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

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Discussion Overview

The discussion revolves around converting a 0-5V signal to a 4-20mA output using a Howland Current Pump. Participants explore the requirements and challenges associated with this conversion, including circuit design and component selection.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant seeks assistance in converting a 0-5V signal to 4-20mA using a Howland Current Pump, noting that they have misplaced their original notes.
  • Another participant mentions a lack of familiarity with the Howland Current Pump but provides a link to an app note from National Semiconductor that may contain relevant information.
  • A different participant states that their Howland Current Pump is not functioning correctly and specifies the need to convert both a 0-5V signal to 0-20mA and a 1-5V signal to 4-20mA.
  • One participant requests a schematic and test methodology from the user experiencing issues, suggesting that they might assist with the existing design rather than creating a new one.
  • A participant describes their setup using an LM741 op-amp, specifying the need for a 0-20mA output with a 250-ohm load and mentions the saturation voltage of the op-amp and compliance voltage considerations.

Areas of Agreement / Disagreement

Participants express varying levels of familiarity with the Howland Current Pump and its application, leading to differing approaches and suggestions. The discussion remains unresolved regarding the specific design and troubleshooting of the circuit.

Contextual Notes

Participants have not provided complete schematics or detailed test results, which may limit the ability to diagnose issues effectively. There are also assumptions regarding the input and output conditions that have not been fully clarified.

Who May Find This Useful

This discussion may be useful for individuals interested in circuit design, particularly those working with current pumps and signal conversion in electronic applications.

DaineAtkins
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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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