Thanks Chris,,   I have a little breadboard that I use to start with, 
then when I'm happy with the results I move it to a project board!   For 
a while, I will crunch numbers for component values for my 4.5 second 
system, then we will play,,  ha!!    I spent about 28 years repairing 
aircraft electronics and test systems!   Didn't do much engineering,, 
ha,  but with the little heads up, I should be able to figure it out 
now.     Looks like I will set the unity gain at about 4.5 sec  and the 
cut off at about 60 seconds with a gain value of about 6 db per octave  
per stage  and see what happens,,,   hopefully that will give me a good 
signal response to about 30 seconds?    If it proves to be a problem, 
I'll try a cut off of about 40 seconds and response to about 20 seconds?
thanks again for the help and opamp advice,
  Stephen

ChrisAtUpw@....... wrote:
> In a message dated 2006/12/05, skmort@............ writes:
>
>> OK, so which components would we change, and to what value for a 2
>> Hz and a 0.222 hz (4.5 sec) system?
>> I might have to break out my soldering iron, ha!
>> Thanks,
>> Stephen
>
>
> Hi Stephen,
>
>        If f is the resonant frequency of the sensor, you make 1 / 
> 2xPixfxCxR1 = 1.09 according to Roberts. I am not sure exactly why he 
> chose this. It could explain the small hump in the combined 
> characteristic.
>        The Max gain is R2 / R1
>        The lower turnover frequency is 1 / 2xPixC1xR2 This has been 
> set to ~1/2 the lowest response frequency in the Roberts circuit.
>        You need two units in series.
>        Roberts reported significant levels of VLF noise, so it might 
> be a good idea to follow up the compensation circuits with a two / 
> four pole high pass Butterworth filter set to about the lower desired 
> frequency.
>        If you want to use the circuit at long periods, you may need to 
> use some CAZ opamps MAX430, LTC1150 etc. They reject 1/f noise. 
> Otherwise LF411, OP07, LF412 etc are OK
>        The optimum place to insert this circuit is between the first 
> opamp and the low pass filters.
>
>        How about investing in a temperature compensated soldering iron 
> which plugs in.....? Or make an Experimenter Board plug in version first?
>
>        Regards,
>
>        Chris Chapman



  


Thanks Chris,,   I have a little breadboard that I use to start with,
then when I'm happy with the results I move it to a project board!  
For a while, I will crunch numbers for component values for my 4.5
second system, then we will play,,  ha!!    I spent about 28 years
repairing aircraft electronics and test systems!   Didn't do much
engineering,, ha,  but with the little heads up, I should be able to
figure it out now.     Looks like I will set the unity gain at about
4.5 sec  and the cut off at about 60 seconds with a gain value of about
6 db per octave  per stage  and see what happens,,,   hopefully that
will give me a good signal response to about 30 seconds?    If it
proves to be a problem, I'll try a cut off of about 40 seconds and
response to about 20 seconds?

thanks again for the help and opamp advice,

  Stephen



ChrisAtUpw@....... wrote:
In a message dated
2006/12/05, skmort@............ writes:

  

  
OK,
so which components would we change, and to what value for a 2 

Hz and a 0.222 hz (4.5 sec) system?

I might have to break out my soldering iron, ha!

Thanks,

Stephen
  

  

Hi Stephen,

  

       If f is the resonant frequency of the sensor, you make 1 /
2xPixfxCxR1 = 1.09 according to Roberts. I am not sure exactly why he
chose this. It could explain the small hump in the combined
characteristic.

       The Max gain is R2 / R1

       The lower turnover frequency is 1 / 2xPixC1xR2 This has been set
to ~1/2 the lowest response frequency in the Roberts circuit.

       You need two units in series.

       Roberts reported significant levels of VLF noise, so it might be
a good idea to follow up the compensation circuits with a two / four
pole high pass Butterworth filter set to about the lower desired
frequency.

       If you want to use the circuit at long periods, you may need to
use some CAZ opamps MAX430, LTC1150 etc. They reject 1/f noise.
Otherwise LF411, OP07, LF412 etc are OK

       The optimum place to insert this circuit is between the first
opamp and the low pass filters.

  

       How about investing in a temperature compensated soldering iron
which plugs in.....? Or make an Experimenter Board plug in version
first? 

  

       Regards,

  

       Chris Chapman