10/2/2020 8:48 AM | |
Joined: 9/23/2005 Last visit: 10/18/2024 Posts: 4760 Rating: (727) |
I'm naive about what it takes to control an burner, but maybe there you will find an answer. |
Regards, |
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10/2/2020 4:11 PM | |
Joined: 7/7/2010 Last visit: 10/18/2024 Posts: 15326 Rating: (2432)
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Pardon my ignorance about using Safety PLCs, but I thought there were ways to transfer data between Safety and non-Safety portions of the PLC using a DB. If this is indeed the case, can't you put the value requiring a SQRT calculation in that DB, and then the main PLC scan sees the value, calculates SQRT and sends it back in a different spot in that or another DB. Or, you can, umm, cheat. https://www.analog.com/media/en/technical-documentation/data-sheets/AD532.pdf This chip can be configured to output a +/-10V signal that is the SQRT of the input voltage signal. So, you can parallel the flow signal to a properly configured circuit with this chip and send its output to another safety analog input. If you need redundancy, you can use 2 parallel circuits and set it up as needed. |
science guy |
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10/3/2020 3:00 PM | |
Joined: 2/18/2017 Last visit: 9/29/2022 Posts: 27 Rating: (1) |
Unfortunatelly that is not an option either. the calculations all have to be done inside the safety plc. It was my idea too to have the normal PLC program take care of the heavy lifting but the safety supervisor of the company we mainly do work for requires that all calculations be done in safety logic. It's complete s--t, I know, nothing I can do about it though... Regarding that hardware trickery you are suggesting, really never thought about it... Sounds cool I would have to dig into it and see if there is something we can do to maybe put the thing on a breadboard inside some kind of case to put it on a DIN-Rail inside a cabinet... It's a wild idea though XD As an extra addition to my case... the furnaces we normally build have from 8 to 11 zones... each zone has at least 2 flow transmitters that have to be treated this way... that makes from 16 to 22 at least... you understand what my problem comes from... Also this whole deal comes from that company not wanting to spend enough money on proper flow transmitters that do the root extraction inside the device itself... because that would solve the whole dilemma... |
Last edited by: x007alfa at: 10/03/2020 15:07:37Last edited by: x007alfa at: 10/03/2020 15:08:18 |
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10/5/2020 2:29 PM | |
Joined: 7/7/2010 Last visit: 10/18/2024 Posts: 15326 Rating: (2432)
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That's an excellent suggestion. Toss the calculation over to the main PLC, and upon return (to the Safety side of the PLC), square the returned value to verify the value has been properly calculated. Although, I still like that external sqrt calculator chip idea. https://www.digikey.com/catalog/en/partgroup/pcb-for-din-rail-mount-multi-board-box/65298 has breadboard solutions with enclosures for Din-Rail mountable solutions. Looks like with proper layout, an entire "loop" of transmitter sqrt calculator chips could be installed. This would of course raise the cost and development time relative to passing the value to the main plc and back again for verification. |
science guy |
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