Keeping track of machine utilization

Hey guys,

I am trying to calculate my machine utilization time for each shift. Currently what I do is, at the start of the 8 hour shift, I start a timer/counter combination to count for 8 hours. This is my total available time the machine is available to run.

I then keep track of how long the machine has been running using more timers/counters. So after 1 hr, if the machine has only ran for 30 mins, its utilization will be 50%.

It works great except for one problem. What happens when the power gets turned off? My total available time will not be accurate. I could lose an hour, 4 hrs etc.

Does anyone have any tricks/suggestions for solving this, without powering the PLC up all the time? Is there a way to calculate the available time a different way, by comparing it to the PLCs clock? The answer is alluding me at the moment. I know the % wont be reported with the power off, but an accurate number when I power back up would be great.

Thanks,

Yes, you are dealing with a tricky situation when trying to do this only utilizing machine power. I believe you will find most OEE monitoring systems live external to the machines they are monitoring and tend to be powered all the time.

As you suggest, doing your comparisons to the PLC clock is a viable technique. That's the way I would go.

Steve

mutabi said:

What happens when the power gets turned off? My total available time will not be accurate. I could lose an hour, 4 hrs etc.

Click to expand...

Why not just use a timer with a retentive accumulator? You didn't mention your platform, but if it was Allen-Bradley you'd use RTO. If power was lost, both timers would stop but retain their memory. At power-up your calculation would be accurate and the timers would continue from where they left off.

EDIT: After rereading your post I think I misunderstood. You essentially need the "total time" timer to keep running with the power off while the "run time" timer is stopped? If that's the case, you'll have to go with Steve's suggestion. Real-time clock is the only way to go.

I always base my timing on things like this on a real time clock (if it is supported). You can use first scan to time stamp when the PLC is booted back up. You can create a "Last" scan just by updating a time stamp buffer every scan. When you see first scan you know that the value in the buffer was the clock at the time the PLC went down.