Controlling air core meters

[Jeroen]

Hi,

I'm in the process of designing an air core meter controller using a few
opamps and two DAC's. I'm wondering if it's better to use open loop voltage
or current mode feedback control. The angle of deflection only depends on
the ratio of the current through the windings, but not both windings are
exactly the same, so voltage control would be less ideal, though errors
could be could corrected by the software.
I've looked into the Philips SA5775, but these are difficult to get hold of
in very small quantities.

Jeroen

 

[Spehro Pefhany]

On Thu, 29 Apr 2004 17:17:33 +0200, the renowned "Jeroen"
<sink@null.dev> wrote:

Hi,

I'm in the process of designing an air core meter controller using a few
opamps and two DAC's. I'm wondering if it's better to use open loop voltage
or current mode feedback control. The angle of deflection only depends on
the ratio of the current through the windings, but not both windings are
exactly the same, so voltage control would be less ideal, though errors
could be could corrected by the software.
I've looked into the Philips SA5775, but these are difficult to get hold of
in very small quantities.

Jeroen

I don't seem much reason not to use voltage drive. That's what the
Philips chip does, and it's good enough for automotive meter.

Using voltage drive, there is an additional error (linearity error)
source from the self-heating of one coil relative to the other and the
tempco of the coils +4000ppm/K. This could be avoided using a
regulated supply and current drive, but it may not be significant in
your application.

Where did you get the air core movements in "very small quantities" ?

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Jeroen]

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> schreef in bericht
news:ge8290tvpbf4lapj8hqi5gkm8bouq4on5b@4ax.com...

On Thu, 29 Apr 2004 17:17:33 +0200, the renowned "Jeroen"
sink@null.dev> wrote:

Hi,

I'm in the process of designing an air core meter controller using a few
opamps and two DAC's. I'm wondering if it's better to use open loop
voltage
or current mode feedback control. The angle of deflection only depends on
the ratio of the current through the windings, but not both windings are
exactly the same, so voltage control would be less ideal, though errors
could be could corrected by the software.
I've looked into the Philips SA5775, but these are difficult to get hold
of
in very small quantities.

Jeroen

I don't seem much reason not to use voltage drive. That's what the
Philips chip does, and it's good enough for automotive meter.

Using voltage drive, there is an additional error (linearity error)
source from the self-heating of one coil relative to the other and the
tempco of the coils +4000ppm/K. This could be avoided using a
regulated supply and current drive, but it may not be significant in
your application.

Where did you get the air core movements in "very small quantities" ?

Just using parts from junked instrument panels. I have not yet succeeded in
finding a supplier

Jeroen