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Hi,

I am working on a hydraulic unit that has two LVDTs (position transducers). I don't know what is the purpose of those dash lines. I wasn't able to find my answer on Google. My experience tells me those dash lines could mean they are mechanical linkages or optional connections, but neither case makes sense to me.

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  • \$\begingroup\$ Could this be an indication of the phase relation between those coils. \$\endgroup\$
    – Sean
    Commented Sep 28, 2016 at 23:40

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A proper schematic for LVDT's looks as follows

The common phases are noted by the position of the dots. enter image description here enter image description here Excitation of sine is on single top "primary" coil in all cases and position is detected by ratio of coupling to differential output "secondary" coils with BLU/GRN usually joined into 1 wire.

When centered, they will have equal amplitude and opposite polarity because one secondary is wound in the opposite direction, so that signal is inverted compared to primary.

Dotted lines make no sense electrically for sensors ( no pun intended ) but for optional grounding depending on winding layers for optimal protection from EMI such as lightning, perhaps dotted line shows optional connection for ground connection as an EMI shield.

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  • \$\begingroup\$ I was thinking the dotted lines are for ground connection, but if that is the case, wouldn't both transducers have the same dotted lines between wires? \$\endgroup\$
    – Sean
    Commented Sep 29, 2016 at 16:00
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Dashed lines can mean a few things:

  1. Mechanical connection between two components, which can indicate that when one component changes, the other one is changed at the same time.

  2. Either field wired, factory wired, or pre-installed components.

  3. Components that are used only in special circumstances.

I'm thinking it could be #1 in your case because when something happens on the 'C' or 'E' side, it looks like that change will be felt on 'A' or 'B', respectively.

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  • \$\begingroup\$ If it is a mechanical connection, wouldn't both transducers have the same dash lines? \$\endgroup\$
    – Sean
    Commented Sep 28, 2016 at 23:46
  • \$\begingroup\$ To be honest, I don't know enough about LVDTs. Never worked with them, but I know they are electromechanical transducers. Maybe transducer (60) behaves differently from transducer (87) (depending on type, wiring, voltage, etc.). I think you should be able to deduce what is different by knowing what's on the other side of all those letters on the right (P-J). \$\endgroup\$
    – DigitalNinja
    Commented Sep 28, 2016 at 23:51
  • \$\begingroup\$ Doh... not right, I meant on the left hand side of your diagram (the terminal block or whatever it is with the series of letters). \$\endgroup\$
    – DigitalNinja
    Commented Sep 28, 2016 at 23:59
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My guess is they're indicating an allowed internal connection. As in, A could be internally connected to C or E, but not both, and not to anything else.

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Are the transducers optional? Could it mark the necessary wiring to remove one or more LVDT units from service? Could you post photos? Why do you want to know?

An LVDT has a primary AC powered coil (the one at the top of your diagram), and two sensing coils (Vcoil1 - Vcoil2 = linear position).

See also: http://www.te.com/usa-en/industries/sensor-solutions/insights/lvdt-tutorial.html

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  • \$\begingroup\$ The LVDTs are internal to the unit. Can't take a photo unless we tear it apart. \$\endgroup\$
    – Sean
    Commented Sep 29, 2016 at 15:47

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