drbitboy
Lifetime Supporting Member
@GrizzlyC is there any mixing in the tank? Is the fluid around the upper termperature sensor able to mix, by forced convection, or natural convection, or by conduction, with the fluid around the lower temperature sensor? From the last plots it is apparent there are two measurement and control systems involved, and there is also almost certainly cross-talk, in both the process and the control responses. It is also likely that the calibration between the temperature sensors differs. So the only way to keep both measured temperatures (PVs) at the same setpoint would to be to have one fluid section's physical (not measured) temperature be warmer than the second*, while continually removing extra heat from the cooler second fluid setion to balance the heat flow at steady state.
* although the PVs would read the same value
Are these actual measured valve positions, or are they the post-processed (rounded, clamped) PID output CV signals sent to the valves?
Do you have plots of the data when P was 35 and I was 60?
Your location says Alberta, CA. Is this process affected by, or open to, or insulated from, outdoor diurnal (or varying indoor) external temperatures? What do the temperatures outside the tanks look like througout a typical day?
* although the PVs would read the same value
Are these actual measured valve positions, or are they the post-processed (rounded, clamped) PID output CV signals sent to the valves?
Do you have plots of the data when P was 35 and I was 60?
Your location says Alberta, CA. Is this process affected by, or open to, or insulated from, outdoor diurnal (or varying indoor) external temperatures? What do the temperatures outside the tanks look like througout a typical day?
Could you please double-check that the PIDs are configured to use the Dependent model? Although if it was Independent with the quoted I values as Ki, then then the process would be swinging wildly.It seems that the higher the I the more reactive the CV
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