analog help

I have a flow meter that I set up on a machine. I have the analog signal coming into the plc and all is well.. My problem is tring to catch the value before it drops off. I have 2 lube signals coming into the processor. i latch both the signals and then i have it so when the inputs drop out the rung goes true. Then i believed I would have the analog signal at the point right after the flow meter stopped. Doesn't seem to be catching it at the right time.. any ideas?

Can you post your current code? Might be something simple, hard to judge with the limited amount of info provided.

Are you trying to catch the peak value?
What do you mean by

i have it so when the inputs drop out the rung goes true

Click to expand...

?

I am trying to catch the highest analog signal before it drops out.. The analog signal is not held, so when my meter counts it will go to the value i want to look at and then start dropping. I have it set so when my two lube signals come on they latch in. Then when those signals go out I use a ONS to look at my analog signal. But I keep getting different counts.. Should I use a STI for this program? I will post the code if I can have someone tell me how to do it on rslogix5 Thanks...

poisonfrog said:

I will post the code if I can have someone tell me how to do it on rslogix5 Thanks...

Click to expand...

Put the .rspfile into a .zip file and post it.

poisonfrog said:

I am trying to catch the highest analog signal before it drops out.. The analog signal is not held, so when my meter counts it will go to the value i want to look at and then start dropping. I have it set so when my two lube signals come on they latch in. Then when those signals go out I use a ONS to look at my analog signal.

Click to expand...

that should be pretty easy, of course there a hundred things that we don't know about your application...

Try giving us some more details!

poisonfrog said:

Should I use a STI for this program?

Click to expand...

I really doubt that you need a critically repeatable scan time. Why did you think you need an STI?

Ok, I have my file now. I hit browse at the bottom and selected the zip file. Every machine cycle a die needs to be sprayed. What I am trying to do is to get the machine to fault out if the lube meter goes too low or high. I use a histogram and see the values come in and they look good. It seems that I get different values, and I wasn't sure if scan time was messing with this or not...thanks

How do I put the actual picture of my ladder logic in? Thanks again

"I am trying to catch the highest analog signal before it drops out.."

Don't you mean "the last analog signal"?

If so, then while the flowmeter is running, grab and save the analog signal on every scan!

Then, when your rung goes true, use the last value you saved.

If, on the otherhand, your description is a little off and you really are looking for "the greatest value" of a fluctuating signal, then grab the value on every scan, however, before saving the value, compare it to your last saved value. If the new value is greater than the previously saved value then over-write the previously saved value with the new value.

Otherwise, do nothing with the current value and leave the previously saved value as is.

Are you watching both lube signals in parallel or series?

Could it be that one lube pump might be running a bit after the other turns off?

Are your lube signals auxillary contacts from the lube pump contactors or are they output signals to the contactors?

Your analog signal is more likely to be consistent if your lube signals are the output signals to the contactors.

I have the lube 1 and lube 2 outputs coming in as the inputs. I latch them in and have (in series) the rung go true when they turn off.. so 2 latches and 2 xio in series. I would like to post the code but haven't figured out how to do it other than the zip file. Yea i want the last analog signal.. Basically what I have set up is a less than and a greater than statement, with a bit as the trigger(the series statement above) and a ONS to send the analog signal through the greater than and less than statements. The analog signal floats at around 2 or 3 goes up to 20-21 and back down to 2 or 3. When it goes up, I'm spraying lube. I want to catch the maximum value from the point when I call for it to the time I stop calling...This i figured would have been handled by the statement above. If the flow is low I want a fault and if it goes above the high limit, I want a fault..It seems to be sometimes catching it and Most of the times not.. How can I catch this? Anyone who can help me with putting the ladder logic on the screen would be a help.... Thanks guys

I am going to try to get it to work by using the sample program above... Thanks!

I used the sample from above and it worked great.... Thanks for the help guys

You used my sample?

I posted that to show what I would do based on the very limited information we had so far.

For future reference....
If you want to post a "picture" of the program, like I did:

Either use a dedicated screenshot program or,

1) With the program open on your computer, press alt+print scrn or ctrl+print scrn.

2) Open MSPaint, and from the "Edit" menu, select paste.

3) MSPaint might ask if you want to resize the area so your image will fit; select yes.

4) Crop the image down so that just the part you want to post is there.

5) From the "File" menu select "Save As"

6) I usually do a .gif, seems to be the best quality for these types of screen shots.

7) Attach the file to you post the same way you attached the .zip file above.


Remember to save the image as something other than .bmp. A .bmp will not display in the post but will act as an attachment like the .zip file above.

Go to the "practice posting" area and try it out.

Yea, I made a couple changes but other then that it did exactly what I wanted.. I'll try a practice post of the ladder logic... Thanks again