In a message dated 03/02/2010, gmvoeth@........... writes:
Are you able to provide us with a mag/coil design with three wires
specifically designed to work
with a differential amplifier.
This would mean a center tapped coil with two wire each one going to + and
- and the third wire
going to neutral ground ?
Hi Geoff,
Sure, but is there any problem in doing this?
The ordinary single channel opamp with 4 resistors to give a
'differential' opamp circuit normally has a single 'floating' coil eg LT1007. The
feedback maintains the same voltage on both the +ve and -ve inputs, so the
coil drives a resistance of 2 x Rin + Rcoil. With high efficiency NdFeB
magnet blocks, this low impedance can significantly damp the mass and can even
damp it beyond critical. The input impedance relative to analogue ground is
different for the two inputs.
If you use a true differential input opamp, like the INA118, the input
impedances to both inputs are very high both relative to one another and
to analogue ground. You need to use two reels of wire to wind one coil. It
is an advantage if you can arrange for the two wires to be twisted together.
Alternatively, you can buy dual core insulated wires. The centre of the
coil is earthed.
You can't separate the coil design from the amplifier circuit design.
I hope that this helps.
Regards,
Chris
In a message dated 03/02/2010, gmvoeth@........... writes:
Are you=20
able to provide us with a mag/coil design with three wires specifically=
=20
designed to work
with a differential amplifier.
This would mean a=
center=20
tapped coil with two wire each one going to + and - and the third=20
wire
going to neutral ground ?
Hi Geoff,
Sure, but is there any problem in doing this?=
The ordinary single channel opamp with 4 resi=
stors=20
to give a 'differential' opamp circuit normally has a single 'floating' co=
il eg=20
LT1007. The feedback maintains the same voltage on both the +ve and -ve in=
puts,=20
so the coil drives a resistance of 2 x Rin + Rcoil. With high efficie=
ncy=20
NdFeB magnet blocks, this low impedance can significantly damp the ma=
ss and=20
can even damp it beyond critical. The input impedance relative to analogue=
=20
ground is different for the two inputs.
If you use a true differential input opamp,=
like=20
the INA118, the input impedances to both inputs are very high both relativ=
e to=20
one another and to analogue ground. You need to use two reels of wire to=
wind=20
one coil. It is an advantage if you can arrange for the two wires to be tw=
isted=20
together. Alternatively, you can buy dual core insulated wires. The=
centre=20
of the coil is earthed.
You can't separate the coil design from the=
=20
amplifier circuit design.
I hope that this helps.
Regards,
Chris