PLC LOGO! Simulation help...

[GalacticPigeon]

Hi all,

I'm having a bit of difficulty when it comes to the final question of my assignment, and wondered if anybody could shine some light on it for me. I've been trying and trying for hours but just cannot seem to get my head around it, to the point of I'm questioning everything I'm doing now.

Any help in this would be MASSIVELY appreciated. (I have included the attachment of the image in reference to 'the application above illustrates...')

Below is the assignment question:

The application above illustrates a simple stirring application in a lemonade factory.

a)Use LOGO to design and build the above system, using function block or ladder logic, which will control the operation as follows:

When the Start ‘push to make’ (not toggle) switch (I1) is pressed/released, and gets latched on (B1: RS latch), the start ‘fill’ pump (Q1) will be energized and the tank will start to fill.
The pulses generated by flow meter 1 (B5: pulse generator) should be used to increment the counter (B6: Up/down). Tank level full is when the counter function on = 10 and tank low level is when counter off = 1. These values can be used as feedback to control the pumps (instead of the high/low level sensors shown above) and can be called the ‘tank high/low level count indicator’ (Q5 or use a flag M1)
When the full liquid level in the tank is sensed by the tank high/low level count indicator (Q5), the fill pump will be shut-off and the FULL light (Q2) on the control panel is to be energized.
When the tank is full, start the mixer (Q3) and run for 10 seconds (B8: off-delay timer).
When the 10 seconds has expired, stop the mixer (Q3) and start ‘empty’ pump P3 (Q4).
Pump 3 (Q4) will be required to run until the tank is empty.
The pulses generated by flow meter 3 (B15) should be used to decrement the counter (B6: Up/down). Tank empty can be detected by the high/low level count indicator (Q5 or use a flag M1) to switch off the pump
When the stop button (I2) is operated, the process must stop immediately (Q1, Q3, Q4).

b)Test your LOGO build and comment on your testing using LOGO simulation mode. This requires at least 3 print-screens of testing the system using the LOGO simulator below at the filling, mixing and emptying stages



Many thanks in advance!

Ross

 

[parky]

I think you need to clarify a few things, for a start, when the empty cycle is complete do es it re-fill the tank, or does it reset the run latch this is not stated, yet again, very poor description of a process so many holes in the operation.
It is a simple process but why bother with the level sensors ? are they there for safety i.e. if for some reason it hit the high level is it supposed to stop a scenario is if the flowmeter failed then you would not get the pulses & the tank would keep filling.
Same with the low level, assume the flowmeters for some reason were not calibrated to within a small tollerance perhaps the tank would empty as no more pulses from the discharge flowmeter.

 

[GalacticPigeon]

Hi, thanks for the response.

To be honest with you, you have all the information I have. I thought it was just me struggling to clarify things in my head, but clearly not alone. It just seems so overly vague.

I have actually managed to get something like on the LOGO! simulation software (after a long time of head scratching!) to replicate what they're asking, so I guess I'll see how I get on once submitted for marking.

 

[parky]

Some pointers, assume that the latch for the start is enabled & not reset at the end of the sequence then all you need to do is Start the pump, enable the counter & allow it to count up to the value i.e. 10, the best way is to set a latch call it the fill latch, when the counter reaches 10 (I suggest make it greater or equal to [ >=] as if a pulse occurs outside the bit of logic it may not see the 10 so jump from 9 to 11 & the compare would not see the 10 (probably not important on a simulation but in real life this can happen).
Then also use the counter complete bit to reset the pump latch & set another latch for the mix time, this is then used to run a mix timer, when this completes the timer contact is then used to reset the time latch & set another for the discharge & so on.
Should the start latch be disabled i.e. stop button pressed then just reset all the latches. I do not know what you are supposed to do if this happens do you manually empty the tank, leave the sequence as is & then on a restart carry on but you only have a very poor description of a working process.

 

[parky]

Here is a quick one i did in about 15 mins, not got logo & the way some of their counters/timers etc. work may be different, I have also used a ton timer I hate TOF ones & does not fit into the code very well I have also included a oneshot pulse to reset the run latch after discharge.

 

[drbitboy]

13 FBs in LOGO!, not counting the four input blocks and four output blocks.

It might be a few less if I used RS blocks instead of Start/Stop Circuit patterns.

 

[parky]

As this is an assignment & knowing how tutors think it may be better to follow their supplied documentation, Although I think it makes sense to use your own way of doing the logic the tutor seems to indicate the use of certain types of timer/counter etc. however, If I was that tutor I would look for the pupils own thoughts on how to do it, this shows the pupil has that special something that could make a good programmer.