Welcome back to linear circuits. Today we're going to be talking about the
linear variable differential transformer. We'll introduce LVDT sensors, which are
devices that are used, that make use of mutual inductance for their measurement
and show the applications where they can be used.
In the previous lesson, we talked about the ideal transformer model.
And how we can find the various voltages based upon the number of turns and the,
the way that the mutual inductions works. We're going to make use of that analysis
today to see a little bit about how these LVDT systems work.
We'll start by explaining the behavior of these systems and how they operate, and
then identify how you can find the relative position measured by an LVDT
based upon the magnitude and the phase of the measured voltages.
So, first of all, an LVDT, we can put up a little bit of a technical drawing here
to show how they're constructed and how they work.
We have first of all, a source right here, some kind of input that is putting
a sinusoid on a primary coil, right here. And this blue bar is a ferrous core, and
this ferrous core can move. Then we have two secondary coils: one is
wrapped in one direction, the other is wrapped in the other direction and they
are connected together. I will be designating the voltage cross
one of the secondary coils as v1 and voltage cross the other as v2.
Now, given the sinusoidal input, I see that we get a, an output that's
sinusoidal here for v1 and an output here for v2.
Now, v2 is in the opposite direction or opposite phase of v1.
Here it goes up, here it goes down first. And that's because this coil is wrapped
in the opposite direction. But both of these secondary coils are
responding to a current put through the primary.
If I take the voltage across the whole thing, we can take the sum of v1 plus v2
to find that v out is approximately zero. It's almost flat.
This indicates that our bar is in a neutral position.
And in LVDT the bar is the thing that moves.
So, as I move this bar, we change the mutual inductance.
This v2 coil, this secondary, is now not as inductive mutually to the primary.
Because there's no ferrous core moving through it.
However, v1 continues to be just as linked as before.
So, v1 has the same voltage measurement here, v2 is now flat.
And so, we see that v out again is sinusoidal.
If I move the bar the other direction, the opposite happens.
Now, v2, remember, had an opposite phase. It started down, somewhere up, and now it
starts down. Typically, we're going to find that the
bar is going to be somewhere in between the two extremes.
So here, v1 is at its maximal value, v2 has a smaller amplitude.
And when I put them together, Vout has the same phase as v1, but a smaller
amplitude. This means that it is somewhere between
the neutral state and the maximum v1 state.
So, consequently, amplitude shows the amount of displacement, and phase shows
the direction. If it's in the same phase as the input,
then that means that it is in this positive direction.
If it's in the opposite phase of the input, it's in the negative direction.
An LVDT could be diagrammed sort of like this, where we see that there is a
primary coil here in the middle and then two secondary coils.
And these represent r, wires that are wrapped around and around again and
again. And it's here cutaway.
And then here we have the ferrous core, which is connected to a piston that can
move back and forward. This allows the mutual inductance to
occur. And by taking measurements, we can see
how far this is displaced. It's capable of very high precision since
we have devices that are able to very accurately measure voltages.
It's completely electrically shielded. So, the moving parts here are protected
from the wires. There's no actual connection, there's it
doesn't have to touch it just needs to be close.
And so, consequently, LVDTs can operate in very extreme conditions without any
problem. We also see that there's all sorts of
ability of removing this core, replacing it if there's some mechanical problem
with it. So, LVDTs often find application in
situations where you need precise measurements.
Perhaps to make sure that a, a factor line is producing devices that have
correct measurements to spec, their specifications, and they can operate in
very extreme conditions without harm to the devices.
All you need to be able to do is get to the wires to measure.
So, in summary, we've described the behavior of LVDT sensors and described
how to identify the position based on amplitude and the phase.
Then we describe benefits of using such a sensor.
And this concludes the Modulel five material so, we will have a wrap up and
that will conclude the course. That's all then.