Protection & Housings
Typically, users prefer compact designs, as long as the housing may not act as the probe carrier (see example YARA N Sensor).
A compact design implies that components are close together. In respect to electronics it is an advantage of lines are short. On the other hand, power lines or such carrying pulsed signals should not be too close to video cables carrying small analog signals. Additional shielding might be necessary.
Compact housings typically have lower weight too. Otherwise, the selection of components (incl. power supplies) define the overall weight; often, not much can be done about this.
For lab-oriented use size is not critical, cassette based 19” housings are offering a high flexibility, for light sources and spectrometer modules can be easily exchanged, to optimize such a system to varying demands. This is quite useful during the development of metrology methods.
Functional components such as light sources and spectrometer may be separated. Two smaller compartments might be better than one bigger. Also, the big heat source light source can be kept at distance from the heat sensitive device spectrometer. However, it should be kept in mind, that the operation of a source and a spectrometer is not independent: on-off control, flash trigger, counter, shutter all may interact with the main operating electronics. Back to top ▲
Heat Generation and Dissipation
Less is often more, definitively the case when it comes to energy consumption and heat dissipation. Main consumers are the light sources, for these are quite inefficient. LEDs as efficient sources have drawbacks such as high sensitivity of the wavelength emission on temperature and driving current. High-sensitive spectrometers and probe setups with high efficiency lower the demand on light generation.
Another heat generating devices are thermo-electronic coolers. One should always consider twice if it is necessary to cool a detector chip. At short integration times this often can be omitted. A high-sensitivity spectrometer and high-efficiency measurement setups are again beneficial.
Heat generating devices should not be placed to components which are temperature sensitive such as detectors. This influences the arrangement of components. Back to top ▲
Arrangement of Components
This topic influences most others, so please check these for details and considerations: heat dissipation, electronical interference, compactness, positioning of interfaces. Arranging components is one of the main design tasks. Back to top ▲
Modern designs try to avoid any parts which require maintenance. In case of light sources, this cannot be fulfilled, for there is none which lives forever. Some have to be exchanged frequently such as D2 and halogen ones (every quarter at 24/7 operation). In such cases, ease of access is an important design requirement. If not possible, such source might be replaced by a flash source with
longer lifetime and service intervals. Therefore, easy replacements of light bulbs have to be taken into account while designing light sources. Back to top ▲
Positioning of Interfaces
The classical arrangement is optical interfaces on front while the electrical connections are on the back. Integration of spectrometer units into bigger cabinets or racks change requirements to allocating all interfaces on one side (call it front).
Connectors such as SMAs for fiber-optics should not be too close together, so the attachment of cables can be handled stress-free.
Mechanical interfaces are given in case of rack-mount housings. For customized housings, these have to be matched to the installation conditions. This is also valid for the other interfaces. Needless to say, that the positioning of threaded holes and such have to be closely correlated with the material strength of the enclosure and, to a lesser extend if panels are strong enough, the distribution of weight inside. Back to top ▲
Depending on environmental conditions, different requirements to house the functional components are required.
A housing may have to protect against:
- Electro-magnetic interferences (both ways)
- Hazardous material
The protection demand is defining the outer hull / housing to integrate all necessary component. The good protection against dust and water requires a seamless enclosure A good shielding against electric interference from outside comes along, but the heat dissipation becomes a challenge, for no venting openings or fans are allowed. It is important to keep in mind to avoid any excessive heat generation inside a tight housing, e.g. strong incandescence light sources, cooling of detectors and such. Any internal TE cooling elements should be avoided, for they generate heat net-wise. Heat exchangers (heat generating device on one side of the box, a cooling finger or even a thermo-electrical element on the other (outside) of the box. In many cases, just a massive metal housing works. Water cooling would be the last resort.
To protect a hazardous environment from blowing up, ex-proof cabinets are used and have additional requirements: over-pressure inside the housing to avoid any gas to leak in from outside, also restrictions about energy input respectively available inside the housing. Back to top ▲
Document with definition of the individual protection classes / zones (e.g. https://r-stahl.com/en/global/home/)
Visual aspects play typically no bigger role in industrial applications. Other aspects such as ease of access, error free operation are of higher importance. On the other side, painting a housing in company colors doesn’t hurt the performance, while other gimmicks might, at least cost. Back to top ▲