RSLogix 500 Output Force

Is there any way to force an analog output directly to an integer value with RSLogix 500, or must you convert it to binary and force all the bits?

Thanks,

Rob

Greetings Rob ...

Is there any way to force an analog output directly to an integer value with RSLogix 500, or must you convert it to binary and force all the bits?

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the answer that you want is that you can NOT change the "radix" and just type the decimal value directly into the “Force File” - so in that context, you must "force the bits" ...



but ... the real answer is that you can NOT force the output BITS/BOXES at all ... you can only force the VALUE which is sent out to the output module ... in other words, when you force an output, the value of the bits (the boxes on the PLC’s data table) do NOT change ...



there is an Email Quiz in the “Sample Lessons” area of my website that explains this concept ... or just call me up ...

Rob,

It depends on what you mean by "to force". Here is one way to "force" (to compel, constrain, or oblige) an analog output to be equal to some integer value.

Greetings Rob ...



as my distinguished colleague Lancie1 has said, it depends on what you mean by “force” ... I took your original question in a rather strict interpretation - meaning to use the software’s built-in “force” feature ...



as Lancie1 has pointed out there is more than one way to force a cat ...



in case you’re talking about the built-in “force” feature, here is a quick demo lesson taken directly from the PLC Boot Camp (using ControlLogix hardware) ...







here a junior programmer is trying (unsuccessfully) to test his “alarm rung” by forcing the analog output value ... the meter (output device) in the field reads 18.0 mA because of the “force” ... but the VALUE in the tag (Local:7:O.Ch0Data) still remains at its “program controlled” setting of 6.0 mA ... so the GRT tests FALSE - and the HORN does NOT sound in the field ...



moral of the story: you can force an output SIGNAL - but you can NOT force the output VALUE in the PLC’s memory ... specifically, whenever you force an OUTPUT, the ONE/ZERO status of the bits/boxes in the data table does NOT change as a result of the force ...



once again, I’m talking about using the built-in “force” feature ... Lancie’s way would tend to turn the HORN device in the field ON ...


PS Edit ... I didn't mean to take the thread away from the original SLC-500 platform discussion ... it's just that I haven't cleared away the student wiring exercises from last week's class yet - and the ControlLogix hardware was already connected and handy ... the same effect demonstrated above will be seen with the PLC-5 and the SLC-500 platforms ...

Which I've always found as a huge deficiency in AB products. Even the old TI505 stuff allowed you to force both I/O and internal bits and even words and they altered the state of the object in the logic as well as the real world I/O point. I've never understood the reasoning behind AB's model.

Thanks everyone, I did mean force in the strictest sense, using the force files. For instance, to force a control valve to 50% open without on-line editing of the logic.


Thanks again,

Rob