Memosens sensors save time, improve accuracy and lower costs

©Endress+Hauser

The DO measurement takes place in the middle of a lagoon where the site's waste effluent is reoxygenated before being transferred to settlement tanks and discharged into the river. For health and safety reasons, any work at the lagoon has to be carried out by two people, making the on-site calibration of sensors a labour-intensive task. "It was a waste of resources," explains Ian Castle, DS Smith Kemsley's Instrumentation & Electrical Control Support Engineer.

With Memosens digital sensors, all operation and calibration data is stored in the head of the sensor. They can be pre-calibrated and simply replaced in the field, cutting the time spent at difficult-to-access measuring points. Because each sensor holds its calibration data, the sensors can be rotated periodically, keeping the freshest sensor in the process while the other is cleaned, calibrated and allowed to rejuvenate in the lab or workshop.

And as Memosens technology offers non-contact transmission of the measured value from the sensor to the transmitter, the problems of corrosion, leaks and measured value distortion from moisture are avoided. Convinced of the benefits, DS Smith replaced all of its pH sensors used in the effluent treatment process with Memosens sensors and is now trialling the introduction of Memosens sensors for dissolved oxygen.

According to Ian Castle, the main benefit has been the efficiency gains. “With the other manufacturer's pH probes it took perhaps an hour to clean and calibrate them," he says. "Now I can do this in the lab, in a nice clean location, using the Memobase Plus software. It takes me a few minutes to change the probes on site and the job is done. It saves an awful lot of time, it really does."

The accuracy of the measurement has also improved, proven by the readings given by the two pH transmitters required for regulatory purposes. "The two meters correlate very closely to one another, within about 0.02 pH," explains Ian Castle. "Our measurement didn't used to be as accurate as that. It's probably because we're now able to calibrate in a much more controlled environment."

The improved performance hasn't cost the company any more – in fact, operating costs have gone down because a more common, cheaper buffer solution can be used and the sensors last longer. "The Memosens sensors cost about the same as the old ones but I'm not having to buy new ones all the time," confirms Ian Castle.

A big advantage for DS Smith is that Endress+Hauser's Liquiline transmitter and Memosens pH sensor have MCERTS certification from the Environment Agency. Complying with MCERTS gives the regulators confidence that a company is monitoring its emissions. The Memobase Plus software used to calibrate the sensors also helps with compliance as all calibration records are stored digitally. "That was another big plus," says Ian Castle. "I've a record of all calibrations should the EA want to look."