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YOKOGAWA PH201G-A1*A/TB
Product Introduction:
The PH201G-A1A/TB is a smart pH and ORP (Oxidation-Reduction Potential) analyzer/transmitter from Yokogawa’s FLXA202/FLXA21 series. It provides continuous, real-time measurement of pH and ORP values in industrial process streams. The “G” designation indicates a glass electrode sensor type. The “A1A” output configuration provides 4–20 mA DC + RS-485 (Modbus RTU) communication. The “TB” suffix indicates a terminal box enclosure configuration.
Detailed content
Measurement Principle:
- pH Measurement: A glass electrode and reference electrode form an electrochemical cell. The voltage difference between the two electrodes is proportional to the hydrogen ion activity (pH) in the solution, following the Nernst Equation: E = E₀ − (2.303RT/F) × pH
- ORP Measurement: A platinum (Pt) or gold (Au) indicating electrode measures the overall redox potential of the solution relative to the reference electrode, expressed in millivolts (mV)
Technical Specifications:
| Parameter | Specification |
|---|---|
| Model | PH201G-A1*A/TB |
| Measured Parameters | pH, ORP (mV) |
| pH Range | -2.00 to +16.00 pH |
| ORP Range | ±1500 mV |
| pH Accuracy | ±0.005 pH |
| ORP Accuracy | ±1 mV |
| pH Resolution | 0.001 pH |
| ORP Resolution | 0.1 mV |
| Output (A1*A) | 4–20 mA DC (isolated) + RS-485 (Modbus RTU) |
| Power Supply | 12–36 V DC (2-wire or 4-wire) |
| Temperature Compensation | Automatic (Pt1000 RTD, built-in) |
| Electrode Type (G) | Glass pH Electrode + Ag/AgCl Reference |
| Process Connection | 1/2″ NPT, 3/4″ NPT, or Flange (DIN/JIS/ANSI) |
| Process Temperature | 0°C to +120°C (32°F to +248°F) |
| Process Pressure | Up to 0.6 MPa (87 psi) |
| Protection Class | IP66 / IP67 (with TB terminal box) |
| Wetted Materials | SUS316L, PEEK, PTFE |
| Communication | RS-485 Modbus RTU (9600/19200 bps) |
| Approvals | ATEX, IECEx, FM, CSA, SIL2 |
Structural Features:
- Wall-mount or pipe-mount transmitter housing with TB terminal box for field wiring
- Glass pH electrode with double-junction Ag/AgCl reference for contamination resistance
- Built-in temperature sensor (Pt1000) for automatic temperature compensation
- IP66/IP67 rated enclosure suitable for outdoor and washdown environments
- Large LCD display with backlight for local readout
Performance Parameters:
| Parameter | Value |
|---|---|
| Response Time (pH) | ≤ 30 seconds (95% of step change) |
| Response Time (ORP) | ≤ 15 seconds (95% of step change) |
| Input Impedance (pH) | ≥ 10¹² Ω |
| Calibration | 2-point or 3-point automatic calibration |
| Slope Check | Yes — automatic electrode health diagnosis |
| Alarm Outputs | 2 relay outputs (optional) |
| Isolation | 1500 V AC (input to output to power) |
Key Advantages:
- Ultra-high accuracy (±0.005 pH) — suitable for critical process control
- Glass electrode with double-junction reference — extended life in dirty or fouling solutions
- Built-in temperature compensation — eliminates need for separate temperature transmitter
- RS-485 Modbus communication — direct DCS/PLC integration
- SIL2 functional safety certified — suitable for safety-instrumented systems
- Terminal box (TB) enclosure — protects wiring connections in harsh environments
Applicable Industries:
- Water and Wastewater Treatment
- Chemical and Petrochemical Processing
- Pharmaceutical Manufacturing
- Food and Beverage
- Pulp and Paper
- Semiconductor Manufacturing (Ultrapure Water)
- Mining and Metallurgy
Installation Requirements:
- Install in a location accessible for electrode maintenance and calibration
- Ensure adequate flow velocity (> 0.3 m/s) past the sensor to prevent stagnant zones
- Mount the electrode at least 300 mm below the liquid surface (submersion type) or use appropriate immersion assembly
- Use shielded cable for RS-485 communication — ground shield at one end
- Connect power supply with correct polarity — reverse polarity will damage the transmitter
- Provide adequate drainage if installed outdoors to prevent water ingress into the terminal box
Usage Precautions:
- Glass electrodes are fragile — handle with extreme care; never touch the glass bulb
- Store the electrode in pH 4 or pH 7 buffer solution when not in use — never let it dry out
- Calibrate at least every 2 weeks in critical applications; weekly in dirty process streams
- Clean the electrode regularly with mild acid (HCl) or pepsin solution for protein fouling
- Replace the reference electrolyte as per maintenance schedule (typically every 3–6 months)
- Do not exceed +120°C process temperature — glass electrode will degrade
- Avoid measuring pH in non-aqueous solvents unless specifically rated for that application
- Do not subject to mechanical shock or vibration beyond rated specifications
