I have been looking into building some electronic differential level gauges based on a decades old design used by many providers including Mahr Federal. This is the type of gauge I intend to replicate;
I believe these are based on a Linear Variable Differential Transformer of which I have an overall understanding of. However, the particular type of LVDT used by MahrFederal utilises a shading loop as the moveable item that varies the output voltage/reading. I need some help to understand how this is working.
This is the system drawing that Mahr provides and shows the workings quite well. All components are connected other than the pendulum that holds the shading loop. My assumption is that as the shading loop moves left or right, it 'bleeds off' some of the magnetic flux to the secondary coil on that side and thus alters the output voltage/reading?
the primary coil is around the middle leg of the core but that leg does not connect to the other side of the core so how is the magnetic flux flowing?
the shading loop appears to be around a brass (?) bar so how it it doing anything?
I cannot actually see the secondary coils in the picture. I would have expected them to be visible around the 2 sides legs of the core.
The cross sectional area of the lower horizontal part of the core is smaller. This would reduce the magnetic flux flowing through that area but I cannot work out how it fits into the puzzle
I am sure that once I fully understand these physics basics that I will have specific Arduino questions to follow!!!!!!!!
Cheers mate. I have already read that. I understand how LVDT's work, I am trying to understand how this specific device is working due to the inclusion of the shading loop. Trying to call out to the physics wizards!!
I would guess the brass ring has an induced current flowing through it and that changes the flux picked up by the secondary coils and the phase between them ?? Either that or some change in resonant frequency .
it is an EI structure core. the scheme is a balenced 3 winding transformer.the secondery windings are loacated symmetrically on the two arms of EI core.
the schematic is as follows
pic2
there are several ways to disturb the banlancing, one way is as follows,the "E"part is fixed, while the "I" part is floating, they are used in motion controls like flight throttle
PIC3
notice that the both secondary windings are light loading!! so there are other way to influent the balancing.
thats the mahr way, it is a shading loop consist of a copper cloesed loop, the shape doesnt matter much, there will be a current in the closed loop. the current will generate a flux that cancels the main flux generated by main widing , which breaks the balance. and the linearity is pretty good from my test
hope that would help
Through the air gap! Magnetic fields do exist in space you know. The flux from the centre limb divides equally between the two side limbs if the shading loop is in the middle. The secondary coils on these would be connected in series-opposed so in the centre position the voltages cancel. If the shading loop moves to one side the eddy current induced in it will reduce the flux in that limb and allow more to the other limb so a net secondary voltage will result. The size of this depends on the deflection and the phase relative to the primary determines the direction.
