Converting 0-5V to 4-20mA using a Howland Current Pump for Scientists

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The discussion focuses on converting a 0-5V signal to a 4-20mA output using a Howland Current Pump. Users share resources, including a National Semiconductor app note that provides both basic and detailed analyses of the Howland Current Pump. The original poster seeks assistance with circuit design and methodology, specifically mentioning the need for a 0-20mA output from a 5V input. Suggestions include using a 250-ohm resistor for low impedance applications. The conversation emphasizes the need for schematic sharing to facilitate further help.
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I have a 0-5V signal which I need to convert 4-20mA by using a Howland Current pump.
I know that there are more steps to the whole process but I have misplaced all my notes that I originally had. Could someone please help?
 
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I fully admit that I've never heard of (or at least don't remember) the Howland Current Pump. However, the first Google Thing that comes up when Googling for Howland Current Pump:
http://www.google.ca/search?q=howland+current+pump

...is an app note from National Semiconductor entitled "A Comprehensive Study of the Howland Current Pump". Quickly perusing it, it seems to present a basic inspection analysis as well as a more detailed mathematical analysis (for both basic and improved variants).

Does this help?
 
The Howland Current Pump doesn't seem to be working properly.
Basically, I need to convert a 0-5V signal to 0-20mA
and a 1-5V signal to 4-20mA.
If anyone could please help me a.s.a.p!
 
Can you post your schematic, and your test methodology / results? Or are you asking us to design your circuit for you?

While we can't do the latter, we might be able to help you with the former.

If you're not worried about output impedance / voltage levels, and have (very) low input impedance (e.g. op-amp driven output driving an analog current meter) you could just use a 250 ohm resistor.
 
I am using a LM741 with an input of 5V and I need a 0-20mA output with a 250ohm load
I know that the saturation voltage of the op-amp is +/- 13V. I have calculated my design using a compliance voltage of 5V.
How do I post my schematic?
 

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