2/2/2019 2:23 PM | |
Joined: 2/1/2019 Last visit: 12/9/2022 Posts: 24 Rating: (0) |
Hello, first time using LOGO and also trying to make a functioning PLC-program. And well I thought I was finally there but you guessed it... Problem: We'd like to keep a buffer tank filled with mixed gas (N2/CO2) in the range of 5 - 8 bar. So that when the pressure in the tank hits the lower threshold of 5 bar the valves should be open, and should be closed at 8 bar and stay closed until the next filling cycle is started at the lower threshold. This would be the normal filling cycle. And of course it should also start filling (have the valves open) when the measured pressure is below the lower threshold of 5 bar. And would like to use two different info screens/flags in combination with this; white back light for filling during 5 - 8 bar, and amber back light if the pressure is under the threshold of 5 bar. LOGO 8 with TDE Pressure sensor is from 0-10 volt (0-10 bar) Mixing of the gas is an autonomous process and started when the shut-off valves are opened inline with the gas mass flow meters/controllers. Issues: So I wrote a little program for this and thought it was ready only to find out the next morning this wasn't the case, of course. (& The relay/output was continuously switched when the pressure kept going back and up from 8.0 to 7.9 bar. You'd think we might be able to pass this issue by setting a on/off delay. But then it's still a problem also even more because the tank is small and usage/flow of the gas from the tank is little. I'm sure there is but I've got no clue how this could be done in a simple and elegant way with LOGO. Attached both PLC-programs: gas_buffer_tank_pressure_range.zip
I've tried: basic functions (AND, NAND, OR, NOR), threshold trigger, analog comparator, analog threshold trigger, analog watchdog, analog differential trigger, latching relay. Should I look into analog ramp? That would mean first going from analog to digital to: analog-digital-analog-digital. I've searched this forum and found some interesting stuff but still either it didn't work out or not completely as desired. Here my two sample programs, the original one and the best one after all trial and errors. With this 1st one, the problem is described above; it wants to start filling again when the pressure drop right under 8,0 bar. Switching the output should be done after pressure is dropped to 5 bar (or lower). With this 2nd one, where the valves are open by default and switched off by the pressure-values. The tank is now being filled only after it gets to the lower threshold but sequence/routing is not right and also this way different info screens/flags is a problem for both conditions. Was thinking this would've been easier with a Arduino with a relayshield. Easier/flexibility with a looping program of functions and tracking the status. Because I was also thinking of maybe trying to keep track of the fact that once the tank has been filled up to 8 bars the state-tracking bit should be set to 1 and stays 1 until pressure drops to the lower threshold of 5 bar (with small delay). Then filling should only start when either one of the following conditions are met: tankPressure: <= 5 bar AND stateTracker: 0 or: tankPressure: <= 4.5 bar
Attachmentgas_buffer_tank_pressure_range.zip (292 Downloads) |
Last edited by: openLoop at: 2/2/2019 2:24:10 PMLast edited by: openLoop at: 2/2/2019 2:27:17 PMLast edited by: openLoop at: 2/2/2019 2:28:13 PM |
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2/2/2019 2:58 PM | |
Joined: 12/18/2014 Last visit: 9/25/2024 Posts: 33834 Rating: (4205)
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I have created an example for you. In the message texts, I have saved myself the texts that you can do best yourself. AttachmentFilling_control_FS4.zip (284 Downloads) |
This contribution was helpful to1 thankful Users |
2/2/2019 10:09 PM | |
Joined: 2/1/2019 Last visit: 12/9/2022 Posts: 24 Rating: (0) |
Attached your sample program with some minor tweaks. Added two ANDs, to test if conditions are made to activate the right message text on the TDE. It looks like everything is working and functioning as we'd like. Will test it monday/tuesday morning on the LOGO! of the gas mixing station. Just need to add the info for the message texts for the LOGO! TDE and the messaging/signaling for when the pressure measurement for the proces gas (flow from the mix/buffertank) drops <3 bar. (But that's a simple thing to do). Thank you for showing me how it's done, a nice solution. Definitely learned something here from you, how to correctly use the invert/activation with the thresholds and such. AttachmentFilling_control_FS4_texting.zip (265 Downloads) |
Last edited by: openLoop at: 2/2/2019 10:11:30 PM |
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2/3/2019 1:38 PM | |
Joined: 12/18/2014 Last visit: 9/25/2024 Posts: 33834 Rating: (4205)
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Then take this version. There instead of a third threshold trigger an AND block. AttachmentFilling_control_FS4_V2.zip (269 Downloads) |
This contribution was helpful to1 thankful Users |
2/3/2019 2:06 PM | |
Joined: 12/18/2014 Last visit: 9/25/2024 Posts: 33834 Rating: (4205)
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Or this version with only one message text and constant pressure display.
AttachmentFilling_control_FS4_V3.zip (285 Downloads) |
This contribution was helpful to1 thankful Users |