S7-200 ~ Analogue Module

Hi,
I need all the assistance I can get.

SCENARIO:
I am going to be using an analogue module for the first time.
The PLC is S7-226 with a Analogue module with 1-IN/4-OUT.
I am going to use a Weighing module to give me 4-20ma.
This W/module gets data from 4 load cells, which I will engage and disengage, using a Air Cylinder.


APPLICATION (OPTION 1): (Analogue 4-20mA)

I'll skip the unneccesary details.

I need to enage the LOADCELLS, so that I start getting the reading from the Analogue moduel, this will be the TARE weight (TARE is total of the patform + conveyor + the empty carton that moves on to this conveyor)

Then I start feeding the carton, and monitor the reading until the desired is achived. shut of the hopper and move the conveyor to bring in the next carton.

ONE THING TO REMEMBER IS, I WILL NEVER BE REQUIRED TO CHANGE THE NET WEIGHT. to clarify, I would say this is not a PID kind'a environment, as all I do will be to turn ON and OFF, the hopper (feeder). (Strictly no Analogue outputs!)



APPLICATION (OPTION 2): (Digital output)


The Metler Toledo guy has also offer a mini-controller with 1-IN/3-OUT. what I was planning to do was use this. why? read on and advise if I am thinking correct.

same application, the carton comes and PLC engages the loadcells, and gives the INPUT to weight controller, which in turns 'ZERO's the counter, I start pouring in the product, until the Controller it self gives me the Digital output, so that I can turn of the hopper.


Advantages:

1) I will evade the Analogue programming, de-bugging, ......
2) still the use has the option to increase or decrease the preset value.
3) Analogue module is expensive, I save money too.


One last thing, since the application does not require a PID programming, just need to monitor the ZERO (x mA) and final (xx mA). do some maths, and I have the result.
The only dis-advantage I see is, if I program the PRESET weight (in mAmps) within the program, the user can never change it, and if want to program it in such a way, that the Preset can be defined, in the HMI, this means more work.


and hey! dont start thinking, I'm afraid of Challenges, but time is short and I have to finish the procurement & installation of all Elec.'s in next 20days. (wish me luck)

.... more questions later.

First statement by mjamil
I am going to be using an analogue module for the first time.

and then mjamil wrote

and hey! dont start thinking, I'm afraid of Challenges, but time is short and I have to finish the procurement & installation of all Elec.'s in next 20days.

Click to expand...

Those two statements scream "Go with Option 2!!!".

You don't want to be learning something new WITH a deadline looming. Be happy you HAVE an option 2!... :nodi:

beerchug

-Eric

Oh, and good luck!...

Both scenarios could work, and the best would depend on your setup.

Option 2 would be OK if you don't have to log the weights or pass the information to a Scada system.

Option one you could do this, as well as automatically adjust the setpoint weight if required.

There is an option 3, it is use a Bus system.
Mettler Toledo panels usually come with a Profibus option, so you could use this in stead of an analog card. This may not be any cheaper than using analogs, but it is more resistant to noise, and it is easier to see that you are getting the same value in the meter and the PLC.

In addition, I think the bus option has better diagnostics and other cool features.

I would go for this option.

Doug

Digital is in!

Thanks Eric, for your advice, the "Digital" option was the one I thought to better (so far!) but ya'know there is a un-definable thirst for learning or should I say extraordinary Aggressiveness, that keeps bugging me, insisting me to take a risk!

but just for my info, if god forbid, I do land-up doing the ANALOGUE module, what would be the consequences, if

1) The analog module for S7-200, is a 12Bit unit, from what I know. However, I was reading the controlled of Load cells give me a 16-bit resolution.

WHAT & WHERE, could go wrong? considering too much ACCURACY is not required.

and, the value I get from the controller, say AWx.x, this comes in what form? and how do I program (or set) the minimum (4mAmps) and the maximum (20mAmps)?