Using an Exposed Sensor Connector to Sustain Harsh Process Conditions

A large multi-national; pharmaceutical manufacturer in the United Kingdom was producing a fermented product that had to be approved and finalised by one of their divisions located in mainland Europe. This was achieved by retaining the partially completed products in their original fermentation vessels and shipping them to the division via road transport.

When the products arrived they were immediately transferred from the fermentation vessels that were then returned to the United Kingdom. Once the vessels were received they were stripped of their ancillary equipment, which includes temperature and pressure instrumentation, then placed in an autoclave for sterilisation. Once the autoclave sterilisation process was completed, the ancillary equipment was refitted and the fermentation vessels made ready for the production of more fermented product.

Clients were experiencing a frequent problem which involved the removal and refitting of the temperature sensor, specifically the handling of the PT100 resistance thermometer during the activity and attempting to achieve a credible pressure seal after refitting the equipment. A manufacturing company was invited to look into the possibility of developing a temperature sensor that could remain fitted to the vessel even during the sterilisation process.

Seeing as the PT100 resistance thermometer now needed to remain on the vessel, it became clear that some sort of quick release connector would be needed. Such a release connector also needed to withstand being exposed to frequent sterilisation cycles; many types were considered but the majority were unsuitable because the connector body needed to be in Grade 316 stainless steel whilst resisting sterilisation temperatures and pressures whilst being simple to use and robust enough to withstand the processes.

Manufacturers carried out comprehensive, in-depth research before making the final decision to use a connector typically used for aerospace and military purposes but produced in the necessary Grade 316L stainless steel. The connector utilised a hermetic glass seal able to operate up to 250ºC whilst resisting differential pressures of 69 bar. The connector also had six connecting pins in gold-plated nickel, which allowed either a duplex PT100 with a three wire configuration or a single PT100 with a four wire connection to be used. The connection itself was a bayonet type with outer location pins designed to ensure the correct orientation. temperature sensor

The female connector was spring loaded for a tight and firm fit, whereas the male connector was welded into a machined shell made from the Grade 316L stainless steel, which in turn was welded to a 6.0mm diameter sensor sheath made from the same material.

As the female connector would only be exposed to ambient conditions, making it in stainless steel was unnecessary, so it was made in nickel-plated aluminium instead. Teflon® insulated signal transmission lead wires were held within a silicone rubber sleeve and a flexible stainless steel conduit for mechanical protection.
Once the unit was developed it was named the SSA200. The client initially took a delivery of 10 units for testing and evaluation, and several fermented product batches were produced and shipped. All 10 of these units performed to specification, resulting in the client placing an order for another 60 units for the remaining fermentation vessels.

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