Yokogawa PH450G EXAxt pH/ORP 4‑Wire Converter

Product Description

The PH450G is a discontinued 4‑wire multi‑variable pH and ORP (Redox) converter manufactured by Yokogawa under the EXAxt series. It adopts a high‑resolution graphical touch‑screen HMI and high‑impedance sensor input circuit. The transmitter continuously measures pH value, ORP and process temperature with built‑in advanced temperature compensation and pre‑loaded calibration standards. It provides two analog 4‑20mA outputs, four SPDT relay contacts and HART digital communication. The rugged field‑mount housing is designed for long‑term continuous operation in chemical, water and power‑plant environments with humidity, dust and vibration. It is widely available as spare replacement hardware for existing liquid analytical monitoring loops.

Product Functions

• Online high‑precision measurement of pH, ORP and medium temperature for liquid process monitoring
• Advanced automatic temperature compensation and stability detection to improve measurement accuracy under varying working conditions
• Dual 4‑20mA analog outputs and four independent relay contact outputs for alarm, control and wash cycle triggering
• HART protocol communication, supporting DTM/DD files for handheld configurator, HMI and DCS system connection
• Built‑in PID control function and automatic sensor washing cycle to reduce manual maintenance workload
• Dynamic sensor impedance diagnosis, electrode fault detection and event log storage with time stamps
• Touch‑screen local configuration, multi‑language display and real‑time diagnostic warning messages for on‑site maintenance

Application Scenarios

• Water and wastewater treatment plants for pH neutralization and ORP disinfection monitoring
• Thermal power boiler feedwater, ultra‑pure water and condensate chemical monitoring systems
• Chemical, pharmaceutical and food processing production‑line liquid‑phase analysis and control
• Pulp & paper industry bleaching process redox and pH monitoring control loops
• Mining and metal surface treatment wastewater treatment and chemical dosing control
• Spare replacement and maintenance retrofit of aging Yokogawa EXAxt450 analytical transmitters

Common Problems

• Unstable or drifting pH readings：contaminated pH electrode, aging reference sensor, incorrect calibration or cable leakage interference
• HART communication failure：incorrect wiring polarity, incompatible DTM driver, damaged communication circuit or poor terminal contact
• Analog output signal deviation：loop load impedance out of range, parameter misconfiguration or internal DA circuit degradation
• Relay alarm or wash cycle cannot be triggered：wrong threshold setting, stuck relay contacts or damaged output drive circuit
• Touch‑screen malfunction and touch offset：aging touch panel, moisture intrusion or calibration parameter loss
• Sensor diagnostic persistent fault alarm：electrode glass membrane fatigue, broken sensor cable or corrosion of wiring terminals
• Loss of historical log data after power outage：internal backup battery depletion or flash memory aging