avatar: Loretta
Loretta
1 posts
Replied to Loretta's post on August 14th, 2012

How do I measure the radius of the Baxter Clinifuge - Heraeus?

avatar: Glenn PICKETT
Glenn PICKETT
63 posts
Replied to Loretta's post on August 16th, 2012

 Hi Loretta,

It is not so easy for an angle rotor as you need to measure the distance from the centre of the axis (shaft) to the farthest point from the centre.

However, I can tell you that the radius for the standard rotor supplied is 9.65 cm / 96.5 mm.

In general, for any centrifuge:

Calculate the radius from a given RCF and rpm

Radius [mm] = RCF [x g] / (1.118 x (Speed [rpm]/1000)²)

Where to measure the radius

maximum radius, Rmax, the distance from the centre of the drive axis to the farthest point of the tube from this central point. Most frequently, the radius is measured in mm. as this gives a whole number, e.g., 123 mm.

Note: When using adaptors, the above radius value is reduced by the thickness of the bottom of the adaptor.

The minimum radius, Rmin, is the distance from the centre of the axis to the surface of the liquid closest to the centre of the axis allowing for this surface to be vertical. Let us consider a rotor with a maximum radius of 160 mm containing a tube where the liquid is filled to a height of 40 mm above the base of the vertical tube.

swing-out rotor, simply reduce the value of Rmax by the height of the liquid in the tube, so in our example the Rmin is 160 mm minus 40 mm = 120 mm.

angle rotor, you will have to use geometry to calculate the value of the radius. Angle rotors are quoted for the angle from the vertical. If the rotor has a 35° angle (h), then the Rmin is calculated according to:

Rmin = Rmax – (Height of liquid in vertical tube x sin h)

Rmin = 160 – (40 x 0.574) = 160 – 22.96 = 137.04 mm

Some protocols require that a defined RCF be applied at a boundary, e.g., between aqueous and a non-aqueous solvents. To calculate this, measure the height of the boundary from the bottom of the tube and subtract this value from the Rmax (in a swing-out rotor).

Best regards,

glenn.pickett@a-a-marketing.com

avatar: Glenn PICKETT
Glenn PICKETT
63 posts
Replied to Loretta's post on August 16th, 2012

By the way, don't forget that using adapters usually changes (shortens) the radius as the tubes are not reacing the bottom of the rotor - swing-ouy or fixed angle.

Best regards,

Glenn PICKETT