Calibration and Metrology

Masy Perfects Unique Temperature Calibration Bath Process

Remarkable uncertainty is a win for customers

Let’s take a brief look at how it started. A temperature calibration bath is a calibrator with a uniform fluid enclosure adjusted to specific temperatures for test points. Why do metrologists love them? Calibration baths offer large volume and flexibility for calibrating temperature sensors that vary in shapes and sizes. The devices use a stirred fluid, such as water, silicone oil, ethanol, or methanol, to provide thermal contact in a stable and uniform temperature for sensor calibration. Masy uses Fluke calibration baths which are renowned worldwide for their performance. But, we didn’t stop there. Read on to learn how our groundbreaking methods deliver an extremely tight tolerance using traditional temperature calibration baths.

The Situation

Masy has the best calibration specialists, equipment, and laboratories. Over the years, our experts realized a significant challenge for customers. We noticed that there were essentially two choices to calibrate an SPRT standard. First, a fixed point calibration is a costly, very tedious, time-consuming process that gives an uncertainty that might be way too tight and more than they need. The second option is the traditional method of putting the SPRT in a bath for calibration, which results in an uncertainty that is too high and unacceptable for anyone who has made the financial investment in an SPRT. As a result, customers were left with only one practical option and forced to incur the unwanted cost burden.

Recognizing the situation, our team continuously revisited our processes and honed best practices looking for a solution. Not only to help our customers but to also create efficiencies and improve results that would take our calibration services to the next level. Examining the traditional use of temperature calibration baths, we realize several factors exist despite the highest quality equipment. As the mixer moves liquid around, there are inevitable uniformity issues. For example, you would need many thermocouples or RTDs around the bath to map the variations from the far corners, to the top and bottom locations. Other variables include changes in stirrer speed, voltage, and liquid viscosity. Sensor placement depth can also determine uncertainty with two-tenths to two-hundreds of a degree variation. These are inherent challenges that exist even with sophisticated devices and trained technicians.

The Masy Method

Using a traditional bath, our goal was to minimize these factors for the best possible uncertainty. Our team hypothesized that a block in the center of the bath with specific sensor placement would contribute to a tighter uncertainty. We tested that theory for blocks of various materials across various bathy types, i.e., salt. The results showed that the block acted as a conductor and an equalizer for a much more stable and uniform bath.

Next, we looked at tuning options from Fluke, the bath developer. Fluke offers an option for fine tuning your bath called “Super-Tweak” resolution mode. This shifts the controller display so that you can adjust the bath set-point to the fifth decimal place and gets you closer to an absolute temperature than any other controller. This helps remedy the issues with a proportional controller constantly adjusting heating and cooling to stabilize the temperature. However, remember that if you successfully get one sensor at plus or minus two-tenths of a degree, sensors in other places of the bath likely have more significant fluctuations. The ability to make such adjustments is valuable but only with a trained specialist and even with experience. The process requires much trial and error, time, and patience. Given the years of experience and metrology expertise, our team created exclusive algorithms and programs to perfect the fine tuning very quickly in each instance yielding very tight minute temperature variations.

Another factor contributing to diminishing accuracy is the strain on SPRT standards. First, we must acknowledge that a temperature standard that is good for -200o C to 660o C and moves from extreme cold to extreme hot stresses the resistor. This natural stress changes the measurement and causes the uncertainty to get broader and broader. Masy uses many SPRT standards calibrated for a very narrow ITS 90 range to circumvent this problem to minimize the strain. This prevents the sensors from facing broad variations in temperature and keeps the uncertainties very tight.

A Huge Win for Customers

Masy has a unique advantage over other calibration providers. With unbridled ingenuity, we have instituted proprietary best practices that combine a custom material block, expedited super tuning, and the ideal use of specific SPRTs at limited ranges to deliver unmatched uncertainties. As a result, we have successfully demonstrated a repeatable process that saves customers significant time and money. In addition, we have perfected a process that allows customers to get 5 or 6 millikelvin uncertainty calibration at a competitive price with an SPRT temperature bath calibration procedure—rivaling the more expensive alternative of a fixed point calibration.

Like many other business areas, Masy has invested countless hours and money into optimizing processes that ultimately benefit our customers. We have the remarkable ability to provide customers with an option for world-class calibration services beyond what any other lab can offer. When the NIST accreditation body visited to accredit our uncertainty for the baths, the representative proclaimed that it was “not possible.” Of course, we invited him to investigate. Further, we demonstrated our processes and we passed. Masy took the superb technology offered in the Fluke unit as designed and coupled it with years of knowledge to improve upon the precision and thus the service level for our customers.

For nearly 40 years, customers have trusted Masy for top-quality SI traceable calibration services, quick turnaround, letter-perfect certificates and the lowest industry uncertainties. Visit for a full scope of our calibration capabilities or call 1-978-433-6279.