Hello everybody,
I'm developing an Inductive sensor, and I'm quite new in this field. I've found the best inductance values, coupled with capacitors to stay on the 500KHz frequency. I've chosen not shielded, ferrite core inductors, which seems to work better, I guess because they increase magnetic field.
I've chosen the target material to be Stainless Steel, which is optimal to achieve maximum distance.
Well, the problem is, that I want to reach a target which is at 5mm from my sensors, but actually I'm only sensing at 1.5mm. I'm thinking about increasing a lot the current, which is directly related to the magnetic field. But since this is a long life, battery powered application, I wanted to make sure that I'm doing everything right, before increasing the power consumption.
I also know that current is directly related to magnetic field, but magnetic field strenght decrease with distance with a square relation. To obtain the result that I want, I'd have to multiply current at least x8.
I'm buying random inductance to make some tests, because I could not found some "Sensing specific inductances". As long as you know, do they exist? Or they're all using common inductances?

Best Regards,
Davide.

 

Are you sensing change in frequency or induced voltage ? Is this RFID
application ?

The problem is both field strength and receiver sensitivity.

Regards, Dana.

 

It's really similar to a Metering application, I have to sense a rotating piece of metal. I want to use 2 coils to sense direction.
I'm sensing the voltage change, but I would like to avoid a threshold too low to keep the higher noise immunity.

Kind Regards,
Davide.

 

Several thoughts -

1) Maybe a sampled data approach to minimize measurement time, hence power
consumption.

2) Is environment high common mode ? if so differential receiver great for noise
reduction.

3) One coil transmitter, the other sense ? Increase number turns in coils ?

I find the problem interesting, the 5mm distance would not have struck me as
a big challenge, which as you say it is.

Regards, Dana.

 

Is it because you are working with Stainless Steel, its permeability really low -

https://www.engineeringtoolbox.com/permeability-d_1923.html

Regards, Dana.

 

We are sampling with the same max frequency sampling calculations.
Of course, in that case differential receiver would be a solution. But rather than external noise, I'm scared about the tolerances of Inductors and capacitors (typically +-10%). If I have a low threshold, forced by low voltage changes from target / no target, I may count something with a different LC. (Capacitors are also variable in temperature)
All the inductors are transmitting to see where there is a target and where there's no target. To get rotation with a state machine principle. (Present, Not Present, Not Present / Not Present, Present, Not Present / Not Present, Not Present, Present)

For the permeability.. well I've chosen stainless steel because it looked like to be optimal
https://automation-insights.blog/2010/04/12/inductive-proximity-sensor-targets-material-does-matter/
I may do some other reasearch to know exactly what is the best material. Anyway, with other pieces of metal that I have here I'm just sensing slighly better, but it seems to be a "metal mass" relationship rather than the material.

Thanks you,
Davide.

 

Sounds like a cal cycle of some sort to take out errors ?

In your case measure actual values/error of L and C used in sensors ?

One method used by measurement manufacturers in high precision instrumentation
is during manufacturing removing errors, time, frequency, voltage, current, temp
during manufacturing test by running a cal routine where DUT communicates to
external high precision instrumentation over a simple serial link, and stores correction
factors derived from its calculations vs external measurement systems. This approach
allows a low precision DUT design to take on higher accuracy than if it had to rely
on its own low precision measurement facilities.



Regards, Dana.

 

Sounds like you are making lots of assumptions about a fairly complex idea.
The 'tell' is your choice of stainless steel as a target.

Care to provide some background on the problem you are solving?
There is always a better cheaper faster way.