Application and Necessity in Building Services
In the UK building services sector, pH measurement is frequently sidelined until a failure occurs. However, BSRIA BG29/21 and BG50 guidelines emphasize that water chemistry is the primary factor in lifecycle management. A pH shift of even one point represents a tenfold change in acidity or alkalinity, which can rapidly strip protective magnetite layers from steel pipework or lead to the pitting of copper heat exchangers. Operating within a tight pH window—typically 9.0 to 10.5 for mild steel systems—is critical for inhibition.
Industrial pH sensors are no longer simple laboratory probes. In a plant room environment, they must withstand vibration, pressure fluctuations, and electrical noise from Variable Speed Drives (VSDs). Engineers must specify sensors that integrate directly into Building Management Systems (BMS) or PLC frameworks, providing real-time data for automated dosing pumps. This shift from manual sampling to continuous monitoring reduces the risk of human error and ensures compliance with environmental discharge permits.
Beyond corrosion control, pH sensors play a vital role in microbiological control. In cooling tower applications, the effectiveness of oxidising biocides like chlorine or bromine is highly dependent on pH. If the pH rises too high, the biocide remains in its less effective ionised form, increasing the risk of Legionella proliferation. Accurate, real-time pH data allows the controller to modulate acid or base dosing precisely, maintaining the system within safe and efficient parameters.
- Monitoring LTHW and CHW closed loops to prevent corrosion.
- Controlling blowdown and biocide efficacy in open-circuit cooling towers.
- Neutralising trade effluent prior to discharge into local sewers (to comply with Mogden formula requirements).
- Optimising chemical flocculation in water treatment plants.
Frequently asked questions
What is the maximum cable length for a pH transmitter?
- While standard analogue sensors are prone to electrical interference, modern smart transmitters with M12 connectors digitise the signal at the probe level, allowing for cable runs up to 30m without signal degradation.
How often should a pH transmitter be calibrated?
- In a typical cooling tower or closed-loop LTHW system, sensors should be calibrated monthly using pH 4.0 and pH 7.0 buffer solutions to account for electrode drift.
Can pH sensors be used in high-pressure lines?
- Standard industrial electrodes are generally rated up to 6 bar at 25°C. For high-pressure boiler feed or industrial processes, specialised high-pressure glass and housings are required.
What is the correct way to store a pH sensor?
- Never store a pH probe dry or in deionised water. It must be kept in KCL storage solution to maintain the hydration layer on the glass bulb. If it dries out, the response time becomes sluggish or fails entirely.
