Need to find deflection

[denniskthomas]

Hello ,

I am doing in project with one Mild Steel rode.Here I am getting a maximum deflection of 20 micro meter only when I apply a rotational force.Is there any way to detect this much small deflection.
I can use strain gauge to detect this ,but the problem is I want to do this project under water.So it is not possible.

So it will be very helpful if anyone help me.

---------- Post added at 14:57 ---------- Previous post was at 14:53 ----------

now i am using the principle of metal detector to detect the deflection.The principle is that when an conductor cuts a magnetic field,it will change the value of magnetic field.Since the deflection is very less,so it is very difficult to get variation by this method.
can anyone help me?

 

[FvM]

I can use strain gauge to detect this ,but the problem is I want to do this project under water.So it is not possible.

It's a question of insulation, I think. With AC bridge supply, no electrolysis would occur.
An inductive proximity sensor with continuous analog output should do. It has to placed very near to the rod to get high sensitivity. The more serious problem will be probably to achieve a rigid supporting construction.

 

[denniskthomas]

It's a question of insulation, I think. With AC bridge supply, no electrolysis would occur.
An inductive proximity sensor with continuous analog output should do. It has to placed very near to the rod to get high sensitivity. The more serious problem will be probably to achieve a rigid supporting construction.

Hello friend,thanks for your reply.
Insulation is the main problem for strain gauge.
I have doubt ,whether this inductive proximity sensor can give a stable output?now we are using an arrangement like this.one metal piece is cutting an electromagnetic field.The main problem that we are facing is ,the stability of output.Can u give me a guidance to increase the stability ?

 

[FvM]

I have no particular suggestion. The cause of instablity should be investigated. If it's stable under quiet conditions, it's probably a problem of mechanical instabilty, not related to the measurement principle.

 

[denniskthomas]

Yes sir....that may be the reason.
In our ckt,we r using this Inductive Proximity Sensors as an inductor in a colpits oscillator.When there is a change in inductance,the frequency also wants to change accordingly.That is our principle.But the problem is ,for a constant position the sine wave which we obtain from this oscillator is not stable.Its frequency is varying abruptly ,......

 

[FvM]

Abrupt frequency changes may also indicate instable oscillator operation. Operating the inductive sensor as a variable impedance (e.g in a bridge circuit) with an external fixed oscillator is probably more stable. Or connect it to a stable LCR meter.

 

[denniskthomas]

k sir....i wil test .Thank u very much for your valuable guidance