General Foundation® Fieldbus transmitter

for pH and Redox (ORP)

Specifications Model PH202G-F

Flexibility, low maintenance and low installation costs are

among the benefits of the EXA PH202 pH transmitter. Designed
to meet the exacting requirements of measuring pH and ORP in
the modern industrial environment, it contains many features to
ensure the best precision whatever the application.

This transmitter is housed in a robust IP65 field mountable case.

The Foundation® Fieldbus digital communications and a clear
LCD makes the PH202G-F a compleet industrial analyzer.

The famous EXA sensor diagnostics are enhanced by an

improved impedance check, and the addition of a logbook
feature. Calibration history is available in the display, and full
logbook data is accessible via Foundation® Fieldbus
communication. The logbook is used to store important
configuration, calibration and diagnostic data. Prediction of
sensor failure is possible by reference to the logbook.

Microprocessor-aided calibration uses internal buffer tables and

stability checking to ensure maximum accuracy with minimum
effort. Process temperature compensation enhances accuracy in
applications where the influence of temperature is seen in
process pH changes. pH and Redox measurements can be
made simultaneously when an appropriate sensor combination is
used.

FEATURES
● Universal pH/ORP, dual high impedance inputs
● On-line sensor checking
● Foundation® Fieldbus interface (DD available)
● Event logbook in software
● Process temperature compensation
● Differential input amplifier with equipotential screening
● Freely configurable ITP, slope and assymmetry
● Easy to use EXA control panel
● Password protection for all levels of software

SYSTEM CONFIGURATION

Sensors Cables Fittings Transmitters Accessories

GS 12B6C3-02E-H
2nd Edition
2

ACCURATE pH MEASUREMENT With this 3-level user-friendly approach, the instrument can be
Electrode selection operated by anyone. Commissioning is straight-forward.
In order to make precise pH measurements, there are a number Specialist functions, available via access codes, are invisible
of pre-requisites. Special attention should be paid to the choice during normal operation. All three levels can be separately
of the sensors to ensure compatibility with the chemical protected against unauthorized access by a password system
composition of the process fluid. The speed of response using a three digit code.
required, the solids content and the flow rate of the fluid are also
contributory factors. Other Yokogawa specification sheets cover SENSOR CHECKING
the choice of sensors. Any Yokogawa sales office can provide On-line checks
expert advice. Real-time sensor checking in the 2 wire transmitter is one of the
most important features of the EXA PH202-F transmitter.
Converter design
The system should be designed to minimize the effect of external By special circuitry on the input board an alternating voltage is
influences. The EXA series features dual high impedance input applied to the liquid earth pin and the sensors. The impedance of
amplifiers in a differential configuration with liquid earth. This the measuring electrode (pH-glass or ORP-metal electrode) and
system is used to ensure compatibility with most available sensor reference electrode are independently measured. The measured
combinations. It also provides excellent noise rejection, values are compared to limiting values.
minimizing the stray signals that can affect industrial pH
measurements. Earth loop currents in damp and damaged Sensor Checking
cabling are eliminated by the equipotential screening. Faults
The pH-sensor is checked for low impedance to detect breakage
Maintenance of the bulb and for high impedance to detect an open circuit.
It is important that the system is well maintained. The electrodes The Redox sensor is checked for high impedance to detect an
must be properly cleaned and regularly calibrated. Yokogawa on- open circuit.
line cleaning systems may be used where there is significant The reference electrode is also checked for high impedance to
fouling of the sensors. Other influences from the electrode detect fouling of the diaphragm, poisoning of the reference liquid
holders can be less obvious, but important none the less. Well or non immersion of the sensors.
designed fittings make it easy to provide the routine maintenance The fault are automatically transmitted as a status along with the
needed for best accuracy. Flow through, retractable and process value.
immersion assemblies are available. The fault is also flagged on the display by a special marker field
and an error code in the message display.
The selection of the buffer solutions is important to ensure the
best possible calibration. Yokogawa strongly recommends the Off-line checks
use of NIST (NBS) buffers. These are chosen as primary buffer During calibration of a pH measuring system, the response of the
standards because of the maximum buffer capacity exhibited by sensors is measured and checked. Sensitivity calculated and
these solutions. Commercial buffers (adjusted with NaOH) have checked. During calibration of an ORP measuring system, the
the limited advantage of an integer value, with the disadvantages drift of the sensors is calculated and checked. If any of these are
of loss of buffer capacity and greater temperature dependence. outside the limits, an error is signaled.
Yokogawa sets the pH/temperature relationships for NIST buffers
in the software of the EXA pH converters. This combination The comprehensive combination of on-line and off-line checking
provides the best calibration possible. monitors all key aspects of the measurement to give an early
warning, if the reading is faulty.
Dual amplifier system
The input amplifiers both have a very high input impedance
(≥ 1013 Ω). This means the PH202 is capable of accepting glass,
enamel and metal measuring- and reference sensors. Together
with the ability to configure the ITP (isothermal point), the system
can be adapted to accept almost all sensor types. MΩ kΩ

