Understanding Overhead Stirrer Terms

What’s “fuzzy logic?”

It’s not a description of the “thinking” that seems to go on in Congress, but instead a term applied to a way technical equipment is automatically controlled.  In this post we list many of the terms you’ll need to know when you shop for an overhead lab stirrer.

 Why You Should Understand Overhead Stirrer Terms

CAT Scientific’s scientific overhead stirrer offerings has been selected to give researchers in pilot plants and laboratories a choice of models that allow them to specify the model that best fits their requirement.

These versatile overhead mixers are used for applications involving sample sizes to 200 liters and those likely for processing samples that either have, or will develop, viscosities too high to be properly mixed by magnetic stirrers generally limited to samples up to 10 liters.

Taking the above note a step further, sample viscosity, either at the outset or as it changes during processing is an important consideration in specifying an overhead lab stirrer.  This is because stirring tool configurations, described below, react differently to viscosities.

But we get ahead of ourselves.  So to get to the point of this post we provide this handy

Alphabetical Glossary of Common Overhead Stirrer Terms

Auto Power Reduction:  The stirrer drive motor senses increasing sample viscosity. Above a certain limit it reduces stirring power to avoid overheating and possible burnout. (See also viscosity.)

Chuck Capacity:  The widest diameter stirring paddle shaft that the stirrer will accept.   CAT shafts are typically 6, 8 and 10 mm in diameter.

Encoder Wheel:  Allows operators to easily set parameters including speed, timing, and other settings.

Fuzzy Logic: The logic applied to the control of the overhead stirrer.  The term means reasoning that is approximate rather than fixed and exact.

IP:  Ingress protection, typically a 2-digit designation indicating protection against solid objects and dust (the first digit from 0 to 6) and moisture (the second digit from 0 to 8).  Higher numbers signify better protection for the electronics and controls operating the stirrer.

LCD:  The liquid crystal display showing operating data actual and/or programmed into the overhead stirrer control panel.

Microprocessor Control:  A term applied to the technology that monitors and controls the operation of programmable overhead stirrers.  It includes the RS232 interface that enables networking with other lab equipment, printers, and computers.

Ncm: Newton centimeter – a unit of torque or energy equal to 0.01 Newton meters.  A higher number usually equates to more power to process higher viscosity samples but it also can indicate limitations in stirring speed.  As examples:

  • The CAT R80D-PC overhead stirrer for dynamic viscosity has a torque rating of 80 Ncm over its entire speed range of 20 to 700 RPM.
  • The 2,000 RPM R100C unit, in contrast, has a maximum torque of 150 Ncm but is limited to 20 minutes of operation at that value.
  • Our most powerful stirrer, the R100CT, has a 600 Ncm rating but only stirs to 500 RPM.

(See also Torque and Viscosity.)

Permissible Ambient Temperature:  The temperature range in the environment where it is OK to operate the overhead stirrer.  A range of 5⁰ to 40⁰C is typical.

Safety Systems:  Features that include the stirring paddle being stuck or blocked; drive motor temperature monitoring, and a self-test of all safety functions after the equipment is turned on. If the system detects a malfunction the unit will either slow down or shut off until the condition is rectified.

Soft Start-Stop: A desired feature for variable speed stirrers to avoid splashing when powering up and cutting back on stirring speed.

Steplessly Adjustable Speed:  The ability of an overhead stirrer to smoothly ramp up and down the stirring speed.

Stirring Tools: A range of paddles, impellers and blade configurations attached at the bottom of the stirring shaft.  The configurations and geometries are designed to perform different types of stirring action.  Here’s a brief introduction to stirring tool configuration.

Torque: A measure of how much force acting on an object causes that object to rotate about an axis.

Torque Output Display:  A feature of the CAT R100C overhead stirrer, it is a display of true torque at the shaft in Ncm.

Viscosity:  Thickness or stickiness; ease or difficulty in flowing.  High viscosity materials place a resistance on the overhead stirrer paddle and motor.  (See also Ncm and Torque.)

Volume:  In this instance the volume of product the overhead stirrer is capable of handling in a beaker or flask.  It ranges from 35 liters in our R20 model to 200 liters in the R100 models.  Note that viscosity must be taken into account along with stirring speed when considering the volume of sample to be processed.

We hope you find this information helpful.  But if you need more input please contact us with questions you have on selecting an overhead stirrer or for other information on the CAT Scientific line of laboratory and pilot-line processing equipment.


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