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op-amps single channel or instrument ?

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  • Dave Mucha
    Hi all, I have a 0-5 volt signal into my ADC and was looking for a way to change the input range before the ADC to get a little better resolution. A 10:1 is
    Message 1 of 9 , Dec 1, 2003
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      Hi all,

      I have a 0-5 volt signal into my ADC and was looking for a way to
      change the input range before the ADC to get a little better
      resolution.

      A 10:1 is the maximum amplification I would be using and it is all in a
      linear fashion.

      That said, I can use a single channel of an op-amp to get
      amplification, but in looking for the most appropriate op-amps, I keep
      coming across instrumentation op-amps and they typically use 3 or 4
      channels.

      I have found stuff on how to use them, but not why to use one style
      over another. I guess that by using both the inverting and non-
      inverting, that any temperature or power changes will be negated and
      the output will remain accurate.

      Can anyone offer better facts than my conjecture?

      Dave
    • Steve
      If your signal is single ended, I see no advantage in using a balanced amplifier. Especially if it is all on the same PCB and you are careful to avoid ground
      Message 2 of 9 , Dec 1, 2003
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        If your signal is single ended, I see no advantage in using a balanced
        amplifier. Especially if it is all on the same PCB and you are careful
        to avoid ground current loops.

        A reason to go differential would be if the signal starts out 10 feet
        or more away. Then you want it to send a differential signal from the
        sensor.

        Steve Greenfield aka Alien Steve

        --- In Electronics_101@yahoogroups.com, "Dave Mucha" <dave_mucha@y...>
        wrote:
        > Hi all,
        >
        > I have a 0-5 volt signal into my ADC and was looking for a way to
        > change the input range before the ADC to get a little better
        > resolution.
        >
        > A 10:1 is the maximum amplification I would be using and it is all in a
        > linear fashion.
        >
        > That said, I can use a single channel of an op-amp to get
        > amplification, but in looking for the most appropriate op-amps, I keep
        > coming across instrumentation op-amps and they typically use 3 or 4
        > channels.
        >
        > I have found stuff on how to use them, but not why to use one style
        > over another. I guess that by using both the inverting and non-
        > inverting, that any temperature or power changes will be negated and
        > the output will remain accurate.
        >
        > Can anyone offer better facts than my conjecture?
        >
        > Dave
      • rgsparber@aol.com
        In a message dated 12/1/2003 9:34:02 AM Central Standard Time, dave_mucha@yahoo.com writes: I have a 0-5 volt signal into my ADC and was looking for a way to
        Message 3 of 9 , Dec 1, 2003
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          In a message dated 12/1/2003 9:34:02 AM Central Standard Time, dave_mucha@... writes:
          I have a 0-5 volt signal into my ADC and was looking for a way to change the input range before the ADC to get a little better resolution.
           
          A 10:1 is the maximum amplification I would be using and it is all in a linear fashion.
           
          That said, I can use a single channel of an op-amp to get amplification, but in looking for the most appropriate op-amps, I keep coming across instrumentation op-amps and they typically use 3 or 4 channels.
           
          I have found stuff on how to use them, but not why to use one style over another.   I guess that by using both the inverting and non- inverting, that any temperature or power changes will be negated and the output will remain accurate.
           
          Can anyone offer better facts than my conjecture?

          Dave
          I'm a bit confused here. Your ADC has an input range of 0 to 5V. What is the desired input range of your system? Are you saying that you want it to be 0 to 0.5V with the x10 amp? What input resistance do you want and what frequency range do you expect.
           
          Assuming you want a x10 amp with less than 10K input resistance, any old cheap OP amp should work fine given proper external circuit.
           
          Rick Sparber
          rgsparber@...
        • rtstofer
          Once again, I have to recommend Op Amps For Everyone , a free book available at www.ti.com. Particularly appropriate for single supply rail-to-rail op amp
          Message 4 of 9 , Dec 1, 2003
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            Once again, I have to recommend "Op Amps For Everyone", a free book
            available at www.ti.com. Particularly appropriate for single supply
            rail-to-rail op amp circuits which will allow you to scale and
            offset in one operation.

            Chapter 4 is what you need.

