How Ramp Heating in Hotplate Magnetic Stirrers Improve Results

Ramp heating is a highly useful function to achieve more precise control over temperatures used in hotplate magnetic stirrers.  These stirrers find wide application in chemical and biological laboratories of industrial enterprises, universities and pharmacies.  Their function is to help researchers develop processes that later are scaled up for commercial production.

Hotplate magnetic stirrers equipped with a ramp heating feature allow a closer prediction to how final processes should be structured.

This post will look at

  • How magnetic hotplate stirrers operate
  • Ramp heating: how researchers control sample heating and cooling
  • Features to look for in a hotplate magnetic stirrer

How Magnetic Stirrers Operate

The principle is quite simple.  Flasks and beakers are placed on a stationary plate mounted on the unit.  Below the plate is a motor-powered magnet, the speed of which is controlled by the operator. A specially coated bar magnet is placed in the beaker or flask that contains samples to be processed.

When activated the motor-powered magnet rotates, thus causing the magnet in the sample container to rotate.  The mounting plate remains stationary.

For basic magnetic stirrers operators can set stirring speed and time.   Hotplate magnetic stirrers provide control over the sample heating and cool-down temperatures by increasing and decreasing heat then removing heat to the plate holding sample containers. Hotplate magnetic stirrers such as the CAT MCS 77 and MCS 78  are examples.

These stirrers can process samples to 10 liters in size at temperatures to 440⁰C and at stirring speeds from 60 to 1600 rpm.  A soft-start feature avoids sample splashes – a major concern at high temperatures.  The plates are made of Ceran; other models have anodized aluminum plates.

Ramp Heating: How to Control Heating and Cooling

Controlling the heating and cooling cycle when operating a magnetic hotplate stirrer is important when establishing production processes.  An example of uncontrolled heating is your microwave oven.  Except for your selection of power levels, the heat is there almost instantly when activated.

You have some degree of control over ramping heat with your kitchen stovetop burners but it requires constant monitoring not to scorch the sauce or spoil the soup.

Ramp heating means applying heat gradually to samples in a hotplate magnetic mixer.  It is accomplished by programming the unit to apply, hold and reduce heat as desired.

There are two ways to accomplish ramp heating using the CAT MCS 77/78 units.

The first (and recommended method) measures and controls the heating and cooling temperature of the sample; the second only measures and controls the temperature of the hotplate.  For the sake of simplicity (and for more satisfactory results) we describe the first (recommended) method.

Certain hotplate-equipped CAT magnetic stirrers, notably the MCS 77 and 78 but others as well,  have a program enabling researchers to precisely control the heating and cooling rate of samples.  In order to do this the magnetic stirrer must be equipped with an optional Pt100 temperature probe that effectively takes over the operation of the magnetic mixer once you have programmed it.

Using the CAT MCS 78 programmable stirrer as an example the ramp function is engaged by pressing the ramp key on the control panel.  That makes sense, doesn’t it?  This enables researchers to set the desired slope of liquid temperature in increments of 1⁰C per hour by using the up and down keys.

In the case of the CAT MCS 78 stirrer its maximum heating temperature is 440⁰C, so setting the ramp value to 440⁰ per hour effectively disables the ramp function.

An example is always good, right?  If you select a heating ramp of 50⁰C per hour and the actual probe temperature at the beginning is 100⁰C the sample will reach the set temperature of 150⁰C in one hour.

Controlled cooling is also managed with the ramp function and Pt100 temperature probe.

Note that this function is engaged to set the maximum increase and decrease of sample temperature over the selected time period.   Obviously one will not be heating water to 440⁰C.  The sample’s ability to be heated to the selected temperature depends on the boiling point or other characteristics of the sample.

Oh, and if you are curious, the “other method” is accomplished using the unit’s keyboard.  But again, this measures the hotplate temperature, not the sample temperature.  That’s why we strongly urge investing in the pT100 temperature probe

Further Functionality

The MCS 77 and companion MCS 78 hotplate magnetic stirrers are equipped with a multifunction timer supporting individual temperature and stirring profiles over a period of time.  This feature controls stirring RPM, hotplate and probe temperature, up and down temperature ramping and a cyclic mode to repeat the number of execution cycles.

While we used the CAT MCS 77 and 78 models in this post other CAT magnetic stirrer models have similar features but without the ramp heating option.  The best way to get answers to your magnetic mixing challenges is to ask us a question.  We’ll get back to you as fast as we can with the right information and recommendations.

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