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Answered

PWM output wiring

Barnhart 12 months ago in Expansion modules / XA2 • updated by Gustav Widén (System support) 4 months ago 1

Why must a PWM output be wired as shown below in the XA2 manual?


When I've worked with mobile style PLC's in the past: It's just 1 pin for an output that delivers a PWM signal to a solenoid, then the other pole of the solenoid is wired to a common ground.


Why must there be three pins involved for this? Why shouldn't you wire one pole of the solenoids to a common ground (same potential as battery negative)?


Thanks in advance.



Answered

Old topic, but worth answering. 

The proportional outputs on the XA2 are primordially designed to be used with the COUT function, a closed loop current control PWM that combines three pins to drive one valve section. 

This three-pin combination is both a way of using one COUT current measurement circuit for a two-solenoid valve section, and a way of improving safety by controlling the load on both high-side and low side (in case of a wiring or electronics fault). 

For a valve like the Parker L90LS, you would use the XA2 outputs configured as COUT. 

But if you want to drive coils that are outside of the 100-2000 mA range, you can configure the same pins as open control PWM. By using the same configuration as COUT, you get one valve section per group of three pins.

On the XA2, you could just use the high-side, but then you'd need to use two high-sides to control one valve section. 

One thing to consider when using the XA2 COUT pins in open control PWM mode is the use of diodes. 

(not shown in the diagram, but in the notice below)