YOKOGAWA PH200 User manual

IM 12B6C2-E-H
6th edition
Instruction
Manual Model PH200
2-wire pH transmitter
YOKOGAWA

FAIL
HOLD
MEASURE
AUT.CAL
MAN.CAL
DISPLAY
TEMP.
YES NO
ENT
OUTPUT
SET HOLD
SERVICE
*
NO MODEYES
>
ENT>
MODE
TEMP.MAN
HOLD
pH
mV
FAIL
HOLD
MEASURE
AUT.CAL
MAN.CAL
DISPLAY
TEMP.
YES NO
ENT
OUTPUT
SET HOLD
SERVICE
*
NO MODEYES
>
ENT>
MODE
TEMP.MAN
HOLD
pH
mV
OUTPUT HOLD
FLAG
MEASURED
VALUE DISPLAY
MESSAGE DISPLAY
KEY PROMPT FLAGS
SELECTION KEYS
YES : Accept setting
NO : Change to new setting
ADJUSTMENT KEYS
>: Choose digit for adjustment
^: Adjust digit (to decrease pass
through zero)
ENT : Enter new value
NOTE: The first digit changes from 1, -1, - to blank
SELECT MODE
MEASURE/MAINTENANCE
Can be used to escape program at any
time
MANUAL TEMPERATURE
COMPENSATION FLAG FAIL FLAG MENU POINTER FLAGS
MENU FOR MAINTE-
NANCE FUNCTIONS
(see chapter 5)
MENU FOR COMMIS-
SIONING FUNCTIONS
(see chapter 4)
SELECT MODE
MEASURE/COMMISSIONING
IM 12B6C2-E-H

IM 12B6C2-H-H
CONTENTS
1. INTRODUCTION ..................................................................1
1-1. Application......................................................................1
1-2. Required components for pH measurement...................1
1-3. Identification ...................................................................1
2. TECHNICAL SPECIFICATIONS...........................................2
2-1. General specifications.....................................................2
2-2. Functional description.....................................................3
3. INSTALLATION AND WIRING .............................................4
3-1. Installation and dimensions.............................................4
3-1-1. Installation site ...................................................4
3-1-2. Mounting methods.............................................4
3-2. Wiring of sensors............................................................6
3-2-1. General precautions...........................................6
3-2-2. Additional precautions for installations in
hazardous areas ................................................6
3-2-3. Liquid earth........................................................6
3-2-4. Access to terminal and cable entry....................6
3-2-5. Connection diagram for sensors........................7
3-3. Wiring of power supply...................................................8
3-3-1. General precautions...........................................8
3-3-2. Additional precautions for installations in
hazardous areas ................................................8
3-3-3. Connection of the power supply........................8
3-3-4. Switching the instrument on...............................8
4. COMMISSIONING..............................................................11
4-1. Operations overview .....................................................11
4-2. Output range adjustment.....................OUTPUT...........12
4-3. Set up the HOLD function ...................SET HOLD........14
4-4. Sensor selection and diagnostics..................................16
4-4-1. Selection of measurement and reference
electrode..........................................................16
4-4-2. Selecting a temperature sensor .......................16
4-4-3. Off-line calibration checks................................16
4-4-4. On-line impedance chacks ..............................16
5. MAINTENANCE..................................................................17
5-1. Automatic calibration...........................AUT.CAL...........18
5-2. Manual calibration ...............................MAN.CAL .........20
5-3. Selecting a value to display .................DISPLAY...........22
5-4. Temperature compensation.................TEMP ...............24
5-5. Hold output function.....................................................26
6. TROUBLE SHOOTING.......................................................28
6-1. Introduction ..................................................................28
6-2. Error messages and explanation...................................29

