New To PLCs

[willf650 0]

I'm new to PLCs and am currently taking Instrumentation Tech. at a local comunity college. I've have never done anything with a PLC or ladder logic and have only physically seen them at a few plants. I wanted to mess around with one so I bought an Automation Direct Click PLC. I work on HVAC controls for work so I programed this thing in ladder logic to do a simple system I know. It's a simple hot water system with a lead/lag/fail pump routine. Could you guys take a peak and tell me if this is a route you would have taken for this program or what you would recomend instead. The system is enabled based upon a fall in outside air temperature below setpoint and disabled on a rise above setpoint plus a deadband. The lead pump is enabled and once flow has been established the boiler turns on. The auto pump rotation can be eanbled/disabled. The lead pump can be manually rotated via a modbus command or a physical switch. When the lead pump rotates the lag pump will not be turned off until the new lead pump is established to be running. When the system shuts down the boiler is disabled and the pumps will continue to run for a short time to pull residule heat out of the boiler. When either pump fails or a binary failure input from the boiler is active and alarm light is lit. Bear in mind my only ladder logic training is reading the instructions for this click PLC. The one thing I was not sure about was I set a couple of timers up to keep track of total pump run time but wasn't sure whether the timer registers default to milliseconds or automaticly scale themselves to what unit the timer is configured for. I have a math function converting the milliseconds to hours but it may not be needed. Here's a pdf of the ladder logic