Test & measurement
At the beginning, it was the vision of a 100 per cent process-compatible pH sensor. The first pH sensor from the Memosens family, introduced in 2004, not only fulfilled this requirement thanks to digital measurement value storage and transmission, but revolutionised previously time- consuming maintenance and calibration activities. Today, Memosens technology covers all liquid analysis measurement parameters, and with the new generation – Memosens 2.0 – has evolved into a digital ecosystem that fully exploits the opportunities that digitalisation currently offers. All of these advantages were well received
were sent from the pH electrode to the transmitter in the form of electrical voltages, the analogue data transmission was prone to interference. The critical points were primarily the interfaces from the sensor to the cable and from the cable to the transmitter. Penetrating moisture and contact corrosion frequently led to interference with the signal transmission and thus to noisy signals or incorrect measurement values. For this reason, the typical service technician toolkit included an electrical hairdryer to blow-dry the contact points if needed. Help came in 2004 with Memosens technology
A
developed by Endress+Hauser. The measurement values are transformed into a stable digital signal in the sensor head and then sent to the transmitter using contactless induction technology. The galvanised separation of the electrode and transmitter, and the digital transmission of the measurement values, eliminated the possibility of tampering, plus cable breaks could be immediately detected. The new Memosens pH sensor featured a completely sealed anti-twist bayonet lock, which meant that the plug-in head and cable coupling could even be placed under water. It also offered more flexibility in terms of the cabling. While the analogue sensor technology restricted the cable length to a maximum of 20m, the digital technology extended it to 100m. Last but not least, Memosens sensors were approved for use in explosive environments.
nalogue pH measurements for liquids were still the standard 20 years ago. Although the measurement values
by the market, prompting Endress+Hauser to port Memosens technology to other measurement parameters. In 2006 came the redox sensor, followed in 2007 by sensors for amperometric oxygen measurements and conductivity and then for chlorine measurements in 2008. In 2012, combined electrodes for simultaneously measuring pH, redox and rH were then introduced. Furthermore, a key milestone for the simple application of the digital sensor family was the introduction in 2011 of a multiparameter 4- wire transmitter (Liquiline CM44) featuring up to eight measurement channels, which for the first time enabled “plug-and-play”. As soon as a Memosens sensor is connected, it is recognised by the transmitter and automatically read out.
FAsT replAceMenT insTeAd oF TiMe-consuMing on-siTe service During the first years of the development of Memosens technology, digital interference-free data transmission was the focus. It soon became apparent that the novel technology possessed even more potential. If the sensor and process data is stored directly in the sensor, then maintenance, configuration and calibration no longer have to be carried out at the measuring point and instead can be performed in a lab or a workshop under controlled conditions. Instead of carrying out time-consuming activities in the field, the service technician simply swaps out the sensor, thus eliminating the need to transport the tools and control and cleaning solutions that were previously required for an on-site service call.
For servicing, this translated into a small
revolution. The time required for each measuring point was reduced from 20-30 minutes to just a few minutes. For a medium- sized process with 40 analysis loops that are serviced once a week, the resulting efficiency gains are easy to extrapolate. Furthermore, the simple replacement of the sensor required no specific qualifications on the part of the service personnel. Now all that was required was an expert in the lab. Beginning in 2005, with the introduction of the Liquiline CM42 generation of transmitters, these benefits could be fully exploited, and the first calibration was outsourced to the lab. The data stored in the sensor head includes
the following: initial commissioning date/time, duration of use, maximum values (> pH 12, < pH 2, temperatures exceeding 80°C and 100°C as well as the maximum respective temperature reached) and maintenance- related information such as number of sterilisation cycles, delta zero point and delta slope. Other relevant properties are stored in the software of the Liquiline transmitter.
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November 2021 Instrumentation Monthly
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