Easier way to have multiple calls to a coil

[viscoelastic]

I understand not being able to use a coil more than once, but there has to be an easier way to do it than the way I did it in the attached image.  Thanks all

[Ausman]

There is.  Use O49 & O50 as direct actions.  You can do this, thereby eliminating MB100 & MB101.  You simply have O49 & O50 as direct contacts, replacing MB100 & MB101 in your rung 4.  Or alternatively in your case, just do rung 4 again using your I0 & I1, given that they are linked to the "drive" action.

cheers,

Aus

[viscoelastic]

Hi Ausman, I don't follow you. Would you mind elaborating on "direct action?"

Thanks,

Paul

 

[Ausman]

Have a squiz at this.  Hopefully it makes sense.  And "direct action"?  "drive" action.

cheers,

Aus

[viscoelastic]

Absolutely, much better! Thank you Ausman!

[Ausman]

And now for my pearls of wisdom.  They are all related to thinking many steps away from what you are immediately doing, and trying to forsee any consequential occurrence.  You have a clever controller that can likely do a lot more than you are presently asking.

1).  I am assuming (using memories of past questions) that you have a drive system that raises or lowers something in a tank, and when this drive mechanism is not moving it is locked by a clutch/brake or similar that uses power to unbrake, being a failsafe as it is braked without power.

2).  Unless your contactors for the drive motor have auxiliary contact sets mechanically preventing the other direction contactor from engaging when the "first" one is on, you should do such a switch action in your program.  This is not hard, it is simply an inverted contact from the other input placed in the relevant rung before the output.  The reason for this should be self-explanatory.

3).  Given delays between brakes unlatching and the time involved for your motor to turn on, perhaps a timer on the relevant output might improve performance, noise, or wear and tear on the machine, or even all 3.  Without observing the mechanicals in action, I don't know the answer.  If the motor is a DOL you may well have strain (you can't see) being put on the mechanism as it spins up against residual braking effort as the brake disengages.  I am talking of a timer of only 1/10ths of seconds, but you might be amazed at how much smoother you can make things when you look into the "total" mechanics of how things work.  I have my saying about a multitude of humans I see, it is "ZMS".    Zero Mechanical Sympathy.   These are the truck drivers who wear out their prime mover twice as quickly as the smooth driver.  The car owner who slams the door each time.  The kid who kicks the dishwasher door closed.  You get the picture!  A really close look at your mechanicals might show you are able to implement vast improvements to life and smoothness.  As a quick example of this sort of thing, listen to a 24vdc relay in action with and without a clamping diode.  You can actually hear how the clamping makes the relay much happier.

4).  Further to point 3), you are engaging the brake immediately the motor call is stopped.  This likely also needs a small delay to allow the motor to spin down without heaps of strain.

5).  Using the outputs as inputs is the method I use in all my error checking routines.  I don't use Visi's inbuilt alarm systems.  Mine incorporate checking loops with a defined set of operations if there is a failure noticed, with an ultimate lockout if the problem persists.  And as an example of how I do things, I have a current detector on one wire to a 3 phase drive.  If there is no current a small delay after the actual plc call happens, then there is an issue.  Most people only use the switches on the contactor overload to check if the motor is going, (ie if the overload has tripped it says the motor is off) which in certain circumstances can give totally false readings and depending on the way things work might be disastrous.  My method covers ALL bases.....if the call is done and the motor isn't drawing power then there is an issue.  CBs, contactor, overload, isolator at the motor etc etc.

Some might view these thoughts of mine as "pernickety" but I always try to build things with full attention to all details to ensure the best operation possible.  You can have a machine that works ok, but you can also have one that works really really well.

cheers,

Aus

[viscoelastic]

Thanks Ausman.

I will take any advise I can get, and I must say; you have a good memory. I do deal mostly with tank farms. This is a whole different application. This one is a foam saw that we pulled out all the old antiquated batch controllers and started from scratch with a PLC. How the measurement works is the motor with the brake runs the saw head down and rotating an encoder. When the counts/measurement reaches the set point the motor stops and the brake stops the head.  This was truly a definition of what you called "Zero Mechanical Sympathy"  ( a term I  like and now committed to memory) .  How I improved on that is; I replaced the reversing cross the line starters with a freq drive. As the head reaches 10%  its target point I ramp the drive down from 60 Hz to 20 Hz then at the target point stop the drive and apply the brake. This increased accuracy to within 0.015 mm and gave the brake some sympathy it deserved. As for the code that you saw, that was manual control from the joystick. The only time it gets used is in an emergency that a blade brakes or something that you have to move the head out of the way or rotate the table. 

If you're interested, I can post some pictures of this enormous saw. It boasts a 30' (9m) diameter rotating table, can cut material up 118" (3m) wide and 60" 1.5m high.

I sincerely appreciate all your help. I would never have got this far on my projects without people like you to help.

I do not know what country your in, (assuming Australia) so I used both imperial and metric units in my response. We are in the US but our company is 90% metric.

Thanks again,

 

 

 

[Ausman]

Thanks Visco.

Yes...Australia...where we have been metric for ages but imperial is still in common enough use.

Put some pictures on the "just finished a project" area.  Oddball things are always good to see.

If during programming things a thought doesn't actually show up in any literature, try to do what you want anyway.  It will either work or not!

And often once you've done a layout in the ladder it shows how you can make it much simpler.  I once spent ages working out a host of MBs all turning on a few outputs, and it took many many rungs and many lines.  With it in front of me on the screen, all the myriad common combinations became obvious and it ended up in just a few rungs of 1 or 2 lines each.  Then your brain says "why didn't I think of that in the first place?" and the other nasty part chimes in with "because you are a dumbdumb!"

We all learn something new everyday.

cheers,

Aus

[kratmel]

Hi, Visco

You described the algorithm of the system with a VFD.
I usually use the VFD internal option to control the brake.

The brake active when the VFD reaches zero speed and there is no command to move in the forward or reverse direction.
This eliminates the problems of controlling the VFD in different modes, for example, JOG, FIXED SPEED.

No need to control the brakes with the PLC. This is especially useful when lifting or lowering some part of the mechanisms.

However, the VFD must be able to control the brakes.

[dub]

Hy!

Which type of converter do you use?

Dub

 

[viscoelastic]

@kratmel  Absolutely, this weekend I came in and used one of the dry contacts on the drive to fire the relay for the brake. Again, one of those simple things that I did not think of. Thanks for the tip!