PROCESS TEMPERATURE COMPENSATION

EXA instruments offer a simple and effective process temperature YOKOGAWA
Made in the Netherlands
YOKOGAWA

compensation in addition to the usual compensation to the

Nernst equation. The figure below shows the strong change in
pH with temperature, caused by the dissociation constant of
water changing. This effectively shifts the neutral point from pH 7.
In order to reliably control the pH of solutions it is necessary to
compensate for the changes. The EXA transmitters have a
simple-to-operate system of process temperature compensation
to provide optimum accuracy and best control. An application
where this is particularly important is in the measurement of
alkalized boiler feed water.

THREE LEVEL OPERATION

The EXA PH202-F transmitter uses a 3-level operating system.
Advanced functions are separated from conventional operation to
avoid confusion.

MAINTENANCE level : Normal day to day operation

COMMISSIONING level : Paring commissioning BREAKAGE FOULING
SERVICE level : Only for specialist functions
NON-IMMERSION
GS 12B6C3-02E-H
 3
PH202 Specifications E. FF specifications : Twisted 2-wire with shield.
A. Input specifications : Dual high impedance inputs (2 x F. Housing : Cast aluminium case with chemically
1013Ω) with provision for liquid earth resistant coating, cover with flexible
connection. Suitable for inputs from polycarbonate window. Case color is
glass or enamel pH & reference off-white and cover is moss green.
sensors and ORP metal electrodes. Cable entry is via two 1/2” polyamide
B. Input ranges glands. Cable terminals are provided
- pH : -2 to 16 pH for up to 2.5 mm2 finished wires.
- ORP : -1500 to 1500 mV Weather resistant to IP65 and NEMA
- rH : 0 to 55 rH 4X standards. Pipe, wall or panel
- Temperature : -30 ºC - 140 ºC (-20 - 300 ºF) mounting is possible using optional
- 8k55 sensor : -10 ºC - 120 ºC (10 - 250 ºF) hardware.
- NTC10k : -10 ºC - 120 ºC (10 - 250 ºF) G. Data protection : EEPROM for configuration and
C. Temperature compensation logbook, and lithium cell for clock.
- Range : Automatic or manual copensation to H. Watchdog timer : Checks microprocessor
Nernst equation. Process I. Automatic safeguard: Return to measuring mode when no
compensation by configurable keystroke is made for 10 min.
coefficient. Compensation for total J. Operation protection: 3-digit programmable password.
range of selected temperature K. Regulatory compliance
sensors (see B). Adjustable ITP (Iso- - EMC : meets council 89/336/EEC
thermal point of intersection). - Emmission : meet EN 55022 Class A
D. Calibration : Semi-automatic using preconfigured - Immunity : meet EN 61000-6-2
NIST buffer tables 4, 7 & 9, or with L. Sensor impedance checking
user defined buffer tables, with : Independent impedance check on
automatic stability check.Manual measuring and reference sensor
adjustment to grab sample. Slope elements, with temperature
and Asymmetry Potential setting. Zero compensation. Display of sensor
point can be selected for calibration impedance on message line of
and display instead or As. Pot. display. FAIL flag in event of “out of
(IEC 7146-2) limits” impedance.
E. Logbook : Software record of important events M. DD Specification : The PH202 Device Description is
and diagnostic data. Available available enabling communications.
through FF interface.
F. Display : Custom liquid crystal display, with a CABLES AND TERMINALS
main display of 31/2 digits 12.5 mm The PH202 is equipped with terminals suitable for the connection
high. Message display of 6 alpha- of finished cables in the size range: 0.13 to 2.5 mm (26 to 14
numeric characters, 7 mm high. AWG). The glands will form a tight seal on cables with an outside
Warning flags and units (pH and mV). diameter in the range of 7 to 12 mm (9/32 to 15/32 inches).
G. Power supply : 9-32 volts.
H. Input isolation : 1000 V DC Signal processing (pH/ORP/rH)
J. Shipping details : Package size w x h x d With the correct sensor configuration, the PH202 can measure
290 x 225 x 170 mm. pH, ORP and rH. (ORP is the oxidation reduction potential,
Packed weight approximately 2.5 kg. including the effect of pH. The rH value is ORP compensated for
Operating specifications the effect of pH). Combinations of pH and ORP or pH and rH can
A. Performance pH: be displayed simultaneously.
- Linearity ≤0.01 pH
:
- Repeatability ≤0.01 pH
:
Model Suffix Option Description
- Accuracy ≤0.01 pH
:
code code
Performance :
ORP
PH202G pH/ORP transmitter
- Linearity ≤1 mV
:
General Purpose version
- Repeatability ≤1 mV
:
PH202S pH/ORP transmitter
- Accuracy ≤1 mV
:
Intrinsic Safe version
Performance Pt1000 Ω, 3 kΩ Balco, 5 k1Ω, 350Ω
:
Type -E Milli-amp (+HART®) version,
6k8Ω, NTC10kΩ
European style
- Linearity : ≤0.3 ºC
-U Milli-amp (+HART®) version,
- Repeatability : ≤0.1 ºC
North American style
- Accuracy : ≤0.3 ºC
-C Milli-amp (+HART®) version,
Performance : Temperature with Pt100 Ω
Canadian style
- Linearity : ≤0.4 ºC
-F FOUNDATION® Fieldbus version
- Repeatability : ≤0.1 ºC
-N Non-Incendive Milli-amp
- Accuracy : ≤0.4 ºC
(+HART) version
B. Ambient operating :-10 to +55 °C (10 to 130 ºF)
-B Non-Incendive FOUNDATION®
temperature Excursions to -30 to +70 °C
Fieldbus version
(-20 to 160 ºF) will not damage the
-E Always E
instrument, specification maybe
Options /H Hood for Sun Protection
adversely affected
/U Pipe & Wall mounting hardware
Drift < 500 ppm/°C
/SCT Stainless steel tagplate
C. Storage temp. : -30 to +70 ºC (-20 to 160 ºF)
/Q Calibration certificate
D. Humidity : 10 to 90% RH, non condensing.
/T Turck Fieldbus connector