IM 12B6C2-E-H
7. SERVICE MODE.................................................................30
7-1. Introduction.................................................................30
7-2. Access to service settings...........................................31
7-3. Temperature function...................................................32
7-4. Temperature sensors...................................................32
7-5. Sensor checking..........................................................33
7-6. Display resolution ........................................................34
7-7. Signalling of fail condition ............................................34
7-8. Stabilization check.......................................................34
7-9. Auto return..................................................................35
7-10.Buffer tables................................................................35
7-11.Temperature adjustment..............................................36
7-12. Manual adjustment of ITP, slope and
asymmetry potential....................................................36
7-13. Passwordprotection by three digit code......................37
7-14. Restore default settings ..............................................37
8. CLASSIFICATION...............................................................38
8-1. Cenelec........................................................................38
8-2. FM................................................................................39
9. CHANGE FROM PH TO ORP MEASUREMENT ..............40
9-1. How to change from pH measurement to
ORP measurement.......................................................40
9-2. Commissioning the transmitter .....................................40
9-3. Maintenance of the transmitter .....................................40
9-4. Special features............................................................40
9-5. Wiring diagram .............................................................41
9-6. Buffer values.................................................................41
APPENDIX A............................................................................42

IM 12B6C2-E-H
1-1. Application
The EXA PH200 transmitter is a 2-wire pH
instrument intended to be used in industrial
installations in the field. For easy maintenan-
ce and operation it should be located close
to the sensors. It is powered from a remote
low voltage DC power supply through the 2-
wire connection. The EXA PH200 is compa-
tible with most commercial available pH sen-
sors and fitting systems.
The instrument is available in two versions:
- A general purpose version for use in safe
areas.
- An intrinsically safe version for use in
hazardous areas. The instrument can then
be installed in Zone 1 with the sensors in
Zone 1 or Zone 0.
The micro-processor is used in this instru-
ment for continuous sensor diagnostics,
flexible on site commissioning and fine tu-
ning by advanced functions.
In general a pH loop can be set up for diffe-
rent purposes:
- To be part of a total process control sys-
tem
- To indicate dangerous limits of a process.
- To monitor product quality.
1-2. Required components for pH
measurement
1. A pH electrode and a reference electrode
or a combined pH-reference electrode.
2. A temperature sensor Pt100 (according
to IEC 751 or DIN) or Pt1000
3. A fitting for the above electrodes with
accessories
4. Signal cables with or without extension
boxes, etc.
5. The EXA PH200 2-wire transmitter with
mounting accessories for wall or pipe
mounting
6. A DC power supply (nominal 24 V DC)
with cabling and optional zener barriers
or an intrinsic safe power supply
7. Peripherals: e.g. strip-chart recorder,
panel indicator, PID-controller.
1-3. Identification
The instrument has an identification label,
which is fixed to the front plate.
This serves as a reference for the full model
code, power supply voltage and serial num-
ber. This label also carries authorised marks
to certify compliance with the current regula-
tory norms.
1
1. INTRODUCTION
MODEL
SERIAL NO.
SUPPLY

2-1. General specifications
A. Intrinsic safety
– BASEEFA : Certified by and meets the require-
ments of EEx [ia] ib IIC T4 of CENE-
LEC
Certificate nr. : 89C2379)
– FM : For IS CL1, DIV1, GP ABCD
T3B for TA-30 to 70 °C
T4 for TA-30 to 40 °C
Approval report: J.I. 1Y1A7.AX
– CSA : For Ex[ia] Class 1, Div. 1, Groups C
and D, T4A
Approval file: LR 102851-1
B. Indicating range :-1 to +15 pH.
C. Transmission signal : 4 - 20 mA DC; max. load 550 Ω
D. Transmission range : 0 - 14 pH.
User programmable to any range
with a minimum span of 1 unit.
E. Power supply
– Model PH200G : 17 - 40 V DC,
dependent on load
– Model PH200S : 17 - 31,5 V DC,
dependent on load
F. Climatic conditions
– Ambient temperature : -10 to +55 °C
– Storage temperature : -30 to +70 °C
– Relative humidity : 10 to 90%
– Weather protection : Rain and dust-tight IP65 (NEMA 4X)
G. Housing
– Material : Cast aluminium with chemical resi-
stant coating
– Window : Flexible poly-carbonate
– Colours : Moss green/off-white
– Cable glands : Polyamide
– Cable entries : Two
h ” glands
Hose connection optional
– Earth connection : For external ground
H. Mounting possibilities
– Surface mounting : Two M6 bolts, 9 mm length
– Wall/Pipe mounting : With optional mounting kit
– Sunlight protection : With optional hood
– Panel mounting : 154 x 172 octagonal with
30 mm corners (fixing with self-tap-
ping screws
I. Shipping details
– Dimensions : 162 x 178 x 115 mm
– Package : 225 x 225 x 220 mm
– Weight : ca. 2,5 kg
J. Safety and security
– Data protection : EEPROM memory
– Interference test : According IEC 801
– Power down : No affect, reset to measurement
2. TECHNICAL SPECIFICATIONS
IM 12B6C2-E-H
2

