Online Residual Chlorine/pH Controller
Industrial-grade multi-parameter controller for continuous monitoring of residual chlorine (0.001-10 mg/L), pH (0-14), and temperature with 4-20mA output and Modbus communication.
Louise Corscadden, PhD
Director of Science · ConductScience
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The Online Residual Chlorine/pH Controller is a multi-parameter industrial water quality monitoring instrument designed for continuous measurement and control applications. The controller simultaneously monitors residual chlorine concentration, pH, and temperature with integrated alarm functions for process control applications. The system features a 96×96mm panel-mount design with digital display and provides both analog output signals and digital communication capabilities for integration into industrial control systems.
This controller employs electrochemical measurement principles with automatic temperature compensation to maintain measurement accuracy across varying process conditions. The device supports both manual and automatic temperature compensation modes, with high input impedance (≥1×10¹²Ω) for stable pH measurements. The integrated RS485 communication with Modbus protocol enables remote monitoring and data logging capabilities essential for industrial water treatment operations.
How It Works
The controller employs electrochemical sensing technology for both pH and residual chlorine measurements. pH measurement utilizes a glass electrode system that generates a millivolt signal proportional to hydrogen ion activity, with the high input impedance (≥1×10¹²Ω) preventing signal degradation. The residual chlorine sensor uses amperometric detection principles, where chlorine species are electrochemically reduced at a working electrode, generating a current proportional to concentration.
Temperature compensation is achieved through integrated RTD or thermistor sensors that provide real-time temperature data to the measurement algorithm. The controller applies automatic correction factors to both pH and chlorine measurements, accounting for temperature-dependent electrode response and chemical equilibrium shifts. The dual-parameter design allows simultaneous monitoring with independent alarm setpoints for each parameter.
Signal processing includes amplification, filtering, and linearization of raw electrode signals before conversion to standardized 4-20mA output signals. The integrated microprocessor handles calibration data storage, temperature compensation calculations, and communication protocol management for seamless integration into industrial control systems.
Features & Benefits
Product Name:
- Industry online residual chlorine/pH controller
Measure range & Accuracy
- 0-14 (pH) ±0.02pH
Resolution:
- 0.01pH, 0.01mg/L(residual chlorine),0.001mg/L(HOCL)
Input Resistance:
- â¥1x10 ¹²Ω
Temp Compensation:
- Manual / Auto temperature compensation
Communication:
- RS485, standard Modbus
Signal output:
- 4-20mA output, Maximum loop 750Ω, 0.01%FS
Power supply:
- 220V AC 10%,50/60Hzz
Hole size
- 91x91mm
Research Domain
- Analytical Chemistry
- Environmental Monitoring
- Food Science
- Industrial Hygiene
- Microbiology
- Pharmaceutical QC
Automation Level
- semi-automated
Brand
- ConductScience
Size
- 96x96x115mm
Weight
- 0.9KG
Weight
- 1.98 kg
Dimensions
- L: 3779.53 mm
- W: 3779.53 mm
- H: 5.0 mm
| Feature | This Product | Typical Alternative | Advantage |
|---|---|---|---|
| Measurement Resolution | 0.01 pH units, 0.01 mg/L residual chlorine, 0.001 mg/L HOCL | Entry-level controllers often provide 0.1 pH resolution and limited chlorine resolution | Higher resolution enables more precise process control and earlier detection of water quality deviations. |
| Communication Protocol | RS485 with standard Modbus protocol | Basic units may only offer analog outputs or proprietary communication | Standard Modbus enables easy integration with existing industrial control and data acquisition systems. |
| Input Impedance | ≥1×10¹²Ω | Lower-cost controllers may have reduced input impedance specifications | High impedance ensures stable pH measurements with minimal electrode loading and extended sensor life. |
| Multi-Parameter Display | Simultaneous display of chlorine, pH, temperature, output current, and alarm status | Single-parameter displays require manual switching between readings | Concurrent parameter visualization improves process understanding and reduces monitoring time. |
| Temperature Compensation | Manual and automatic temperature compensation modes | Some basic units offer only manual compensation or no compensation | Automatic compensation maintains accuracy across temperature variations without operator intervention. |
| Power Supply | 220V AC ±10%, 50/60Hz | Varies by model, some require external power supplies | Standard industrial voltage rating with wide tolerance ensures reliable operation in most facilities. |
This controller combines multi-parameter measurement capabilities with high-resolution sensing and industrial communication protocols. The integrated design reduces panel space requirements while providing comprehensive water quality monitoring functionality suitable for demanding industrial applications.
