The Hellma laboratory probes illustrate the beginnings of the probe production with the use of quartz measuring heads. The development of the monolithic measuring heads was the result of many years of experience in the quartz-glass processing and cuvette production. These measuring heads are an integral part of the Excalibur laboratory probes, but also the Excalibur Extremely Precise process probes.
A unique case is the all-quartz probe, which is available exclusively from Hellma-Analytics. In the process edition with axial measuring gap, the entire probe including the flange is made of quartz glass. The probe is made entirely of quartz and no seals are used, making the probe resistant to organic solvents and many strong acids.
Process probes and measuring cells are usually made from stainless steel, but can be upgraded to Hastelloy.
Some probes, such as the Falcata line, are available in titanium. The titanium allows the windows to be brazed, eliminating the need of elastomeric seals.
For special applications, more specialized materials such as PTFE can be used. PTFE probes and measuring cells are particularly resistant to strong acids and bases.
The increasing demands for extremely high temperature- and chemical resistant products require a highly specialized technique for the permanent bonding of components. For this, the components, once assembled, are heated in an oven to a temperature far below the melting point of the glass used. This heating serves to strengthen the bond between the joined components.
The main advantages of this technology are that fewer optical components are needed and fewer phase transitions take place. These factors increase the overall transmission. Another benefit is the high precision, the resulting high path length accuracy and a better transferability of the methods between identical probes.
In a monolithic measuring head several functions are combined into a single optical component through a bonding process (see above). The number of phase transitions of the measuring beam is reduced to a minimum, resulting in very high light throughput.
Transmission probes and measuring cells with a monolithic head are a specialty of Hellma Analytics and have a much higher transmission than other technologies. At the same time they offer an unsurpassed precision and reproducibility of the optical path length.
High equality elastomer seals are extremely versatile through the use of different compounds. The material is tailored to the particular application in order to ensure a long service life. However, the elastomers are subject to an aging process which is increased by high temperatures or chemical attack by the measuring medium.
It is recommended to replace the seals regularly. A maintenance service is offered for process probes and measuring cells.
Sapphire windows can be brazed with titanium. Since the use of titanium results in limitations in strength and its possible temperature range, this technology can only be used with certain products.
Some products have an additional window on the inside to help protect the internals in the case of a probe failure. For example, the probe tube of the Excalibur HD FPT immersed in the process is hermetically sealed. Behind the second window is a secondary-containment that includes the optical connectors. In the event of damage, the risk of media leakage can be drastically reduced.
Some optics are hermetically sealed and filled with a protective inert gas under slight overpressure (e.g., Excalibur HD FCP cell). This significantly reduces the risk of moisture or contaminants penetrating the optics. These can also be used at lower temperatures (<5 ° C) without internal flushing.