i will try and explain in great detail so not to get any complaints :)

i am about to do a project that requires the use of 4 digital outputs that are controlling 4 x SSR and i am using PWM within the program to control them, the issue i have is that i due to external influences i can only ever control 2 x SSR at any one time. is there anyway to cascade the PWM for this?

the timebase (periodic time) will be adjustable and so will the 

Thanks

the system is being powered by a generator and because of the nature of the SSR controlling some medium wave Infra Red immitters, the generator does not like and can not cope with the sudden surge in demand.

cascade defined as using the output of one PMW to initiate the second PMW and so on but only allow any 2 outputs on at any one time.

The above was an example, this is why i have asked the queston because i am unsure on how to cascade the ouptuts.

Each of the 4 x Outputs would have their own PWM but i just need them to operate that only 2 are on at any one time no matter what the periodic time was set to etc. 

thedodgy1

the system is being powered by a generator and because of the nature of the SSR controlling some medium wave Infra Red immitters, the generator does not like and can not cope with the sudden surge in demand.

cascade defined as using the output of one PMW to initiate the second PMW and so on but only allow any 2 outputs on at any one time.

PWM: Pulse width modulation. That means a fixed frequency and variable pulse width.

Yet your description leaves the impression that it is a 50% pulse width and variable pulse frequency. Do I understand correctly: When pulse 1 is ON then pulse 2 should be OFF -- at the same frequency. It would be like having the normally open contact and normally closed contact of the same relay to be connected.

So what would the pulsing frequency be? 

the periodic time would be 1s but this may change and i think the pulse would be 500 (50%) but again this could change.

i have mentioned tot he client that they need a generator that can cope with the demand but i suspect its more to do with it not be a linear demand.

ixo65

If your generator is having trouble turning on the load through the LOGO!, you might want to consider an external inrush current limiter.

 unfortunatly we are switching over 600amp

thedodgy1

I need to somehow invert the PWM so that the off time becomes the on time and vice a versa

It is my opinion that the LOGO! is the wrong solution to the problem. The built-in variability of the LOGO! timing is a problem. The cross-over from off-to-on and on-to-off may present peak consumption when using a complimentary output pair.

From your descriptions I have doubt if you are looking to use a 50% duty cycle or a variable one. A duty cycle of 50% and more will have overlapping on-state of the two outputs, no matter what your control philosophy is.

The LOGO! is not a device that can deliver the safety controls reliably as you may need for manipulating 600A. I recommend against using a LOGO! Not fully understanding your use case makes it impossible to suggest something else with confidence.

One idea for complimentary output from a PWM is provided, but know that timing variations is expected.