Keypad Question

HoldenC

Member
Join Date
Sep 2012
Location
Cumberland, KY
Posts
215
First off, I want to say I am fairly new to PLC's. I took a couple college classes and read a couple books. I believe i have a fairly good understanding for the most part.

Here is the question :

Say you have a manufacturing plant, with a few hundred motors. All motors are given numbers from say 100-400. You have 1 STOP button, 1 START button, and a keypad. How could you start or stop any one of the motors with those controls ?

There is a auto-start sequence to start everything in order, but im talking about only shutting off one motor.

Hope my question was clear.
 
Hi, and welcome to the forum!

Is there some visualization of what you tap in with the pad? A screen? A display? Evt 300 LEDs? Then it is no problem.

What PLC type do you use?

Kalle

If you don't have a visu, you could type 123+start and 123+stop, a start, stop, 000 or any invalid number must reset the number register. But it is not wise to do it like this, not having a feedback of what is registered in the controller. Kkkeypad ripriprppllplle.
 
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You have 1 STOP button, 1 START button, and a keypad. How could you start or stop any one of the motors with those controls ?
If the keypad is a HIM control module hooked to a Variable Frequency Motor drive for each of the 300 motors, then all you need to do is press the RUN or STOP button on the keypads.

Is this a test question? It seems to lack some critical details for a real plant.
 
Yes, the keypad has a 3 digit read out at the top.

The keypad is set up like this:

1 2 3
4 5 6
7 8 9
B 0 B

The B stands for blank key.

We are using AB PLC5


No test question here. I just worked at a place before that had this set up.
 
Does this keypad have a software program that allows programming using PLC tags? If so, you could make one of the blank buttons a Start input key for a motor number from 100 to 400, and the other a Stop key for stopping any motor from 100 to 400.
 
Im sorry. I think i explained things badly.

The keypad has 2 blank keys that erase the number currently typed in. Right next to the key pad are 2 buttons. A START and a STOP.

I mean how could you set up the logic so that i could say type in "156" and hit the START button and have that motor start running.

I know im way out of my league but could you somehow set up the keypad as a analog input and set up a EQUAL command if possible.
 
do you mean to start and stop individual motors for test purposes whilst the line is shutdown or to stop and restart a motor whilst the line is running?
 
Im sorry, i have no access to the part number or manufacturer of the keypad.


Here is a scenario where the kay pad would come in handy.

Say coal is dumped on to BELT LINE 100.
Belt Line 100 dumps onto belt like 200
Belt Line 200 dumps on to 300 ect, ect up to belt line 800.

There is a auto start feature. Belt line 800 starts then a few seconds later 700 stars, then 600, all the way back to 100.
Timers are placed between each belt start so that they dont pull too many amps.

Now, say belt 400 starts slipping and needs to be shut off fast. When i shut 400 off, i would want 500 and the belt further down the line to keep running. Belts 400 and before to stop running.

I did this by typing in "400" into the keypad then hitting the stop button.


Is this one of those questions where it will vary by manufacturer and type of keypad ?
 
Is this one of those questions where it will vary by manufacturer and type of keypad ?
A big YES on that, Holden. Keypads have differing capabilities. Some have buttons that can be reprogrammed, some do not. Even worse, it depends on what the keypads are connected to (the PLC brand and model - Allen Bradley PLC5 I think you said), whether you have access to the PLC5 program and can modify it to perform different logic.

To allow a Start or Stop with accompanying Motor Number, you would have to reprogram the Start and Stop routines inside the PLC5 program. Can you make a screen shot of the PLC5 program Start-Stop rungs for one of the motors?

Now, say belt 400 starts slipping and needs to be shut off fast. When i shut 400 off, i would want 500 and the belt further down the line to keep running.
When I program a series of conveyors, I always include interlock logic for both startup and shutdown. Then if any conveyor stops (for whatever reason) the interlock on the next one uptream causes it to stop, and the third upstream conveyor is stopped by the second one, and so on until all upstream conveyors are shut down. The downstream conveyors are allowed to keep running until manually shut down. I would bet $10 that your coal conveyor PLC logic is set up the same way, otherwise you would get some really bad spills, sooner or later.

For the start-up, the interlocks allow the fartherest downstream conveyor to start first, and the next upstream conveyor starts second, and so on until all are running.

I mean how could you set up the logic so that i could say type in "156" and hit the START button and have that motor start running.
It seems that you are using poor logic. If the Start and Stop buttons next to the keypad are presently set to perform motor start-stop for a specific motor, then most likely you will not want to (or be allowed to) change those functions.

Instead, any changes to allow a keypad (existing keypad or a new one with required additional functions) to add a new function (where the keypad becomes a control for ANY motor, not just the one controlled by the existing Start-Stop buttons) should be made totally in and on the keypad, not changing the existing Start-Stop buttons at all.

PS: Back in my young days, I spent many days at the old TVA Cumberland Fossil Plant designing and installing scrubber systems.
 
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Thanks for the help.

Sorry about taking so long to reply. I was moving and had to get my dsl services moved.


Unfortunately, i do not have access to the logic anymore. I do not work there anymore.


Can you explain how you write interlock logic ? Im still a little confused on how to set up a auto start, and auto shut down.



I was working at a plant in Cumberland, KY. Used to be ran by ARCH back in the 80s i believe.
 
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Can you explain how you write interlock logic? I'm still a little confused on how to set up a auto start, and auto shut down.
Holden,

Interlock logic was first used with auxiliary contacts on motor starters. In a string of series-feeding conveyors, you want upstream conveyors to shut down if a downstream conveyor stops for any reason. By using a N.O. contact from downstream Converyor 2 motor starter in the start control circuit of upstream Conveyor 1, you could prevent Conveyor 1 from starting or running unless Conveyor 2 was also running. If there was a Conveyor 3, then a N.O. contact from Conveyor 3 was used in the start control circuit of upstream Conveyor 2, and so on for all conveyors in a string. Each conveyor motor starter (unless it was the first or last) had two wires from the next downstream conveyor motor starter contact wired into its control circuit, and in turn had two wires from the next upstream conveyor motor starter connected to a N.O. auxiliary contact on its motor starter.

PLC interlock logic simply duplicates the old motor starter interlocks, and additionaly also allows easilly adding a start-up and shut-down time slot for each conveyor. Note that the start-up and shut-down routines do not have to depend on the interlock logic, because they have slightly different purposes. The interlock logic is only to prevent spills, and the start-up logic mimics the interlocks to some extent, but adds the time factor to allow a conveyor to get up to full speed before starting the next one upstream. This helps to reduce the plant KWH Demand factor. The shut-down routine often allows time to empty each conveyor before shutting it down. This helps to prevent caking on the belt, and also allows empty-belt start-ups and lowers the motor start-up currents.

A picture is worth more than all the above, so here is a picture of a string of 3 coveyors with interlocks and also start-up and shut-down timers. The conveyors start up with a 3 second delay between starts, and shut-down with a 10 second delay to allow each to empty.

Conveyors with Interlocks and Timers.jpg
 
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