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Comments needed on this circuit
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 |
#2
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I read in sci.electronics.design that gmv wrote (in
iUyGd.9393$OF5.5238@attbi_s52) about 'Comments needed on this circuit', on Sun, 16 Jan 2005: I am seeking recommendations to stop or significantly reduce this electrical disturbance. The offending device is actually a heat pump and the signature of the disturbance is quite different depending upon whether the device is heating or cooling. The unbalanced input stage is wide open to every disturbance under the sun. You need a balanced input stage and a twisted-pair shielded cable to your sensor. With that huge gain in the first stage, I suspect the whole design, frankly. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
#3
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You are probably right.
I am trying to go as cheap as absolutely possible. Is it possible to use a diff amp on the input if there is no center tap from the sensor ? Surprisingly this circuit produces fairly good results so long as there is no electrical disturbances in the vicinity. I have found using electrolytic condensors works quite well so long as you do not use them in a feedback type filter. "John Woodgate" wrote in message ... I read in sci.electronics.design that gmv wrote (in iUyGd.9393$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. 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 |
#4
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I read in sci.electronics.design that gmv wrote (in
29AGd.9749$EG1.1390@attbi_s53) about 'Comments needed on this circuit', on Sun, 16 Jan 2005: I am trying to go as cheap as absolutely possible. Is it possible to use a diff amp on the input if there is no center tap from the sensor ? Centre-tapping is not necessary unless your source and amplifier input both have very high common-mode impedance. In that case, putting a pair of resistors (preferably closely matched in value) in series across the sensor and grounding their junction may help. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
#5
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"gmv" wrote in message news:iUyGd.9393$OF5.5238@attbi_s52...
http://files.photojerk.com/gmvoeth/diagram1.gif Hello, Hi. 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. The first three steps should be to convert your single-ended preamplifier into a differential configuration, extend the shield to the rest of the cable and around the geophone, and tie the shield to the same ground the input diff-amp uses as reference. At the same time, I would redistribute the gain so that, rather than x 2947 followed by x 1, you would have x 54 and x 54.5. This would prevent overload of the input stage on signals that are going to be rejected by subsequent filtering. The circuit shown below has approximately the same input impedance, gain, and frequency response as your original two stages with the above suggestions incorporated. || .------||----. | || | | 12n | ___ | ___ | .----o---|___|--o-o----|___|---o | | | | | | 1.07k | 57.6k | | | | |\| | | .-. '-|-\ | || |\ | | | | ---------o-----||----o---------------|+\ | | | 511 .-|+/ || | | ---. | '-' | |/| .-. .---|-/ | | | | 47u | | | |/ | | | | | |348k .-. | | | ___ | ___ '-' | | | | .--o---|___|--o--o---|___|---. | | | 348k | | | | | | '-' | | | 1.07k | 57.6k | | ___ | ___ | | | | | o---|___|---o---|___|--' | | | || | | | | .---| '-----||----o === 2.00k 107k | '--| | || | GND '----| | 12n | '---| === GND (created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de) -- --Larry Brasfield email: Above views may belong only to me. |
#6
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"gmv" 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. 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 |
#7
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On Sun, 16 Jan 2005 13:37:00 -0800, Larry Brasfield wrote:
The circuit shown below has approximately the same input impedance, gain, and frequency response as your original two stages with the above suggestions incorporated. I'd break this between the two opamps, and use a differential output amp for U1, and put that part of the circuit at the sensor. || .------||---. | || | | 12n | ___ | ___ | .----o---|___|--o-o----|___|--o | | | | | | 1.07k | 57.6k | | | | |\| | |\ | .-. '-|-\---------o-----------||-----o---------------|+\ | | | | cable | | | | 511 .-|+/---------------------||---- | ----------.---|-/ | | | | '-' | |/| At this point I gave up on trying to do ASCII art. Hopefully, it gets the point across. .-. | |/ | | | 47u | | | | | | | |348k .-. | | | ___ | ___ '-' | | | | .--o---|___|--o--o---|___|--. | | | 348k | | | | | | '-' | | | 1.07k | 57.6k | | ___ | ___ | | | | | o---|___|---o---|___|--' | | | || | | | | .---| '-----||---o === 2.00k 107k | '--| | || | GND '----| | 12n | '---| === GND (created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de) (royally munged by Rich Grise) Cheers! Rich |
#8
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"Rich Grise" wrote in message news