IM 12B6C2-E-H
2-2. Functional description
The EXA PH200 is a real time micro-control-
ler operated pH analysing system. It uses a
dedicated micro-controller with exclusively
developed software to control all functions
necessary in such a system. The input and
output functions are concentrated in the
analogue section of the instrument. Even
these functions are operated through special
interfaces designed to give a minimum of
interference problems to the digital func-
tions. The digital and logic functions are
designed to operate securely. The unique
FAIL-function can give a warning when the
micro-controller has found a fault in the
measuring loop. This is accomplished by
sending a discrete 22 mA signal on the out-
put. The micro-controller checks the working
of the analogue to digital input converter cir-
cuit and watches over the conversion to the
output signals. By using non-volatile memory
(EEPROM) for the essential in formation the
operating parameters are fixed in memory
without the need for a battery. The software
is designed with the user in mind. It uses a
simple step by step, question and answer
style to communicate with the operator by
giving messages on the second line of the
display and indicating which keys are to be
pressed in the display too.
The user-interface is limited to a basic set of
6 keys accessible through the flexible win-
dow cover. The keys are scanned conti-
nuously and actions are taken immediately.
An extensive system of checking va lues and
parameters is implemented in the software .
The 2-wire design gives maximum flexibility
of operation with other industrial instruments
and controlling systems. An intrinsically safe
version is available for hazardous areas. The
rugged housing is designed for outdoor use
(IP65). In addition it is shaped in a way that
indoor panel mounting is also possible. The
optional universal mounting kit includes
brackets for all mounting methods. The
commissioning of the instrument can be
performed on site or in advance. A three
level operating system keeps the approach
clear and distinguishes between every day
operation and maintenance against one time
operations like commissioning or fine-tuning.
All this makes the EXA PH200 operate like a
normal analogue transmitter with a number
of additional functions.
These extra functions are only possible by
using a micro-controller at the heart of the
system:
• Sensor checking durig measurement (1)
• Simplified calibration through a semi-
automatic sequence.
• Additional process temperature compen-
sation can be activated.
• Simple range adaptation making it a ver-
satile instrument.
• Wide selection of temperature sensors.
• A HOLD-function for the output.
• Three buffer tables can be programmed.
• Programmable isothermal point of inter-
section.
• Protection against unauthorized access
by a passcode.
(1) European patent No. 0241601
US patent No. 4777444
3

3. INSTALLATION AND WIRING
IM 12B6C2-E-H
3-1. Installation and dimensions
3-1-1. Installation site
As the transmitter is a rain-tight type it can
be installed outdoors as well as indoors. It
should, however, be installed as close as
possible to the sensors avoiding long cable
lengths between sensors and transmitter.
The certified version can be installed in
Zone 1.
Select an installation site where:
- mechanical vibrations and shocks are
negligible;
- no relay/power switches are in the direct
environment;
- the transmitter is not mounted in direct
sunlight and severe weather conditions;
- maintenance activities are possible (no
corrosive atmospheres).
The ambient temperature and humidity
should be within the limits of the specifica-
tions .
3-1-2. Mounting methods
The EXA PH200 transmitter has universal
mounting possibilities:
- panel mounting using selftapping screws
- surface mounting on a plate (by bolts
from the back)
- wall mounting on a bracket (e.g. thick
brick wall);
- pipe mounting using a bracket on a hori-
zontal or vertical pipe (maximum diame-
ter 50 mm).
4
Panel mounting Surface mounting
DimensionsCut-outs for panel mounting
2 x M6 (Screws)
Unit: mm (“)Unit: mm (“)
154 (6.06`) 162 (6.4)
180 (7)
77
115 (4.5)
30 1.2)
30 (1.18)
172(6.77)
2x ø4
min. 203 (8)
min. 229 (9)

