monitoring and compare problem

Folks,

A basic beginner with a small problem but huge problem.

I need to monitor the 'run time' of 3 separate engines, then compare and shut down the engine with the highest 'run time'.

I have completed some small basic programs using rto timers but cant understand how i will be able to compare 3 values as i believe most basic plcs only use a compare with 2 inputs.

any basic tips to help out?

Its my first attempt at this, started off with an allen bradley micrologix500 but as i only have 8-10 inputs a friend is pushing me towards the telemechanque zelio 'smart relay' application.

you need do this with separate compare inscructions. First compare runtimes of pumps 1. and 2.
If pump 1. have bigger time, then put bit1 on And if pump 2. have bigger time, then put bit2 on.


After that compare pumps 2. and 3. and use also these bits

if bit1 is on and compare time1>time3 is true => pump1 have biggest time
if bit1 is on and compare time1<time3 is true => pump3 have biggest time

if bit2 is on and compare time2>time3 is true => pump2 have biggest time
if bit2 is on and compare time2<time3 is true => pump3 have biggest time

Lare many thanks, would you use a RTO timer to monitor pump/engine times

It depends of it what is maximum time what RTO timer can count on PLC (support) and also of application (how long timer is needed)

On some PLC's timer uses one memory word for timing (32767 or 65535 is maximum delay for seconds, minutes, hours)

If RTO gives enought long time, then there is no need to use different inscructions.

On PLC code you also maybe need to care of situation, if runtimes are same on all pumps for some reason.

If you are intending to "balance" the run-hours of these 3 engines, perhaps you should read mine (and others) comments in the following threads...

http://www.plctalk.net/qanda/showthread.php?t=67719

http://www.plctalk.net/qanda/showthread.php?t=65837

Balancing the run-times is often the "wrong" thing to do, since scheduled (and unscheduled) maintenance would occur at roughly the same time.

I would certainly use RTO timers, but I would most likely use the timers to time for 1-hour (3600 seconds), and use counters to count the "hours run". Even if your counter is limited to 32,767 counts, that equates to just over 1365 days, or well over 3 years.

Thanks people need to have a good think on this as this is just one part of my project, but thanks again, will keep you posted