How to build a 4-20 mA source for testing?

hi guys i like the look of the 4-20mA & 2-10Vdc Current Generator , how hard is it to build one, has anyone got a picture of the one they have build, what's needed thanks stu
Easy I built MikeVT version in less than 30 minutes, it don't look pretty but did the job I needed.

holy guy
your problem is with the resistors, make one a little different so you can use it even lower the 32 is a little high (some machines can not cope above 25 mA.
Use a variable resistor (potmeter to find both setting and then solder the value with a fixed one in.


An RTD simulator is very easy to build by using some resistors and a turnswitch.
best is to use a four deck switch and soler the resistors direct on the switch.
Thanx for you input, i thought it may be the resistors. Guess its time to play around with the soldering iron again.

I just downloaded a resistance table for RTD (Pt100) so i'll pick some resistance values from it to make the simulator.

Here is a simpler version of mine without the milivolt source.

If you look at the upper diagram it shows how it works.
The lower diagram shows the actual circuit.

The nice thing about this it both sources and simulates, it doesn't even need a battery to simulate.

A page or so back I show the full blown version with thermocouple / RTD simulation (millivolt / resistance)

I made mine over 30 years ago, in that time i have replaced a couple of switches and many batteries but it's never needed re-calibration.

Roy

Thanx Roy, I saw you version earlier in the post but i was unsure on how to build it, I was unsure of the symbols you used. Do you have a parts list for your simulator? I like how you can simulator mV & resistance.

Thanx again folks for your help :)
 
I, too often, get the credit for this tester. I was steered, by the fine folks on this forum, to a post by Panic Mode, which is where the design/idea came from. I'll attach a schematic, which includes a parts list to this message. I don't think I have photos of my build anymore, but I built it from the schematic, using Radio shack parts and a plastic project box.


Mike


Analog Signal Source Schematic.GIF
 
MIKE!!!!!

I built 2 of these for about 30 bucks! I'm currently using them and they work GREAT!

Just put a milliamp meter in the loop and you've got QUITE the little "calibrator".

The LAST calibrator I bought complete was about 700 bucks.

Thanks,

Stationmaster

What milliamp meter have you used just getting parts to make one thanks stu
 
I have a quick photo of one I built. Literally from the parts bin I have accumulated. I only needed 4-20mA so no voltage output. Smaller piece of breadboard could have been used, but the idea was to put it in a box. I run it from the 24VDC supply that is in all the panels I have, so I just tap into that for the power, then use the output to simulate the inputs. Quick an easy and has saved my bacon many times. I keep thinking I need to add a small LCD display etc but I just use my meter in line with the output and it works fine like that.

http://s1314.photobucket.com/user/Tricky4a/media/4-20mAPart1_zps13c2d916.jpg.html

http://s1314.photobucket.com/user/Tricky4a/media/4-20mAPart2_zps9c96f838.jpg.html?sort=3&o=0

If the photos do not show up I will re post. I tried to insert them in the post but no luck.
 
lcd display is nice, however please feed it from a simple 9 volt battery, as these small ones of 6.95 need separate supply. standard 200 mV so just a resistor of 10 ohms is enough.
the supply can also be a 9 volt battery btw, as long as the input is low enough. 250 ohms is only 5 volts and this circuit will work still.
 
I, too often, get the credit for this tester. I was steered, by the fine folks on this forum, to a post by Panic Mode, which is where the design/idea came from. I'll attach a schematic, which includes a parts list to this message. I don't think I have photos of my build anymore, but I built it from the schematic, using Radio shack parts and a plastic project box.


Mike

I cannot get switch (U/I) part. I am not a pro. I understand all scheme but what is that ------- line means? Is it 3 contact switch or 6 contacts switch?
 
It's a DPDT (double pole - double throw). So it would have 6 terminals.

Thank you! If I use micro adjustable resistor instead of R2 and R4 can I manage to have 4-20ma instead of 3-21ma? Or it is not connected?

I mean I can read scheme in perspective to solder it up but I do not exactly understand how it works. Sorry for dummy question ;).
 
as the resistor is 560 ohms and the curent is 20 mA the resistor will heat up in a short even 10 watts so a micro is not big enoug.
 

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