Calcium Hardness Measurement: Process Hardness Analyzer
Calcium hardness measurement in boiler, cooling and process waters: ion-selective electrode online analyzer for scaling and softener control.
Measurement methods: Ion-Selective Electrode
What is calcium hardness and why is it measured?
Water hardness refers to the amount of calcium and magnesium ions dissolved in water; calcium hardness is the part due to calcium. When heated and evaporated, hard water leaves a layer of scale on heat transfer surfaces; this layer reduces energy efficiency and causes clogging in pipes and exchangers and overheating in boilers. Hardness is therefore monitored continuously for early detection of hardness slip at the softener outlet in boiler feedwater, for scale control in cooling systems and for process water quality.
Where is hardness measured?
- Softener and ion exchanger outlets: In controlling resin exhaustion or leakage.
- Boiler feedwater: In preventing scale formation.
- Cooling systems: In tracking the scaling tendency of circulating water.
- Process waters: In water quality control for detergent, dye and food processes.
How is calcium hardness measured?
Online hardness analyzers work by the ion-selective electrode (ISE) method. A calcium ion-sensitive electrode and a reference electrode produce a voltage dependent on the calcium activity in the sample; an automatic temperature compensation (ATC) probe corrects the measurement for temperature. The electrode signal is converted to concentration by calibration with standard solutions. The analyzer can generate an alarm when a threshold is exceeded at the softener outlet and provide information for the regeneration decision.
Choosing a hardness analyzer
- Measurement range and sample composition
- Electrode life and calibration frequency
- Standard solution kit and maintenance plan
- Alarm and output connection to the control system
Calcium hardness measurement with Tetra
Tetra supplies the Thermo Orion 2120XP calcium hardness analyzer in Türkiye and provides installation, supply of reagents and consumables, commissioning, calibration and service.
Frequently asked questions
What units is water hardness expressed in?
Hardness is mostly expressed in mg/L CaCO₃. In French hardness degrees, 1 °fH corresponds to approximately 10 mg/L CaCO₃, and in German hardness degrees, 1 °dH corresponds to approximately 17.8 mg/L CaCO₃. Calcium hardness can also be reported in mg/L Ca; when comparing, check which form is used.
Are calcium hardness and total hardness the same thing?
No. Total hardness is the sum of calcium and magnesium; calcium hardness shows only the part due to calcium. Because a calcium ion-selective electrode does not measure magnesium, total hardness can be markedly higher than calcium hardness in waters with a high magnesium share. If total hardness is required, EDTA titration or colorimetric analyzers designed for total hardness are used.
How is hardness slip monitored at the softener outlet?
Hardness at the softener outlet is normally very low; when the resin is exhausted, the value starts to rise. A threshold is defined on the online analyzer to trigger an alarm, and the regeneration time is determined from this information. If measuring at very low hardness levels, confirm that the analyzer's lower measurement limit suits the application.
What affects a calcium electrode's measurement?
Changes in ionic strength and some metal ions can affect the electrode response, so sample conditioning and calibration are important. Temperature changes affect the voltage, so automatic temperature compensation is used. Deposits on the electrode surface and aging slow the response; a drop in slope indicates that it is time to replace the electrode.
Products measuring this parameter
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