# LM35 and 4-20 mA output

I have a school project where I have to test a sensor and then measure the output with a multimeter.

I'm using a LM35DZ piece which gives as output itself a linear voltage of 10mV/C degree.

However, one requirement of this project is to have at the very ending a current between 4-20 mA.

The temperature in my hometown is about 25 degrees, so I'm willing to set my 0% (4mA) as 20 degrees, while 100 degrees would be my 20mA output. I've seen a couple of solutions involving transistors and potentiometers.

My rough set is receiving 5V at +Vs' leg of the LM35, GND grounded and the Vout goes directly to non-inverting input of a u741 operational amplifier, while I have a classical non-inverting amplification configuration.

The big deal here is I am struggling to transform this 0.2V into 4mA and further the 1V voltage into 20mA.

Any ideas/explanation attached (as I am also writing a report about it) of how to do it?

Appreaciate the attention and hope to hear something soon!

• Have you got a better IC than a u741!? They are terrible! Commented Apr 1, 2015 at 0:16
• Have you tried any of the 4-20mA current ouput circuits available online? Commented Apr 1, 2015 at 0:16
• it's pretty simple stuff,check here allaboutcircuits.com/vol_3/chpt_8/7.html Commented Apr 1, 2015 at 0:18
• Why are some schools spending their time assigning projects using 45+ year old technology? (µA741 - 1968, 4-20 ma current loop - 1950's) Commented Apr 1, 2015 at 0:43
• Sex is around since the dawn of man, and it appears not to have gone out of fashion. 4-20 mA loops are still widely used in the industry, despite all the fancy new buses and protocols available. Mostly for legacy, but also for robustness. And you can add a Hart to it, if you want. Sadly the 741 is way way out of fashion, but it can be useful to use a piece of junk (with all due respect for Fullagar and - in a way - Widlar) to study on. Its limitations are a good school after all. Commented Jul 14, 2016 at 1:20