School PLCs

Hello folks,
We have been gifted with some NO4I analog output cards for our SLC500 trainers.
Do you guys have any suggestions for a simple output device that we can make ourselves (times 8)that will help demonstrate how analog works?
Thanks

Probably the most industry applicable and most frequent would be controlling a VFD from a PLC start stop fwd reverse and speed control.
The applications of this are
pump speed control (more less heat cooling etc),
HVAC fan speed control for temperature CO2, makeup air etc etc.
Machine tools, hoists, elevators, conveyers, the list goes on and on

Valves with proportional control

Position control of
cylinders (hydraulic pneumatic etc),
ventilation dampers - would be good - components are small, low weight and power, cost quite low easy to set up and easy to see what is going on.

Heater control - can be a little tricky with only a PLC often done with a pulse width modulation so maybe a little over students head

Dan Bentler

For a trainer, you might just want to get some analog meters.

EDIT: Since your cards are current output cards, you'd need load resistors to convert the current to a voltage for the meter in my link.

Paul

here's a little benchtop unit that I use in my classes ... the knobs are for two potentiometers and provide 4 to 20 mA analog input signals ... the meter can be wired directly to the analog output module that you've mentioned ...

I built six of the "boxes" myself in a couple of hours - mostly from "shelving" and "tile board" material available very reasonably from Lowes ...

TIP: to protect the meter movement, hide a small diode in the circuit ... sooner or later (probably sooner) some student will "reverse the polarity" and hook the circuit up backwards ... the diode will prevent any reverse current flow that would otherwise peg the meter backwards ...

Thanks guys, especially Ron and the diode suggestion.
The students are conscientious adults in some part of the trade but I have a stack of smoked transformers that were connected backwards.
Learning is about making mistaaks.

gas said:

Thanks guys, especially Ron and the diode suggestion.
The students are conscientious adults in some part of the trade but I have a stack of smoked transformers that were connected backwards.
Learning is about making mistaaks.

Click to expand...

Well as my chemistry instructor said
Sometimes we instructors forget you are here to learn.

I did like the diode idea and really think it a good one for students. 50 cent diode saves $10 meter - seems cost effective to me.

Dan Bentler

Or a really cheap DVM:

I buy these for $3 or $4 on sale at Harbor Freight. Disposable. Shows current directly. Has a 20mA scale setting.

Dan

personally I like the analog (non-digital readout) meters – at least they work better for my purposes ... it's easier for the students to see the output signal SMOOTHLY increase and decrease ...

later in the class we do troubleshooting exercises like "double-coiling" the analog outputs – for example with a rogue Message command "accidentally" sent over the Data Highway Plus network ... as the two controlling rungs "fight" over the meter, it's very easy to see the needles kick and jump at random times ... I've never been able to get the same picture across while using digital-type meters ... the numbers change – but it's not as easy to see the back-and-forth action of the conflicting signals ...

going further ... I DO use a digital meter for other exercises – particularly when doing the "analog scaling" thing ... I'll have to check into those "disposable" meters that danw mentioned ... I've been using my Fluke - and having to keep a very close eye on it ...