hello

I want to control  amount of flow  that works with a step motor. i want to close loop control so do you think i should buy FM355 s ? because when I read the manual of FM355 s i understood that i cannot send a direction command, is it true or not?I read FM355 has pulse command but it does not have direction one!

thanks

Hello,
The FM355 S has two digital outputs per controller:
- open
- close

These outputs can be used in a so called 3 step controller:
- opening (pulse of variablel length)
- do nothing
- closing (pulse of varaible length)

This has nothing to do with a true "step motor" that is used for positioning.
As described in the manual of the FM353.

Could you be more specific on the "step motor" you want to use?

thanks for your answer,

I want to use a driver for control of step motor. I want to move step motor in 2 direction. so I need 2 output for my driver, one for direction and another for pulse. so do you recommended i should use FM353 instead of FM355? 

step motor has 17.8 Nm, 2phase (3.1 A) 

Hello,
If you have an external driver for your step motor, you could consider to use FB42 (CONT_S)  that you find in the standard library  under the folder "PID Control Blocks".

It also works with two outputs with opening pulses and closing pulses.
But now you can add a small program part to convert that to direction and pulses.
See suggestion in the pdf in annex.

You than call the FC1 in a time triggered OB (OB35).

I don't know how dynamic the flow control must be.
And if this will be fast enough for your control.
The minimum pulse will be the length of OB35.

To be tested ...