designing a DAQ

Hi all,
      I have to design a data acquisition system for two different
signals. One is within the frequency range 300 hz (+ or - 25 Hz) and
the other one is less than 5 Hz. I do not know the amplitude ranges of
these frequencies(I guess it may depend on the sensors used). I do not
know how to select the sensors and how to design the other hardware.
If you can either give a pointer to me or if you could tell me what
are the dos and dont's and the important things to consider while
designing. Can I design a single daq card that can capture the 300Hz
and 5 Hz signals. I just know that I need to use a D/A converter and a
signal conditioning (amplifier and filter) circuit. How to proceed.
Are there any proper commercial techniques related to DAQ design? I
have collected some data from some micrcontroller project sites but I
am seeing some expert comments or suggestions  being passed in this
group and I want to get some suggestions.

Thanks in advance.

On Dec 6, 5:34=A0pm, kkrish <clearminded.kkr...@gmail.com> wrote:
> Hi all,
> =A0 =A0 =A0 I have to design a data acquisition system for two different
> signals. One is within the frequency range 300 hz (+ or - 25 Hz) and
> the other one is less than 5 Hz. I do not know the amplitude ranges of
> these frequencies(I guess it may depend on the sensors used). I do not
> know how to select the sensors and how to design the other hardware.
> If you can either give a pointer to me or if you could tell me what
> are the dos and dont's and the important things to consider while
> designing. Can I design a single daq card that can capture the 300Hz
> and 5 Hz signals. I just know that I need to use a D/A converter and a
> signal conditioning (amplifier and filter) circuit. How to proceed.
> Are there any proper commercial techniques related to DAQ design? I
> have collected some data from some micrcontroller project sites but I
> am seeing some expert comments or suggestions =A0being passed in this
> group and I want to get some suggestions.
>
The design depends on your exact requirements.
There are many processors/controllers that have support for
multilpe DACs. Else, you can use a single DAC that can have multiple
channels. There are many opensource tools like COMEDI are very
famous in DAQ world. Further, RTlinux also supports COMEDI.

Karthik Balaguru

In article <5ff71e1c-dd15-469b-a80b-9e2d130a2034
@g22g2000prf.googlegroups.com>, clearminded.kkrish@gmail.com says...
> Hi all,
>       I have to design a data acquisition system for two different
> signals. One is within the frequency range 300 hz (+ or - 25 Hz) and
> the other one is less than 5 Hz. I do not know the amplitude ranges of
> these frequencies(I guess it may depend on the sensors used). I do not
> know how to select the sensors and how to design the other hardware.
> If you can either give a pointer to me or if you could tell me what
> are the dos and dont's and the important things to consider while
> designing. Can I design a single daq card that can capture the 300Hz
> and 5 Hz signals. I just know that I need to use a D/A converter and a
> signal conditioning (amplifier and filter) circuit. How to proceed.
> Are there any proper commercial techniques related to DAQ design? I
> have collected some data from some micrcontroller project sites but I
> am seeing some expert comments or suggestions  being passed in this
> group and I want to get some suggestions.
> 
> Thanks in advance.
> 
The first thing you should research is the difference between a
D/A converter (DAC) and an A/D converter (ADC).  If you are acquiring
data, you need an A/D converter.

The next thing you need to do is get firm specififications on the
input signals and sensors.  Without those specifications you
will have a tough time designing a good system.

A good place to start would be the National Instruments web
sit,   www.ni.com.   They've been in the PC data acquisition
business about as long as there have been PCs.  I'm sure they
have notes and white papers on the general process of
data acquisition.


Mark Borgerson

On Dec 6, 12:40=A0pm, Mark Borgerson <mborger...@comcast.net> wrote:

> The first thing you should research is the difference between a
> D/A converter (DAC) and an A/D converter (ADC). =A0If you are acquiring

Well, maybe, but he said DAQ - Data AcQuisition, not DAC.

