Forums

Dual Offest Sub-audio Test Signal

Started by Unknown May 23, 2014
Can someone please help with this project. I am unable to find
anything similar in the form of an existing design.

The objective is to apply a 10Hz test signal, generated with a lab
function generator, to two air core solenoids of 50R.

OK, here is the different part.

One solenoid must be fed with a positive offset signal, and the second
with an identical negative offset signal.

Given a 12VDC supply, each signal would be 4Vpp, offset 1V, one above
and one below DC.

This diagram shows it in detail:

http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000

I am guessing this can be done with a BD139/BD140 pair or similar
running off a split 12V supply with a virtual ground.

However, I am uncertain how to configure the supply so as to offset
each rail from ground to achieve the desired effect. 

Or perhaps there is another approach. Any advice would be very much
appreciated.

John Gillmore
<jgillmore@netscan.com>
> Can someone please help with this project. I am unable to find > anything similar in the form of an existing design. > > The objective is to apply a 10Hz test signal, generated with a lab > function generator, to two air core solenoids of 50R. > > OK, here is the different part. > > One solenoid must be fed with a positive offset signal, and the second > with an identical negative offset signal. > > Given a 12VDC supply, each signal would be 4Vpp, offset 1V, one above > and one below DC. > > This diagram shows it in detail: > > http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 >
** I see a pair of 4V p-p sine waves, one with +3V offset and the other with -3V offset. FYI: The DC offset of an AC signal normally refers to the deviation of its AVERAGE value from zero.
> I am guessing this can be done with a BD139/BD140 pair or similar > running off a split 12V supply with a virtual ground. > > However, I am uncertain how to configure the supply so as to offset > each rail from ground to achieve the desired effect. > > Or perhaps there is another approach. Any advice would be very much > appreciated.
** You need to supply one end of each solenoid with a *solid* +/- 3V, then use a pair of electro caps of about 1000 uF to couple the 10Hz to the other ends - orient the electros accordingly. A regular bench generator will likely not have enough current output - so use an audio power amp to boost it. ... Phil
On 2014-05-24, jgillmore@netscan.com <jgillmore@netscan.com> wrote:
> > Can someone please help with this project. I am unable to find > anything similar in the form of an existing design. > > The objective is to apply a 10Hz test signal, generated with a lab > function generator, to two air core solenoids of 50R. > > OK, here is the different part. > > One solenoid must be fed with a positive offset signal, and the second > with an identical negative offset signal. > > Given a 12VDC supply, each signal would be 4Vpp, offset 1V, one above > and one below DC. > > This diagram shows it in detail: > > http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000
solenoids have two ends can you use a single ground centred 4V p-p signal and then connect the other end of one solenoids to +3V and the other to -3V -- umop apisdn --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
On a sunny day (Sat, 24 May 2014 12:12:27 +1000) it happened
jgillmore@netscan.com wrote in <8puvn9leks6kp7g3j9et6s9jnp24eda17l@4ax.com>:

> >Can someone please help with this project. I am unable to find >anything similar in the form of an existing design. > >The objective is to apply a 10Hz test signal, generated with a lab >function generator, to two air core solenoids of 50R. > >OK, here is the different part. > >One solenoid must be fed with a positive offset signal, and the second >with an identical negative offset signal. > >Given a 12VDC supply, each signal would be 4Vpp, offset 1V, one above >and one below DC. > >This diagram shows it in detail: > >http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 > >I am guessing this can be done with a BD139/BD140 pair or similar >running off a split 12V supply with a virtual ground. > >However, I am uncertain how to configure the supply so as to offset >each rail from ground to achieve the desired effect. > >Or perhaps there is another approach. Any advice would be very much >appreciated. > >John Gillmore
Inductors are best driven with a current source, as internal resistance is temperature dependent, as you probably want a fixed number of Ampere-turns. Just use a transistor driven by an opamp on a 12V supply, and reverse the connections for once coil... +12 10 Hz | +12 signal inductor2 (reverse connected) | | | [ ] === inductor1 (normal connected) | | \ | [ ] <------|+ \ c | bias | >--- b NPN /// --|- / e | / | -------------| | Rsense (1 Ohm?) | /// ?
On Sat, 24 May 2014 06:19:23 GMT, Jan Panteltje <panteltje@yahoo.com>
wrote:


