Quick Question

Cryometrix

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C
Join Date
Dec 2014
Location
Utah
Posts
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So I am not a programmer, so excuse my ignorance and lack of knowledge, but I need to make an edit to the PLC ladder logic. Here is the scenario. On our HMI (E1071) we have a switch which can be turned on which turns on M604. When M604 turns on, it allows some valves to open. If the power turns off and back on, M604 resets to off, so the valves turns off. Is there an easy way to get this to stay on even if the power is turned off and then back on?

Thanks for your help!
 
Use a contact of M604 to hold itself energized and make sure that M604 is "Retentive".
I have no idea how to do this in an unknown PLC but the concept is the same in them all.
 
Retentive Bit

The simple method would be to use a Latched/Set bit. However, you will find many on this forum opposed to using those - and one-shots as well. You need to manage them accordingly via first-scan housekeeping and be good at finding/monitoring them throughout spaghetti logic as well. In your application most of this wouldn't apply as long as it's safe for the process to maintain the state of the output between power cycles.
 
Making it retentive is probably the best way to do it, all it does is remember the state of the bit when power is off, shouldn't be any new code to write.

I am not familiar with Mitsubishi PLCs so I can not tell you the exact steps but the help file might have something
 
from what I have read, any relays from 500-1023 are latched relays, so that save their state when powered off. I am using M604, but it is not saving its state when powered off.
 
so if I use M1024, its default after restart is on. So even if I shut the unit off with M1024 off, when it turns back on, M1024 is on. Latch is set for 500-1023.
 
Do you want to restart in the mode (enabled or disabled) that was present at power-down?

Or do you want it to start-up always enabled?
 
Hello,
You need to go to the PLC parameters in the project tree and under the device tab you can assign the range of relays you want to be latching.


Hope this helps,
Dave

plc's fx parameter example.PNG
 
dave, I looked at the plc parameters and it is set to have 500-1023 latching. I am using M604, so it should be latching. What could cause it to reset. M604 is only mentioned on the one line of code, I do not see anything that is resetting it.
 

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