The PH450 pH analyzer provides the best accuracy in the industry, featuring an advanced temperature compensation functionality, preloaded calibration standards, stability checks, and online sensor and analyzer diagnostics to provide verifiable results.

This four-wire, multivariable analyzer combines pH with temperature and ORP (Redox) measurement, all of which can be utilized through the different output functions: two mA current outputs, four independent SPDT contact outputs, and HART. Dynamic sensor checking and wash cycle functions assure trouble free and accurate analysis with minimum maintenance.

Unique Human Machine Interface

The PH450 has a high-resolution, simple touchscreen menu structure with five language options, so information is clearly visible and easily accessible to the operator. Simply select the language of choice and on-screen instructions assure that the best configuration for the application is obtained.

Ideal for Ultrapure Water Applications

The PH450 offers self-diagnostics and process temperature compensation to provide accurate pH measurements in high purity water. One of these temperature compensation methods, the NEN6411 algorithm, takes into account the dissociation of water in strong acid and alkaline solutions, which is especially useful for pH measurement in Pure and Ultrapure water as found in Power Generation Water Chemistry.

Additional Features

  • Capable of analyzing pH, ORP or rH and Temperature measurements at the same time with the same sensor
  • Full PID control possible for both acid and alkaline addition simultaneously
  • Dual High Impedance Capability, allowing for Differential pH/ORP measurements
  • Enhanced diagnostics, process trending graphics and on-screen logbooks for data storage
  • Two mA-outputs and four SPDT relay contacts with display indicators
  • Hart® Communications
  • FM Class 1, Div.2, Group ABCD, T6 for Ta-20 to 55°C
  • IP66/NEMA4X 1/2 DIN enclosure for Field Mounting and Panel Mounting
  • Three sets of preloaded pH buffer standards (NIST, US and DIN) cover most commonly used pH calibration practices
  • Supports many temperature compensation elements and sensor types


The Yokogawa EXAxt PH450G is a converter
designed for industrial process monitoring, measurement
and control applications. This instruction
manual contains the information needed to install,
set up, operate and maintain the unit correctly.
This manual also includes a basic troubleshooting
guide to answer typical user questions.
Yokogawa can not be responsible for the
performance of the EXAxt converter if these
instructions are not followed.
1-1. Instrument check
Upon delivery, unpack the instrument carefully
and inspect it to ensure that it was not
damaged during shipment. If damage is found,
retain the original packing materials (including
the outer box) and then immediately notify the
carrier and the relevant Yokogawa sales office.
Make sure the model number on the nameplate
affixed to the side of the instrument agrees with your
order. Example of the nameplate is shown below.

1-2. Application
The EXAxt converter is intended to be used
for continuous on-line measurement of pH
and/or Redox in industrial installations. The
unit combines simple operation and microprocessor-based
performance with advanced
self-diagnostics and enhanced communications
capability to meet the most advanced requirements.
The measurement can be used as part
of an automated process control system. It can
also be used to indicate operating limits of a
process, to monitor product quality, or to function
as a controller for a dosing/neutralisation
Sensors should normally be mounted close to
the converter in order to ensure easy calibration
and peak performance. If the unit must
be mounted remotely from the sensors, WF10
extension cable can be used, up to a maximum
of 60 meters (150 feet), with a BA10 junction
box, and up 10 meters standard sensor cable.
The EXAxt is delivered with a general purpose
default setting for programmable items (see
Chapter 5). While this initial configuration
allows easy start-up, the configuration should
be adjusted to suit each particular application.
An example of an adjustable item is the type
of temperature sensor used. The EXAxt can
be adjusted for a number of different types of
temperature sensors.
Details provided in this instruction manual
are sufficient to operate the EXAxt with all
Yokogawa sensor systems and a wide range
of third-party commercially available probes.
For best results, read this manual in conjunction
with the corresponding sensor instruction
Yokogawa designed the EXAxt converter to
withstand industrial environments. It meets all
the CE regulatory standards. The unit meets or
exceeds stringent requirements (see section
2) without compromise, to assure the user of
continued accurate performance in even the
most demanding industrial installations.


A) Inputs specs : Dual high impedance input (≥ 1012Ω)
(under referance conditions)
B) Input ranges
pH : -2 to 16 pH
ORP : -1500 to 1500 mV
rH : 0 to 100 rH
– Pt1000 : -30 to 140ºC
– Pt100 : -30 to 140ºC
– 350Ω (DKK) : -30 to 140ºC
– 5k1 : -30 to 140ºC
– 6k8 : -30 to 140ºC
– PTC10k : -30 to 140ºC
– NTC 8k55 : -10 to 120ºC
– 3kBalco : -30 to 140ºC
C) Accuracy
pH input : ≤ 0.01 pH
ORP input : ≤ 1 mV
Temperature : ≤ 0.3 ºC (≤ 0.4 ºC for Pt100)
Step response : < 4 sec for 90% (pH 7 – pH 4)
Note on performance specifications
The following tolerance is added to above performance.
mA output tolerance: ±0.02 mA of “4-20 mA“
D) Transmission signals
General : Two isolated outputs of 4-20 mA. DC with common negative. Maximum
load 600Ω. Bi-directional HART® digital communication, superimposed
on mA1 (4-20 mA) signal
Output functions : Linear or Non linear (21-step table) output for pH, temperature, ORP or rH
Control function : PID control
Burnout function : Burn up (21.0 mA) or burn down (3.6 mA) to signal failure acc.
Adjustable damping. Expire time
Hold : The mA-outputs are frozen to the last/fixed value during calibration/
E) Contact outputs
General : Four SPDT relay contacts with display indicators
Switch capacity : Maximum values 100 VA, 250 VAC, 5 Amps.(*)
Maximum values 50 Watts, 250 VDC, 5 Amps.(*)
Status : High/Low process alarms, selected from pH, ORP, rH and temperature
Configurable delay time and hysteresis
Failure annunciation
Control function : On/Off, PID duty cycle or pulsed frequency control
Wash : Contact can be used to start manual- or interval time wash cycles
Hold : Contact can be used to signal the Hold situation.
Fail : Contact S4 is programmed as fail-safe contact
(*) Note: When contact output current is more than 4 Amps. ambient temperature should be
less than 40ºC.

