How can we use a potentiometer to measure an angle between two moving links?

Question

I want to measure and plot a graph of an angle in my project. But i don't know how to do it. Can i use a potentiometer? If yes, how? If no what can i use?

Answer 1

Yes, you can use a potentiometer for this, but you have to be careful about your choice of potentiometer.

If you attach the potentiometer to one of the links so that as the other link moves relative to the first link it turns the potentiometer, then you can use the potentiometer to measure the angle. The potentiometer has three leads. The two outside leads take an excitation voltage (say 5V DC). The middle lead will then "output" a voltage relative to the excitation voltage (it does this with a voltage divider circuit within the potentiometer). You will need to calibrate your potentiometer, but you should get a linear relationship between the angle between the links and the voltage read at the middle lead.

Now, most potentiometers cannot be rotated continuously. That is, they have a hard stop at (very often) 180 degrees. There are continuous rotation potentiometers, but you will have to seek them out. Only use a standard potentiometer ("pot") if your two links won't ever move more than 180 degrees away from each other.

Otherwise, a common way to measure angular deflection is with a shaft encoder. You can buy these pre-built or build one yourself.

For the simplest shaft encoder, imagine that you have a shaft that rotates when one link turns relative to the other. If you painted a series of black and white lines on that shaft and then place an optical sensor looking at the shaft, then you can count each time that the shaft moves from white to black. If you count the rotations and know it's only rotating in one direction, then you can figure out the angle between the two links.

Now, if you add a second sensor and a second set of lines to that shaft, you can get direction out of the encoder too. That is, based on the signals received simultaneously from BOTH sensors, you can tell if the shaft is rotating left or right, and thus you can have software keep track of its angle. See the "Gray coding" example in the "Rotary encoder" source below for more information.

Now, both of these solutions (potentiometer and shaft encoder) require that you have some sort of data acquisition hardware that will let you take this data and process it. The potentiometer is an analog sensor (though you can purchase digital pots). If worse comes to worst, if you're careful about your choices with the potentiometer, it's possible to use the microphone input into a sound card as a simple analog data acquisition device. You'll still need software able to acquire from it though. The shaft encoder is (in general) a digital device. There's no simple way to acquire digital data without additional hardware.

I hope that gives you some direction.

Answer 2

The above answer is quite thorough but there are simpler methods to using the data provided by the potentiometer. You simply need to calibrate the pot in the first place. For instance, at 0 degrees you are at 0ohms. At 90 degrees you are at 50ohms. Therefore if you are getting 20ohms resistance from the pot, you know you are at 36 degrees.

(90/50)x20 = 36 degrees.

If you know two reference points in your range, you can easily work out the angle at which the links are at. It simply becomes a ratio.

If you are using this as an input into a machine/PLC, then go with a shaft encoder. Much more precise and reliable.

Answer 3

If you attach the 2 ends of the links to a potentiometer, you could do it: one end to the fixed end and the other to the moving end. When you connect the current, you can use the variable resistance to plot the angle (you will need to calibrate it first).
Every angle would have a different value.
Hope this helps

Answer 4

I'm not sure how to measure an angle between two moving links, however, I can tell you that you cannot use a potentiometer for this. A 'pot' is an electrical device with a variable resistance (for example, an analog volume knob on a stereo or an electric guitar).
Perhaps somebody else knows the proper tool?

Answer 5

The reference to the term 'Measure' in your question would seem to indicate you will need a instrument that is capable of reading & displaying the measurment. The potentiometer is only a electronic component that is not capable of measurment. Only as part of a electronic circuit can this be achieved...