IM 12B6C2-E-H
5
Option /M: Universal wall/pipe mounting kit
Pipe mounting
(vertical) Pipe mounting
(horizontal)
2” Pipe 2” Pipe
Wall mounting
115
(4.53)
70 (2.75)
56 (2.2)
200
(7.87)
2x ø6.6
(0.26)
4x ø10
(0.4) 77 (3.03)

IM 12B6C2-E-H
3-2. Wiring of sensors
3-2-1. General precautions
Generally, transmission of signals from pH
sensors is at a very low voltage and high
impedance level. Thus a lot of care must be
taken to avoid interference. Before connec-
ting sensor cables to the transmitter make
sure that next conditions are met:
– the sensor cables are not mounted in
tracks together with high voltage and or
power switching cables
– only standard coaxial electrode cables or
extension cable are used
– the transmitter is mounted within the dis-
tance of the sensor cables (max. 10 m)
– the setup is kept flexible for easy inser-
tion and retraction of the sensors in the
fitting.
3-2-2. Additional precautions for instal-
lations in hazardous areas
Make sure that the total of capacitances and
inductances connected to the input termi-
nals of the EXA PH200 do not exceed the
limits given in the certificate.
This sets a limit to the cable and extensions
used.
– Grounding:
• If the sensors are mounted in a grounded
fitting, the external earth connection on
the left hand side of the transmitter must
be connected to "protective" earth.
•If the sensors are mounted in a fitting iso-
lated to ground, it is recommended (not
required) to connect the earth connection
on the left hand side of the transmitter to
"protective" earth.
– The intrinsic safe version of the EXA
PH200 instrument can be erected in
Zone 1.
– The sensors can be installed in Zone 0 or
Zone 1 if a safety barrier according to the
limits given in the system certificate is
used.
3-2-3. Liquid earth
In all circumstances, the sensor side of the
measuring loop must be grounded to the
measuring liquid. The EXA PH200 uses
advanced differential high impedance input
circuits. This technique calls for a grounding
to the liquid. In addition to that the sensor
checking circuits also use the liquid earth for
measurement of impedance of the sensors.
All Yokogawa fittings have provisions for this
connection. It is usually called liquid earth in
all our manuals.
A separate connection should be made to
the terminal numbered 14 in all cases to get
a proper and stable measuring loop.
3-2-4. Access to terminal and cable
entry
1. To access terminals remove the front
cover of the EXA PH200 by releasing the
4 captive screws.
2. Thread the sensor cables into the con-
nection space and connect the cables to
the terminals as indicated in the wiring
diagram. Make sure all connections are
firm and do not touch each other.
3. Screw the gland securely and tighten it to
keep out moisture. DO NOT use a
wrench to tighten the nut.
4. The optional hose connection is used to
guide the cables coming from an immer-
sion fitting through a protective plastic
tubing to the transmitter.
6

IM 12B6C2-E-H
7
3-2-5. Connection diagram for sensors
+-G 1112 14 13 1715 16
Rd Bl Rd Bl Rd Bl
+-G 1112 14 13 1715 16
Rd Bl Wt RdBl
+-G 1112 14 13 1715 16 +-G 11 12 14 13 1715 16
T1 T2 SE RE GE S
Rd=Red, Bl=Blue, Wt=White,
Single electrodes
Temperature Combined
Liquid earth
Temperature - Reference pH
Pt 100 AgCl glass
(Pt 1000) (other) (other)
EXA compact and retractable electrodes pH∑Combined electrode
Combined electrodes
Liquid earth
Connect the numbered cable leads to the
corresponding terminals

