Signal Conversion

[rad74ss]

I am building a test stand on wheels that is a copy of other stands we use. I put in for some Johnson A350P controls to do my 0-10VDC and 4-20mA input signals.

My boss told me that several years ago they had used a 500 Ohm resistor, a 280 Ohm resistor, a 2K ohm wire wound potentiometer and a 10VDC power supply to get a 4-20mA signal. I found the old test stand and hooked it up (what was left of it) and it didn't work. My boss told me it did before.

So I need help from people with more electronics experience to help me out. Is it possible to do it with the parts stated above? Would it need an op amp to do the conversion?

It looks like the power was connected to each side of the pot, the 280 Ohm resistor was hooked to the pot slide, the other side of the 280 was hooked to the 500 Ohm resistor, and the other side of the 500 ohm was hooked to the same side of the pot as the negative 10V.

Thanks for your help.

Robert

 

[Russlk]

A 2K pot and 500 ohms will produce 4 to 20 mA into a short circuit load but if the load is 280 ohms, the supply voltage will have to be 11.12 volts.

 

[rad74ss]

I have a PDF that I made of the old test stand when I was trying to figure out how it was wired. I just joined yesterday so if someone could direct me on how to get that into the thread I will put it in there.

Thanks,

 

[rad74ss]

0-10,4-20 drawing

It helps if you read all the way to the bottom of the page. Here is the PDF of what the board was wired like.