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Awilder1015 posted a topic in Allen BradleyI have an application that I'm having trouble figuring out. Basically, I want to make an automatic hot/cold water faucet for a beer brewing process. I will have 2 control valves, one for hot water, and one for cold water. The hot water supply will be at about 200F, and the cold water will be around 60F. Each will receive an analog command signal, 0-100%. There will also be a flow meter and a temperature sensor, and these will each generate an analog signal. There will be 2 different user-settable setpoints: Flow rate and Temperature. The temperature setpoint will always be between 140F and 180F, so a mix of both hot and cold water will always be required. Flow rate will be variable depending on the grains being used and the speed that grain is being added to the process. I'm imagining that there should probably be two PID loops, using two PIDE function blocks. One will take the Temperature Setpoint, the other will take the Flow rate setpoint. The temperature sensor's analog signal will be the process variable for the Temperature PIDE block, and the flow rate will be the process variable for the Flow rate PIDE block. This all seems fairly straight forward. The issue comes with deciding how the Control Variables should be set up. Since I have only one temperature PID loop, how can I use the one Control Variable to actuate both valves to hit the temperature setpoint? If I can figure out how one CV can control two valves, how can I use the CV from the flow rate PID loop to then adjust the valves to hit the flow rate setpoint when both valves are already receiving a signal from the temperature PID loop? It seems like the separate PID loops will be fighting each other. Is there some way around this problem? This might be a good candidate for a Cascaded PID loop, but I'm not sure because the two PID loops are going to be about the same speed. Thank you for your help!
174 downloadsThis logic demonstrates the construction and cascading of counters that count from 0 to 9. This logic also illustrates the construction of counters that count from 1 to 10 (not useful for cascading). The difference is mainly in the comparators used to reset the counters. There is one small additional detail. Can you find it?
View File FC3 Counter Demo This logic demonstrates the construction and cascading of counters that count from 0 to 9. This logic also illustrates the construction of counters that count from 1 to 10 (not useful for cascading). The difference is mainly in the comparators used to reset the counters. There is one small additional detail. Can you find it? Submitter pop29684 Submitted 03/24/16 Category PLC Sample Code