To PLC or not to PLC UV Systems – Alternatives for UV System Control

Key to UV process control is the ability to deliver the correct dose at the correct time to ensure compliance with the discharge permit limits. Both manual and automatic control strategies are used within the industry. For automatic control, flow, UV intensity, and UV transmittance are used to control the emitted dose.With flow control, the number of lamps energized increases or decreases with the flow being discharged from the facility. This type of process control does not take into account for decreased output of the lamp as a result of aging or changes in water quality. Flow control is generally used on the low pressure-low intensity systems. Dose pacing based on intensity is generally used on low pressure-high intensity and medium pressure UV systems using either on-line intensity or on-line transmittance. Intensity-based control allows for the dose to be adjusted in response to lamp output and changing water conditions. On-line transmittance allows for adjustments to be made based on lamp output and water quality.