# Hall effect torque sensor

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#### Ana Rodriguez

I have a magnet coupled to a gearbox with a relationship of 13000 rpm:1, I need to measure torque in the gearbox. I was trying to measure it with strain gauges but the device is very small (1.5 cm diameter tops) and the accuracy is almost none. I know that Hall sensors would help me on this but to be honest I don't know how to couple them. (Torque is going to be small, approximately from 0.002 mNm to 1.5 Nm)

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#### oj

Ana,

If you can measure the speed of the shaft and if you know how much power you are driving the gear box, you can calculate torque:

torque = power / shaft speed

Of course you'd have to account for small errors like losses due to motor efficiency and friction.

The easy but expensive way is to buy a torque measurement dyno that can measure torque directly.

I am assuming that you are trying to use the Hall sensors to measure speed? The Hall Sensors must be spaced 120 electrical degrees apart and you'd need to build a tachometer to measure speed--seems like a lot of work.
Usually, each hall sensor has a face plastic body and 3 leads. Two leads are for the + and - power. The output must be pulled up with a resistor.

Good luck,
oj