NateA2 - building an Electronic Level

Hello All, and NateA2,

In NateA2's photos of his Federal electronic level, it didn't look
like a LVDT implementation to me.

It is not very clear what is going on in that level.

The moving part, I think, is a copper or brass loop, and it is moving
along a brass bar. The photos are not defined enough to tell.

If the moving part is copper or brass, it's not an LVDT.

If the bar is brass then I'm not sure what's going on.

An LVDT has to have a moving part that magnetically couples
the sensing coils to the primary coil. You can move the coupling
rod or the coils. If these parts are brass, then no magnetic coupling
occurs.

If the bar, the loop travels along, is iron/steel, then the loop
can act as a magnetic shading device.

The coils appear to be mounted above the iron loop/core on that flat
section the wires are connected to.

I would love to know all the real details of this device.

Is the manual, for this device, on-line somewhere, and does it explain
the device in more detail?

Regards to all,

Paul

toolnuts said:

Hello All, and NateA2,

In NateA2's photos of his Federal electronic level, it didn't look
like a LVDT implementation to me.

It is not very clear what is going on in that level.

The moving part, I think, is a copper or brass loop, and it is moving
along a brass bar. The photos are not defined enough to tell.

If the moving part is copper or brass, it's not an LVDT.

If the bar is brass then I'm not sure what's going on.

An LVDT has to have a moving part that magnetically couples
the sensing coils to the primary coil. You can move the coupling
rod or the coils. If these parts are brass, then no magnetic coupling
occurs.

If the bar, the loop travels along, is iron/steel, then the loop
can act as a magnetic shading device.

The coils appear to be mounted above the iron loop/core on that flat
section the wires are connected to.

I would love to know all the real details of this device.

Is the manual, for this device, on-line somewhere, and does it explain
the device in more detail?

Regards to all,

Paul

Click to expand...

If you are really interested, ISTR PM member Gernoff being done with the need of his Federals and offering them for sale.

Monarchist said:

If you are really interested, ISTR PM member Gernoff being done with the need of his Federals and offering them for sale.

Click to expand...

I am interested, but I can't seem to find a post with the federals
listed for sale.

Paul

toolnuts said:

I am interested, but I can't seem to find a post with the federals
listed for sale.

Paul

Click to expand...

May have been in one of our emails. Just PM him and ask. Can't hurt.

The moving element in the LVDT of the Federal electronic level is a copper ring; in effect a shorted turn on a transformer. It's attached to the pendulum in the level body and detects perturbations of the pendulum by tilt in a gravitational field. It's theoretically sensitive to parts of arc seconds but practically speaking the concept is limited to arc seconds by the connected '70's era electronics

The shorted turn is concentric to and magnetically coupled to the alternating field of the LVDT primary.(carrying 5 KHz or so) AC excitation. Thus the flux distribution in the transformer changes in response to movement of the pendulum carrying the shorted turn along the flux axis of the transformer altering the excitation field inducing response in the divided secondary. And so movement of the copper shorted turn affects the differential voltage at the LVDT output terminals in accordance with long established theory.

This arrangement is as sensitive and repeatable as the more traditional moving ferrite cored LVDT and is therefore an LVDT in all but polarity sense of response. The Federal lever head uses the same technique if not the identical parts.

Forrest Addy said:

The moving element in the LVDT of the Federal electronic level is a copper ring; in effect a shorted turn on a transformer. It's attached to the pendulum in the level body and detects perturbations of the pendulum by tilt in a gravitational field. It's theoretically sensitive to parts of arc seconds but practically speaking the concept is limited to arc seconds by the connected '70's era electronics

The shorted turn is concentric to and magnetically coupled to the alternating field of the LVDT primary.(carrying 5 KHz or so) AC excitation. Thus the flux distribution in the transformer changes in response to movement of the pendulum carrying the shorted turn along the flux axis of the transformer altering the excitation field inducing response in the divided secondary. And so movement of the copper shorted turn affects the differential voltage at the LVDT output terminals in accordance with long established theory.

This arrangement is as sensitive and repeatable as the more traditional moving ferrite cored LVDT and is therefore an LVDT in all but polarity sense of response. The Federal lever head uses the same technique if not the identical parts.

Click to expand...

Hi Forrest,

In the photos, it looks like the bar the loop is traveling along is brass. If the bar was magnetic
then I could see the loop acting as magnetic 'shorting' element. Actually it would act the same way
a shaded pole motor works, which is not magnetic shorting but a phase shifting mechanism.

Also note that there is a magnetic shorting element just above the bar, and it is iron/steel ie: magnetic.

So Forrest, you had a Federal - do you know the truth of all the materials - did you take a peek?

Did you ever sell your Federal, if not I would be interested - [email protected].

In the mahr/federal literature, in their diagram, they show the loop encompassing the bottom
of the magnetic core (which it does not) which would imply they are using the shaded (pole)
method. Also, in their diagram, they show a truncated E core, which make it entirely a different
magnetic situation. Without the truncated E core, there is only a single magnetic loop and the
shading would affect both pickup coils equally.

As I said before I am baffled by the conflict in the different facts available to me. Since I
don't have the money they are asking (but not getting) I thought I might try my hand at making
one.

I think that what I see in NateA2's photos are misleading me. I feel like there is something I
am not seeing or missing.

Regards to all

Paul