F) Contact input : Remote wash cycle start.
G) Temperature compensation
Function : Automatic or manual
Compensation to Nernst equation
Process compensation by configurable temperature coefficient,
NEN6411 for water or strong acids/bases or programmable matrix
H) Calibration : Semi-automatic 1 or 2 point calibration using pre-configured NIST,
US, DIN buffer tables 4, 7 & 9, or with user defined buffer tables, with
automatic stability check
Manual adjustment to grab sample
I) Logbook : Software record of important events and diagnostic data readily
available in the display or through HART®.
J) Display : Graphical Quarter VGA (320 x 240 pixels) LCD with LED backlight and
touchscreen. Plain language messages in English, German, French,
Spanish, Italian, Swedish ,Portuguese and Japanese.
K) Shipping details
Package size : 290 x 300 x 290 mm (L x W x D) (11.5 x 11.8 x 11.5 inch)
Package weight : app. 2.5 kg (5.5 lbs)
Converter weight : app. 1.5 kg
L) Housing : Cast aluminum housing with chemically resistant coating;
Polycarbonate cover with Polycarbonate flexible window
: Protection IP66 / NEMA 4X / CSA Type 3S
Colour : Silver grey
PH450G-A(D)-A : IP66 cable glands are supplied with the unit
PH450G-A(D)-U : NEMA 4X close up plugs are mounted in the unused cable entry holes
and can be replaced by conduit fittings as required
Pipe, Panel or Wall mounting using optional hardware
Optional conduit adapter
G1/2, 1/2NPT or M20 female
M) Power supply
PH450G-A : Ratings; 100-240 V AC Acceptable range; 90 to 264 V AC
Ratings; 50/60 Hz Acceptable range; 50 Hz ±5%, 60 Hz ±5%
Power Consumption; 15 VA
PH450G-D : Ratings; 12-24 V DC Acceptable range; 10.8 to 26.4 V DC
Power Consumption; 10 W
N) Safety and EMC conforming standards ,
Safety : EN 61010-1
CSA C22.2 No.61010-1
UL 61010-1
FM3611 Class I, Div.2, Group ABCD,T6 for Ta -20 to 55ºC
EMC : EN 61326-1 Class A, Table 2 (For use in industrial locations)
EN 61326-2-3
EN 61000-3-2 Class A
EN 61000-3-3
Korea Electromagnetic Conformity Standard
Installation altitude: 2000 m or less
Category based on IEC 61010: II (Note)
Pollution degree based on IEC 61010: 2 (Note)
Note: Installation category, called over-voltage category, specifies impulse withstand voltage.
Category II is for electrical equipment.
Pollution degree indicates the degree of existence of solid, liquid, gas or other
inclusions which may reduce dielectric strength. Degree 2 is the normal indoor


3-1. Installation and dimensions
3-1-1. Installation site
The EXAxt 450 converter is weatherproof and  can be installed inside or outside. It should, however, be installed as close as possible to the sensor to avoid long cable runs between sensor and converter. In any case, the cable length should not exceed 50 metres (162 feet). Select an installation site where:
• Mechanical vibrations and shocks are negligible
• No relay/power switches are in the direct environment
• Access is possible to the cable glands (see figure 3-1)
• The converter is not mounted in direct sunlight or severe weather conditions
• Maintenance procedures are possible (avoiding corrosive environments)
The ambient temperature and humidity of  the installation environment must be within
the limits of the instrument specifications. (See chapter 2).

3-1-2. Mounting methods

Refer to figures 3-2 and 3-3. Note that the EXAxt converter has universal mounting capabilities:
• Panel mounting using optional brackets
• Surface mounting on a plate (using bolts from the back)
• Wall mounting on a bracket (for example, on a solid wall)
• Pipe mounting using a bracket on a horizontal or vertical pipe Size nominal 50A

The PH450 is supplied with terminals suitable for the connection of finished wires in the size range of 0.13 to 2.5 sq.mm. ( 26 to 14 AWG).
The cable glands supplied will form a tight seal on cables with an outside diameter of 6 to 12 mm (0.24 to 0.47 inches). Unused cable entry holes must be sealed with cable glands including the close up plugs supplied.

The PH450 is supplied with terminals suitable for the connection of finished wires in the size range of 14- 26 AWG. The cable entry holes are sealed with FM certified plugs. Prior to cable entry the plugs can be removed with allen key size 3/8” The cable conduit fittings can be mounted in the holes of the housing as required. The cable glands supplied with the unit will give a tight seal on cables with outside diameter of 0.24 to 0.47 inches.


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