dbh6
Lifetime Supporting Member
Hello All,
I am currently updating an existing vessel that has 6 valves for a customer. I'm new to plc's but picking it up pretty well.
I trying to understand what is going in this routine such that, the routine is primarily used for heating and cooling. I went over the program but due to my lack in experience, was not able to fit it together. Here is what i understood so far, in the Main routine on rung 1, every 6 seconds we compare the old temperature value to the new, to calculate the rate at which the temperature changes every 6 seconds (0.1 min). Also we calculate the average change in temperature. Now when calculating the average change in temperature, i would have took the (final temp - intial temp)/(time = 6secs), but i don't know how the program calculated the average change in temperature over the past 6 seconds, and how it calculated the average change in temperature over the past minute. Then their are routines for both heating and cooling labeled rtn_Cool, rtn_heat. I understand what is going on from rungs 0 to 7 in those heating and cooling routines but the rungs that follow is where i start to get lost. I understand how PID's work but how the program uses 2 PID's thats what i need clarification on. Maybe use one PID to control when the heating and cooling is on and the other to control how often they are on ????? If anyone can try and explain roughly what happens in these routines labeled Main routine, rtn_Cool amd rtn_Heat, i would appreciate it. I just want to understand it correctly. Programming software is RSlogix 5000. I have attached the program. Thanks in advance.
I am currently updating an existing vessel that has 6 valves for a customer. I'm new to plc's but picking it up pretty well.
I trying to understand what is going in this routine such that, the routine is primarily used for heating and cooling. I went over the program but due to my lack in experience, was not able to fit it together. Here is what i understood so far, in the Main routine on rung 1, every 6 seconds we compare the old temperature value to the new, to calculate the rate at which the temperature changes every 6 seconds (0.1 min). Also we calculate the average change in temperature. Now when calculating the average change in temperature, i would have took the (final temp - intial temp)/(time = 6secs), but i don't know how the program calculated the average change in temperature over the past 6 seconds, and how it calculated the average change in temperature over the past minute. Then their are routines for both heating and cooling labeled rtn_Cool, rtn_heat. I understand what is going on from rungs 0 to 7 in those heating and cooling routines but the rungs that follow is where i start to get lost. I understand how PID's work but how the program uses 2 PID's thats what i need clarification on. Maybe use one PID to control when the heating and cooling is on and the other to control how often they are on ????? If anyone can try and explain roughly what happens in these routines labeled Main routine, rtn_Cool amd rtn_Heat, i would appreciate it. I just want to understand it correctly. Programming software is RSlogix 5000. I have attached the program. Thanks in advance.