Dissolved Oxygen Analyser (OxySense S2) Removes the Need for a PLC
Programmable Logic Controllers (PLCs) are widely used in the water treatment industry. However, they can be extremely costly and require lots of maintenance, which can pose greater financial challenges for smaller companies. Pi recently encountered one such customer and were able to meet all the stated criteria and more- eradicating the need for a PLC.
A water treatment plant based in South America approached Pi with the intention of purchasing a dissolved oxygen sensor, OxySense S2. The OxySense S2 from Pi measures dissolved oxygen in water samples using luminescence technology. Blue light is emitted from a blue LED inside the sensor. This excites the lumiphore within the sensor and this excitement causes the lumiphore to emit red light. The amount of red light emitted depends on how much dissolved oxygen is present. The more oxygen present, the more ‘quenching’ occurs, which reduces the intensity of red light emitted. The intensity of red light emitted is measured by a photodiode and this reading correlates to the amount of dissolved oxygen present in the sample. As well as the intensity of the red light, there is a phase shift which is also related to the amount of oxygen present.
What sets the OxySense S2 apart from other optical dissolved oxygen sensors is the AutoClean and AutoVerify components. The OxySense S2 can be fitted with an optional self-cleaning system whereby a jet of clean water or air is passed over the sensor to reduce fouling. In most wastewater applications where the OxySense S2 is used, air is used in the AutoClean as opposed to water. This allows the sensor to ‘AutoVerify’. When air passes over the sensor, the sensor senses a rapid increase in the amount of oxygen present, verifying that the sensor is working optimally. In cases where this dramatic increase is not detected, the sensor sends an error message alerting the user of potential issues.
The customer quickly realised that the additional functionality available with the OxySense S2 eliminated the need for physical inspection, saving both time and money.
All of Pi’s sensors are available to purchase alongside a CRIUS®4.0 or CRONOS® controller. These controllers can be equipped with PID to calculate the output to the inverter, which in this case, controls the output of the air pump to optimise the aeration lane and reduce electricity consumption. This site also had dual pumps, so the addition of the Timer/Scheduler, Duty Standby and two 4-20mA outputs from the CRIUS®4.0 allowed for duty rotation of the pumps, ensuring even workload distribution. Finally, digital inputs connected to the alarm relays of the pumps allows for immediate pump switching, so that if one pump develops a fault, the other is automatically utilised. This maintains process uptime.
In short, the initial brief was to purchase a dissolved oxygen analyser. However, with some Pi expertise and expert knowledge, this water treatment plant obtained a new, cost-effective water treatment controller. To learn more about Pi’s products please visit: https://www.processinstruments.co.uk/