Dear all,
I've performed some isothermal experiments using TGA under different conditions. When running the the experiments for 40, 50 and 60 degree centigrade, the results are quite logical, but when using 70 degree centigrade, an overshooting is observed which takes quite long, almost half of total drying time. what can be the reason!? and how I can solve it? As I cannot change the set up of the experiments, how I can manage it?
Thank you in advance.
Elham
Did you apply a temperature ramp to reach the plateau temperature ? If not, you could add a a reasonable ramp (e.g. 5°/min) from RT to the final temperature to your temperature program.
You may consider to implement one or more of the following suggested actions: (i) reduce the initial heating rate ― before the isothermal step ― to some feasible value; (ii) decrease room temperature (possibly by using air conditioning system); (iii) keep some adequate furnace cooling system active to facilitate temperature control (e.g. fan); (iv) increase the purge gas flow rate (yet not excessively); (v) revise PID control parameters in order to reduce or avoid the noticed temperature overshoot. It may help to check the temperature versus time plot.
Most modern balances have tunable PID parameters, which change according to the temperature range where it is controlling.
I recommend you to check the PID parameters and see if this is happening in your case.
If this does not solve the problem, you can edit the parameters by yourself (for example, decreasing them by 30% and try again).
Dear Carlos,
Thank you for your help, but I think I need to run experiments with the same conditions but temperature and relative humidity which I am going to investigate so as to have the comparable results.
It seems the best solution is revising PID control parameters.
all the best
Dear Juliette,
At first I ran the experiments using ramp 40/min and I had overshooting. So, to solve the problem I am performing now by 5/min but the problem is still available.
Thank you a lot.
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