bernardcth
Member
Hi,
I'm trying to program a cascaded loop using PIDE to control the dewpoint of a room through a HVAC system. The problem i'm having is with the control action (E=PV-SP or E=SP-PV) at the slave loop.
The master loop is looking at the dew point at the production floor while the slave loop is looking at the supply duct's dew point.
The idea is to prevent the dew point in the production room from increasing beyond a setpoint (e.g. 3 degC)by modulating the heater bank's output (0-100% at the slave loop). No problem with the master loop. The problem is with my save loop as the range can deviate between -20 to +20 degC. So, any control action (E=PV-SP or E=SP-PV) at the slave loop that i chose to use gives me a one way ticket whenever the slave PV value falls into the negative value.
e.g. my CVEU (range -20 to 20) on the master loop is 15 degC due to the increasing dewpoint in the production floor. this is used as my setpoint in the slave loop. To increase my output, i should use E=SP-PV. This would eventually lower down my supply duct's dewpoint and eventually would lower down the dewpoint of my production floor. The slow reaction of the changes in dewpoint in the production floor thus causes the dewpoint in the supply duct to sometimes fall below 0 degC. So, if i use the said control action, my E would always get stuck in the positive region and i would have 100% out all the time even if my primary error had been resolved. The problem goes the other way round if i were to use the other control action.
i hope i am not too long winded and hope that my situation here had been clearly specified.
I'm trying to program a cascaded loop using PIDE to control the dewpoint of a room through a HVAC system. The problem i'm having is with the control action (E=PV-SP or E=SP-PV) at the slave loop.
The master loop is looking at the dew point at the production floor while the slave loop is looking at the supply duct's dew point.
The idea is to prevent the dew point in the production room from increasing beyond a setpoint (e.g. 3 degC)by modulating the heater bank's output (0-100% at the slave loop). No problem with the master loop. The problem is with my save loop as the range can deviate between -20 to +20 degC. So, any control action (E=PV-SP or E=SP-PV) at the slave loop that i chose to use gives me a one way ticket whenever the slave PV value falls into the negative value.
e.g. my CVEU (range -20 to 20) on the master loop is 15 degC due to the increasing dewpoint in the production floor. this is used as my setpoint in the slave loop. To increase my output, i should use E=SP-PV. This would eventually lower down my supply duct's dewpoint and eventually would lower down the dewpoint of my production floor. The slow reaction of the changes in dewpoint in the production floor thus causes the dewpoint in the supply duct to sometimes fall below 0 degC. So, if i use the said control action, my E would always get stuck in the positive region and i would have 100% out all the time even if my primary error had been resolved. The problem goes the other way round if i were to use the other control action.
i hope i am not too long winded and hope that my situation here had been clearly specified.