On Sun, 16 Jan 2005 13:37:00 -0800, Larry Brasfield wrote: The circuit shown below has approximately the same input impedance, gain, and frequency response as your original two stages with the above suggestions incorporated. I'd break this between the two opamps, and use a differential output amp for U1, and put that part of the circuit at the sensor. I agree that such a solution would provide lower susceptibility to noise pickup. However, given that the OP has gotten useful results already, and that line-frequency noise is not particularly significant in seismic signals, I figured the simpler solution would be to revise the existing circuit. It will likely work well enough to keep the noise from taking the input stage into overload, so whatever measures were good enough before to take out the 60 Hz and low harmonics should be more than good enough after applying those changes. Another consideration: This is obviously a one-off, amateur solution. The concept of good-enough applies more than usual in such situations. -- --Larry Brasfield email: Above views may belong only to me. |
#9
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gmv 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. 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 its obviously a Hi-Z problem due to the nature of your app. Microphone wire is crap most of the time from what i have seen. you could try some tightly shielded RG174.. in any case, after looking at your circuit i think moving it all to the location of the sensor and having a low Z output. or at least move one stage to give you a unity gain with low Z, make sure you use Large by pass caps in the sensor end for the +/- lines to keep the EMF out of that. your basicly picking up the EMF and your cable is the secondary. |
#10
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Jamie wrote:
gmv 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. gmv its obviously a Hi-Z problem due to the nature of your app. Microphone wire is crap most of the time from what i have seen. you could try some tightly shielded RG174.. And lose the twisted pair? Bad idea. With a differential input amplifier and shielded microphone wire, you can have several hundred feet of wire between the microphone and the amplifier without any problems. I see no problem in the setup of the OP. -- Reply to nico@nctdevpuntnl (punt=.) Bedrijven en winkels vindt U op www.adresboekje.nl |
#11
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gmv 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. 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. Is that 432 ohm at the sensor something you added or is it internal to the geophone? Your input lines are not "balanced", a terminology which simply means each input line from the sensor has identical impedance to your circuit common over all frequencies in this case. Your interference problem runs deeper than just electrical. From your description, it is clear that the heat pump assembly is transmitting shock and/or acoustic wave components into the ground that are within the frequency range of the geophone. |
#12
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In article ,
Larry Brasfield wrote: [...] line-frequency noise is not particularly significant in seismic signals, 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. -- -- forging knowledge |
#13
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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" wrote in message news:iUyGd.9393$OF5.5238@attbi_s52... http://files.photojerk.com/gmvoeth/diagram1.gif this file is now circuita.gif Hello, The circuit above has been used by me for the last year to receive regional and teleseismic signals but I have been plagued by a problem that requires me to seek help. The lead in cable is a shielded, twisted pair, microphone cable. Its shield stops maybe 2 feet from the sensor. The sensor cable itself has no shield. Its entire length is approximately 50 feet and parallels a major airconditioner power supply line about 4 or 5 feet away for maybe 30 of the 50 feet. Every time the Air conditioner comes on a tremendous electrical disturbance is generated in the input of this circuit causing the class "A" baseline to follow a nonsymmetrical cycle of waveform maybe 30 to 60 seconds in period. I am seeking recommendations to stop or significantly reduce this electrical disturbance. The offending device is actually a heat pump and the signature of the disturbance is quite different depending upon whether the device is heating or cooling. I am unable to relocate the sensor so other solutions are necessary. Any help here is appreciated. gmv |
#14
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"gmv" wrote in message news:yLXGd.11857$EG1.6658@attbi_s53...
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. That circuit would reject common-mode noise better if the two branches consisting of 2.2k+120k resistors both had equal capacitors across the 120k resistors. You should also be aware that using 3 op-amps for an instrumentation amplifier can be done with better common mode rejection using the popular circuit diagrammed below: |\ ----------|+\ | -------o---------. .-|-/ | | | |/ .-. | 100k 100k | | | | ___ ___ | | | 20k '--|___|--o---|___|- | '-' | | | | | | | | | | '------------o | | | | |\| | .-. '--|-\ | | | | ---' | | 2k .--|+/ '-' | |/| | | .------------o | | | | | | 100k | 100k | .-. ___ | ___ | | | .--|___|--o---|___|-. | | | 20k | | | |\| '-' | | '-|-\ | | === | -------o---------' GND ---------|+/ |/| (created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de) -- --Larry Brasfield email: Above views may belong only to me. |
#15
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gmv wrote: 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" wrote in message news:iUyGd.9393$OF5.5238@attbi_s52... http://files.photojerk.com/gmvoeth/diagram1.gif 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 That's a lie if I ever heard one. |
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