IM 12B6C2-E-H
3-3. Wiring of power supply
3-3-1. General precautions
Do not activate the power supply yet. First
make sure that the DC-power supply is
according to the specifications given.
WARNING: DO NOT USE ALTERNATING
CURRENT OR MAINS POWER SUPPLY! !
The cable leading to the distributor (power
supply) or safety barrier transports power to
and output signal from the transmitter. Use a
two conductor shielded cable with a size of
at least l.25 mm2and an outside diameter of
9 to 15 mm. The cable gland supplied with
the instrument accepts these diameters. The
maximum length of the cable is 2000 metre.
This ensures the minimum operating voltage
for the instrument.
3-3-2. Additional precautions for instal-
lation in hazardous areas
1. Ensure that the total of capacitances and
inductances connected to the terminals
of the EXA PH200 do not exceed the
limits given in the certificate of the safety
barrier or distributor.
2. The cable used should preferably have a
BLUE colour or marking on the outside.
3. Grounding:
• If the transmitter is mounted on a
grounded surface (e.g. a metal frame
fixed in the soil) the shield of the 2-wire
cable may NOT be connected to
ground at the distributor.
• If the transmitter is mounted on a non-
conducting surface (e.g. a brick wall) it
is recommended to ground the shield
of the 2-wire cable at the distributor
end.
4. Installation for EEx ia (sensors in Zone 0
or 1):
Generally, the distributor with input/out-
put isolation has no external earth con-
nection. If there is an earth connection on
the distributor and the external connec-
tion of the transmitter is connected to
"protective" earth, the shield of the 2-wire
cable may NOT be connected to "protec-
tive" earth at the distributor too.
3-3-3. Connection of the power supply
The terminal strip is accessed as was
described in § 3-2-4. Use the left-hand
gland to insert the 2-wire cable to the trans-
mitter. Connect the supply to the terminals
mar ked +, - and G as is indicated in the
figures on pages 9 & 10.
3-3-4. Switching the instrument on
After all connections are made and checked,
the power can be switched on from the dis-
tributor. Observe the correct activation of the
instrument at the display. If for any reason
the display does not indicate a value, con-
sult the trouble shooting section.
8

IM 12B6C2-E-H
Dependance of load to supply voltage
9
Wiring diagrams for power supply
General purpose design
pH-transmitter
EXA PH200G
Sensor
Distributor
Output
Supply
NOTE:
The outside earth terminal should be connected to site ground by a large area conductor (e.g. a flat earth strip) for
best protection against interference.
1200
1000
800
600
400
200
01718 20 24 40
Ohm
550
Supply voltage (V)
Load resistance (Ω)
+
–+ –
G

Wiring diagrams for hazardous areas
IM 12B6C2-E-H
10
Intrinsically safe design
(CELENEC standard EEX ib [ia] IIC T4)
pH-transmitter
EXA PH200S
Intrinsically safe design
(CELENEC standard EEX ib [ia] IIC T4)
pH-transmitter
EXA PH200S
EEx ib
Certified safety barrier
EEx ib
Certified distributor with
input/output isolation
Electronic current
limiting barrier
Vmax: 31.5 V
lmax: 35 mA
Pmax: 1,1 W
Zenerbarrier with
resistor
Vmax: 28 V
lmax: 93.3 mA
Pmax: 0.66 W
Shunt zener barrier or
supply unit or
isolated repeater
Vmax: 22 V
Imax: 85 mA
Sensor
Distributor
Output
Supply
Sensor
Output
Supply
Protective earthProtective earth
Protective earth
Hazardous area Safe area
Zone 0 or 1 Zone 1
Hazardous area Safe area
Zone 0 or 1 Zone 1
+
–+ –
G
+
–+
–
G

