Hello out there, I am currently building a small vibration testing device. The vibration has to be read from a spinning shaft.(1/2 inch or about 12mm diameter shaft) The unit cannot touch the shaft physically. I would assume this would mean a laser diode system would be needed probably similar to that used in a mouse. The system should be able to read the vibration ( the amount the shaft runs out of true) Imagine an observer standing close to someone spinning a hula hoop.As the hoop approaches and retreats from the observer, then that observer has to calculate the distance the hoop rim appears to move fore and aft. The system has to be able to calculate the same way and a definitive readout has to be given. I don't need it to calculate the actual runout distance of the shaft, it will be fine as long as the readout is proportional to the shaft runout.(ie it could readout as a varying voltage) I need a circuit diagram and some advice on the components needed. Thankyou for your time and your help.
Geoff.com

 

Hi Geoff,
What is the shaft material/size,dia, speed?
How much out of true/balance movement are you expecting?

Eric

 

[quote=ericgibbs]Hi Geoff,
What is the shaft material/size,dia, speed?
How much out of true/balance movement are you expecting?

Hi Eric,
The shaft diameter is 12mm (about 1/2 inch). The rotational speed is six to eight thousand RPM. The shaft runout at maximum is expected to be in the order of forty thou (about 1 mm) The shaft material is common aluminium or an aluminium alloy. The shaft and bearing housing are being machined up this week.Thankyou for your reply.
Geoff.com

 

[quote=Geoff.com]Hi Geoff,
Reason for asking material type was to see if a 'capacitive' type sensor could be used to detect the 'out of balance runout'.
Looking at the spec of the shaft I would consider a differential capacitive sensor solution.

Eric

EDIT:Look at this example.

http://physics.mercer.edu/petepag/tutorial.html

 

I would think a laser aimed at the edge of the shaft with a phototransistor on the other side would give a signal that is modulated with a sine wave. The difference between min and max of the modulated wave would be proportional to the runout. Though it wouldn't be linear, it would be related to the cross sectional shape of the beam. With proper adjustment of the beam and calibration of the received signal, you should be able to directly measure actual runout.

 

Hi Eric,
Thankyou for your reply, and after looking at the editor's tutorial, I feel it would be prudent to look at the differential capacitive type sensor. I am a real novice in the electronic side of things. I can get a little help from a family member, but a circuit diagram or two with some component values would be a godsend.
Kind Regards
Geoff.com