Hi Everyone

The problem seems like an easy one: I am controling (among other stuff) a water valve in an automated testing system with the LOGO. Sometimes the valve is not opened for some time. So if the valve has not been opened in 4 days (96hrs) the PCL should force the user to flush the system first (open the valve for 1-2minutes) before using the water for other stuff.

I've implemented this functionality and it seems to work nicely. I'm using a "switch off delay" that is triggered by the closing of the valve and is set to 96hrs. This works great. Except, if the power to the PLC is switched off (btw: what's the effect of "remanence" on the switch off delay? I could not really find out)...

So I wanted to use the date from the RTC to check if the last use of water was more than 4 days ago. The date is stored in VB985..987. But I can't find a way to read them from within the LOGO Program. Analog Network input can't read those addresses (I'm sure I could have found a way to get rid of the upper 8 bits if necessary).

Also, the annual time switch does not seem to support parameter input, so just feeding that thing with dates until it switches on so I know the current date does not work.

And placing 44 of those (31 days, 12months, 1 leap year) feels like sloght overkill to me...

I'm hoping that I overlooked a really simple solution. Please let me know...

bet regards, kruemi

Instead of an off-delay timer you also can use an asynchronuous pulse generator and an up/down counter, which has remanence. Reset counter with opening of the valve and count up with the pulse generator, e.g. 0.5s+0.5s = every second. If counter value is greater then 3600s*24h*4d, then you can act something with the counter output. The only problem is, that the counter value will not be increased without supply.

Regards, Scorp

Thank you both for the comments.

Not being able to read this information is really unfortunate. I think I'll just stick with the 96hr switch off delay and just wire M8 to the reset so that on power on the system has to be flushed anyway.

Sometimes I'm "a bit" stubborn and so I went looking for a way to still wrangle to date out of the PLC. So my crazy Idea is, that despite the fact, that the year timer has no facility to set time and date from within the LOGO I can expose that data wia VM Memory (R/W).

Next question: Why doesn't it work (in simlation at least?)

(I'll attach the program in the next post)

And here is the program itself...

By the way: If I remove the Year time switch the data is written to the VM-Memory nicely. So it seems that the time swich overwrites the data before reading the changes...

Such VM mappings are only readable, the controller will overwrite the values of NAQ1 and NAQ2 cyclic with the values of the year timer. Therefore if e.g. VW0 is mapped for any block, then you can't use it once more.

Regards, Scorp

Scorp

Such VM mappings are only readable, the controller will overwrite the values of NAQ1 and NAQ2 cyclic with the values of the year timer. Therefore if e.g. VW0 is mapped for any block, then you can't use it once more.

Regards, Scorp

 Are you sure about the "readable"?

Because according to the documentation and also the symbol in the VM-Manager those values are R/W. So I should be able to write them by Modbus for example.

But I also know that I've had my fair share of "funny" behavior with reading and writing VM memory and Modbus accessing the same coils (worked flawlessly in simulation but did not react to changes sent by modbus or even started to oscillate when activated)..

So you might refer to another kind of "read only"?

kruemi

So you might refer to another kind of "read only"?

Yes another kind of "read only", which means the Logo program. Editable parameter can be used in messages as read/write or from external devices with S7 or modbus protocol.

I had the same idea in the past, your plan will not work.

Regards, Scorp

Scorp

 

kruemi

So you might refer to another kind of "read only"?

Yes another kind of "read only", which means the Logo program. Editable parameter can be used in messages as read/write or from external devices with S7 or modbus protocol.

I had the same idea in the past, your plan will not work.

Regards, Scorp

 Thank you.

So my crazy idea won't work sadly. It won't let me shoot into my own foot trough my left ear canal. So now it's either sticking with the delay or the counter or update the time of the time switches from the computer that controls the whole thing every time the vlve is opened (which is not really what I want because a "self contained" and automatic solution in the PLC would have been much nicer :)

All in all I've learned some stuff, thank you both for your time and expertise!