PRH - Flexible Modular Design

Every process line has a particular function and performance requirement. Close co-operation with the customer is key to ensuring the refractometer system is installed successfully. A basic design is adapted and configured to take account of the technical needs and budgetary limitations of the customer.

The basic process refractometer system comprises four elements:

The system sensor is the PRH Refractometer - a compact, fully sealed robust unit, constructed in 316 stainless steel, which can be attached to a variety of manifold types to give an assembly that is compatible with the existing process line and meets industry standards for safety and hygiene.

Materials of construction and seals are selected to have widespread product compatibility. The instrument is sealed to prevent ingress of dust and moisture. The sapphire prism and flow chamber are designed to withstand typical line pressures and rigorous cleaning conditions.

The reading scale and measuring accuracy are selected to suit the product type and required measuring performance; temperature compensation is used to counteract fluctuations in product temperature. Standard scales include Refractive Index and Brix with sugar (sucrose)-based temperature compensation, but other scales (% concentration) and temperature compensation relationships can also be used.

The instrument incorporates an LED display, which can show the reading (concentration) or product temperature and alarm condition. The instrument also monitors continuously the quality of the prism surface and alarms can be triggered by this parameter. Output signals in either digital or analogue form are available via a junction box.

The PRH Refractometer has been designed to function continuously without the need for frequent calibration. However, if necessary, in-situ calibration may be performed using a special maintenance software package. Calibration is routinely performed as part of a service, which will be required at intervals depending upon the nature of the product and installation type, but typically six-monthly.

A manifold is needed to attach the PRH Refractometer to the process line, either directly or within a by-pass loop. The type of manifold will vary according to the product being measured, pipe dimensions and line coupling and quality and hygiene standards demanded by the process, for example, crevice-free welds, polishing etc. In some cases it may be possible to mount a refractometer onto a product tank using a special flange.

Special manifolds may incorporate a prism-cleaning device such as a water or steam jet or even an ultrasound probe. This optional feature may be recommended where products cause periodic 'fouling' of the prism. This can be a problem when the fluid contains particulate or colloidal material that can adsorb onto the prism surface and cause a film to build up over a period of time. When adhesion is weak and the film can be easily removed by agitation, a perpendicular manifold in which the flow is directed at the prism face may be effective in preventing excessive fouling. Manifold orientation is also important.

A number of manifold designs, based on regular pipe dimensions and couplings (imperial and metric) are offered as standard components. Typical couplings include IDF, RJT, Swagelok and Tri-clamp. However, many manifolds are made to order according to customer specifications and a B+S engineer will help the customer to decide the best configuration.

A Data Capture Software Package can be used to log and display results. Data are stored in files that correspond to pre-determined intervals (seconds to hours), thus providing flexibility to breakdown product runs into manageable periods for analysis. Recorded parameters are: Refractometer reading (e.g. product concentration), product and instrument temperatures and prism quality.

Results are displayed numerically and also as line charts which can be customised in terms of time-scale and numerical range. Alternatively, data files can be analysed using standard office software such as a spreadsheet or database.

The Maintenance Software Package enables periodic calibration of the refractometers and (re)setting of instrument parameters such as scale, temperature compensation and alarm and analogue set points. This software can also be used to set up a network of instruments. Plant or contracted service engineers responsible for instrument and network maintenance can use this package.

A PLC package can be supplied for specific plant control functions. Specialist engineering services may be required for certain installations.