GS 12B6C3-02E-H
4

DIMENSIONS AND MOUNTING

162 (6.4)

min. 203
(min. 8.0)
180 (7) 154
(6.06) 30 (1.18)

(1.18)
30 (1.2)

30
(min.9.0)
min.229

(6.77)
172
92 (3.6)
115 (4.5)
2x ø4
(0.16)

1/2" SUPPLY SPACING PANEL

CUT-OUT DIMENSION CUT-OUT DIMENSIONS

1/2" INPUT

56±0.2
(2.20) M6 bolts (2x)

Panel cut-out, spacing and mounting Dimensions

wall mounting pipe mounting pipe mounting

(vertical) (horizontal)
56
(2.20)

2x ø6.5
(0.26)
(7.87)
200

4x ø10
(0.4)

145

70 (5.70)
(2.75)
2” ND. pipe
Option /U: Universal pipe/wall mounting kit

Universal pipe/wall mounting

YOKOGAWA HEADQUARTERS YOKOGAWA CORPORATION OF AMERICA Yokogawa has an extensive sales and
9-32, Nakacho 2-chome, 2 Dart Road
Musashinoshi Newnan GA 30265 distribution network.
Tokyo 180 United States
Japan Tel. (1)-770-253-7000 Please refer to the European web-site
Tel. (81)-422-52-5535 Fax (1)-770-251-2088
Fax (81)-422-55-1202 E-mail: info@yca.com (www.yokogawa-europe.com) to contact
E-mail: webinfo@mls.yokogawa.co.jp www.yca.com
www.yokogawa.com your nearest representative.

YOKOGAWA EUROPE B.V. YOKOGAWA ELECTRIC ASIA Pte. Ltd.

Databankweg 20 5 Bedok South Road
3821 AL AMERSFOORT Singapore 469270
The Netherlands Singapore
Tel. +31-33-4641 611 Tel. (65)-241-9933
Fax +31-33-4641 610 Fax (65)-241-2606
E-mail: info@yokogawa.nl E-mail: webinfo@yas.com.sg
www.yokogawa-europe.com www.yokogawa.com.sg

GS 12B6C3-02E-H
Subject to change without notice Printed in The Netherlands, 02-301 (A) Q
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