Electricity + Control January 2017

DRIVES, MOTORS + SWITCHGEAR P ESSURE + LEVEL MEASUREM NT

dresses these issues: A diaphragm seal system with a dual diaphragm and diaphragmmonitor- ing removes the risks and the consequential damages as described. Using this patented system, the space between the two diaphragms is evacuated and the vacuum can be monitored with a measuring instrument. The type of monitoring can be specified individually, de- pending on the sensitivity of the process. With regular on-site visual inspection, for example, it is sufficient to check a pressure gauge with green-red display, in other cases an optical or acoustic alarm in the control room may be required. When using media with a high risk potential, the operator can use a pressure switch which will im- mediately halt the process in the event of any damage. Should the wetted diaphragm become damaged, the second diaphragm forms a reliable seal to the process and maintains the pressure monitoring until the damage has been rectified. Since a break within the system is detected and reported immediately, no microbes can get past the diaphragm undetected. Other options are available which can mechanically or electronically identify a failure in the diaphragm seal. If a seal is broken during maintenance or calibra- tion the operator will immediately see this condition and will prevent a defective unit from being reinstalled. Furthermore, the ‘alarm’ is reported immediately in the event that the diaphragm is damaged. This prevents a defective instrument being installed in the process. The safety function of this self-monitoring diaphragm seal system simultaneously optimises the protection of the non-process side: In the event of a damaged diaphragm, no dangerous substances can escape into the environment. When a company uses such a device it shows due diligence that the system is monitored through an automated system and is not left to manual inspection of a seal area. In spite of the extremely high level of automation in pharmaceutical processes, not everymeasuring point absolutely has to be catered for electronically. For such cases, diaphragm pressure gauges with flush diaphragms are particularly worthwhile. These enable the measurement of low pressures and are exceptionally safe in overload as a result of their design. They keep the process sealed, even with pressure surges. Nevertheless, operators can also prepare themselves for the case of any possible damage to the diaphragm element. For such pressure gauges, the company also offers diaphragmmonitoring, which will immediately indicate any rupture in the pressure element. Diaphragm pressure gauges are suited mainly for mobile tanks, in which intermediate and end products are stored or transported to the next processing stage. They monitor, for example, the filling and the inert gas blanket. The dimensions of such containers are getting smaller and smaller, as the pharmaceutical industry is increasingly turning to the development andmanufacture of individual medicines. Processes with small units and batches are the result. The measuring instruments for the corresponding tanks therefore have limited space available. This can quickly become tight for diaphragm pressure gauges: The lower the pressure to be measured, the larger must be

the diaphragm diameter and, with that, also the process connection. To address this problem, the company has developed a new pressure gauge for small external areas: The model PG43SA-C measures in the low- pressure ranges with a proportionately much smaller diaphragm. This instrument combines the reduced con- nection size with a further specific feature that is particularly im- portant for such measuring requirements on tanks: It is autoclavable. The pressure gauge can be sterilised with the vessel under saturated steam conditions at temperatures up to +134°C, without needing to be dismounted. The process thus remains sealed, also in the mobile phase, and the quality assurance is preserved. Conclusion The more critical the pharmaceutical process – for example, produc- tion of injection materials – the more important is the consistent maintenance of the sterile boundary in the manufacturing process. Risk prevention has, with the measurement technology used, an equally high requirement as accuracy and reliability of the process. The particular challenge is to merge the technical functionality and physical design features into an economical solution. For pharma- ceutical processes are getting increasingly more efficient in view of the competitive situation – but without ever compromising safety.

• Pressure measuring instruments are subject to the highest safety criterion: The protection of consumers. • Damage to instruments occurs for various reasons and could lead to product contamination. • A special solution which addresses all the risks has been developed.

take note

Joachim Zipp is the Global Market Segment Manager Food and Pharma at WIKA, Germany. Enquiries: WIKA Instruments. Tel +27 (0) 11 621 0000 or email sales.za@wika.com

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