Slc-504 / Remote I/o // Flex I/o

A bit off the main highway question....
Even though I am in the middle of a monster project on
a system with Modicon Quantum 324 processor, much momentum i/o,
lexium servo drives, robot drives. and good gracious only
know what else is in th e project,,, I somehow come home in the
evening and play with an old SLC5/04 and a bunch of remote I/O
and flex I/O which is going to kinda keep up with the ol homestead
here...A toy from the junk piles of industry....
Now part of this project with the remote DC I/O is to control
to some extent a small HO gauge train layout, so that part of the
lay out can operate its normal freight routes automatically...
AS I said a "TOY"... But this toy is also a great learning
application... and one day hope to have intellutions as the
engineer to track system interface.... nope not rich, just a
junk collector....
Now that we have a bit of background presented... The question IS:
Since I have scrounged this from junkpiles, I have not had the
good fortune to find an analog output module for the SLC chasis..
I need to vary a DC voltage to accelerate the engines, and not
just turn the power on and let it rip.... With an analog module
I could set the ramp up time, and get a great acceleration curve.
And do the same thing, and get a nice decel curve... but a resister
switched into the circuit will work for the decel...
Now do I put a resister and big cap across a couple of outputs
to generate the acceleration curve to a full run voltage, """or"""
has someone got a "pulse width modulation" routine tucked up
their sleave somewhere that could be programmed into a SCR dc output
which then would drive a electrolytic cap to give a good smooth
curve....
Or can anyonme give me any other ideas... varying the frequency
of the output into the cap would also do it, but there again
a sweep generator would have to be written into the SLC.....

As a last resort, I will run out to the shop, grab some electronic
parts, and PC board, and build a sawtooth generator to give me
one nice sawtooth to accelerate the engine from a dead stop....
and simply use the PLC to turn it on and off....
As we build the new system. optical switchs and prox switchs are
being build in to control points to tell the system where things are
on the tracks....amazing what folks throw away.... Difused optical
switch mounted in station.. train comes into station, switch sees train,
train stops, passengers get off, and train pulls out of station when timer times out....

Actually as I think about it, a driver for some type of heater
control probably would give the PWM output....

I toss all this out for thought... What can we come up with....

Tim Jones
Conyers, Georgia
[email protected]

To get an analog output card real cheap:

Go to ebay (www.ebay.com) and search with a suitable string like "Allen Bradley analog".

You should get a number of hits, and if you are lucky, there will be something that you can use.

As many here know, I'm against "home brew" stuff. In your case though, it's FOR home use, so I'll make an exception...

You seem to be knowledgeable when it comes to electronics, so pardon this simplified explanation... Someone else may find it useful.

You can make a simple D/A converter with a handful of relays and resistors. How many you need will be determined by what resolution you need. You can even eliminate the relays if you have an isolated relay output card (one common per point) laying around. Basically just a PLC controlled decade resistance box...

Just wire up a circuit like this...

  | <------------VARIABLE RESISTANCE -----------> |

  |                                               |

  |      R1              R2              RX       |

  +----/\/\/\/----+----/\/\/\/----+----/\/\/\/----+

  |               |               |               |

  |    RELAY 1    |    RELAY 2    |    RELAY X    |

  +------] [------+------] [------+------] [------+

.
This would be a "3-bit" D/A converter. By turing on different combinations, you can get 7 different values (8 when you include zero ohms (dead short) when all relays are ON). You can add as many relay/resistor circuits as needed to increase the resolution. Just stick them in between the "> <" in the circuit below...

  | <----------------VARIABLE RESISTANCE ----------------> |

  |                                                        |

  |                                                        |

  |      R1              R2                       RX       |

  +----/\/\/\/----+----/\/\/\/----+-->  <--+----/\/\/\/----+

  |               |               |        |               |

  |    RELAY 1    |    RELAY 2    |        |    RELAY X    |

  +------] [------+------] [------+-->  <--+------] [------+

.
Another idea might be to connect a slow speed motor to a potentiometer and control it's direction (CW/CCW) with the PLC. For your application, this might make for a nice, smooth ramp!

That is, if you can't find an analog card cheap at Ebay as Jesper suggested...

beerchug

-Eric

The AB instruction set manual for the SLC _used_ to give an example for turning the output of a PID block to a pulse train (mostly for heater control) controlling a single output. If this would work for you maybe someone has the older ISR or possibly its still in the newer ones.

Yep, I remember that, and I have been looking for some of my
old SLC manuals....
We also kicked this around a bit at work, and by using a pair of
timers a counter, and an add and a subtract block, the balance
between the two counters can be manlipulated, by changing the time
presets in the timers, adding to one, and subtracting from the other,
longer on times, and shorter off times... Just have to develop and
try the circutry and add an electrolytic to smooth out the step...
Trying to use the least output possible, as this also operates
all the switchs, (14) and each switch requires two + an actuating, isolated output..common to a block of switchs..

This slick will also run the alarm system, the pool, the outside lighting, the flower watering system, and anything else I can
find to add, until I run out of remote I/O... My wife wants to
know if I can rig something that will cook diner automatically...
Each seperate function will be a subroutine of its own, and
will all operate from a master program....Anybody got any old
blue hose remote I/O they don't want... ??????