In article <b0b676dc-cd0c-4586-9bbf-9e8a66e84cd1
@o9g2000vbj.googlegroups.com>, zwsdotcom@gmail.com says...
> On Dec 6, 12:40=A0pm, Mark Borgerson <mborger...@comcast.net> wrote:
>=20
> > The first thing you should research is the difference between a
> > D/A converter (DAC) and an A/D converter (ADC). =A0If you are acquiring
>=20
> Well, maybe, but he said DAQ - Data AcQuisition, not DAC.
>=20
What he said was:

" I just know that I need to use a D/A converter and a
signal conditioning (amplifier and filter) circuit. "


Mark Borgerson

On Sun, 6 Dec 2009 04:34:13 -0800 (PST)
kkrish <clearminded.kkrish@gmail.com> wrote:

> Hi all,
>       I have to design a data acquisition system for two different
> signals. One is within the frequency range 300 hz (+ or - 25 Hz) and
> the other one is less than 5 Hz. I do not know the amplitude ranges of
> these frequencies(I guess it may depend on the sensors used). I do not
> know how to select the sensors and how to design the other hardware.
> If you can either give a pointer to me or if you could tell me what
> are the dos and dont's and the important things to consider while
> designing. Can I design a single daq card that can capture the 300Hz
> and 5 Hz signals. I just know that I need to use a D/A converter and a
> signal conditioning (amplifier and filter) circuit. How to proceed.
> Are there any proper commercial techniques related to DAQ design? I
> have collected some data from some micrcontroller project sites but I
> am seeing some expert comments or suggestions  being passed in this
> group and I want to get some suggestions.
> 
> Thanks in advance.

While I hate to be blunt, you seem to not understand what you're
doing.  Now that's far from a crime, but that being the case, and in a
world saturated to the gills with commercially available data
acquisition cards in every combination of form factor, speed,
resolution, and range, do you really want to be building this yourself?

I'm an instrumentation guy, I've got a bias towards selling my stuff
(though it sounds like what you're looking for would be lower end than
anything I could offer you).  But it sounds like you're spotty on the
theory side of things and have no experience designing this kind of
hardware.

And so before you get too deep into planning your "design", you want
to:
A) Figure out what your actual system requirements are.  So far,
you know that you've got "signals", and their approximate frequencies,
but nothing more about them.  You'll never get anywhere from there.
What are you actually trying to sense and why?  Then you figure out the
transducers to turn that information into an electrical signal, and
THEN you'll know what you need in terms of data acquisition hardware.

Then B), take a step back to the build/buy decision, and try to get real
pricing on something that will accomplish your task.  I second
someone's recommendation to look at National Instruments.  They're a
competitor of mine, but there's no denying that their webpage is a
cornucopia of information for someone trying to get a feel for what
sorts of DAQ hardware is out there.  Then once you've got an idea of
what you're looking for, go to Google and see who else can do it for
you.  It very well may be that a couple hundred dollars will get your
problem solved.

-- 
Rob Gaddi, Highland Technology
Email address is currently out of order

In article <20091207092840.000039c7@unknown>, 
rgaddi@technologyhighland.com says...
> On Sun, 6 Dec 2009 04:34:13 -0800 (PST)
> kkrish <clearminded.kkrish@gmail.com> wrote:
> 
> > Hi all,
> >       I have to design a data acquisition system for two different
> > signals. One is within the frequency range 300 hz (+ or - 25 Hz) and
> > the other one is less than 5 Hz. I do not know the amplitude ranges of
> > these frequencies(I guess it may depend on the sensors used). I do not
> > know how to select the sensors and how to design the other hardware.
> > If you can either give a pointer to me or if you could tell me what
> > are the dos and dont's and the important things to consider while
> > designing. Can I design a single daq card that can capture the 300Hz
> > and 5 Hz signals. I just know that I need to use a D/A converter and a
> > signal conditioning (amplifier and filter) circuit. How to proceed.
> > Are there any proper commercial techniques related to DAQ design? I
> > have collected some data from some micrcontroller project sites but I
> > am seeing some expert comments or suggestions  being passed in this
> > group and I want to get some suggestions.
> > 
> > Thanks in advance.
> 
> While I hate to be blunt, you seem to not understand what you're
> doing.  Now that's far from a crime, but that being the case, and in a
> world saturated to the gills with commercially available data
> acquisition cards in every combination of form factor, speed,
> resolution, and range, do you really want to be building this yourself?
> 
> I'm an instrumentation guy, I've got a bias towards selling my stuff
> (though it sounds like what you're looking for would be lower end than
> anything I could offer you).  But it sounds like you're spotty on the
> theory side of things and have no experience designing this kind of
> hardware.
> 
> And so before you get too deep into planning your "design", you want
> to:
> A) Figure out what your actual system requirements are.  So far,
> you know that you've got "signals", and their approximate frequencies,
> but nothing more about them.  You'll never get anywhere from there.
> What are you actually trying to sense and why?  Then you figure out the
> transducers to turn that information into an electrical signal, and
> THEN you'll know what you need in terms of data acquisition hardware.
> 
> Then B), take a step back to the build/buy decision, and try to get real
> pricing on something that will accomplish your task.  I second
> someone's recommendation to look at National Instruments.  They're a
> competitor of mine, but there's no denying that their webpage is a
> cornucopia of information for someone trying to get a feel for what
> sorts of DAQ hardware is out there.  Then once you've got an idea of
> what you're looking for, go to Google and see who else can do it for
> you.  It very well may be that a couple hundred dollars will get your
> problem solved.
> 
LOL!  I pointed out National Instruments, because they're NOT a 
competitor of mine---at least not until they can put together
a system that runs on 15mA and will fit inside a 3"  ID pressure
case.

