How Microprocessors Improve CAT Hotplate Magnetic Stirrer Performance

Hotplate magnetic stirrers perform mixing cycles that can reach temperatures as high as 450⁰C (840⁰F).  Accidents or malfunctions at these temperatures can result in significant problems – including burns to lab personnel and damage to adjacent equipment.  In this post you will understand how microprocessors contribute to processing accuracy and safety in CAT hotplate magnetic stirrers.

But first:  A brief intro to hotplate magnetic stirrers.  For those of you familiar with this lab equipment, feel free to skip to the role of microprocessors in their operation.

What is a Hotplate Magnetic Stirrer?

Benchtop hotplate magnetic stirrers incorporate a motor-powered rotating magnet in their base.  This is the only moving part.  Beakers and flasks containing samples to be processed are placed on the unit’s stationery plate.  Along with the sample the container holds a loose, coated bar magnet called a flea.

When the unit is activated the motor-driven magnet causes the flea to rotate as well, providing the stirring action.  Stirring speeds can be controlled up to 1600 RPM.  A slow start helps avoid splashing media from a beaker.

Magnetic stirrers equipped with a hotplate base add the capability of heating samples during the stirring process as noted above.  They are also equipped with a timer, allowing researchers to attend to other tasks while the mixer does its job.  Digit LED displays show programmed and actual performance values.

The Role of Microprocessors in CAT Hotplate Magnetic Stirrers

Every CAT Scientific hotplate magnetic stirrer has a microprocessor control (MC) system.  Here’s a bit of background.  Then we will give you more on what they control.

Microprocessors first came into use about 30 years ago.  Their first application was in electronic calculators.  Today, applications are practically endless.

What do they do?  As the name suggests they are small (micro) and they control things (process).  Do some web research  and you will learn that these clever devices are found in appliances, automobiles, smoke alarms, battery packs, your DVD system and iPods.  For example.

CAT first incorporated MCs in 1991.  That hotplate magnetic mixer has been updated and along with others in our line of magnetic stirrers is offered today by CAT Scientific.

In this application the MC is a critical component of not only the operation of the magnetic stirrer but also is a key component in the equipment’s active and passive safety elements.

Scientists and researchers can program the magnetic mixer but it is the microprocessor control that takes over to make certain that the parameters are being met.  Parameters monitored, together with the optional but recommended Pt100 temperature probe include

  • Maximum temperature
  • The safety temperature
  • The liquid temperature
  • The shutoff function timer

The microprocessor detects whether the probe temperature changes in relation to the hotplate temperature.

That is, according to the probe the liquid temperature is not increasing but the hotplate temperature is.  In this situation the cause could be that the liquid is below the level of the probe tip, which could be caused by evaporation or a leaking container.

If this occurs the microprocessor turns off the heat but starts or continues the stirring function until the liquid cools down.  A warning light is illuminated on the mixer control panel display.  The mixer is then shut down.

Participating in this decision making on the part of the MC is the magnetic stirrer’s fuzzy logic feature.

What’s Fuzzy Logic?

Together with the MC feature CAT Scientific magnetic stirrers feature something called fuzzy logic control.  It’s a funny term as it suggests that something may not be just quite right.

Fuzzy logic is not like “black or white” or “yes or no” but instead more like shades of gray. As defined by contributors to Wikipedia it takes into account approximate values in making a decision on continuing the operation of the mixer.

A third party to managing your CAT magnetic stirrer is a feature called PID-controlled temperature curves.   A good conversation starter (or killer as the case may be) at your next cocktail party is explaining that PID = proportional integral digital controller.

PID partners with its pal fuzzy logic to adjust the operation of your equipment to minimize errors or deviations from the parameters you set.  It can also manage the temperature ramps of the stirrer, or how hotplate heat is applied and adjusted throughout the process.

If you’d like to know more about the CAT line of magnetic stirrers feel free to contact us with your questions.

 

Bob Wilcox

Bob Wilcox has represented CAT Scientific’s family of homogenizers, magnetic stirrers, liquid handling and related laboratory equipment since 2002 when Staufen, Germany-based CAT Ingenieurbüro M. Zipperer GMbH established operations in North America. Bob oversees CAT Scientific laboratory apparatus sales and service organization from the company’s headquarters in Paso Robles, CA. He also is in charge of the parent company’s line of JetCat jet turbines, turboprop, and helicopter power plants for hobbyists’ radio controlled fixed wing and helicopter model aircraft. -- Earlier in Bob’s career he was involved in visual and special effects as well as camera and electronics supervisory responsibilities for the motion picture and television industry.

Leave a Comment