Previous sensor designs used in chemical process vessels required the manufacturer to stop production, drain the chemicals and get a technician inside the tank to install a new sensor. With this design, the temperature sensor can be replaced without stopping production.

In many chemical processes, the size of the process equipment makes ease of maintenance and repair critical issues.

Here's what happens when you mix three parts determination, on challenging design and a tight deadline -- all together in a glass-lined chemical reactor vessel.

Pfaudler Inc., based in Rochester, NY, is a supplier of glass-lined equipment such as reactors, storage vessels, columns and mixer systems. Brad Lesmeister and Pete Bernier of Burns Engineering worked with Bud Gruver, Pfaudler's manager of quality assurance and product engineering, to design a sensor for Pfaudler's chemical reactor vessels.

The chemical and pharmaceutical industries use these glass-lined reactor vessels to mix two or more chemicals in a safe, sterile environment. Pfaudler's Glasteel material -- glass that is fused with steel -- is a strong, virtually corrosion-proof composite material that ensures product purity. Pfaudler's chemical reactor vessels can be built to hold from one gallon to tens of thousands of gallons of chemicals.

Inside the vessel is an impeller that mixes the chemicals and a baffle that ensures proper mixing. The temperature sensor is located inside the baffle.

The Challenge

Pfaudler needed a new sensor design, and time response was a critical design factor.

"Although glass is a great insulator and it protects technicians from chemicals, it also works against you when you are measuring a change in temperature," Gruver explained.

"The new sensor needed a response time of 15 sec or less," noted Bernier, technology manager at Burns. "In control situations, you always want to have your sensor coupled as well as possible to the process. You want to see the change in temperature as it's occurring."

The new sensor also needed to be easy to re-move and replace. In the past, mounting the sensor configuration meant drilling a hole through the baffle and sealing it with a gasket. Oftentimes, chemicals would eat away the gasket, then destroy the leadwires or sensor, or contaminate the process. If this happened, the manufacturer would have to stop production, drain the chemicals, clean the tank, and get a technician inside the tank to install a new sensor - an expensive, time-consuming, noxious process.

The Solution

With ideas, parameters and objectives set by Pfaudler's Gruver, Burns Engineering was ready to begin designing.

"We came up with a sensor that you could insert from outside the process," Bernier said. "The tip-sensitive sensor and baffle receptacle were co-designed by personnel at Burns and Pfaudler."

The design allows Pfaudler to remove the sensor from the baffle and install a new sensor without having to drain the process or go inside the vessel.

"We used a segmented sheath design. The baffles can be 13 to 15' long. The ceilings aren't that high, so a rigid sensor that would go up and hit the ceiling could not be used. With this design, as the technician removes the sensor, the sheath comes apart in 3' sections," Bernier explained.

Burns tested the new design as well, according to Lesmeister, engineering and quality manager.

"Within a two-week period, we developed a new design, built prototypes and tested the design against a competitor's baffle for time response and removeability. After testing and approval at Burns, the prototypes and the competitor's baffles were sent to Pfaudler headquarters in Rochester," Lesmeister said.

The Results

The new sensor design has worked well, according to Gruver. "This solution provides a better, more convenient way to measure temperature inside the vessel and makes Pfaudler more competitive in the marketplace."

Pfaudler Inc., Rochester, N.Y., manufactures glass-lined equipment such as reactors, storage vessels, columns and mixer systems. For more information from Pfaudler, call (585) 235-1000 or visit Burns Engineering Inc., Minnetonka, Minn., manufactures temperature sensors such as RTDs and thermocouples as well as temperature transmitters and other process sensing and control instrumentation. For more information about Burns Engineering Inc., call (952) 935-4400 or visit