Hello everyone.

I am having an issue with my program.

I am controlling my PLC Logo as follows:

•  M1 =  1 =>  Q1 = 1  (on) 
•  M1 = 0  =>  Q1 = 0  (off). 

However, when I disconnect the power, Q1 turns off even though I had previously set M1 to 1.

Do you have any solutions to ensure that if M1 was set to 1 before a power loss, Q1 will remain on after power is restored?

Thank you.

P/s: In attached file is image of my project.

tran_hau

Hello everyone.

I am having an issue with my program.

I am controlling my PLC Logo as follows:

•  M1 =  1 =>  Q1 = 1  (on) 
•  M1 = 0  =>  Q1 = 0  (off). 

However, when I disconnect the power, Q1 turns off even though I had previously set M1 to 1.

Do you have any solutions to ensure that if M1 was set to 1 before a power loss, Q1 will remain on after power is restored?

Thank you.

P/s: In attached file is image of my project.

Hello.

The picture you show does not match what the text is saying. The circuit does not have real meaning.

Making Q1 = True after a power outage may not be a good idea. You are the master of this design. So please consider the safety implications; ensure there are no dangers.

Having "REM = ON" on the SR latch is a good idea. This attribute makes that the SR latch retains its state through a power outage. Now consider if it is possible to have the communications partner use two triggers: Trigger 1 is to make Q1 True. Trigger 2 is to make Q1 False. See the picture sample.

Figure 1. Dual triggered output.

Note that the sample the state of the output is controlled by two network bits. If communications is lost, the state of Q1 remains in the last state. This will help with the power up procedure.

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An alternate option also uses x2 communication bits. Bit V0.0 is active when the communication is as expected. V0.1 is for the state of Q1. The difference here is that Q1 can be forced to False if the communication bit is off for too long.

Figure 2. Change state of output if permission received.

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A further development is where V0.0 of our previous example is not simply read as True. In communications, there is a chance that a bit will remain False/True if communications is lost. That is a problem for the control system. Better to have the V0.0 bit from before change to a pulse.

A small circuit then evaluates if V0.0 is changing state. This would give the control system an indication that the communications is healthy. See Figure 3 what replaces the V0.0 of Figure 2.

Figure 3. Healthy communications if bit pulses regularly.

Hi,

a LOGO! 8.4 has an additional retentive memory rage (VRx). This can be used to solve such RQ.

AutoGen_380038

Hi,

a LOGO! 8.4 has an additional retentive memory rage (VRx). This can be used to solve such RQ.

Sir, I am uncertain how your response is helping. The client triggers the output via communications. How would the VRx bits be used to resolve the client's problem of retaining the output state when the LOGO! reboots?

Thank you ixo65 for making this test.

The original trouble I foreseen is that it takes a while to re-establish communications between two network peers after a power outage. I do not know when does the LOGO! decide to replenish VRx with the network provided data.

Additionally could I please trouble you with x2 test?
What will happen if ..
A)
1. M1 is switched True on the right side.
2. The connection between the left side and right side is disconnected.
3. What is the state of VR0.0?

B)
1. M1 is switched True on the right.
2. Left side is placed in STOP.
3. The connection between the left side and right side is disconnected.
4. Left side is placed to RUN.
5. What is the state of VR0.0?

No need to make the trouble for a screencast video.
I trust your judgement on this case.