4mA - 20mA Control Circuit

[Mrs. Robot]

Good day!

For a personal project I'm using 4 proporcional valves. To control these valves, I've implemented a control circuit. The function of this circuit is that, depending on the voltage input ( range of 1V to 5V) it transforms it to a current output (range 4mA to 20mA). Hence the valves need a voltage input of 24V, I've implementes a 24 voltage source for each valve.

Here's the thing guys, each valve counts with it's personal 24 voltage source and a 4mA-20mA control circuit. But, when I run the whole system: ALL the valves at the same time, this 24V doesn't maintain at 24V.... it drops down to about 15V on each valve.

I'm not really sure why this is happening, maybe there's something I'm missing out. Thanks for taking the time to read me and hopefully answer me back.

 

[Harald Kapp]

Check the rated output power of your 24 V power supply. It needs to be higher than the sum of the power requirements of all the valves together. Otherwise it will limit the current and the output voltage will fall, as observed.


Feliz aňo nuevo,
Harald

 

[Mrs. Robot]

Thanks for your reply. Each valve is connected to its own voltages source like I mentioned. Even so, I have checked it's rated power and it's under the circuit's requirements. All the circuits are running through a 5Amp AC transformer. Each valve is asking for about 0.5Amp, hence 2Amp + any other minor current needed in the circuits, no more then 3Amps. It has plenty of current supply.

 

[Harald Kapp]

Please supply a circuit diagram of your setup.

 

[Mrs. Robot]

Sure, I'll upload the diagram as soon as I get my hands on my PC device.

 

[Mrs. Robot]

@Harald Kapp, here are, in .pfd format, the schemes for the voltage sources and for the Voltage-Current converter

 

[Harald Kapp]

The bridge rectifiers are wired incorrectly. You're using them as half wave rectifiers (diodes) only. Thus you use only 1/2 of the potential output from the transformer.
See e.g. here how a bridge rectifier is wired correctly.

 

[Mrs. Robot]

Hey, you're right. Later in the day I'll fix this issues and let you know if this got better... or worse.

 

[Mrs. Robot]

@Harald Kapp Hey, thanks for pointing the rectifier issue. Problem solved, thanks.