When using a magnetic stirrer, the two main factors you can control are speed and temperature (the latter with a hotplate stirrer). In most cases, the ability to increase speed gradually is beneficial, and in some cases, increasing heat gradually can be desirable too.
Speed ramping and ramp heating both offer benefits, including improving safety and lowering the chance of ruining or losing your sample. In this post, we’ll look at the full set of advantages of both features.
Speed ramping enables you to increase the speed of the stirrer slowly, instead of having it start quickly. Speed ramping has a couple of main benefits:
- It prevents splashing which can be caused by reaching fast speeds too quickly. If samples spill, this can cause a safety issue, especially when handling corrosive materials. Plus, you’re running the risk of losing some of your precious sample.
- Speed ramping can also prevent decoupling (spin out) of the magnetic stir bar, which is another common issue when reaching high speeds too quickly.
Ramp heating gradually increases the setpoint temperature and helps avoid thermal shock. Thermal shock occurs when different areas of an object expand by different amounts due to applied heat. This can cause ceramic hotplates or glass sample vessels to crack.
Some models, such as the Jeio Tech TS Advanced Hotplate Stirrers have options when it comes to temperature control, and you can decide how quickly you would like the plate to heat up. However, speed ramping can also be achieved with models that don’t have the feature built in, by using special thermoregulators or controlling the temperature manually.
Using a Thermoregulator for Ramp Heating
Some hotplate stirrers are compatible with sensors such as the VTF EVO Vertex Digital Thermoregulator that give you increased control over temperature settings. This one in particular will wirelessly connect to your PC, from which you can monitor and control the temperature in real time.
While some thermoregulators (such as the basic VTF model) allow for accurate maintenance of a set temperature point, the EVO version also comes with software that allows for heat ramping control. This enables you to program the system such that the temperature increases at a specified rate.
If you need to be able to set and forget it, then this is a great solution. Of course, these thermoregulators aren't exactly inexpensive. For example, a basic VELP VTF Digital Thermoregulator costs $320 while the EVO model along with the Wireless DataBox will set you back $669. For comparison, the relatively simple Scilogex PT1000 temperature probe costs $120 (more on that one below).
Ramping Heat Manually
If a thermoregulator isn’t in the budget, you could ramp up the heat manually. The simplest (and most inexpensive) way to ramp heat a sample would be to manually increase the heat setting gradually, using the controller. Bear in mind, using this method, you’re only controlling the temperature of the plate and not that of the sample.
To make this a more accurate process, you can use a stirrer fitted with a probe, such as the aforementioned PT1000 RTD temperature probe, which works with certain Scilogex hotplate stirrers.
The probe measures the actual temperature of the sample and sends the reading to a microprocessor which will adjust the temperature such that the set point temperature is constantly maintained. Although, to gradually increase the temperature, you’ll need to be keeping an eye on it yourself.
Some hotplate stirrers, such as the Talboys Professional above, include a probe, while others feature one as an optional accessory bundle.