J
James Arthur
Is there such a thing as a 3-lead LVDT?
I picked up a Starrett model 712-2 gaging head at
a swapmeet, without the electronics.
This ancient gadget measures linear displacement very
accurately and repeatably over a small range of travel.
Googling suggests it's an LVDT, but the connections seem
strange--it only seems to have three active leads.
Does that make any sense?
The connector looks like this:
3
. - .
. O .
/ \
2 . O O . 4
. O .
. 6 .
\ O O / 5
1 . .
._n_.
And the continuity measurements are:
1. ------- ---
^
2. n/c 43 ohms
V
3. ------- ---
^
4. n/c 43 ohms
V
5. ------- ---
6. shield, 2 ohms to LVDT casing
I opened the connector to confirm 2 and 4 are definitely
not connected, the cable only has 3 wires + braided
shield, the shield does connect to the 712-2 case,
and nowhere else.
Inside, a plunger moves a ferrite-looking rod
in and out of a bobbin, presumably the LVDT coils,
but I dare not peek--the tiny windings must be
micro-fine.
Are there LVDTs like this needing only three wires,
or are they possibly measuring just the differential
inductance to get displacement?
TIA,
James Arthur
I picked up a Starrett model 712-2 gaging head at
a swapmeet, without the electronics.
This ancient gadget measures linear displacement very
accurately and repeatably over a small range of travel.
Googling suggests it's an LVDT, but the connections seem
strange--it only seems to have three active leads.
Does that make any sense?
The connector looks like this:
3
. - .
. O .
/ \
2 . O O . 4
. O .
. 6 .
\ O O / 5
1 . .
._n_.
And the continuity measurements are:
1. ------- ---
^
2. n/c 43 ohms
V
3. ------- ---
^
4. n/c 43 ohms
V
5. ------- ---
6. shield, 2 ohms to LVDT casing
I opened the connector to confirm 2 and 4 are definitely
not connected, the cable only has 3 wires + braided
shield, the shield does connect to the 712-2 case,
and nowhere else.
Inside, a plunger moves a ferrite-looking rod
in and out of a bobbin, presumably the LVDT coils,
but I dare not peek--the tiny windings must be
micro-fine.
Are there LVDTs like this needing only three wires,
or are they possibly measuring just the differential
inductance to get displacement?
TIA,
James Arthur