potentiometer resistance selection
potentiometer resistance selection
(OP)
We will be using a linear potentiometer in an industrial application. The product this goes into may be used in a range of conditions, and we need to try to accommodate noisy environments.
The pot will be supplied with a 10VDC source and output to a (typically) 1MΩ analog input.
We plan on having a 6" unshielded lead with twisted wires, which will terminate to an M8 connector. From there a shielded cable will be used for the remainder of the length (up to maybe 3-5m long).
The resistance options we have available are:
1k
2.5k
5k
10k
20k
50k
Which of these would you choose, and why?
Is there other noise-mitigating techniques we should employ?
EM interference and how that relates to impedance selection is definitely a blind spot for me!
The pot will be supplied with a 10VDC source and output to a (typically) 1MΩ analog input.
We plan on having a 6" unshielded lead with twisted wires, which will terminate to an M8 connector. From there a shielded cable will be used for the remainder of the length (up to maybe 3-5m long).
The resistance options we have available are:
1k
2.5k
5k
10k
20k
50k
Which of these would you choose, and why?
Is there other noise-mitigating techniques we should employ?
EM interference and how that relates to impedance selection is definitely a blind spot for me!





RE: potentiometer resistance selection
RE: potentiometer resistance selection
TTFN (ta ta for now)
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RE: potentiometer resistance selection
It's not such a critical value that you can't stick to 'even' decade values: 1, 10, .... Having an 'even' decade value makes the voltage division ratio obvious, especially with 10 volts input. Someday it'll save a minute when troubleshooting. A trivial detail, but why not?
1k means 10ma and 100 mW dissipation. That's low power, but could be lower.
So 10k seems about right.
1M input is fairly high, so the non-linearity introduced by the wiper load is negligible. If the input Z was lower, then you'd have to double check the linearity. Might be worth calculating it anyway, and comparing it to the pot's linearity and your requirements.
Since it's a pot, it's presumably not moving very quickly. You could put a capacitor from the wiper to ground to reduce EMI noise before the noise confuses your digital filtering. Perhaps a series L too, if the environment is RF noisy.
Critical applications (automobile throttles) may use two pots (mechanically linked, measured separately) to provide failure detection. That's something worth considering carefully.
In formal design processes, one could end up with a 5 or 10 page Design File Memo to document this sort of small decision.
RE: potentiometer resistance selection
I do not know how noisy the environment will be. This will be used in a product we provide to customers who will use it in a range of industrial machinery in manufacturing environments. Typical sectors are automotive, medical, and consumer products.
The voltage tolerance must be 100 mV or less, and preferably 20 mV or less.
Thanks for your response VE1BLL, some good considerations there.
RE: potentiometer resistance selection
The pot's linearity (resistance vice position) might be the deciding factor for that.
20mV on 10V is very tight.
If that's what you meant.
--
If you're 'buying in' the potentiometer and assembling it into the assembly, then have a conversation with the application engineer at the pot vendor. Typically they'll be a vast store of useful knowledge and advice. They might be aware of some unexpected detail about advantages and disadvantages of various part numbers.
RE: potentiometer resistance selection
Our design engineer has had some higher-level talks with the manufacturer but I think you're right that it's time for me to get involved and dive into these details.
RE: potentiometer resistance selection
BUT the RIGHT VALUE SHALL be less than 1 Kilo Ohms
if 10 kilo Ohms is a common value so what???
For the reason go to : youtube.com and search for :daveross problem solver
GOOD THINKING=TO RESULTS
RE: potentiometer resistance selection
A 10-turn pot might be more practical.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: potentiometer resistance selection
IRstuff, this is a linear pot, not a rotary. And 20mV is the ideal number, 100mV the more realistic one.
RE: potentiometer resistance selection
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm