HARD-406 Water Hardness Sensor
The Apure HARD-406 is listed as an online ion-selective system for hardness monitoring, reported as CaCO3. Verify the supplied calcium/magnesium response and calibration against the hardness composition of the intended water.
- Stable performance
- Quick installation
- Long life
Water hardness is commonly reported as the calcium-carbonate equivalent of the relevant dissolved ions, principally calcium and magnesium. It is not the simple sum of their concentrations in mg/L. The listed HARD-406 uses ion-selective measurement with temperature compensation; the actual membrane response, calibration and treatment of the calcium/magnesium ratio must be defined for the supplied system.
| Reported quantity | How to interpret it |
|---|---|
| Calcium, mg/L as Ca | A calcium-ion concentration; not the same numerical quantity as calcium hardness expressed as CaCO3. |
| Magnesium, mg/L as Mg | A magnesium-ion concentration; its CaCO3-equivalent factor differs from that of calcium. |
| Total hardness, mg/L as CaCO3 | A defined equivalent concentration. Confirm the instrument calibration and which ion contributions are included. |
Illustrative hardness calculation
When a reference analysis reports calcium and magnesium separately in mg/L, their hardness contribution is approximately 2.497 × calcium + 4.118 × magnesium, in mg/L as CaCO3. For example, 10 mg/L calcium and 5 mg/L magnesium contribute about 45.6 mg/L as CaCO3. This calculation explains the reporting basis; it does not establish that HARD-406 measures two independent channels or guarantees every water composition.
Validate and install
- Compare representative samples with a suitable independent hardness method on the same CaCO3 basis. Include the calcium/magnesium ratios and other ions expected in the process.
- Check the actual selectivity, conditioning and calibration procedure. A Nernst-type potential response alone does not prove a universal direct measurement of the total concentration of two ions.
- The existing reference-system statement cites 100 KPa (1 Bar); this is not a substitute for the complete probe process-pressure rating. Confirm the listed 3/4 NPT thread, process limits, sealing and access for service.
- Follow the supplied cleaning, storage and verification instructions. The listed RS485 Modbus RTU output and optional 4–20 mA output require separate digital settings and analog scaling checks.
The listed range and original numerical limits are retained. The existing description identifies a PVC-membrane construction; confirm the actual supplied membrane and calcium/magnesium response. The resolution unit typo “0.1mgL” is corrected to “0.1mg/L” without changing its value. Confirm the electrode configuration, hardness calibration, accuracy basis and the temperature/pressure/pH conditions for the actual assembly.
| Brand | Apure |
|---|---|
| Model | HARD-406 |
| Measuring range | 0-1000.0mg/L |
| Resolution | 0.1mg/L, 0.1℃ |
| Accuracy | ±10% FS, ±0.3℃ |
| Signal outputs | RS-485 (ModbusRTU), 4-20 mA (optional) |
| Listed operating conditions | 0～40℃, ≤0.2MPa, pH:4～10 |