IM 12B6C2-E-H
4-1. Operations overview
NOTE: All 3 levels can be separately protected by a password (see §7-13).
11
4. COMMISSIONING
Routine Use Chapter
MAINTENANCE AUT.CAL Calibration with buffer solutions 5-1
Operation by keys through MAN.CAL Calibration in process 5-2
closed cover DISPLAY Show or fix additional values 5-3
TEMP Select automatic or manual
temperature compensation 5-4
HOLD Switch HOLD-function on/off 5-5
COMMISSIONING OUTPUT Adjusting the output function 4-2
Operation by *-key when SET HOLD Activating the HOLD-function 4-3
cover is removed
SERVICE SERVICE Finetuning the performance 7
Operation by coded entry
from commissioning

1. Access output
Remove cover by releasing 4 screws.
Access to commissioning menu
Select output function
Select OUTP
Confirm selection
2. Adjust low span value
Display will show *4 mA
Adjust value for low span
Select digit to adjust
Adjust digit
Confirm adjusted value
3. Adjust high span value
Display will show *20 mA
Adjust value for high span
Select digit to adjust
Adjust digit
Confirm adjusted value
Return to measurement
4-2. Output range adjustment
YES
ENT
>
^
ENT
MODE
>
^
NO
IM 12B6C2-E-H
12
ESCAPE TO MEASURE can be used at any stage to abort operation.
WARNING: If the HOLD function is activated the instrument returns with the question HOLD (flashing); answer YES or NO or
MODE again to return to measurement.
x
MODE
OUTPUT
SET HOLD
SERVICE
YES NO
YES NO
MODE *
OUTPUT
SET HOLD
SERVICE
YES NO MODE
ENT
OUTPUT
SET HOLD
SERVICE
YES NO MODE
ENT
pH

IM 12B6C2-E-H
1. What is the Output-range?
The display will always show the actual value
between -1 and 15 pH.
The output range is a linear function of mA
versus pH and is fixed by two points.
As the output is fixed to 4..20 mA the two
points of the linear function have to be pro-
grammed to set the range.
The factory setting is a full range of 0..14pH.
Any value between -1.. + 15 pH is accepta-
ble for both points. A minimum span of 1
unit must be kept.
An error E19 will point to not acceptable
values.
NOTE:
1. The linear output signal is limited to 3.9 to
20.5 mA giving a safety area of 2.5% at
both ends.
2. Values below 3.9 or above 20.5 mA are
not related to input values and signal a
malfunction.
2. How to adjust?
EXAMPLE:
The EXA PH200 has to be programmed for
a range of 2 ... 12 pH.
Adjust 4 mA to 2.00 pH
Adjust 20 mA to 12.00 pH
The instrument will now correct its calcula-
tion for the output signal accordingly.
3. Calculation example
The current to be set at the output is calcu-
lated as follows:
pH - pHmin
mA = x 16 + 4
pHmax - pHmin
pH = actual value
pHmin = value at 4 mA
pHmax = value at 20 mA
pHmax - pHmin = span (≥1 pH)
It is advisable to choose a span devisable by
10, 5 or 2 for easy reading on scales.
4. Other possibilities
Set a 22 mA signal on the output, when
FAIL is on (see §7-7).
13
4-2. Output range adjustment

4-3. Set up the HOLD-function
IM 12B6C2-E-H
1. Access to HOLD-function
Remove cover by releasing 4 screws.
Push this key to select
Commissioning mode
Select HOLD
Move pointer to SET HOLD
HOLD = HOLD-function
Confirm selection
2. Activate HOLD-function
Display shows actual status
*H.OFF = HOLD not active
*H.ON = HOLD activated
Activate (deactivate) HOLD
Changing setting
Confirm setting
*H.FIX = HOLD fixed value
*H.LST = HOLD last value
Select HOLD fixed or last
Change selection
Confirm selection
3. Select value to hold
Display shows current setting
Adjust fixed value
Select digit to adjust
Adjust value of digit
Confirm setting
Return to measurement
14
OUTPUT
SET HOLD
SERVICE
YES NO
YES NO
MODE *
.
OUTPUT
SET HOLD
SERVICE
YES NO MODE
ENT
.
YES
ENT
>
^
NO
YES
NO
YES
NO
x
ESCAPE TO MEASURE can be used at any stage to abort operation.
WARNING: If the HOLD function is activated the instrument returns with the question HOLD (flashing); answer YES or NO or
MODE again to return to measurement.
MODE
MODE
OUTPUT
SET HOLD
SERVICE
YES NO
YES NO
MODE *

