Need help…

[Stephen O’DonnellParticipantKarma: 15Rank: Padawan]

Hello,

Im wondering if someone could point me in the right direction on a problem I have. Bit of background about me, I am only an electrician and occasionally asked to make changes to plc code on site so I am very new too it.

 

The problem I am having is we just got new plant installed, and basically theres a setting on a panelview thats adjustable by operators locally on the panelview but not remotly on Scada. This new plant is in place of old plant so I have basically reassigned all bits too suit the new however when trying to allow Scada control of setpoint it is overwritten by the local panelview and vice versa. I have tried using the move function etc, and I think I should have a conditional bool that when true will let me move a new value into the setpoint. Having trouble here on writing a code to do this successfully can anyone help?

 

Thanks so much in advance

[Sean TerrellModeratorKarma: 187Rank: Jedi]

Hi Stephen,

It sounds like you do need a conditional bool that you can unlatch after either the PV or the SCADA has sent a new SP. I have to do something similar with a SCADA permissive in some cases where if a shutdown occurs, operators cannot just start it back up. Unfortunately Cygnet SCADA requires a good bit of scripting to make a momentary pushbutton, its easier to unlatch from the controller.

For Example, Have both the SCADA and the PVP write the setpoint to the tag SP_HMI (int, or real, or whatever)

rung 1) if SP_HMI > 1,  SP_BOOL (OTL)

rung 2) if SP_BOOL then MOV SP_HMI to the desired Setpoint tag

Rung 3) if SP_HMI > 1 and SP_BOOL then OTU SP_BOOL and branch around the OTU to add a second “output” of MOV 0 to SP_HMI

 

[PLCGuruKeymaster]

Hi guys and welcome to the forum!

Just following this thread to see the outcome and to say welcome.

Fred

[Stephen O’DonnellParticipantKarma: 15Rank: Padawan]

Thanks very much for a speedy replies folks. Not in work today but will try this tommorrow looks like I have the latch bits set up wrong i think and unlatching too quick. I used a timer to unlatch which I am guessing is not correct. Will keep yous posted on how I get on. Again thanks so much guys

[George BarnetteParticipantKarma: 171Rank: Jedi]

Stephen, Hi. I am new to this forum, and Fred and the other folks are really sharp. Welcome. I wouldn’t say you are “only” an electrician. I have been an industrial controls electrician for over 20 years and good ones are hard to come by. Plus, I learned PLC programming and troubleshooting with ladder logic on my own, through intellectual property theft (haha), online reading, books, practical experience and the good grace and kindness of others willing to teach me. I love programming because I’m in the office a lot now (getting older) and I still do my own start-ups and De-bugging on my projects.

Anyway, welcome and as to your post, a timer wouldn’t necessarily be the best way to activate an OTU, maybe you could put an equal (EQU) instruction in the rung to unlatch it. Have a great week.

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