problems with howland current source

Discussion in 'Homework Help' started by hunterage2000, May 6, 2012.

  1. t_n_k

    t_n_k AAC Fanatic!

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    I'm still not convinced by this. What's shown is not what I understand to be a Howland pump - which is in fact capable of producing a bipolar output. The circuit shown is clearly not capable of a bi-polar output.

    I'm confused by this image - perhaps you have misinterpreted the meaning of the text.
  2. hunterage2000

    hunterage2000 Thread Starter Member

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    Yeah tnk it is unidirectional, Im not totally sure what is meant by the 4-20mA current output. What I imagined it to be was 4mA for No-load and 20mA for maximum load. I cant find any texts about what they are used for, just the diagram and its equations.
  3. t_n_k

    t_n_k AAC Fanatic!

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    A couple of observations.


    1. It always pays off to have a design specification. Once you have that then you do the design to meet your specification.
    2. Notwithstanding the preceding point - I believe you could have produced a much simpler solution with DC excitation of the load cells. The AC excitation approach seems counter productive.
    Attached is a schematic of a 5V DC excited bridge with 4-20mA output. Purely by way of example, the bridge is arbitrarily assumed to give ±36mV deviation for full a scale 4-20mA output. The 4mA condition would be for -36mV bridge output.

    Attached Files:

    Last edited: May 8, 2012
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