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Help please, need an explanation to control heat element with dig.output - M91

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I need an explanation or example of controling heating element .

i have thermocouple J as a feedbak and output which is energised SSR to switch the heating element


my oplc is : M1-2-UN2


I read that is possible to control with PWM , but im not completely undrstud how to exactly make it on M91


please help




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  • MVP 2023

You didn't say whether you were using PID control or On/Off control.  If you've started a program upload it so we can have a look at what you're trying to do


If you're using PID, you have to understand that PWM is simply turning an output on for a percentage of a pre-defined time period.  The M91-2-UN2 has HSO outputs defined in hardware that make this easy.


Set the output of the PID for 0 - 1000 to correspond to 0 - 100.0%.  This will be what the HSO output is looking for.  The output MI of the PID block needs to be the same one defined in the HSO configuration.


You have to define a Frequency for the HSO, but this number isn't critical.  The HSO wants an MI for the frequency, so pick one you're not using and have it power up to 100 for 100 Hz.  This number will work fine for SSRs.


The Enable MB lets it run.  Turn this on when you want your heater to be active. 


Joe T.

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