Comments needed on this circuit

G

gmv

Guest
http://files.photojerk.com/gmvoeth/diagram1.gif


Hello,

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.

Every time the Air conditioner comes on a tremendous
electrical disturbance is generated in the input
of this circuit causing the class "A" baseline to follow
a nonsymmetrical cycle of waveform maybe 30 to 60 seconds
in period.

I am seeking recommendations to stop or significantly
reduce this electrical disturbance. The offending device
is actually a heat pump and the signature of the disturbance
is quite different depending upon whether the device
is heating or cooling.

I am unable to relocate the sensor so other solutions are necessary.

Any help here is appreciated.

gmv
 
I read in sci.electronics.design that gmv <noemail@please.123> wrote (in
<iUyGd.9393$OF5.5238@attbi_s52>) about 'Comments needed on this
circuit', on Sun, 16 Jan 2005:

I am seeking recommendations to stop or significantly reduce this
electrical disturbance. The offending device is actually a heat pump and
the signature of the disturbance is quite different depending upon
whether the device is heating or cooling.
Click to expand...

The unbalanced input stage is wide open to every disturbance under the
sun. You need a balanced input stage and a twisted-pair shielded cable
to your sensor. With that huge gain in the first stage, I suspect the
whole design, frankly.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
I read in sci.electronics.design that gmv <noemail@please.123> wrote (in
<29AGd.9749$EG1.1390@attbi_s53>) about 'Comments needed on this
circuit', on Sun, 16 Jan 2005:

I am trying to go as cheap as absolutely possible. Is it possible to use
a diff amp on the input if there is no center tap from the sensor ?
Click to expand...
Centre-tapping is not necessary unless your source and amplifier input
both have very high common-mode impedance. In that case, putting a pair
of resistors (preferably closely matched in value) in series across the
sensor and grounding their junction may help.

--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
"gmv" <noemail@please.123> wrote:

http://files.photojerk.com/gmvoeth/diagram1.gif


Hello,

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.
Click to expand...
The first stage should be a differential input. This will eliminate
most of your problems. Try to connect the shield from the cable to
ground of your circuit where the power supply is connected to your
circuit.
I also noticed you are doing a lot of low pass filtering. You could
look into a 'Sallen-key' filter ('Google' for it). This is an easy
filter to construct with an opamp and will probably save you several
opamps.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
 
In article <A8CGd.35$Wu2.1722@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
[...]
line-frequency noise is not particularly significant in
seismic signals,
Click to expand...
This is not true in the general case. I assume that the OP is working at
very long ranges where the frequency content is all very low frequencies.

--
--
kensmith@rahul.net forging knowledge
 
http://files.photojerk.com/gmvoeth/circuita.gif


http://files.photojerk.com/gmvoeth/circuitb.gif


Thanks to input from you guys I tried an instrumentation amplifier
on my input and that seems to have eliminated the 60HZ noise I had
in my first stage.

circuita.gif is the noisy devil.
circuitb.gif is the one I am now using.

gmv






"gmv" <noemail@please.123> wrote in message news:iUyGd.9393$OF5.5238@attbi_s52...
http://files.photojerk.com/gmvoeth/diagram1.gif
Click to expand...
this file is now circuita.gif


Hello,

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.

Every time the Air conditioner comes on a tremendous
electrical disturbance is generated in the input
of this circuit causing the class "A" baseline to follow
a nonsymmetrical cycle of waveform maybe 30 to 60 seconds
in period.

I am seeking recommendations to stop or significantly
reduce this electrical disturbance. The offending device
is actually a heat pump and the signature of the disturbance
is quite different depending upon whether the device
is heating or cooling.

I am unable to relocate the sensor so other solutions are necessary.

Any help here is appreciated.

gmv
Click to expand...
 
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