Profibus pH/ORP Transmitter/ Analyzer

PROFIBUS is an open, digital communication system which covers factory and process automation. This analyzer is designed for 2-wire (loop powered) system configuration with PROFIBUS communication.

Flexibility, reliability, low maintenance and low installation costs are among the benefits of the EXA PH202 pH/ORP analyzers. Designed to meet the exacting requirements of measuring pH and ORP in the modern industrial environment, it contains many features to ensure peak precision whatever the application.

This 2-wire (loop powered) analyzer is housed in a robust IP65 field mountable case. The need for expensive cabling is minimized. 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 through the HART bi-directional communication link, and 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 ORP or rH measurements can be made simultaneously when an appropriate sensor combination is used.

Yokogawa has implemented three leading process Fieldbus technologies in their 202 series: HART, Foundation Fieldbus H1 and Profibus PA. All transmitters are provided with the important and widely used Device Description files that provide information on parameters and other data in each device, as well as the ability to include algorithmic relationships such as calibrations.

  • Universal pH/ORP.
  • Possible to input high impedance reference electrode.
  • On-line sensor checking.
  • Process temperature compensation.
  • Differential input amplifier with equipotential screening.
  • Freely configurable ITP, slope and asymmetry.
  • Easy to use EXA control panel.
  • Password protection for all levels of software.
  • HART®, PROFIBUS-PA, FOUNDATION Fieldbus H1 communications.
Input ranges pH: -2 to 16 pH
ORP: -1500 to 1500 mV
rH: 0 to 55 rH
Temperature: -30 to 140℃
Output ranges pH: Min. 1 pH, Max. 20 pH
ORP: Min. span 100 mV, Max. span 3000 mV
rH: Min. 2 rH, Max. 55 rH
Temperature: Min. 25℃ , Max. 200℃
Output Signal 4 to 20 mA DC loop powered, isolated from input
With the possibility of 21 mA "FAIL" signal (burn up) and 3.6 mA (burn down when HART or distributor comm. is non-used), 3.9 mA (burn down when HART or distributor comm. is used).
Temperature Compensation Range: -30 to 140℃ (for 8k55 sensor -10 to 120℃ ).
Sensor types: Pt100, Pt1000, 3 kΩ RTC, 5.1 kΩ PTC, 8.55 kΩ NTC, 350 Ω PTC, 6.8 kΩ PTC, 10 kΩ PTC. Automatic or manual compensation to Nernst equation. Process compensation by configurable coefficient. Adjustable ITP (Iso-thermal point of intersection).
Calibration Semi-automatic, using tables in transmitter for pH 4, 7 & 9 buffer solutions, or using user-defined tables, with automatic check of measurement stability.
Manual, using standard sample, by correcting reading to value of standard.
Calibration by slope and asymmetry potential setting. (IEC60746-2)
Transmission signal Isolated output of 4 to 20 mA DC. Burn up (21 mA) or Burn down (3.6 mA when HART or distributor comm. is non-used, 3.9 mA when HART or distributor comm. is used) or pulse of 21 mA to signal failure.
Communication HART®, PROFIBUS-PA, FOUNDATION Fieldbus H1
Ambient temperature -10 to 55℃
Humidity 10 to 90 % RH (Non-condensing)
Display Custom liquid crystal display, with a main display of 3 1/2 digits 12.5 mm high.
Power supply Nominal 24 volt DC loop powered system.
PH202G: 17 to 40 V
Enclosure Material Plastic (Polycarbonate)
Area Classification
  • General Purpose
  • Class I Div II (without the use of IS Barrier)*FM/CSA Pending
  • Class I Div I (with the use of IS Barrier)*FM/CSA Pending




±0.01 pH
±0.01 pH
±0.01 pH




±1 mV
±1 mV
±1 mV


The lifetime of a pH sensor has a significant impact on the overall annual costs of a pH measuring loop. Optimizing four key factors will decrease these costs and optimize process control and overall plant efficiency.

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