I need to transmit my measured data of torque and temperature (measured using RTD and strain gauge) from a Rotating shaft running at 7500 rpm through IR communication. Is it possible? does line of sight become a problem? Does the device (transmitter & receiver)needs to be stable for IR data transfer? Will the fast running shaft be a problem? how to accomplish this?

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    \$\begingroup\$ You will have to try that to be sure. I'd say it should be possible. You can solve the line of sight issue by using multiple IR transmitters. 7500 rpm is 125 Hz which is much lower than the 38 kHz modulation many IR remotes use. The transmitted data is OOK modulated on top of that 38 kHz signal. If the receiver can "see" a transmitter (or a reflection) at any time, it should work. \$\endgroup\$ – Bimpelrekkie Jan 24 '17 at 10:14
  • \$\begingroup\$ Do we have IR LEDs that have light emitting angles of about 90 degrees @FakeMoustache? \$\endgroup\$ – dirac16 Jan 24 '17 at 10:39
  • \$\begingroup\$ @dirac16 Find a datasheet for an IR LED and find out. My guess would be that most would have a wider beam than 90 degrees. If you must have 90 degrees, use something to shape the beam. \$\endgroup\$ – Bimpelrekkie Jan 24 '17 at 10:44

Is it possible?

My company uses infra red laser diodes to transmit telemetry data off shafts at data rates up to nearly 700 mega bits per second so there is nothing inherently flawed in this method however, at this sort of speed photodiodes and their amplifiers need to be carefully designed and you do need pretty good alignment.

does line of sight become a problem?

So, assuming you can place the transmitter at the centre line of the shaft-end you should be OK. Lower speeds mean you can use fast LEDs and less problematic (and more sensitive) photodiodes.

Does the device (transmitter & receiver)needs to be stable for IR data transfer?

Stability = no loss of data

Will the fast running shaft be a problem?

Yes, you will need to mechanically balance your add-ons and make sure they can withstand the g-forces. We always make sure that any PCBs are subjected to g-forces that push components towards the PCB they are soldered to (at distances close to the shaft centre-line this is far less of a problem of course).

how to accomplish this?

That's a money question LOL.

Don't forget that you need to supply power to the electronics mounted on the shaft - a battery may be OK but you will need to mount it as close to the centre-line of the shaft as you can AND watch out for imbalances.

A typical car tyre will rotate at about 1400 rpm at 100 mph so balancing is a really big deal.

  • \$\begingroup\$ That's a money question LOL. and/or experience, which you can hire, which costs money as well. \$\endgroup\$ – Bimpelrekkie Jan 24 '17 at 10:45

You've got 120 or 130 revolutions per second. If you transmit ONE BIT per revolution, with 2 measurements of 10 bits or 20 bits total to transmit, you can transmit 6 complete measurements per second.


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