of lower concentration than 4mg l
–1
CO2on the Model 8237
monitor. Lower concentrations of CO2solutions can be prepared with care, but are
of uncertain stability when stored in plastic bottles even with guard tube protection
from atmospheric CO2, making them unsuitable for long term use with the monitor.
No
Advance to next parameter.
Ion Standard 1
Store.
Enable Auto Cals Yes
No
To gain access to the Calibration Page (Operating Page 2), operate the switch.
MANUAL CAL SEQUENCE
Page header.
Ion Std 1
or
Advance to next parameter.
Ion Standard 2
Ion Std 2
or Set the value of the 'High' standard solution (Std 2). The concentrations of the two
standard solutions must differ from each other by a factor of at least four.
Initiate Cal Yes
Enable Automatic Calibrations
Select 'Yes' to enable or 'No' to disable the automatic calibrations.
Initiate Calibration (manual)
Enter must be pressed to initiate a manual calibration.
Select 'Yes' to carry out a manual calibration or 'No' to return to the top of the page.
No
Yes
Calibrating Std 1
Electrode mV
The sensor output can also be displayed during calibration
Toggle between the two displays.
Calibrating Standard 1
The upper display shows the CO2concentration value. The display remains until
a stable output is obtained from the sensor.
Electrode Millivolts
Note. Pressing during a calibration aborts the sequence and returns to normal
operation.
When a stable sensor output is detected the display automatically advances to the
next parameter.
Continued on next page.
–
•
– –
Advance to next parameter.
Store.
Advance to next parameter.
Store.
Enter
Cal
Cal
Enter
Cal
Enter
Cal
Enter
– –
•
– –
– –
•
–
or
or
Cal
Cal
Cal
6PROGRAMMING…
6.2.2 Operating Page 2

16
CALIBRATION PASSED
Calibration Passed
A satisfactory calibration has been carried out.
or
CAL FAILED (SLOPE)
Calibration Failed (slope)
or
or
or
CAL FAILED (SLOW)
Calibration Failed (slow)
Return to top of Operating Page 2.
or
Carbon Dioxide <Unit>
Return to Operating Page 1.
Mode
The monitor was unable to obtain an adequate slope value during calibration. The
slope value required is 70 to 110%.
The monitor was unable to obtain a stable output from the sensor during calibration.
Calibrating Std 2
Electrode mV – – •–
The sensor output can also be displayed during calibration
When a stable sensor output is detected the display automatically advances to the
next parameter.
Toggle between the two displays.
Calibrating Standard 2
The upper display shows the CO
2
concentration value. The display remains until
a stable output is obtained from the sensor.
Electrode Millivolts
Note. Pressing during a calibration aborts the sequence and returns to normal
operation.
Cal Cal
Incorrect code.
Security Code
A security code is required to gain access to all subsequent programming pages. The code is preset at the factory to '0' but can
be changed if required in the Current Output Page – see Section 6.2.5.
or Set the correct security code.
Advance to the first of the programming pages – Set Up Input Page.
SET UP INPUT
Security Code -----
Carbon Dioxide <Units> Return to Operating Page 1.
…6 PROGRAMMING
…6.2.2 Operating Page 2
6.2.3 Security Code Page

17
Enter
Advance to next parameter.
Control Temperature
SET UP INPUT
Control Temp
or Set the required block control temperature within the range 30 to 45C in 0.1C
increments
Ion Units mg/kg
mg/l
Page header.
Ion Units
Select the required display units for CO2concentration.
Store.
Advance to next parameter.
ppm
Store.
Return to top of Set Up Input Page.
Advance to Current Output Page.
CURRENT OUTPUT
or
––
•
–C
or
Enter
or
6PROGRAMMING…
6.2.4 Set Up Input Page

18
Log
Lin
Advance to next parameter.
Output 1 Calibration Hold
CURRENT OUTPUT
Current Output 1 can be held during calibration, if required. Select 'YES' or
'NO'.
OP1 FSD
Page header.
Output 1 Full Scale
Store.
Current Output 1 full scale range: 1 to 1000mgl–1 CO2, i.e. minimum span 1 decade.
Store.
Advance to next parameter.
OP1 Cal Hold
Current Output 1 can be either logarithmic or linear. Select 'Log' or 'Lin'.
Output 1 Law
OP1 Law
Store.
Advance to next parameter.
Advance to next parameter.
Output 1 Zero
OP1 Zero
Set the required concentration value for Current Output 1 zero. Default is 1/10 of
FSD.
Store.
Advance to next parameter.
The current output is assigned to the CO2concentration but is only operative if the relevant output modules are fitted – see
Fig. 2.4.
Yes
No
or Set the required concentration value for Current Output 1 full scale.
Lin
Log
Advance to next parameter.
Continued on next page.
––– • –
–•– –
or
or
Enter
Enter
Enter
or
Enter
Note. If the output 1 Law is linear (Lin), this parameter is omitted and the zero
current output is automatically set to '0'.
…6 PROGRAMMING
6.2.5 Current Output Page