            --- In Electronics_101@yahoogroups.com, rgsparber@a... wrote:
            > In a message dated 12/1/2003 9:34:02 AM Central Standard Time,
            > dave_mucha@y... writes:
            > I have a 0-5 volt signal into my ADC and was looking for a way to
            change the
            > input range before the ADC to get a little better resolution.
            >
            > A 10:1 is the maximum amplification I would be using and it is all
            in a
            > linear fashion.
            >
            > That said, I can use a single channel of an op-amp to get
            amplification, but
            > in looking for the most appropriate op-amps, I keep coming across
            > instrumentation op-amps and they typically use 3 or 4 channels.
            >
            > I have found stuff on how to use them, but not why to use one
            style over
            > another. I guess that by using both the inverting and non-
            inverting, that any
            > temperature or power changes will be negated and the output will
            remain
            > accurate.
            >
            > Can anyone offer better facts than my conjecture?
            >
            > Dave
            > I'm a bit confused here. Your ADC has an input range of 0 to 5V.
            What is the
            > desired input range of your system? Are you saying that you want
            it to be 0 to
            > 0.5V with the x10 amp? What input resistance do you want and what
            frequency
            > range do you expect.
            >
            > Assuming you want a x10 amp with less than 10K input resistance,
            any old
            > cheap OP amp should work fine given proper external circuit.
            >
            > Rick Sparber
            > rgsparber@A...
          • Dave Mucha
            ... The off-board sensor has a 0-5 volt response and reports it s value back to my ADC. a 0 to 100 psi sensor would offer 0-100psi = 0-5VDC. if I can double
            Message 5 of 9 , Dec 1, 2003
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              > Dave
              > I'm a bit confused here. Your ADC has an input range of 0 to 5V. What is the
              > desired input range of your system? Are you saying that you want it to be 0 to
              > 0.5V with the x10 amp? What input resistance do you want and what frequency
              > range do you expect.
              >
              > Assuming you want a x10 amp with less than 10K input resistance, any old
              > cheap OP amp should work fine given proper external circuit.
              >
              > Rick Sparber
              > rgsparber@A...

              The off-board sensor has a 0-5 volt response and reports it's value
              back to my ADC.

              a 0 to 100 psi sensor would offer 0-100psi = 0-5VDC. if I can double
              the input value, that would make the sensor a 0 to 100 with a 0-10V
              range, or a 0 to 50psi with 0-5V, 4x the input would simulate the
              sensor as 0 to 25 psi @ 0-5V. (ADC is 0-5VDC input)

              I do understand that if the device accuracy is 1% of full span ie:1%
              of 100, it too is multiplied. so a 0 to 25 psi range has a 4% error.
              at some point, the error can be greater than the sensing range.

              Since I have a common ground it may be that the single ended input
              means I can use a single op-amp. also since I cannot ampliphy the
              input excessivly, it also seems that a 5x range is all I may be able to
              use, but that should be enough.

              As for the "Op-Amps for Everyone" I think I may need to review that to
              get the theory why a single channel vs the Insturmentation style.

              Dave
              (ps: sorry for the spelling, I'm using my wife's MAC as my AXT power
              supply went POP rather abruptly on Thanksgiving.)
            • Steve
              ... The advantage to differential would be in putting the single ended to differential conversion at the sensor. Then it is more noise resistant. ... Yeah, the
              Message 6 of 9 , Dec 1, 2003
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                --- In Electronics_101@yahoogroups.com, "Dave Mucha" <dave_mucha@y...>
                wrote:

                > The off-board sensor has a 0-5 volt response and reports it's value
                > back to my ADC.

                The advantage to differential would be in putting the single ended to
                differential conversion at the sensor. Then it is more noise resistant.


                > Dave
                > (ps: sorry for the spelling, I'm using my wife's MAC as my AXT power
                > supply went POP rather abruptly on Thanksgiving.)

