Pump Time Cycle Control

I am extremely new to programming in ladder logic. Please help me understand how I should handle the algorithm below.

an automatic RAS/WAS time cycle control will be implemented with operator adjustable setpoints for run time per "on" cycle, and "off time" between starts.

Thank you in advance for your help.

I am extremely experienced at programming in ladder logic. Please help me understand the following:

an automatic RAS/WAS time cycle control will be implemented with operator adjustable setpoints for run time per "on" cycle, and "off time" between starts.

Thank you in advance for your help.

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What does RAS/WAS mean?

What kind of controls/"adjustable setpoints" will the operator have for on/off cycle:

1. Operator sets ON time duration and OFF time duration as seperate entried?
2. Operator sets RUN duration length, and ON (or OFF) duration (with error checking so that RUN > ON)?
3. Operator sets RUN duration length, and a percentage of the ON (or OFF) time?
4. Operator enters two numbers for the ratio of ON to OFF, and the PLC calculates the time based on a fixed RUN duration?
5. Something else?

Or do you mean something more like "on time between starts" and "off time between starts", where the gizmo must run for a minimum time, and rest for a minimum time, but doesn't have to be stopped/started when the times are done?

Tell us what you mean, and then maybe we can help.

First of all, thank you for your patience.

What does RAS/WAS mean?

RAS is a type of recycled water pump and WAS is a type of waste water pump.

What kind of controls/"adjustable setpoints" will the operator have for on/off cycle:

Module position C, Digital Control/Monitor Module, point 3 provides the capability for the operator to manually stop and start the pump. I have to create the ability for the operator to enter the setpoints for run time per "on" cycle, and "off time" between starts.

The trigger for turning on the pump should be the operator turning the pump on manually, however, the pump will run for a period of time (designated by the operator) and must rest for a period of time (designated by the operator) before the pump can be restarted. Very much like you stated below.

Or do you mean something more like "on time between starts" and "off time between starts", where the gizmo must run for a minimum time, and rest for a minimum time, but doesn't have to be stopped/started when the times are done?

I suggest you take a slightly different approach to make setpint entry easier for the opertors. Most RAS and WAS systems (that's Return Activated Sludge and Waste Activated Sludge for those of you on the other end of the food chain) have a flow meter. If that is the case in your facility I suggest you have the operators enter mgd or gpd to return and mgd or gpd to waste. They should also enter number of cycles per day. Then the PLC can start the pump on a schedule using a timer where the preset is = 24 hrs. divided by the number of cycles per day. Totalize the flow during the run cycle until you have pumped the gallons = to total gpd divided by the number of cycles. The pump runs until the total reaches the preset. You add another "spin timer" that inhibits pump starting until the pump has had time to coast to a stop.

If you don't have a flow meter you can instead enter the nominal flow rate of the pump and use a timer to approximate gallons pumped.

Don't forget to add a low level float switch to cut the pumps out if you run the wet well dry, (unless you are pulling right from the secondary clarifier), and a high level float switch to start the pump and prevent flooding by overriding the timers.

As a point of process performance, if you don't have an RAS wet well most operators prefer to pump RAS continuously at a lower rate to avoid ratholing in the secondary clarifier and maintain a constant MLSS (mixed liquor suspended solids.

most operators prefer to pump RAS continuously at a lower rate to avoid ratholing in the secondary clarifier and maintain a constant MLSS (mixed liquor suspended solids.

Click to expand...

Nice read during my morning tea and toast.