micrologix 1200 analog input board

shayne

Member
Join Date
Dec 2002
Posts
7
I'm hoping that on of the PLC adepts can help me with this question. I am going to be taking an analog weight signal from an MMI and using it in an existing MicroLogix 1200 as a permissive for a vacuum pump (0V = pump run, 10V = pupm stop). Do I need an analog input card, or can I place the analog signal into F8 as a value and use cascading timers to continually refresh the value (every 0.2s)? Thanks in advance,

Shayne in Canada
 
Where the MMI get this analog signal from?
Does it get from another PLC? If so you could send the same to 1200 in F8:X and use the upper and lower values to turn the pump on/off.
I am still confuse how the MMI i.e touch-sreen gets this signal?
 
I apologize, when rereading my original post, I realized that I was not very specific. The 'MMI' that I cited is actually a control station where an operator enters a setpoint value for a desired weight. The analog signal is generated from load cells on a weigh up hopper, and the MMI uses this signal to output a discrete signal for SP=PV. Unfortunately, the actual analog signal is also needed for machine interlocks; for example, if the operator abandons a weigh up half way through and therefore SP does not = PV, I want to be able to prevent certain possibilities when no SP=PV discrete signal is being generated. Thanks again for your prompt response.
 
In case of any PLC, the analog-signal can be read through an analog card only.
However, if another processor or controller contains this signal in numeric value, it can be transfered to the PLC through communication.
 
So...

How does the MMI get the analog signal from the load cells?
Does the MMI itself have an analog input?
If so, analog output?
Are you calling the load cell controller/display the "MMI"?
What brand is the MMI and/or loadcell controller/display?


There is probably a pretty good chance that the analog signal from the load cells is already "in" the PLC if the MMI currently displays it, if the "MMI" is a typical operator interface.
 
I think you are describing a system where the load cell is connected to an external controller or limit alarm. Currently the PLC gets a contact closure when the load cell equals setpoint. The output of the load cell is 0-10 VDC. Yes or no?

You need to add an analog card to get the signal into the PLC. Since the output of the load cell is a voltage you can wire the PLC input in parallel with the signal into your existing controller.
 
lets keep this simple, OK?

If the original poster simply needs to

"as a permissive for a vacuum pump (0V = pump run, 10V = pupm stop)"

Why not run the load cells into a panel meter with dual alarm relays, like a Red Lion PAX_ , and use two digital inputs on the 1200, and
move on.

If the display of the weight/load is desired, the PAX will act as a display.

AND, you can show the operator how to change the internal alarm points on the PAX for your process.
 
keep it simple

JD, I think a Red Lion or similar controller that is what he has now, and he wants the analog in his PLC for some reason.

Shayne, additional details are required!
 
I'm just trying to avoid having to buy a 'weighing terminal'

..or whatever the scale guys call them these days.

And, BTW, the PAX_ family has an analog re-transmit
option, which, I know, has nothing to do with the
original post.
 
I realize that I am poor at descriptions, however, I thank you all for bearing with me. Essentially, ignore everything I have described and possibly it can be answered in a question format. If I take a 0-10V variable signal and assign it a destination in a data table eg. F8, can I avoid using an analog input card by constantly overwriting the value in F8 with new values? Again, I would use one timer to actaute a move command (input destination to F8 destination) and use a second timer DN bit to actuate the first timer. I hope this is a bit more coherent, I definitely would not make it as an instructor. Thanks again,
Shayne
 
Simple enough, thank you very much to all for your help. I believe that I will be recosting this project slightly to include some analog input cards. Thanks again,
Shayne
 

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