Quick question about PLC testing

[gareth.cantrill]

In the past i have used a program called Pics Pro to simulate the plant and test my code. However this is expensive. See Pantek for prices.

Another question. Why can you not 'dry test' the plant first (i.e. run the program without product running through the pipes, etc), and then if all seems ok, move on to a 'wet test' where you can simply use something non dangerous (i.e. Water).

Before all of that you should test each device individually with someone on the other end of a walkie talkie confirming that the correct device has opened or is running.

 

[Ron Beaufort]

and just for completeness ...

if you were using Allen-Bradley and RSLogix500 you could put the PLC in the “Test Continuous” mode ... the processor would scan and solve the ladder logic and the “outputs” would light up on the display screen ... but the “outputs” in the field would not be energized ...

in the “Test Single” mode the processor would scan only one rung at a time so that you could watch the ladder logic’s operation in slow motion ... again, the “outputs” would light up on the display screen ... but the “outputs” in the field would not be energized ...

[attachment]

I’m not familiar with your Siemens software but maybe it has such a function too? ... some PLC technicians call this the “dry fire” mode ...

personally, I don’t think too much of this particular “testing” method ... for the same reasons I mentioned back in post #22 ... specifically, just because the “fill valve” lights up on the screen, a wiring or labeling mistake could turn on the “drain valve” when the machine is finally placed into the run mode ...

please note: this isn’t meant to be a “my-software-can-beat-your-software” type of post ...

 

[jlpsmith]

Why don't you get hold of a copy of S7 PLCSIM. This is the simulator software for S7. You can simulate the inputs at a touch of a mouse button. No hazards and not embarrasing if your code doesn't work.

 

[JesperMP]

PLC-SIM is for the S7-300/400 range.
Edgar is using S7-200.

 

[westoes]

you said you were worried about starting pumps while testing your program.your outputs would be would be controlling a contactors for your pumps so isolate the high voltage to the pumps either by isolating their manual motor starters/fuses or even remove their wires from the above mentioned or terminal strip.
myself i like to see contactors/relays actually coming on and off.you would be surprized how many times i have seen incorrect coil voltage contactors/devices or to a lesser extent faulty outputs in control panels.the LED indication on the output card doesn't always relate to a switching of an actual device and i learnt that very early in this game.
if this is not possible then like suggested stand real close to an E/stop pb (and hope like hell it's wired correctly skuller ).

 

[Richard Christian]

PLC Testing

When you haven't got the SIM package, or another PLC, or spare outputs.. which often happens with me on site..

Pull out all the power wires that go to the motors from the contactors and solenoids, everything works except there is none of that electricity stuff going out anywhere.
When you need a feedback from a solenoid valve.. set the alarm delay time up higher (to give you time so..), so when you activate the solenoid.. bridge out the feedback to the supply voltage.

(turning off breakers should give you an alarm if the programme is written correctly..so this wouldn't work)

Live testing is a bit of an art and shouldn't be taken lightly as there are inherent dangers with moving parts and that horrible electricity stuff.. just BE SAFE when your doing this kind of thing.

hope this helps

 

[azecraze]

I have made a habit of putting in one breaker just to feed the outputs so when I want to test, I just throw the breaker and isolate the lot. This might not work for you, but it works for me.

 

[stvsas]

how I do it

I originally write my program wit the inputs and outputs as relays. Then I write a simulation program with timers simulating the action of the inputs. If a cylinder is supposed to extend and then make a prox, I turn on 1 input and have that input start a timer. That timer's done bit would simulate the "extended" prox and also start the next action, ehich is another timer and so on....
Can you use this system?

 

[celso777]

In the case of AB PLC you can test your logic which means you can read in puts process your logic and write yor out put without atuacting phisical outputs. Maybe Siemen has this feature!