Media control and the concept of embedded fluidic systems for instrumentation. By Gary Stevens
We hear much about the use of ‘embedded electronics’ and the ‘intelligence’ that is incorporated into modern instrumentation systems, but less about any advances made to the ‘plumbing’ of these high-tech devices.
Plumbing may seem an archaic expression for describing the routing of a fluidic system in a sophisticated instrument, but if you are still using tubes and fittings to connect ‘everything’ together, that’s exactly what it is.
Although we will always need to use tubes and fittings somewhere in the instrument it is worth considering the alternatives to identify what benefits are available from other technologies. It is worth remembering that a considerable number of faults emanate from leaky connections that find their way inside that pristine instrument we have just designed or purchased.
Analysis of the flow paths of the various media and functions to be controlled is essential to evaluate a suitable method of interconnecting the various elements of a system, taking into account such aspects as internal volume, switching functions, the possibility of pre-mix of reagents, any suspended solids that may be present and materials compatibility.
Conceptually there are a number of alternative methods for connecting discrete fluidic components together:
* Composite functioning components
* Manifolded components
* Manifold-mounted or cartridge components
* Hybrid bespoke components
Composite components are where a specific function has been built into a single entity such as the dual three-way valve shown in Fig. 1. In this device two independent valves are operated together by a single solenoid actuator; this ensures a synchronous operation where it is required.
Manifolded components are just that, a method of assembling a number of similar components to form an array for a specific mode of operation, and a sample of that is shown in Fig. 2. The individual components cannot be serviced independently. However, special designs for in situ cleaning and fast flush purging can easily be achieved.
Manifold-mounted or cartridge designed manifolds are usually client specific and can incorporate various devices from pumps and valves to sensors and passive items such as restrictors and filters. The possibilities are numerous and allow for complex systems with the benefit of minimal external connections, excellent serviceability and good system integrity.
Hybrid or bespoke components are by their very nature designed specifically for a particular function and can be seen as a sub-assembly. The product can be anything from a simple passive flow restrictor with a filter to a fully self-contained pumping and mixing station or anything in between. Fig. 3. shows a double flow restrictor with check valves specially designed into the same body envelope as a standard manifold mounting solenoid valve. Serviceability, rapid change of restrictor size and standardisation of mounting were achieved with this design.
However, whilst being an advocate of modularisation of fluidic systems, the reality is that in some instances it is just not practical, most notably where there are any solids in suspension that can block the flow paths inside a manifolded system.
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Gary Stevens is managing director of NResearch.