The Ohaus Guardian 3000 Hotplate Stirrer

https://eu-en.ohaus.com/en-EU/Guardian3000-3

A hot plate stirrer is an important piece of kit to aid a laboratory technician’s daily work. For it to be useful, it must be reliable, robust and easy to use. The Ohaus Guardian 3000 hotplate stirrer is an example of such a piece of equipment.

There are three different versions available, which differ in the top plate size and material aspect. Two versions have a square ceramic top plate (18 cm x 18 cm and 11 cm x 11 cm respectively) and a maximum operating temperature of 500^OC. A third version has a 13.5 cm diameter round top plate made from ceramic coated stainless steel and a maximum operating temperature of 380^OC. Apart from the different operating temperatures, all three versions are believed to operate in a similar manner.

The version tested by ASE had the 18 cm square ceramic top and was made of cast metal, making it feel solid and robust and weighing just less than 4 kilogrammes.  Once the unit is plugged into the mains, a digital display informs you that the unit is plugged in but switched off. This is quite a useful feature, as it reminds you to isolate the unit at the wall socket when not in use. There is an on / off rocker switch on the front of the unit that is easy to access, but which is recessed to avoid the user turning on the unit inadvertently.

After switching on the unit, the display shows the most recent stirring speed used in rpm, and two alternating temperature values: the hotplate temperature setting when the unit was last used and the current hotplate temperature. There are just two control knobs for the unit: one for temperature and one for speed of stirring and so, by necessity, each knob has multiple functions. The temperature is simple to set, just by rotating the temperature control knob to the required hotplate temperature. Pressing the knob with a long ‘press’ starts or stops the heating process. Pressing with a short ‘press’ allows the user to modify the required temperature during use without interrupting the heating process. Similarly, the stirring speed is set by rotating the speed knob and starting or stopping stirring with a long ‘press’. A short ‘press’ allows the stirring speed to be modified. One of the most useful features of the unit is being able to set the hotplate temperature, knowing that once it reaches that temperature, it will maintain that temperature exactly. This avoids issues such as inadvertently boiling solutions or being unable to leave the unit unattended for more than a few minutes.

One really useful feature is a 10 mm threaded hole to the left rear of the unit. This allows a standard clamp stand rod to be screwed into the unit and so a boss and clamp can be used to hold a thermometer or temperature probe in place. Although these could be held with a separate clamp stand, this integrated set-up does mean that the unit can be moved on a bench more easily. A second really useful feature is a 3-pin DIN socket for a temperature probe, also situated to the rear of the unit. Using the unit with a temperature probe transforms the way in which the unit can be used. A third feature is the illuminated icon to warn you that the hotplate is hot. As soon as the hotplate exceeds 40^OC in temperature, the icon illuminates and remains on until the temperature drops below 40^OC, even when the unit is switched off with the toggle switch.

They say that the proof of the pudding is in the eating and so tests were conducted on the unit, four in total. For each test, a 600 ml beaker with 500 ml of water was placed on the unit, with a stirring speed of 500 rpm. This is a summary of the results:

Test 1: Stirring 50 g of sodium chloride crystals

The sodium chloride crystals were added while the stirrer was switched off. On switching on the unit, the magnetic stirrer started rotating immediately and quickly reached 500 rpm despite being ‘buried’ in solute.

Test 2: Heating 500 ml of water to 50^OC with temperature probe

The water temperature increased at a fairly steady rate of about 1^OC per minute until the temperature reached approximately 47^OC. The rate of temperature increased, then dropped to about 0.5^OC per minute until reaching the target temperature. Once reached, the temperature remained steady at 50^OC. Overall, it took about 40 minutes to complete this test.

Test 3: Heating 500 ml of water to 50^OC without temperature probe (Trial #1)

Setting the hotplate temperature to 50^OC resulted in an incredibly slow rate of heating. The unit quickly and accurately set the hotplate to 50^OC, but this resulted in the water temperature only rising at a rate of 7^OC per hour. This test was not completed. As this method of use was impractical, a fourth test was conducted with a higher hotplate temperature.

Test 4: Heating 500 ml of water to 50^OC without temperature probe (Trial #2)

Setting the hotplate temperature to 300^OC resulted in a fast rate of heating. The water temperature increased at a rate of about 2^OC per minute until the temperature reached 47^OC. At that point, the hotplate temperature was manually reset to 50^OC. Residual heat in the hotplate took the water temperature to 51^OC. Overall, it took about 20 minutes for this test.

The unit has a recommended retail price of £363 and a stainless-steel temperature probe will set you back an additional £105. However, for a busy lab tech, having the facility to make up solutions without having to constantly monitor them is worthy of consideration. If used without the probe, the advantages of the unit’s smart electronics are less obvious. However, having a digital display of the actual hotplate temperature in real time is useful in itself. Another useful facility offered by the electronics are safety controls to stop heating before an over-temperature condition occurs.

The Ohaus Guardian 3000 is a good example of how smart electronics are improving basic laboratory equipment but, to really make the most of it, you really need to purchase the optional temperature probe. The fact that it will heat to a specific temperature and then maintain it is a great feature, and one that would be very useful for the busy lab tech.

The Ohaus Guardian 3000 Hotplate Stirrer – Summary Evaluation

https://eu-en.ohaus.com/en-EU/Guardian3000-3

A hot plate stirrer is an important piece of kit to aid a laboratory technician’s daily work. For it to be useful, it must be reliable, robust and easy to use. The Ohaus Guardian 3000 hotplate stirrer is an example of such a piece of equipment. The Ohaus Guardian 3000 is a good example of how smart electronics are improving basic laboratory equipment

There are three different versions available, which differ in the top plate size and material aspect. The version tested by ASE had an 18 cm square ceramic top and was made of cast metal, making it feel solid and robust and weighing just less than 4 kilogrammes

Very useful features include:

• An on / off rocker switch on the front of the unit that is easy to access, but which is recessed to avoid the user turning on the unit inadvertently.
• Being able to set the hotplate temperature, knowing that once it reaches that temperature, it will maintain that temperature exactly.
• A 10 mm threaded hole to the left rear of the unit. This allows a standard clamp stand rod to be screwed into the unit and so a boss and clamp can be used to hold a thermometer or temperature probe in place.
• A 3-pin DIN socket for a temperature probe,
• An illuminated icon to warn you that the hotplate exceeds 40^OC in temperature
• Safety controls to stop heating before an over-temperature condition occurs

They say that the proof of the pudding is in the eating and so several tests with and without a temperature probe. The test results were positive particularly when a temperature probe was connected to the unit.

The unit has a recommended retail price of £363 and a stainless-steel temperature probe will set you back an additional £105. However, for a busy lab tech, having the facility to make up solutions without having to constantly monitor them is worthy of consideration. However, to really make the most of it, you really need to purchase the optional temperature probe. The fact that it will heat to a specific temperature and then maintain it is a great feature, and one that would be very useful for the busy lab tech.