When it comes time to purchase an In-Line Refractometer, there are many issues to consider to insure that the right unit is selected for the right job. A properly applied instrument will deliver the results that you anticipate and will create a respectful relationship between the customer and the manufacturer. This is as it should be. Lets take a look at some of the issues that deal with the selection of an In-Line Refractometer

First on the list is the product to be measured. An In-Line Refractometer will measure the concentration of most dissolved materials in a solution. Now it is important to understand that the Refractometer makes this measurement by responding to the degree to which the direction of light is changed as it passes between two mediums. One is a known medium the other is an unknown. If the unknown medium (the one we want to measure) is clear and unobstructed and contains only one dissolved substance then there should be no problem. If there is more than one dissolved component of interest in the solution then it becomes impossible( utilizing the principles of Refractometery alone) to distinguish between them and the measurement value will be some composite of the substances. This does not eliminate the potential for a useful measurement however. You see if the dissolved substance we are interested in measuring in the solution is the only variable of any magnitude (ie ..the other(s) are constant or their respective amounts are small in comparison), then we can track the Refractive Index of the solution and reasonably conclude that any changes in RI are the result of the dissolved component of interest.

If the material contains suspended particles (undisolved material), or it is an emulsion liquid, this will also effect the light characteristics and therefore the measurement value. However, the reflected light from these particles can be compensated for in the PR-111 during the calibration process if they are present during the initial setup.

The bottom line is this: Most materials in solution can be measured. If there is any question about the compatibility between the instrument and the product, then perhaps it makes sense to do a product evaluation up front (before the purchase) to determine the feasibility of the application. This evaluation process is offered as a free service by AFAB at this time and is definitely worth doing for products where there is some concern. This is standard practice at AFAB and this service is available to all of our potential customers. We will provide an objective detailed lab report of our findings. This Evaluation Report will identify any problem areas and may very well determine whether the application is a good one or not.

The second and third areas of concern is the operating range of the product and it’s temperature range. The operating range is usually a percent concentration range or Brix range and is determined by the actual process itself. The instrument range should be selected so that it is narrow enough to provide maximum resolution and wide enough to include the minimum and maximum possible variations in product value. Usually there is a target value ( the products normal operating point) and then some reasonable plus and minus value. The product temperature range must also be considered since the Refractive Index (RI) of the product is effected by temperature changes as well and the instrument must be temperature compensated for these temperature changes so that it will not respond to them. So this means we must specify a minimum and maximum temperature operating range. The temperature range should be some target value plus or minus 20 degrees F. (or less). The standard measurement sensor (process probe) has a maximum temperature limit of 250 Degrees F.

The last items on the list are (1.) the product’s operating pressure range ( standard probe max pressure is 150 pounds per square inch) (2.) the operating voltage and frequency values. (120 VAC and 220 VAC are common voltage values and 50 Hz. and 60 Hz are common frequency values) and last but not least (3.) the size and material of the process adapter.

The process adapter is the process - instrument interface. The measurement sensor will be mounted on this adapter and may very well determine the success or failure of a well-intentioned application. These process adapters may be configured to suit the exact needs of the process. The materials range from PVC, Iron Pipe, Stainless Steel, Brass and others and range in size from as small as 0.3cc. (even smaller on special order) to as large as 12 or more inches. They may have flange connections, threaded connections, sanitary connections or whatever. They may even be equipped with a steam purge nozzle and controller, or a self-cleaning unit which uses the process itself to clean the sensor. These cleaning units are used in difficult applications where the process can coat the measurement prism. This coating will affect the measurement value and must be removed. The line size, material and any special requirements should be specified at the time the order is placed. Some typical pricing examples are listed here in our website.

Also please visit the CONTACT US Section of this website to forward this information to us. We will respond back to you with a quotation and/or any questions that we might have about your application.

A well-thought-out application is important to the success of the installation. It is our goal at AFAB to provide to our customers a quality, dependable product at a reasonable cost. We hope that the issues discussed here will provide some in-site to our potential customers and that it will help to insure a successful and profitable installation.

Fred Crawford
Senior Engineer
AFAB Enterprises

For more information contact:
Sales Dept.
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(352) 483-1222
(866) 623-1222
 
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