                Yeah, the keyboards different and the electrons have that Mac smell...
                nice try, Dave. ;')
              • rgsparber@aol.com
                In a message dated 12/1/2003 7:51:12 PM Central Standard Time, dave_mucha@yahoo.com writes: The off-board sensor has a 0-5 volt response and reports it s value
                Message 7 of 9 , Dec 1, 2003
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                  In a message dated 12/1/2003 7:51:12 PM Central Standard Time, dave_mucha@... writes:
                  The off-board sensor has a 0-5 volt response and reports it's value back to my ADC.
                   
                  a 0 to 100 psi sensor would offer 0-100psi = 0-5VDC.  if I can double the input value, that would make the sensor a 0 to 100 with a 0-10V range, or a 0 to 50psi with 0-5V,  4x the input would simulate the sensor as 0 to 25 psi @ 0-5V.  (ADC is 0-5VDC input)
                   
                  I do understand that if the device accuracy is 1% of full span  ie:1% of 100, it too is multiplied.  so a 0 to 25 psi range has a 4% error. at some point, the error can be greater than the sensing range.
                   
                  Since I have a common ground it may be that the single ended input means I can use a single op-amp.  also since I cannot ampliphy the input excessivly, it also seems that a 5x range is all I may be able to use, but that should be enough.
                  Can you tell me the needed input resistance? If you are going to use a bipolar OP amp, then the larger this resistance, the larger the DC offset you may encounter.
                   
                  Also, if you can live with an inverting amplifier, say by reversing the wires from the psi sensor, then a x5 amp could be made using an input resistor, feedback resistor, and (assuming a bipolar OP amp) an input DC offset canceling resistor. Gain equals feedback resistor divided by input resistor but is negative. The offset canceling resistor should equal the input resistor in parallel with the feedback resistor.
                   
                  Rick Sparber
                  rgsparber@...
                • Dave Mucha
                  ... Nope, just teh way teh desks are situated. seems I just cannot type with my hands and arms laying across the desk as she has it. but for the PC, it went
                  Message 8 of 9 , Dec 1, 2003
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                    >
                    > > Dave
                    > > (ps: sorry for the spelling, I'm using my wife's MAC as my AXT power
                    > > supply went POP rather abruptly on Thanksgiving.)
                    >
                    > Yeah, the keyboards different and the electrons have that Mac smell...
                    > nice try, Dave. ;')

                    Nope, just teh way teh desks are situated.

                    seems I just cannot type with my hands and arms laying across the desk
                    as she has it.

                    but for the PC, it went POP in a big way !

                    blew 8 of the 10 caps on the motherboard.
                    and the Hard Disk will not spin up in another computer.

                    Can you say "____________" (insert your favorite profanity)

                    seems I will attempt a brain transplant on the hard drive.
                    swap not only the IDE board on the drive itself, but also the heads
                    inside. Just to save a measly $1,500 from one of those recovery
                    houses.

                    (recommendations more than welcome)

                    I was thinking of just drilling a little hole on the side, but when all
                    the 1's an 0's come out, it gets real hard to tape and staple them onto
                    another drive.

                    Dave
                    (and as you might notice, I wern't a good speller to begin wit.)
                  • Dave Mucha
                    ... I just thought you might like to get an update. I had an old damaged drive, exact same model. platters were trashed, probable dropped, got it from a
                    Message 9 of 9 , Dec 6, 2003
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                      > but for the PC, it went POP in a big way !
                      >
                      > blew 8 of the 10 caps on the motherboard.
                      > and the Hard Disk will not spin up in another computer.
                      >
                      > Can you say "____________" (insert your favorite profanity)
                      >
                      > seems I will attempt a brain transplant on the hard drive.
                      > swap not only the IDE board on the drive itself, but also the heads
                      > inside. Just to save a measly $1,500 from one of those recovery
                      > houses.
                      >
                      > (recommendations more than welcome)

                      I just thought you might like to get an update.

                      I had an old damaged drive, exact same model. platters were trashed,
                      probable dropped, got it from a friend.

                      anyway, a swapping of the IDE controller card on the hard disk itself
                      proved to be successful.

                      It booted and ran fine.

                      I understand that the bad sectors are stored on the IDE card so I
                      will now need to figure out how to erase the stored data and get it
                      to map this drive.

                      I did contact a few recovery houses and found $550.00 to be the best
                      deal, but for that, I can now buy a whole new system.

                      Dave
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