Re: PLC's Microcontrollers, doing it on the cheap

As always, there is more than one way to skin a cat.

The project, as I understood, was to control a heater for an oven
(bath?). Ramp time could be following actual part temperature, or
just by time.

To do time only, it more simple. You could just set a few timers and
thermostats and you're off. This doesn't allow for alarms if the
part never reaches temperature, (door open?) or unlimited numbers of
steps, and unlimited variations of ramp times and soak periods.

PLC's at one time were a erector set of parts. PLC Direct (I have no
affiliation with them) offers a $120 'brick', a $70 analog input
card, (4 channel) and a $99 software. Of course, you have to program
the unit and that means leaning a new software language.

Of course, you need thermocouple transmitters to read temperature.
more parts and more money.

comparing the STAMP PLC to a Brick?

The cost of these devices, is reasonable. I have seen the pictures
of the STAMP PLC. It looks quite good. The Stamp can be programmed
using Basic, (you still need a language) and you could do the same
process.


The STAMP PLC has much more capability. I wasn't sure from the post
if it includes the analog monitoring of temperature either from a 0-
10volt signal or a 4-20mA signal or a possibly even a raw
thermocouple?

The STAMP PLC can be networked, do data logging, output to meters and
display all sorts of things, temperature, time since last action,
time till next, almost anything you would want.

A Brick is a pretty good name. No inherent features. Or, as was
noted, all add-on's at a price.

Regardless of the control device, for this process, they would need
Analog input to monitor temperature of the oven and possibly another
to monitor the part temperature.

Both would control the heater the same way, by turning a heating
element on or off. With a second element, one could have a HI/LOW
function, a third element could be used to maintain BTU input to
correct for losses. What I'm using a lot of words to say is there is
no throttle. A lot of newcommers think in analogue and assume
computers do too.

The user could ramp up temperature to any level, wait until the part
is at that temperature for 'X' hours, then ramp up to another level
wait 'Y' hours, and so on.

As always, there is more than one way to skin a cat. I'm interested
in the process more than the hardware. My parts are all aluminum and
no critical dimensions so I don't have the same problem of heat
treating cast parts.

I think automating the process will yield huge benefits in quality
and repeatability and history for improving the next batch.

I know the guy had looked (is looking) at the FUJI process
controller. It has a couple LED displays, one for temperature and
one for setpoint, will input a thermocouple wire directly (on board
circuit to change to temperature) and an on/off output. I think it
is limited to 4 steps, so he could only have 4 levels of temperature,
and 4 ramping periods.

--- In CAD_CAM_EDM_DRO@y..., "Ron" <ronaldsa@e...> wrote:
> FYI
>
> I Saw this post on microcontrollers, the problem is that you cannot
> really get a PLC for a 100 bucks.
>
> You have to buy all the components separately in most cases.
>
> The Backplane- power supply
>
> The CPU card
>
> The Input or Output card each separate, and you will need both.
>
> Also an ADC card to digitize the analog thermocouple voltage after
> going through an amplifier.
>
> Plus you need to buy the programming software which is 300-600
> dollars.
>
> Thus before you even get started you are now over a thousand
dollars.
>
> Due to this situation, I built a small 8 input and 8 output PLC
> interface style controller which uses the BAsic Stamp from
> www.parallaxinc.com an added plus is that their editor software for
> programming is free.
>
> This has been used in a variety of industrial applications to
provide
> control on the cheap.
>
> The controller board is 289.00 and you can pick from about 4
flavors
> of stamp microcontrollers from 49.00 to 75.00 dollars each,
depending
> on the amount of programming required to accomplish you task.
>
> I downloaded the photos of this controller into the photo archives
in
> CAD_CAM_EDM_DRO. They are stored as bsiov2_2 and bsiov2_3
>
> A second unit will be available shortly which will allow the
> monitoring and control of 16 inputs and 16 outputs.
>
> Both easily control and interface with ADC chips for analog
voltages.
>
> These ADC boards and specialty functions like DAC, PWM output and
> Thermocouples are also in the works. If you have need of such, let
> me know via e-mail. ronaldsa@e...
>
> Attached is more info on the controller:
>
> *******************************************************************
>
> For those working in the industrial environment, Digital Design
> Solutions, Inc. annouces the release of a Programmable Industrial
> Controller ala PLC Style which interfaces with 24 volt input and
> output devices using the ever versatile Basic Stamp module.
>
> All inputs are opto-isolated allowing for a good deal of
> flexibility. The 8 Inputs are easily configured to use with both
> flavors of industrial 24 volt sensors both PNP and NPN optical
photo
> sensors, or proximity sensors. The Inputs will also accept switches
> or contacts, various photo transistors and hall effect sensors with
> open collectors. Input Sensors derive their power from the 4
> terminal input connections. Thus there is no need to assemble a
large
> section of DIN Rail terminal blocks to distribute power to
Sensors.
> A DIN Rail fuse block is recommended to power up this module.
>
> TO-92 Darlingtons are used as open collectors on the 8 Outputs (500
> ma capacity nominal for outputs) with flyback diodes on the board
for
> protection against inductive spikes when coupled with pneumatic
> solenoids, relays or motors. Other features include a 5 volt
> Switching Regulator: This results in high efficiency and low heat
> when converting from 24 VDC to 5 volts with a 1.5 Amp Capacity @ 5
> volts, should one wish to use a power hungry VFD Display with this
> module. An LCD output connector is configured for a pin to pin
mate
> with a Serial LCD Backpack Interface.
>
> This 8x8 Controller comes with DIN rail mountable plastic holder
> ready for your application. Just add power, a BSII or BSIIe, your
> sensors/outputs and some programming to have your industrial
solution
> up and running for a lot less money than an equivalent mini PLC.
>
> The fully assembled controller with DIN rail mounting is available
> for $289.00 For more information contact DDS via e-mail at:
> ronaldsa@e... or call 970-667-4239.
>
> To purchase send check or money order to:
>
> Digital Design Solutions, Inc.
> 1937 Hyde Drive
> Loveland, CO. 80538
>
> VISA is accepted via www.paypal.com
>
> ********************************************************************
>
> >
> > Message: 15
> > Date: Sat, 10 Feb 2001 22:09:12 -0000
> > From: davemucha@j...
> > Subject: Re: cast iron
> >
> > (sorry if is this is a second post, Yahoo and I don't get along,
it
> > sends stuff when I hit the tab key)
> >
> > For a controller, you can get a PLC from
> > www.automationdirect.com for about $100. It'll allow you to
> program
> > any type of ramp up and down and hold cycles you can imagine.
> > A thermocouple will allow you to monitor the temperature and if
you
> > want, a second will allow you to monitor the part in the oven.
> >
> > or if you want, you can visit http://www.parallaxinc.com/ and
get
> a
> > micro-controller and create you own device. Free software and a
> > GREAT list at basicstamps on yahoo
> > http://www.egroups.com/messagesearch/basicstamps?query
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "Smoke" <gordonr@r...> wrote:
> > > Jay, do you know of a source for programable controllers and
high
> > > temperature heating elements we could incorporate into home
built
> > electric
> > > heating/melting furnaces?
> > >
> > > I'd love to build a somewhat larger heat treating furnance and
I
> > know of
> > > others who'd like to do this as well. In fact, I just got a
post
> at
> > > HomeFoundry about a guy that wants to build an elcectric
furnace
> for
> > > controlling temperatures on salt baths.
> > >
> > > Smoke
> > >