4-20ma converted to 0-40ma 3

[topdawg]

I have an Allen Bradley SLC500 PLC that has 4-20ma analog outputs , id like to convert a 4-20ma 24V output signal to 0-40ma 24V . Any ideas how this can be achieved ?

 

[Skogsgurra]

If you can't find a converter that does that - you have tried, haven't you? - then the standard way is to use one 4-20->10V converter and two 10V->0-20 mA converters and wire the 0-20 mA outputs in parallel. Connect all voltage signals together (separate plus and minus, of course).

If you have a PLC with free inputs and outputs, you can do the same thing. But "connect" in the program.

It works because the outputs are true current sources and will not be affected by a companion output working into the same load. At least no as long as you stay below compliance voltage across the load.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[topdawg]

That's alot simpler then I imagined, thanks for your quick response

 

[RajeevCell]

topdawg, do you want to power a 24v device from your PLC output?

For some reason, I thought that you were powering a device that operates at 24Vdc and consumes 0-40 mA current. If this is so, then DO NOT try this way. Use a 24V PSU.

 

[VEBill]

RajeevCell, these are not power supplies. The 4-20 mA (etc.) are analog signals typically used in industrial process control systems.

 

[RajeevCell]

Dear VE1BLL,

I know 4-20 mA is a signaling standard. I work with them. My concern was the OP said he wants "0-40ma 24V". The "24V" part made me wonder about actually what he wants to achieve.

 

[VEBill]

Yes, good catch. Well worth double-checking if the OP is still monitoring.

 

[Skogsgurra]

OP says: "SLC500 PLC that has 4-20ma analog outputs" The added 24 V specifies supply voltage and that can have some significance as to what devices you can use. Had he said 48 V, then most standard devices are out. I cannot imagine that he is after a constant 24 V supply capable of delivering 0-40 mA. No, I can not.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[RajeevCell]

//I cannot imagine that he is after a constant 24 V supply capable of delivering 0-40 mA. No, I can not.//

That's fine. I just thought he MIGHT have meant that.

BTW, are you familiar with any 0-40 mA device?

 

[topdawg]

the device i need to operate is a servo motor at 24V Ma its fully open and 24V 40 Ma its closed

 

[topdawg]

24V and 0 Ma

 

[RajeevCell]

//the device i need to operate is a servo motor at 24V Ma its fully open and 24V 40 Ma its closed//

So, it's a servo-controlled valve, and the 0-40 mA is input to the error amplifier of the servo. Then the solution indicated by Skogsgurra would work fine.