The MP5-A:
A New Standard
in Chlorine Sensor Accuracy
Most chlorine sensor specifications are measured under controlled, static laboratory conditions that never occur in the real world. pH, temperature, and conductivity are held constant during testing — but in an operating water system, these variables change constantly. The MP5-A was calibrated once and tested across the full range of real-world conditions. It stayed within ±4%.
Why Published Specs Don't Reflect Real-World Performance
Chlorine sensor specifications often have no relationship to the real world. The conditions under which published accuracy figures were obtained are frequently not disclosed. pH and temperature are typically held constant during manufacturer testing — conditions that almost never occur in an actual treatment plant or distribution system.
The practical result: sensors that appear accurate in a spec sheet drift significantly when water chemistry changes in the field. This forces frequent recalibrations — wasting labor, increasing operating costs, and creating inconsistent data for operators and management.
Example: Hach CL10f Accuracy Specification
Condition 1: ±3% at constant pH below 7.2 (±0.2 pH unit). Condition 2: ±10% at stable pH below 8.5 (±0.5 pH unit from calibration pH). Hach calibrates separately at two pH ranges and does not specify accuracy under temperature or conductivity variation.
The MP5-A Test: One Calibration, Full Range
Test Methodology
Nine MP5-A sensors were calibrated at a single set of conditions: pH 8.0, chlorine 1.25 ppm, conductivity 2,700 µS, temperature 20°C. After calibration, pH was varied from 6.5 to 8.5, then conductivity was varied from 156 to 10,000 µS, then temperature was varied from 10°C to 35°C. Chlorine accuracy remained within ±4% throughout all tests.
Single Calibration — Wide Range
Nine MP5-A sensors were calibrated once at pH 8.0, chlorine 1.25 ppm, 2,700 µS conductivity, and 20°C. pH was then varied from 6.5 to 8.5. Accuracy stayed within ±4% throughout — no recalibration needed.
Temperature Stability
As temperature varied from 10°C to 35°C, chlorine reading error remained at ±4% or less. Hach does not publish temperature accuracy figures for the CL10f.
Conductivity Independence
Conductivity was varied from 156 µS to 10,000 µS — a range that covers virtually every drinking water source in the U.S. The MP5-A reading varied by only ±4%.
Zero-Chlorine Recovery
The MP5-A can operate at zero ppm chlorine for hours or days. When chlorine returns, it reads very low residuals immediately — including sub-0.1 ppm levels. Membrane sensors cannot achieve this.
Flow Independence
Flow varied from zero to 60 gpm to 120 gpm with virtually no change in signal. This makes direct pipe insertion and dead-end monitoring practical without flow control hardware.
6+ Months Unattended
The self-cleaning system keeps electrodes polished during operation. Combined with a rechargeable battery and low-power mode, unattended operation for more than six months is achievable.
MP5-A vs. Hach CL10f — Head to Head
| Variable | Halogen MP5-A | Hach CL10f |
|---|---|---|
pH Range MP5-A calibrated once at pH 8.0. Hach requires separate calibration at two pH ranges. | check_circle6.5 – 8.5 (±4%) | < 7.2 (±3%) or < 8.5 (±10%) |
Temperature Hach does not publish temperature accuracy specs. MP5-A tested and documented across full operating range. | check_circle10 – 35°C (±5%) | Not specified |
Conductivity Hach does not address conductivity variation. MP5-A accuracy held within ±4% across the full range. | check_circle156 – 10,000 µS (±4%) | Not specified |
Limit of Detection (LOD) Tested per ISO 15839. MP5-A detects chlorine at 3× lower concentrations than the Hach CL10f. | check_circle0.01 ppm | 0.03 ppm |
Limit of Quantitation (LOQ) Tested per ISO 15839. MP5-A quantifies accurately at more than 2× lower concentrations. | check_circle0.04 ppm | 0.09 ppm |
What This Means for Your Operations
Fewer Calibrations
Because the MP5-A maintains accuracy as water chemistry changes, calibration intervals of six months or more are achievable — compared to weekly calibrations required by some competing sensors.
Factory Calibration Ships Ready
The wide accuracy range means many MP5-A sensors will be accurate immediately upon installation, without an initial on-site calibration. Spare sensors can be swapped in without a technician visit.
Remote & Distribution Monitoring
Flow and pressure independence makes direct pipe insertion practical anywhere in the distribution system — dead ends, water towers, remote reservoirs — without flow control hardware.
References
- Australia, W. Q. (2010). Development of Tools for Improved Disinfection Control within Distribution Systems. WQRA.
- Hach. (2023). Hach CL10 Specifications. hach.com.
- HSI Flow Report. (2019). Halogen Sensor Flow Test Report. Incline Village.
- ISO 15839. (2003). Water Quality — Online Sensors/Analysing Equipment for Water. Geneva, Switzerland: International Organization for Standardization.
- Justyn Fields. (2022). Orange County Utilities (FL) Remote Drinking Water Sensor Pilot Program. AWWA Water Technology Conference. Cincinnati, OH.