Practical Tips
Perform calibration using solutions at process temperature and allow adequate equilibration time between calibration points.
Why: Temperature differences between calibration standards and process conditions can introduce measurement errors.
Inspect sensor connections monthly for corrosion or loose terminals that can affect measurement stability.
Why: Poor electrical connections are a common source of measurement drift and noise in electrochemical systems.
Install sensors in locations with adequate flow velocity and representative sampling conditions away from chemical injection points.
Why: Poor sensor location can result in measurements that don't reflect true process conditions or create measurement interference.
If pH readings drift consistently, check reference electrode condition and electrolyte level before recalibration.
Why: Reference electrode problems are the most common cause of pH measurement instability and cannot be corrected by recalibration alone.
Monitor 4-20mA loop resistance periodically to ensure signal integrity, especially in installations with long cable runs.
Why: Excessive loop resistance can cause signal attenuation and introduce noise that affects control system performance.
Implement proper lockout procedures before sensor maintenance and ensure adequate ventilation when working with chlorine solutions.
Why: Chlorine-containing solutions can release hazardous gases, and electrical systems require safe isolation during maintenance.
Store pH buffer solutions according to manufacturer specifications and replace regularly to maintain calibration accuracy.
Why: Degraded calibration standards are a primary source of systematic measurement errors in pH systems.
Document all calibration activities and sensor maintenance in a logbook for trending and validation purposes.
Why: Systematic record-keeping enables early identification of sensor degradation patterns and supports regulatory compliance requirements.
Setup Guide
What’s in the Box
- Online Residual Chlorine/pH Controller unit (typical)
- Mounting hardware for 91×91mm panel cutout (typical)
- Terminal connection diagram (typical)
- User manual and installation guide (typical)
- Power supply cable (typical)
- Calibration certificate (typical)
Warranty
ConductScience provides a standard one-year manufacturer warranty covering defects in materials and workmanship, with technical support available for installation, calibration, and troubleshooting assistance.
Compliance
What calibration standards are required for accurate measurement?
pH calibration requires standard buffer solutions (typically pH 4.01, 7.00, and 10.01). Residual chlorine calibration uses known concentration standards prepared from sodium hypochlorite solutions or commercial chlorine standards. Both parameters should be calibrated using solutions at process temperature when possible.
How does temperature compensation affect measurement accuracy?
The controller provides both manual and automatic temperature compensation modes. Automatic compensation continuously adjusts pH readings for temperature-dependent electrode response (approximately 0.03 pH units per °C). Chlorine measurements are also temperature-corrected for equilibrium shifts between chlorine species.
What is the response time for detecting process upsets?
Response time depends on sensor type and process conditions. Typical pH electrodes respond within 30-60 seconds for 90% of full-scale change. Residual chlorine sensors typically achieve 90% response in 60-120 seconds. Consult sensor specifications for exact response characteristics.
Can the 4-20mA output drive multiple devices simultaneously?
The controller provides individual 4-20mA outputs for each parameter with maximum loop resistance of 750Ω. Each output can drive multiple devices in series provided total loop resistance stays within limits. For multiple parallel loads, signal isolation may be required.
How often should sensor calibration be performed?
pH electrodes typically require weekly to monthly calibration depending on process conditions and required accuracy. Residual chlorine sensors may need daily to weekly calibration in demanding applications. Establish calibration frequency based on drift monitoring and process criticality.
What maintenance is required for long-term reliability?
Regular sensor cleaning, electrolyte refilling for pH electrodes, and periodic replacement of reference electrodes. Verify electrical connections, check communication links, and perform functional testing of alarm outputs monthly. Consult sensor manuals for specific maintenance schedules.
Is the controller suitable for corrosive or high-temperature applications?
The controller housing is designed for standard industrial environments. For corrosive or high-temperature applications, consult product datasheet for specific environmental ratings and consider sensor selection appropriate for process conditions.
How does this compare to portable handheld meters?
This online controller provides continuous monitoring with data logging and alarm capabilities, while portable meters offer spot measurements with higher portability. Online systems reduce labor costs and enable immediate response to process changes but require higher initial investment and installation.
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