Scale output of a potentiometer.
Scale output of a potentiometer.
(OP)
Hey everyone, I'm new here and am a Mechanical so I know very little about this subject and am hoping to find my answer here.
So I'm replacing an old control system with a new one, the only problem is the pot's seem to give different ranges. When 5vdc is applied the output on the old controller gives from 2vdc full rev, 2.5vdc neutral, 3vdc full ahead.
I tested the new controller and w/ 5vdc applied it gives 1 vdc full reverse, 2.5 vdc neutral, and 4 vdc full ahead. The problem is the controller is expecting of an input range from 2-3 w/ 2.5 being neutral and the new controler is giving off 1-4.
Is there any way to scale back the input while keeping 2.5vdc as the center voltage?
Thanks!
Chris
So I'm replacing an old control system with a new one, the only problem is the pot's seem to give different ranges. When 5vdc is applied the output on the old controller gives from 2vdc full rev, 2.5vdc neutral, 3vdc full ahead.
I tested the new controller and w/ 5vdc applied it gives 1 vdc full reverse, 2.5 vdc neutral, and 4 vdc full ahead. The problem is the controller is expecting of an input range from 2-3 w/ 2.5 being neutral and the new controler is giving off 1-4.
Is there any way to scale back the input while keeping 2.5vdc as the center voltage?
Thanks!
Chris





RE: Scale output of a potentiometer.
But an even simpler solution might be to wire in additional fixed-value resistors at each end of the pot so that the wiper explores a smaller section of the 0-5V range. Given the 3-to-1 gain issue, then perhaps these two additional resistors would be the same nominal resistance value as the pot itself.
This solution is based on my interpretation of your issue. I hope that I've interpreted it correctly.
RE: Scale output of a potentiometer.
RE: Scale output of a potentiometer.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Scale output of a potentiometer.
voltages you posted are measured on the output?
If so, then I'd think that the controller likely has some way to scale the range internally.
If not and you are measuring the voltage right at the pot, then the new pot voltages should not matter. What happens in the controller and how it uses the new pot voltage is the important part.
RE: Scale output of a potentiometer.
It is one thing if you are dealing with lab fit up or a home brew but in an industrial envirnment get something with a warranty and manf. support
RE: Scale output of a potentiometer.
Post us the Make/model etc. someone will recognise it.
Regards
Roy
RE: Scale output of a potentiometer.
0 --1K----3K pot---1K-- 5V
| | |
1V 2.5V 4V
0 --1K----1.5K pot---1K-- 5V
| | |
2V 2.5V 3V
More likely your circuit connecting to the pot has lower resistance:
0 --2K----3.0K pot---2K-- 5V
| | |
2V 2.5V 3V
(grr, I wish this site used the same font to write the message as it does to display it - use Courier New font to get the images above to line up again)
Assuming the pot is connected via resistors to 0V and 5V, disconnect your pot and measure the resistance from one side to 0V, and then measure from the other lead to 5V. You should see the same resistance on both sides for balance around 2.5V. Your pot value wants to be 1.5x that resistance.
Note this is one possible case of OperaHouse's solution.
Z
RE: Scale output of a potentiometer.
CODE
| | |
1V 2.5V 4V
0 --1K----1.5K pot---1K-- 5V
| | |
2V 2.5V 3V
More likely your circuit connecting to the pot has lower resistance:
0 --2K----3.0K pot---2K-- 5V
| | |
2V 2.5V 3V
Put "code" "/code" tags around the text you want to have fixed formatting and it should display the same as how you typed it in. Use [] brackets around tags instead of "", I have no idea how to post the tag without it being processed unless I turn off TGML processing which doesn't show anything processed.
This
45678901234567890123456
^ ^
| |
Start End
Will look like this which is how I actually typed it;
CODE
^ ^
| |
Start End
RE: Scale output of a potentiometer.
Z
RE: Scale output of a potentiometer.