Hi all,

I want to monitor the position on a DC motor which will be rotating 340° only (not full rotation). Is a potentiometer a prectival device to use for monitoring the position to the nearest 1° ? Will slight changes to Vcc have a significant effect on the position respective output voltage?

Any help will be highly appreciated.

 

Typically one might use an "encoder"
http://www.automationdirect.com/static/specs/encoderselect.pdf

 

You can get the incremental encoder in 360 pulses per rev.
Did you also intend positioning to a degree? If so what control method are you using?
CUI also have programmable capacitive detection versions quite cheap.
Max.

 

Rotary Encoder Broski!

 

Pots are how most ordinary servo motors for RC work, the 1degree precision might be an issue. Reading it is really simple.

 

US Digital, E5 rotary optical kit encoder available in 360 pulses/ rev. for $ 75. Quaduature signal output with index pulse.

 

Pots usually only have 270 degrees or 300 degrees. Linearity is a problem. Repeatability depends on the driving current or voltage being stable (but we know how to do that). The encoder method seems a lot better for accuracy and being able to cover the whole range you need.

 

Thanks a lot for the replies. Where can I find to buy an optical encoder which is the same size of a standards potentiometer? Also, ere these similar sensors with a single channel (since I do not want to know the direction)?

 

The CUI (DigiKey) are small, but if you don't want to use a quadrature encoder for directional indication, then you would need some absolute type of device.
Encoders can be obtained in absolute, but alot more than a single input, it sounds as if you are limited to a single (analogue) input?
Max.

 

These don't quite meet your specs, but sometimes 1/10 the cost allows for some spec changes.

http://no.mouser.com/ProductDetail/Murata/SV01A103AEA01B00/?qs=%2fha2pyFadug%2f9GU5ixLJlyowGiuWnU%252bnmp8%252bhIT1bbrvAhS60TIOoQ%3d%3d

 

These don't quite meet your specs, but sometimes 1/10 the cost allows for some spec changes.

http://no.mouser.com/ProductDetail/Murata/SV01A103AEA01B00/?qs=%2fha2pyFadug%2f9GU5ixLJlyowGiuWnU%252bnmp8%252bhIT1bbrvAhS60TIOoQ%3d%3d

Did you see the specs on these? 10kΩ ± 30% You would have to plan your circuit for a device that has some leaway.

 

Does it matter as long as when it is in the center you read 1/2 the voltage?

 

Hi,

Sorry for the late reply. I was considering a potentiometer for two reason:
1) because of space
2) to eliminate the calibration process required when using an encoder.

So lets say I use the potentiometer in the link below, will I be able to stop the motor in 1 degrees (2 degrees max.) intervals?
Also, is a potentiometer reliable for repetitive positioning?

http://www.bourns.com/data/global/pdfs/6637.pdf

Thanks in advance.

 

The stated resistance rotation is 340 deg +- 3 deg. If you have some tolerance in motor rotation of 340 deg., then it might work. Stopping motor within +- 1 deg. is doughtfull, unless it is a gear reduced motor- just gut feeling.

 

Hi,

I found a three turn potentiometer which I caqn use for this application. I can apply 15V as Vcc to get from 0V to 5V for a 360degrees rotation.

The motor is with a planitary gear.