Maximum value

I'm using RSLogix 500 Rev 4.50.00

Does anyone know how to capture a maximum value from an analog input over a specified time frame?

Thanks.

From the Silver Platter Department

Sounds like you will need a timer, a Compare, and two move instructions. Throw in a couble of timer bits and a bool and your done.
Here is the code....

XIO B3:0/0 TON T4:0 1.0 10 0
XIC T4:0/TT GRT I:1.0 N7:0 MOV I:1.0 N7:0
XIC T4:0/DN OTE B3:0/0
XIC B3:0/0 MOV N7:0 N7:1

This will work, you'll have to change the addressing to your real world but there you go. Of course you may need to add another timer if you want a delay between measurements.

Quick answer off the top of my head is:

Have a timer for the period of time desired, or depending on which PLC your using, trigger the start/stop with the real time clock.

Lets say N17:0 will hold the max value and I:3.1 is the input.
Then while the timer is timing, or event triggered:
Compare I:3.1 to N17:0,
if I:3.1 is greater than N17:0,
move I:3.1 to N17:0.


When the timer times out you will have the max input value, over the time period stored in N17:0.


Ken


Bitmore beat me to it, but we both have the same basic solution. If your PLC has a real time clock, you could also capture the time at the highest value.

OK, so you've had 2 great examples. An added thought is, are you going to do more testing in another time period? If so and if you want a new maximum just for this next time period then you must set the target (N7:0 in the first example, N7:17 in the second) to zero (CLR N7:XX).

Yep Bernie is right, I forgot to add the function to clear the initial value in N7:0. Good catch Bernie!

Bitmore