PLC and PID algorithm
- Thread starter smsebnaa
- Start date
my project is greenhouse control, so i have 3 inputs ( temperature, humidity and CO2) and 4 outputs (cool fan, heater, fogger, vent). if temperature changed, humidity and CO2 are changing, and if humidity changed, temperature and CO2 are changing , ....
Last edited:
So what is your question?
Temperature is controlled by either cool fan (frequency controlled?) or heater (thyristor controlled, step controlled or on/off?)
Humidity is controlled by fogger (frequency controller or on/off?)
CO2 is controller by vent (frequency controller or on/off?)
You ask if you can do this? Sure, why the hell not?
You mention PID, so I assume you have four continuous controllers?
Are you asking how to do this, or...
Temperature is controlled by either cool fan (frequency controlled?) or heater (thyristor controlled, step controlled or on/off?)
Humidity is controlled by fogger (frequency controller or on/off?)
CO2 is controller by vent (frequency controller or on/off?)
You ask if you can do this? Sure, why the hell not?
You mention PID, so I assume you have four continuous controllers?
Are you asking how to do this, or...
temperature is controlled by heater , cool fan and vent. humidity is controlled by vent and fogger. CO2 is controlled by vent.
every outputs are on/off, you said i should use 4 pids, but there is dependent between parameters.
how to do this project?
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i used hysteresis but i want to change it to PID, because hysteresis is not complete control for multi variable.
Tom Jenkins
Lifetime Supporting Member
Regardless of whether or not you use PID, you will need several strategies. For example, if humidity is high but temperature is low you won't need the fogger. If humidity is low but temperature is low you want heat plus fogger and so on. Some of the items, such as the fogger, may work as well with just a deadband controller as with PID. If CO2 is high and temperature is low you may need to vent and heat. Etc.
there is not any expert fuzzy algorithm for s7-1200 ?
Yes Siemens does have a fuzzy library, however it is expensive, and that is probably the biggest problem.
However you can make your own limited, as the process is rather simple.
Like tom says you will need to see what needs to happen.
with 3 inputs you are having 9 possibilities.
low, correct, high for all three.
so make an array of it.
put in each block what needs to be done, like heater+vent-cooler etc.
Now for the fuzzy part :
if templow and CO2= high then heater=slow, vent=slow
if templowlow and CO2=high then heater=high, vent = off
etc.
find memberships and you will get the outputs from it.
It is a different approach, however i think, when you do a nice job on this you will receive a 90% score.
However you can make your own limited, as the process is rather simple.
Like tom says you will need to see what needs to happen.
with 3 inputs you are having 9 possibilities.
low, correct, high for all three.
so make an array of it.
put in each block what needs to be done, like heater+vent-cooler etc.
Now for the fuzzy part :
if templow and CO2= high then heater=slow, vent=slow
if templowlow and CO2=high then heater=high, vent = off
etc.
find memberships and you will get the outputs from it.
It is a different approach, however i think, when you do a nice job on this you will receive a 90% score.
any outputs are on/off. if I have 4 heaters, 12 fans, 1 fogger and 1 vent, that process (you said;"if templow and CO2= high then heater=slow, vent=slow
if templowlow and CO2=high then heater=high, vent = off") is long and may be PLC is warming?
If the outputs are on/off you can do a timed on/timed off to get a 60% on time for example.
for heaters you can set the time to 1 second, for the fogger to 10 minutes, for vent also 10 minutes.
when you read this in fuzzy a analog value is the result.
why would the plc warm?
for heaters you can set the time to 1 second, for the fogger to 10 minutes, for vent also 10 minutes.
when you read this in fuzzy a analog value is the result.
why would the plc warm?
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