WL-PH-3661 Industrial pH Meter

WL-PH-3661 Industrial pH Meter | Reliable online pH measurement and process integration

The WL-PH-3661 and WL-PH-3669 are intelligent industrial pH meters designed for continuous online monitoring. They receive signals from a compatible pH electrode and temperature sensor, process and display the measurement, and transmit the result to a process-control or monitoring system.

The high-input-impedance measurement circuit is designed for the weak voltage signal generated by a glass pH electrode. Microprocessor-based processing handles electrode calibration, slope correction, temperature compensation, isopotential-point adjustment, and measurement conversion without manual potentiometer adjustment.

The meter displays pH, temperature, electrode potential or output-current information, depending on the selected operating screen and configuration. A 128 × 64 dot-matrix LCD or optional color display provides a clear view of measurements, alarms, and configuration parameters.

Two isolated 4–20 mA outputs, adjustable alarm relays, and RS485 Modbus RTU communication support integration with compatible PLC, SCADA, dosing, and process-control systems.

Main functions

Automatic temperature compensation

When a compatible temperature sensor is connected, the meter adjusts the temperature-dependent response slope of the pH electrode over a range of 5–60 °C.

Automatic temperature compensation corrects the electrode response. It does not necessarily convert the sample to the pH it would have at 25 °C, because the chemical equilibrium and actual pH of the solution can also change with temperature.

Digital calibration and signal processing

The instrument uses microprocessor-controlled functions for:

• Electrode zero adjustment
• Electrode slope calibration
• Temperature compensation
• Isopotential-point configuration
• Measurement-data processing
• Automatic amplifier-zero correction
• High and low alarm configuration

Automatic software correction helps compensate for electronic zero drift caused by component, temperature, and operating-condition changes.

Analog and digital outputs

Two isolated 4–20 mA outputs can be assigned to compatible measurement variables according to the system configuration. RS485 communication using the Modbus RTU protocol allows a host controller to read measurement values and instrument parameters remotely.

Alarm and system protection

Users can configure upper and lower pH alarm points. Alarm conditions are indicated on the display and can activate relay-contact outputs for compatible alarms or control equipment.

An integrated watchdog monitors program execution and helps the instrument recover from abnormal software conditions.

Non-volatile configuration storage

Calibration and configuration parameters are retained after a power failure without requiring a backup battery.

Typical applications

The WL-PH-3661 and WL-PH-3669 can be used for continuous pH monitoring in:

• Municipal water and wastewater treatment
• Industrial water-treatment systems
• Chemical production and dosing processes
• Petroleum refining
• Metallurgical processes
• Pharmaceutical production
• Food and beverage processing
• Textile dyeing and printing
• Power-generation water systems
• Environmental water monitoring
• OEM water-treatment and automation equipment

Pure-water applications

The meter can be used as part of a pure-water pH measurement system when paired with an appropriate low-impedance or pure-water pH electrode, suitable flow chamber, stable sample line, and appropriate electrical installation.

Pure-water pH measurement is particularly sensitive to:

• Unstable sample flow
• Atmospheric carbon-dioxide absorption
• Static charge
• Ground loops
• Reference-junction potential
• Temperature variation
• Air bubbles and sample-line leakage
• Excessive backpressure or negative pressure

The meter alone does not eliminate these online measurement effects.

Suitable operating environments

Control panel installation

The meter is suitable for installation in an indoor industrial control panel or instrument cabinet where:

• Ambient temperature remains between 0 and 45 °C
• Relative humidity does not exceed 90%
• Condensation is prevented
• The instrument is protected from direct water spray
• Excessive dust, vibration, and corrosive vapours are controlled
• A stable 220 VAC power supply is available

No enclosure protection rating has been provided for the meter. Outdoor, washdown, or exposed installations require a suitable protective cabinet.

Process measurement conditions

The connected electrode and process assembly should be selected for:

• Process-liquid temperatures from 5 to 60 °C
• Process pressures not exceeding 0.3 MPa
• The expected pH range and chemical composition
• The required insertion, immersion, or flow-through installation
• The necessary electrode material and reference-junction design

The stated process limits apply to the selected sensor and measurement assembly, not merely to the panel-mounted meter.

Installation and measurement precautions

Electrode compatibility

Confirm the following before ordering:

• pH electrode type and connector
• Temperature-sensor type
• Electrode cable and wiring
• Process connection and holder
• Required reference-junction construction
• Chemical compatibility with the process medium
• Whether the installation is inline, immersion, or flow-through

Cable installation

Keep the high-impedance pH signal cable clean and dry. Moisture, contamination, damaged insulation, or unsuitable cable joints can cause unstable or biased readings.

Route the sensor cable separately from power cables, motors, frequency converters, relays, and other sources of electrical interference. Avoid unnecessary cable extension, even when the installation is within the specified 100 m limit.

Calibration

Use fresh, traceable buffer solutions selected for the normal process range. Allow the electrode, temperature sensor, and buffer solution to reach temperature equilibrium before accepting the calibration.

A successful buffer calibration confirms basic electrode and instrument response under calibration conditions. It does not by itself confirm accuracy under actual online conditions.

Flow and pressure

For flow-through measurement, maintain stable sample flow and pressure. Avoid:

• Stagnant samples
• Trapped air
• Negative pressure
• Excessive backpressure
• Blocked discharge lines
• Direct installation at a chemical injection point

Chemical and hygienic applications

Compatibility must be verified for concentrated acids, alkalis, solvents, oxidants, fluoride-containing media, proteins, oils, and high-solids wastewater.

Use in pharmaceutical or food production does not automatically establish hygienic or regulatory compliance. Required wetted-material, cleanability, surface-finish, and certification documentation must be confirmed separately.

Classification

Product Type

• Controllers & Transmitters

Parameter

• pH
• Temperature
• Electrode potential/mV, if enabled in the supplied configuration

Application

• Industrial Water Treatment
• Municipal Water & Wastewater
• Pure-Water Measurement Systems
• Chemical Processing
• Petroleum Refining
• Metallurgy
• Pharmaceutical Production
• Food & Beverage
• Textile Dyeing & Printing
• Power Generation
• Environmental Monitoring
• OEM Monitoring & Automation Systems