Hello everyone,
I have found this forum very helpful in the past so I came back to ask for more

I want to use some trimming resistors to balance some signals at different points of my circuit, like in a wheatstone bridge. However, I need non-inductive resistors for it. The bourns type potentiometers I am using have an inductance by their nature (as I saw in the internet they are actually coils of wire). Thus I get some variations of the voltage amplitude and phase shift between the two signals when I change the frequency.

My question is:
Has anyone calculated the inductance of these components let's say for 10k or 100k potentiometers because in the datasheets they don't mention how much is the inductance.
I am thinking of using digital potentiometers instead but I have not used them before. Could someone briefly explain to me what I would need to drive them. I suppose a MCU would be necessary for this purpose?

Any help would be much appreciated.

 

Ok I see there are other posts on how to drive the digital pot that were helpful. I should have checked this first. If you can reply to my first question would be great. Thanks

 

Hello everyone,
I have found this forum very helpful in the past so I came back to ask for more

I want to use some trimming resistors to balance some signals at different points of my circuit, like in a wheatstone bridge. However, I need non-inductive resistors for it. The bourns type potentiometers I am using have an inductance by their nature (as I saw in the internet they are actually coils of wire). Thus I get some variations of the voltage amplitude and phase shift between the two signals when I change the frequency.

While wirewound trimpots are inherently inductive because of the coiled resistance wire element, Trimpots with cermet elements aren't inductive and are available in single and multi-turn versions.

Mod edit: fix quote.

 

Use cermet pots, as EM suggested.

 

Thanks for your replies.
Does anyone know how much this inductance might be (orders of magnitude) and if it could be the cause of my signal's behavior at the frequency range 1-15kHz?
If someone else had a similar experience I would like to hear their opinion.

 

if it could be the cause of my signal's behavior at that frequency range?

What frequency range?

 

Thanks for your replies.
Does anyone know how much this inductance might be (orders of magnitude) and if it could be the cause of my signal's behavior at the frequency range 1-15kHz?
If someone else had a similar experience I would like to hear their opinion.

Please post a schematic of your instrumentation, device(s) under test and your test procedure, and a description (tabular data would be nice) of the the phase and amplitude changes which are troubling you.

 

Ok I see there are other posts on how to drive the digital pot that were helpful. I should have checked this first. If you can reply to my first question would be great. Thanks

Others have suggested a type of non wire wound pot. Its still a horseshoe shape and will have more inductance than a straight line (slider pot).

For fixed resistors; carbon composition still turns up occasionally in RF stuff because they're the lowest inductance thru-hole type. The tolerance is usually 10% - sometimes 20% or more.........

Most SMD resistors are just metal film deposited on a slice of ceramic, usually they have pretty low inductance compared to the spiral around the rod on a through hole type. High voltage and/or high resistance SMD parts have a zig-zag or some other pattern to get as much track onto a small surface as possible - that pushes inductance up.

You can get non (or at least low) inductive WW resistors - the spiral of wire comes back the way it came at the end of the former, the two inductances side by side cancel each other out (you hope).