problems with howland current source

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

  1. t_n_k

    t_n_k AAC Fanatic!

    Joined:
    Mar 6, 2009
    5,448
    774
    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.
     
    #21
  2. hunterage2000

    hunterage2000 Thread Starter Active Member

    Joined:
    May 2, 2010
    351
    0
    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.
     
    #22
  3. t_n_k

    t_n_k AAC Fanatic!

    Joined:
    Mar 6, 2009
    5,448
    774
    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
    #23
Loading...