Thanks for seconding my opinion.  The OP does have some basic
research to do.  If he wants more help, we'll need more
information on the system requirements.


Mark Borgerson

Hi all,
Thanks for your replies.

>The first thing you should research is the difference between a
>D/A converter (DAC) and an A/D converter (ADC).  If you are acquiring
>data, you need an A/D converter.

you are right, I wrote it as DAC but actually I meant A/D and thanks
for pointing out the mistake.

> If he wants more help, we'll need more
>information on the system requirements

What are the other information you need? I do not know if the sensor
and sensor connectors I am going to use is a low capacitance or high
capacitance because I do not know what type of sensor I need to
choose. I am going to measure rotational force. Specifically I am
going to measure the amplitude and phase difference of two rotating
forces with a pair of sensors. As of now I assume noise level of the
surroundings is negligible(Of course I have a filter) and I do not
worry about the bandwidth now.  I saw some application notes from IC
manufacturers and NI website(after you said) and I understand
something about what is DAQ but I still need help related to component
selection and hardware.

Thanks in advance.

On Tue, 8 Dec 2009 10:30:57 -0800 (PST)
kkrish <clearminded.kkrish@gmail.com> wrote:

> Hi all,
> Thanks for your replies.
> 
> >The first thing you should research is the difference between a
> >D/A converter (DAC) and an A/D converter (ADC).  If you are acquiring
> >data, you need an A/D converter.
> 
> you are right, I wrote it as DAC but actually I meant A/D and thanks
> for pointing out the mistake.
> 
> > If he wants more help, we'll need more
> >information on the system requirements
> 
> What are the other information you need? I do not know if the sensor
> and sensor connectors I am going to use is a low capacitance or high
> capacitance because I do not know what type of sensor I need to
> choose. I am going to measure rotational force. Specifically I am
> going to measure the amplitude and phase difference of two rotating
> forces with a pair of sensors. As of now I assume noise level of the
> surroundings is negligible(Of course I have a filter) and I do not
> worry about the bandwidth now.  I saw some application notes from IC
> manufacturers and NI website(after you said) and I understand
> something about what is DAQ but I still need help related to component
> selection and hardware.
> 
> Thanks in advance.
> 

What do you mean by "rotational force"?  Are you discussing torque on a
shaft?  What, specifically, are you trying to accomplish?

-- 
Rob Gaddi, Highland Technology
Email address is currently out of order

On Dec 8, 10:30=A0am, kkrish <clearminded.kkr...@gmail.com> wrote:
> Hi all,
> Thanks for your replies.
>
> >The first thing you should research is the difference between a
> >D/A converter (DAC) and an A/D converter (ADC). =A0If you are acquiring
> >data, you need an A/D converter.
>
> you are right, I wrote it as DAC but actually I meant A/D and thanks
> for pointing out the mistake.
>
> > If he wants more help, we'll need more
> >information on the system requirements
>
> What are the other information you need? I do not know if the sensor
> and sensor connectors I am going to use is a low capacitance or high
> capacitance because I do not know what type of sensor I need to
> choose. I am going to measure rotational force. Specifically I am
> going to measure the amplitude and phase difference of two rotating
> forces with a pair of sensors.

What frequencies?  How do you know that you need analog sensors?  It
depends on how you pickup the signals.  Your first task is to figure
out the sensors.

> As of now I assume noise level of the
> surroundings is negligible(Of course I have a filter) and I do not
> worry about the bandwidth now. =A0I saw some application notes from IC
> manufacturers and NI website(after you said) and I understand
> something about what is DAQ but I still need help related to component
> selection and hardware.
>
> Thanks in advance.