Micrologix 1500 used to calculate tak time?

[rkeller]

I am new to the PLC programming world and even newer to this site. I am working on an application using a Micrologix 1500 to control the flow between station on a production line. I was hoping to be able to use internal timers to calculate the average process time (TAK time) at each station. It is turning out to be more difficult than I expected. Am I even able to accomplish this with this PLC alone or will I need other external components to help me out. Anything that will help point me in the right direction would be appreciated.

 

[kamenges]

What do you expect the average process time at each station to be? 10msec, 1sec, 100sec, etc? Getting any resolution on a 10msec process time will be nearly impossible. 100sec process time will be substantially easier?

Why is it more difficult than you expected? What issues did you run into when you tried to do this?

Any specifics you can give will help.

Keith

 

[rkeller]

I am guessing that each process will last for several minutes, probably around 4 min at this point. I was thinking that I could use an internal timer to measure the time it takes for each part moving through that station. I would then need to save that time, add it to the previous times, and then divide that by the number of parts that have been processed in order to get an avg tak for that station. I am just not sure how to acquire the data (times), move them to another location, and then perform the math to acheive an avg. tak time. I am using sensors to posion the part on the conveyor (start of the process) and a push button that the operator can use to signify the end of the process. I am trying to read up on data aquisition in the tutorial but was hoping for some more direct help in here.

 

[ndzied1]

There are a couple considerations when trying to get average cycle times. First, you have to decide how many cycles you want to average over. Let's say 10 for now but it can be anything.

The way that has made the most sense to me is to have a buffer for the cycle times and then another register to hold the sum of the cycle times.

The general idea is after each cycle,

1. Subtract the oldest time from the sum
2. Add the newest cycle time to the sum
3. Replace the oldest time in the buffer with the newest time
4. Calculate the Average by dividing the sum by the number of samples
   [/list=1]
   
   The next consideration is how you handle the buffer. You can use the FFL/FFU instructions or roll your own using indirect addressing.
   
   Then you need to decide what you do when the thing starts up. Do you stuff the buffer with the old average cycle time or just start from scratch. If starting from scratch, then you have to keep track of the number of cycles so far until the buffer is full.
   
   I'm sure I have an example some where if you're interested.