All About Circuits Forum problems with howland current source
 Register Blogs FAQ Members List Today's Posts Search Today's Posts Mark Forums Read

 Homework Help Stuck on a textbook question or coursework? Cramming for a test and need help understanding something? Post your questions and attempts here and let others help.

#21
05-07-2012, 11:35 AM
 t_n_k Senior Member Join Date: Mar 2009 Posts: 4,949

Quote:
 Originally Posted by hunterage2000 The Howland from a book is attached
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.
#22
05-07-2012, 08:17 PM
 hunterage2000 Senior Member Join Date: May 2010 Location: Durham, UK Posts: 298

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.
#23
05-07-2012, 10:25 PM
 t_n_k Senior Member Join Date: Mar 2009 Posts: 4,949

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 Images
 DC excited Load Cell Bridge with 4-20mA output.png (11.4 KB, 11 views)

Last edited by t_n_k; 05-08-2012 at 06:53 AM.

 Tags current, howland, problems, source

 Similar Threads Thread Thread Starter Forum Replies Last Post filonic The Projects Forum 3 04-23-2012 02:50 AM cgama The Projects Forum 10 01-23-2012 11:33 AM Loonie Homework Help 5 11-24-2011 12:05 PM Sajid86 Homework Help 5 05-27-2009 09:20 PM ihaveaquestion Homework Help 23 05-07-2009 09:00 PM

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Electronics Forums     General Electronics Chat     The Projects Forum     Homework Help     Electronics Resources Software, Microcomputing, and Communications Forums     Programmer's Corner     Embedded Systems and Microcontrollers     Computing and Networks     Radio and Communications Circuits and Projects     The Completed Projects Collection Abstract Forums     Math     Physics     General Science All About Circuits Commmunity Forums     Off-Topic     The Flea Market     Feedback and Suggestions

All times are GMT. The time now is 06:29 PM.