Medical Centifuge Calibration

I assume postage has to be included in the cost of "$1,

Take a piece of card, and draw/print a 'Spiral' in dark bold outline.

Stick that on the top of the centrifuge spindle. As the spiral turns, it will appear to 'Expand' at 2mm pitch a 100mm disc will show a 3000 rpm as only 120 rpm, slow enough to count with the second hand of a watch. just two per second.

How about using something that is plastic enough to distort under centrifugal force in the centrifuge. For example you take a blob of putty and roll it into a ball then place it in the centrifuge. If you control the amount of time it is in there you could then relate the amount of deformation back to the centripetal acceleration it has been exposed to. You may need to have several different substances with known deformation characteristics and it wouldn't give you incredibly accurate results but it is a direct measurement of the centripetal acceleration that a sample has been exposed to.

Taking the idea further how about a small spring loaded gauge that has an indicator on it that shows how far the spring has been compressed by a small mass. The indicator need to stay in place after the compression of the spring has ceased and again it would give you a direct indication of the centripetal acceleration. If you made it so that the mass that deforms the spring can be changed you could have different scales for different applications.

How about the olde steam traction engine speed control....

Two balls on levers that rotate at the same speed until the speed increase beyond a limit and the balss fly apart to open a steam vent.... reduce the speed and the balls fall again to close the open steam vent....

John.

Great concept masu, Direct measurement is always best. I am a bit worried about the consistency of the putty, heat would affect that. How about little sachets in aluminium cooking foil of a pigment colloid, that one could mix with a standard volume of water, then one might be able to compare against a colour chart. just dilute with distilled water at S.T.P. and calibrate with a quality centrifuge first. If the pigments were of different size/weight/hue a quite sophisticated analysis could result. Heavy pigments would settle first. These calibrated pigments could be obtained from separation in a known centrifuge, then dried out. Repeat with a different hue. Let's call it the CR4 'Rainbow' calibration.

Sounds interesting and is close to what I had in my mind at first. I think however the small spring gauge with a set of small interchangeable masses might be easier to use. All you would need to do is have some sort of indicator that recorded how far the spring had been compressed and you know the maximum centripetal acceleration it has undergone. You can then reset the marker and you are ready to go again. You could even set it up with a coloured scale yellow for too little green of ok and red for too much and then select the appropriate mass for the speed you are testing.

Thanks to all of you as these are some good ideas.

I think the spring guage seems similar to an idea I had as well...using a centiguge tube filled with a substance, say a fine grain sand, with a metal ball placed on the surface of the sand before centifuging. The depth of the ball after the test should correspond rotational forces. All you would need to do is visually inspect the depth. The question remains if this idea would be consistant?

I suspect that a very slightly unbalanced load on the centrifuge could lead to small vibrations...hence the ball bearing might penetrate deeper into the sand. If one wanted to use a 'Spring-Balance' approach, wrap a suitable spring's last windings with some cotton thread, then place a stiff paper tube inside. wet the cotton thread with ink, spin, and see how far down the tube the ink mark goes....might work?

It might need a few steel washers as extra weight? perhaps a fine scratch, two washers & three pins sandwiched between, over say an aluminium tube or wooden dowel covered in Aluminium foil might be more accurate?

You didn't say where it would be used , but if there's AC lighting you could make an appropritly marked disc to synch with strobe effect. (to see what I mean , get a toy car with spoked wheels and spin the wheel under a light). I haven't done the calcs for 'high' speeds like you have in mind.