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oldnerd

HMI Bit Lamp Object

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I'm new so bare with me. I have ran into something I can not figure out why it does this, need some help from the experts. I have a AB 1769 L33ERM processor with two 1769-IQ16 input modules and two 1769-OB16 output modules. My boss is cheap so he would not buy a PanelView HMI, so I wound up with a Weintek 3105P HMI screen. This was bought from Rohtek and there is no tech support to speak of. Our customer has been running this machine for about four months with no problem. A few days ago the bit lamp on the control screen to tell the operator the e-stop has been pressed came on with out the e-stop being pressed. I had there electrician check the PLC input for voltage and it was at 0 volts. The led for the input on the module was off. I VPN into it and look at the tag in the processor and it was at 0. I went into the HMI software and deleted the bit lamp and re-created it, as soon as I boot up it comes on like the bit from the PLC was on but its not. So I go back and set the bit lamp object to invert the signal it goes off but when the bit in the PLC goes high (pressed the e-stop) it does not come on. The circuit is very simple the e-stops go to the AB safety relay, when the relay is not happy I have a 24 v signal to the PLC input, the HMI bit lamp object turns on when it sees this tag come on. I hope I have been descriptive enough for all to understand, if not let me know and I will try to do better. Thanks for the help in advance.

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In your HMI application, do you have your hard inputs and outputs mapped to Logix tags or is the HMI application mapping I/O points directly?

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Thank you for the help. I had the input to the PLC mapped directly to the HMI. I changed it to a rung of logic where the PLC input bit turned on and output and the HMI read it and problem solved. Still do not understand why it worked for 4 months and all of a sudden started doing this.

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Most of us have been there, oldnerd. I used to always map direct I/O addresses in the HMI until I made a mistake with a maintained button mapped to an output and could not figure out why my darned logic was not controlling the output properly. Good protocol is to create a UDT for HMI Inputs and for HMI Outputs and use these in your program and when your building your HMI. The answer to why it turned up until now is probably network or program scan time. Previously there was enough latency time for the HMI update to be over-written by the logic. Logix CPUs are notorious for not following task schedules properly (something I have personally put many, many hours of R&D time into proving and working around). If your controls system is on the company network, network traffic may affect how your control system scan executes. I always encourage customers to, if they require the control system to be on the company network, to connect through a managed switch (with tweaks on the control system and network side to reduce broadband traffic from the control system). With the news that A-B Logix CPUs are vulnerable from outside hackers should give encouragement for end-users to design precautions to reduce this potential. I stumbled across this some time ago. I believe this site you can search by manufacturer and the US Government will certify known vulnerabilities with their hardware/software. Scary stuff to worry about. https://ics-cert.us-cert.gov/alerts

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Sparky, Thanks, I will do the project different from now on. The advise was sound and when I put in the logic instead of directly inputting to the hmi I had no more problems. It looked to me as though the way it goes is it turns on not off because in worked one way and not the other. I do not like using a off brand HMI with an AB processor, but my boss is super cheap. Thanks for your help.

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