4-20mA output

Hello All

on my alpication, i was programming simens s7-314 2dp analog output +/-10V (+/-32000) for olda valve.

New valve need 4-20mA. and i must convert my prgram to that.

Valve proparties, 4-12mA negative command
12-20mA positive command.

How i scale old program to new?


best regards

crb

If changing card is nit an option you'd have to wire 500ohm to output. Then you'd have to scale 0-10V to 2-6V in integer value for positive and -10-0V to 6-10V for positive ref.

dear balash,

if i use 4-20mA output module which kinde change on program?

best regards

dear All,

any idea?

well, i suppose your program is written for 0-10V for pos ref and -10-0V for neg ref.
as 4-20mA are only positive you will need to adapt that.
so if range from -3200 - 0 forget. also, values from 0-6400 also forget as it is less than 4mA. what you're left with is 6400-32000.
now 6400-19200 equals 4-12mA, and 19200-32000 equals 12-20mA.

but i would be very skeptical using the voltage output for current control as you do not know the resistance of PLC output and valve input, only that you will have 0-10V on that resistor, and although that trick is used for PLC inputs, i never actually heard it can be used for output.

I would suggest replacing the card for one with current output and scaling would be pretty much the same as above.

This is a standard scaling function that will scale from pretty much any value and to pretty much any value.

Ov = [(Osh – Osl) * (Iv - Isl) / (Ish – Isl)] + Osl

Ov = scaled output value
Iv = analog #Input value
Osh = high limit OF the scale FOR the scaled #Output value
Osl = low limit OF the scale FOR the scaled #Output value
Ish = high limit OF the scale FOR the analog #Input value
Isl = low limit OF the scale FOR the analog #Input value

well, if you use TIA, then you have scale and unscale function.
step 7, i think, have SFC105 and SFC106

Fc 105 and 106 are in Step7 and TIA portal
Also analog values 0 to 10 v or 4 to 20 range
0 to 27648 not 32000
-10 to 10 would be -27648 to 27648