Hold for Initialization RSLogix 5000

Hi mates,

Yesterday I was testing an analogic output module (1769-OF8C) . Under the configuration of properties I've seen this option called "Hold for Initialization" and after consulting the documentation I selected it. As far as I have understood, this option allows to hold the current state of the output if any specific events happen.

But the only thing I could notice when I tested the module was, that when "Hold for Initialization" is selected, even if I was forcing to outputing 20mA (when monitoring the output I could read that it was set to 10000 under the percent range output scale), the speeddrives never got those 20mA in their inputs.

When I unselected the option, everything worked ok.
I'm trying to understand what is this "Hold for Initialization" for.

This is what the documentation says:



Hold for Initialization
Hold for Initialization causes outputs to hold present state until the value commanded by the controller matches the value held by the module providing a bumpless transfer.
If Hold for Initialization is selected, outputs hold if any of these three conditions occur:

• initial connection is established after power-up.
• new connection is established after a communications fault occurs.
• transition to Run Mode from Program state
The Output Held bit (see the Input Data file) for a channel indicates that thechannel is holding.

I do not think you would need the Hold for init in most situations. I understand that this function will hold your outputs at a certain level in the event the processor loses communication with the output module (processor on diff rack and powered down, processor goes to from run to program, etc). The mode is designed to allow normal control of the output once the commanded output level is within 0.1% of full scale. So for example you need a valve to stay at whatever its last %open value is when you take the processor to program mode. The ouput card keeps it at its last commanded output level until the processor is back running and commands an output at the same level.

Understand that this is the way I understand this operation to work - I actually have not had to implement anything using this function so take my understanding in that light.

Russell

Thanks Russell. Yes, you are right. I'm not gonna need to implement the Hold for init option in my project. It isn't such a critical control process that I have to keep the CV at a safe outputing level permanently.

Yes this function would definately need to be used carefully, as I can think of more scenarios of disaster than benefit.

Russell