Adjustable Cuurent 0-1A, 18V

[Dado87]

Hello Masters of Electronics,

I'm civil ingeneer, electronics are big unknown to me, but it wakes up my interest. I would like to control proportional pressure with electronic proportional pressure regulator (http://www.festo.com/net/SupportPortal/Files/44239/MPP-3.pdf). If I got right I need to control it with current from 0-1A at constant voltage of 18V. I would like to control it from Arduino.
In last weeks I was looking for helping material on internet... and I found Youtube series from EEVBlog about making own Power Supply Unit. I took out "Costant Current" part, bought 18V, 1A Adapter... Here is Shematic pdf to download http://s000.tinyupload.com/?file_id=15952704714115037076] [url]http://s000.tinyupload.com/?file_id=15952704714115037076 [/url].

First I would really apreciate if someone can take a look onto Shematic and check if it is fine.

Secund thing...I want to reduce Arduino output 0-5V to 0-1V. I tried to do it with putting resistor in series in ratio 4:1 (look at shematic) but I doesnt work, I get much lower reduction as expected. Whats wrong, how ca I achieve it.

Instead of 1Ohm at the end I put 5Ohm resistor at the end for now...I expected current from 0-1A, but I got just 0 - approx.0,6A. Why is this like that?

Any help, suggestion, comment is highly appreciated.

Regards,
Damir

[codeboy2k]

I have no experience with this proportional pressure regulator.  However, I looked at the PDF you linked to from Festo, and it looks like it has 2 voltage requirements

|	Operating Voltage	|	Vop	|	18 V	|
|	Operating Current	|	Iop	|	0.95 A	|
|	Reference Voltage	|	Vref	|	0 - 10 V	|
|	Reference Current	|	Iref	|	0 - 20 mA	|

It looks like the output pressure is set by the Vref input.  In addition, it looks like some of the regulators listed might also be controllable by a 0-20 mA reference current I_ref . But it's really not clear if that's a controlling current input or if it's just the current drawn (sunk) at the reference voltage input (which makes it look like the V_ref input has an input resistance of R = V/I = 10/0.020 = 500 ohms

Here's a chart from the datasheet in the PDF you linked to:



 There is a 3-pin DIN 43650 connector, but the datasheet drawings are lacking the pin spacing.  So it could be either 8 mm spacing, or 9.4 mm spacing. Both are called DIN 43650 Form C.  Nice to have a standard, right They probably don't feel the need to show the connector spacing on the drawings since they expect you to use it with their own contoller, which has the right connector already.

I looked at your schematic, and I won't comment on it because I think you're going about it wrong. What you really want is just 18V@1A operating  voltage and a variable 0-10V pressure setting voltage V_ref as in the graphic above.

Finally the datasheet does not show the pinout for the DIN connector, again this is probably because they expect you to use it with their own controller and so don't feel the need to show the electrical connections on the datasheet.  You might want to call their tech support line to get that information from them. There is only 3 pins, so it's probably GND, V_op, V_ref but only they can tell you which one is which.

So give them a call and see if they will tell you what the pinout is on the DIN connector.

[Paul Moir]

Looking a little closer at the datasheet, those graphs refer to using an MPZ-? controller in conjunction with the MPP valve (top of pg 3 and 4).  If you only have the valve and no controller, you'll have to roll your own control for them.  Likely it'll be a PWM of something like 12-18V.

The pinout fortunately is industry standard; it'll be between pins 1 and 2.   

MPZ Controller:
http://www.festo.com/net/SupportPortal/Files/44243/MPZ-1-24-PI.pdf

[atferrari]

Hola Damir,

You lack of knowledge about electronics (your words) is going to be a problem to replace the functionality of the MPZ controller. Just give a look at the specs and there is a PI process involved.

I did a cursory reading and run across a ramping module that could also be needed, but not sure.

Are you still intending to replace all that with your design?

I would start by getting a more or less solid idea of what a constant current source is. And then, how to control it.

I could not open the schematic's file.

[Dado87]

Hi Guys,

First of all thank to each of you for taking time and writing suggestions and comments.


codeboy2k,
I have right DIN plug, I got it on ebay...it fits

I know for PMZ controller, but it is too expensive (Vref, I ref is for PMZ probably, as Paul also assumed)... I need some low budget solution, at it more exciting .
If we go out from facts:
- behaviour is very linear (after datasheat)
- solenoids are controlled with current - more current more magnetic force in solenoid (I found it on internet.... is it right?)
- operating Voltage 18V - so we need to stay at 18V
- nominal current 1A - what means nominal...isnt it something like maximal?
- we have just 3 Pins... so normal solenoid connection...one pin on each end of solenoid + GND.

After all this I made conclusion that, I need to control my regulator with 0-1A at 18V (Any comments :$)

First I want to build a circuit that will give me that.... so clear control 0-1A with Arduino PWM (or Pot for now). So once more please help me to achieve this step.
...maybe some some link, or shematic...or something...

Another important question:
In accordance with  regulator data....operating Voltage 18V, nominal current 1A.... Can I burn or somehow damage my regulator testing it at different voltages 0-18V and currents 0-1A... so not exceeding 18W?

My Final Goal is to control force of pneumatic cylinder with Arduino micro controller. Yes, MPZ works together with pressure sensor in closed loop, to put out precise pressure...but I got also infos that friction of cylinder can be significant... so with just pressure you cannot control force 100% exact. I made a research and I found that there exists a PID routine for Arduino, so my plan is to make closed loop...Arduino - regulator - cylinder - force sensor to control force exactly. Until there is still a long way...I also need to catch some cheap force transducer on ebay

atferrari,

yes, I still intend to replace PMZ. As I allready mendioned I would like to include PID routine too. Link to Shematic: http://s000.tinyupload.com/?file_id=15952704714115037076
If you can quickly check it and give some changes, approvement...It would be more than perfect

Regards,
Damir

[atferrari]

Hola Damir,

After further reading, found that there is a module to set the reference current but I will refrain myself to post any further because I could mislead you. I am far from being experienced enough to offer any piece of advice.