Alarms

I am fairly new to PLC and am programming my first complete machine. I have a good understanding of the logic to operate the machine.

However I am looking for a good suggestions for identifing alarm conditions. Like if the program stops because of a sensor that was not made. Or if some other condition that should be communicated to the operator.

I am doing this on a Horner PLC which I don't think should matter to much.

Any help on this would be appreaciated.

Thanks

Hi

I usually program in steps. Each step has certain conditions that must be met to continue. I usually have a step timer, so if the timer has elapsed and the condition is not met, i flag up the alarm. This approach needs thinking about when you do the initial programming.

You will need to do some kind of programming for the alarms. Do you want alarm acknowledge / reset capability or will they self clear.

Cheers

CJD1965,

Thanks for the suggestion. I would like the alarms to be reset by the operator. I would also like to provide some insight into what caused the fault. Such as sensor I 57 stuck or something. So if a slide is in the wrong position the operator has a place to start looking. The machine is a 6 station rotary dial with some hidden opeartions.

I have seen timers for each step that should work for a general station fault. I will see what I can do with that.

Thanks again

The hardest, yet most important, part of any automation project is to DEFINE what you want/need.

So, ask yourself the following questions?

What conditions should cause an alarm? How can I detect it (i.e., if you can't detect it, you can't alarm on it...)? How will I notify the operator? How does the alarm reset? How should the alarm be treated (i.e., just notify the operator -vs- cycle stop -vs- shutdown -vs- ...)?

From your last post, you indicate that you need some way of telling the operator what/where the problem is. This can be anything from simply using pilot lights if you only have a few alarms, up to a really large, really elaborate HMI system.

Well I am using a Horner XL6 plc. It is a plc with a built in 6" touch screen. They have a alarm handling feature which works pretty well. My biggest issue is providing the alarm output to the handler. Which will display what ever message I want.

Currently I have a mini program for each of the six stations plus the indexer. When the dial finishes indexing each of the operations start. When each mini program finishes it signals opeation complete. Which then allows the cycle to start again on operator input.

What I would like to see is if a sensor stops the program I would like to send a output to the alarm handler which could display the cause of the stopage. I am not sure how to make this happen just when it is stopping the program.

I am a manufacturing engineer by trade, I specialize in cutting metal. This is a project that was assigned to me and I need to figure this part out.

Thanks for the suggestions.

Is ther a condition that would normally activate with a working senser? if so you could monitor that and if there is no change there ina given time period then you could send the alarm. or if the senser does not change state in a given time period then send an alarm

Think in terms of cause and effect, action and reaction. Every action should have an anticipated reaction...Every cause an effect. When the anticipated reaction doesn't occur, ask yourself possible causes and word your alarms accordingly.

Examples:

If I energize a motor starter, I should see the auxiliary from that starter almost instantaneously. If I don't why? No power, blown fuse, OL tripped, etc.?

If I energize a motor, I should see it rotate. If not, why? Zero Speed switch broke, motor locked up, disconnect thrown, etc.

If I energize a solenoid, I should expect to see the close position sensor de-engergize and the open sensor energize within a reasonable time. If not, why? No Air, stuck valve, blown fuse, etc.

If I move a rotary table to position A, I should see the sensor corresponding to A. If not, why? No power, broken gear drive, etc.?

Get the picture?

Set a different bit in every step and reset that bit with the next step. This way you can track where the program is and tigger comments or suggestions on every bit. USe those bits with timers to trigger alarms if it is stuck too long in a step (This is if you dont have Sequencional function charts in the software as I dont know Horner plcs)

Thank you all for the suggestions. They have all helped me picture what and how I need to do it. Thanks for all the help.

Alarm Characteristics – characteristics of effective alarms include their ability to:

1. Alert (call attention to an abnormal situation)

2. Inform (provide information about the abnormal situation)

3. Guide (expected response)

It is important to adhere to the generally accepted definition of an alarm: that it be an alert to an abnormal situation requiring a response.

Alarm requirements must be considered when the user/system functional requirements are specified; usually near the beginning of a project.

It is important to define, in advance, the attributes of alarms that are important and which will need to be configured into the computer system.

In general, the more alarm attributes that are defined and included in the alarm tag, the more productive that alarm sorting and alarm management will be.