>>This diagram shows it in detail: >> >>http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 >>
>Just use a transistor driven by an opamp on a 12V supply, >and reverse the connections for once coil... > > > +12 > 10 Hz | > +12 signal inductor2 (reverse connected) > | | | > [ ] === inductor1 (normal connected) > | | \ | > [ ] <------|+ \ c > | bias | >--- b NPN > /// --|- / e > | / | > -------------| > | > Rsense (1 Ohm?) > | > /// >? >
Looks to me like two coils driven oppositely, or antiphase. Sorry, but I don't see how this would circuit provide the signal that swings from -1V to -5V, as shown on my diagram. http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 Am I missing something? John Gallimore
On a sunny day (Sat, 24 May 2014 17:00:28 +1000) it happened
jgillmore@netscan.com wrote in <4dg0o9phsbavm6iat7idv8id94ni6tn8nr@4ax.com>:

>On Sat, 24 May 2014 06:19:23 GMT, Jan Panteltje <panteltje@yahoo.com> >wrote: > > >>>This diagram shows it in detail: >>> >>>http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 >>> > >>Just use a transistor driven by an opamp on a 12V supply, >>and reverse the connections for once coil... >> >> >> +12 >> 10 Hz | >> +12 signal inductor2 (reverse connected) >> | | | >> [ ] === inductor1 (normal connected) >> | | \ | >> [ ] <------|+ \ c >> | bias | >--- b NPN >> /// --|- / e >> | / | >> -------------| >> | >> Rsense (1 Ohm?) >> | >> /// >>? >> > >Looks to me like two coils driven oppositely, or antiphase. > >Sorry, but I don't see how this would circuit provide the signal that >swings from -1V to -5V, as shown on my diagram.
Well it can.
>http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000
Thats is not a diagram, but a wave form. I though tyou wanted to drive 2 coils with opposite phase? If only one use one coil ;-) (reverse connected).
>Am I missing something?
I don't know, you be the judge ; -)
>John Gallimore
On 24/05/2014 03:12, jgillmore@netscan.com wrote:
> One solenoid must be fed with a positive offset signal, and the second > with an identical negative offset signal.
I am having trouble understanding what you want. The coils are unaware of ground or of their voltage with respect to ground or of each other. All they see is a current flowing through them. You want a steady current flow through them with 10Hz superimposed? Just wire them in series ?? piglet
"Jan Panteltje"

> > Inductors are best driven with a current source,
** Who mentioned "inductor" ? An air core solenoid with 50 ohms resistance, driven at 10Hz is what the OP has. Need to have at least a couple of H of inductance to matter much at 10Hz. Wanna describe such a solenoid ??? Reckon you could lift it ? .... Phil
On 24 May 2014 04:48:40 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:


>> This diagram shows it in detail: >> >> http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 > >solenoids have two ends can you use a single ground centred 4V p-p signal >and then connect the other end of one solenoids to +3V and the other to -3V >
Here is a circuit where I attempt to do this by using diodes to provide the offset to the two coils. http://www.4shared.com/download/eOKUnhlRce/dual_current_driver.jpg?lgfp=3000 Is that similar to what you have suggested? It is a first try, and I would very much appreciate any corrections or ideas for improvement. Thank you, John Gillmore
On 24/05/2014 09:53, jgillmore@netscan.com wrote:
> It is a first try, and I would very much appreciate any corrections or > ideas for improvement.
When the 10Hz output goes +ve then coil B will see increased current flow and coil A will see decreased current flow. But I thought you wanted the two coils to be in-phase ? If anti-phase is what you want then your circuit is a good start. The amplifier would benefit from overrall feedback. piglet