IM 12B6C2-E-H
1. What is HOLD?
HOLD is a function freezing the output signal
temporary, during normal maintenance, pre-
venting all sorts of alarming situations to
occur.
Two possibilities are generally used:
a. Keeping the output at the LAST value
just before the start of maintenance. This
should be used when recording and not
controlling instruments are connected to
the output signal.
b. Keep the output at a preset FIXED value
which will not cause any of the alarms to
go off or any controlling action to be
taken. This is the preferred situation
when dealing with pH-control systems.
2. How does it work?
The HOLD-function has to be activated from
the commissioning menu before it can be
used.
The EXA PH200 will keep the output frozen
during the following events:
a. Access to the commissioning menu.
b. Access to either of the calibration modes.
c. Switching it from the maintenance menu.
HOLD is signalled in the display by a special
flag.
The operator is prompted to switch HOLD
on or off before returning to nor mal mea-
surement.
3. Example
In a neutralization set-up with both acid and
base dosing systems the neutral value is pH
7.00.
Activate the HOLD function and choose the
FlXed output value.
The span was set for 2-12 pH (see §4-2).
Thus pH 7.00 = 12 mA. Adjust the preset
value for the output at 12 mA.
During maintenance the output will be at 12
mA = pH 7.00 and no acid or base will be
pumped.
4. Auto return
Hold can be de-activated after 10 minutes if
no key is pressed. To cancel this function
(see §7-9).
15
4-3. Set up the HOLD-function

IM 12B6C2-E-H
4-4. Sensor selection and diagnostics
The inputs of the EXA PH200 transmitter are
free programmable for ease of retrofit on
existing installation. Standard glass pH-elec-
trodes, Ag/AgCI reference electrodes and
Pt100 sensor need no programming. If there
is a mismatch of the sensors connected a
fault will be indicated with a signal field on
the display and if activated by a 22 mA
signal.
4-4-1. Selection of measurement and
reference electrode
The EXA PH200 is preprogramed to ac-cept
industry standard glass electrodes and refe-
rence electrodes. Checks for asymmetry-
potential and slope are implemented during
calibration. The on-line impedance check on
both sensors is not initialized unless activa-
ted from the service level §7-5. The EXA is
suitable for all type of electrodes (e.g.
Enamel, Antimony). In §7-3 the specific
Isothermal point of intersection (ITP), slope
(pH/mV) and asymmetry potential can be set
for each type of electrode.
4-4-2. Selecting a temperature sensor
The EXA PH200 has been factory set for a
Pt100 temperature sensor to DIN standards.
This will give satisfactory results when the
normal electrode cable length is used. To
correct for cable resistance it is possible to
calibrate the sensor from the service level
(zie §7-11).
The highest accuracy is obtained by using a
Pt1000 element with the EXA PH200 trans-
mitter. This element gives a ten-fold increase
in resistance dependance over a Pt100 sen-
sor. Setting the instrument for Pt1000 is
from the service level at §7-4.
4-4-3. Off-line calibration checks
The EXA PH200 transmitter incorporates a
checking of the asymmetry-potential after a
calibration has been performed. This is valid
for both manual or automatic calibration.
The actual value can be called up from the
display routine in the maintenance menu
(AS). A large value can indicate a poisoning
of the reference system used. If the asym-
metry-potential exceeds + 120 mV or
-120 mV an error E2 will be generated.
To disable this checking see §7-5.
The EXA PH200 also checks for the slope of
the pH sensor after automatic calibration
has been performed. The actual value of the
slope can be called up from the display rou-
tine in the maintenance menu (SL). The
value is an indication for the "ageing" of the
sensor. If the value stays within the limits of
70 to 110 % of the theoretical value of
59.16 mV/pH at 25°C it is accepted.
Otherwise an error E3 is generated. Disable
this testing from the service level §7-5.
16