Understanding Temperature Controlled Vs Temperature Corrected Refractometers.

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Understanding Temperature Controlled Vs Temperature Corrected Refractometers.

Temperature Controlled Vs Temperature Corrected Refractometers – Rudolph makes two refractometers, the J47 and the J57 that both look similar, both have similar specifications. The J57 is 30% more expensive —why?

Let’s look at this in a brief experiment.

What we have here is 2 nearly identical looking refractometers. The J47 and the J57

These two instruments have very similar specifications and they look almost identical. The only way to quickly tell them apart is the J57 has cooling fins and the J47 does not. What’s the difference in actual operation though?

Temperature Controlled Vs Temperature Corrected Refractometers what is the difference?

The J47 is temperature of corrected while the J57 is fully temperature controlled.

These instruments have both been on for a while and you what you’ll notice is this sitting in a room at ambient temperature the instrument will read approximately 22-23 degrees Celsius.  The J57 being temperature controlled will hold steadily at exactly 20 C.

Why does that matter in a real-world situation? If you’re working in a factory environment where most of your samples are primarily sugar and water, temperature correction will work well.

As an example we will measure something simple like sweet ice tea. You will see it will read about the same on both instruments. However, let’s imagine now that our factory is ISO-certified. In a situation like this all instruments would need to be regularly calibrated back to a traceable standard.

Temperature Controlled Vs Temperature Corrected Refractometers – Using Calibration Standards

What I have here is a calibration standard traceable to NIST which is made for Rudolph by a company named Cargill. While different countries will each have different authorities to answer to, using a traceable standard will always be a component of remaining in compliance. In addition the calibration standard will not be sugar and water based as these are not stable over time.

In this case the standard we will use should measure very close to 9.94 BRIX (Pronounced like bricks). Thus, If the refractometer measures this correctly it proves the refractometer is properly calibrated and within specifications.

If we place the calibration standard on both refractometers they should in theory measure the exact same results. What we find is the temperature controlled refractometer measures the calibration standard almost perfectly. The temperature corrected refractometer however cannot measure the calibration standard since temperature correction will not work on a sample (or standard) that is not primarily sugar and water.

We have just seen exactly why even a refractometer that measures primarily sugar and water based samples will still need to be Temperature Controlled. The issue becomes traceability.

[Refractometers come in many shapes, sizes, accuracies, and with different features. Selecting the right refractometer for your application is often critical! Many applications require samples to be measured at specific temperatures, 20c for example. To determine the BRIX of a sample at 20c two methods can be employed to determine what the BRIX would be at 20C when the sample is not. Method one is to use tables to take the actual reading and mathematically correct back to what the temperature would be at 20C. The second method is to accurately hold the sample temperature at 20C and then make the measurement.]

Temperature correction is acceptable and accurate for certain samples – those samples that are primarily sugar and water will measure well with temperature correction only, even when the sample temperature is far from the desired measurement temperature.

Samples including calibration standards that are not sugar and water based must be measured using accurate temperature control.

Production facilities that require the refractometer be calibrated to a NIST traceable standard must be Temperature Controlled – Why, NIST Traceable standards are not Sugar and water based.

For more advice about selecting the correct refractometer for your application please contact us at Rudolph Research Analytical.