PTC, PT100, PT1000 or whichever type is supported by ATV process or by option card, is additional thermal protection (from the thermal sensor). The existence of thermal sensor does not automatically disable thermal protection provided by the drive that is based on the I2t calculation of the motor current
If both I2t and thermal sensor are enabled and configured, then drive trips whichever of these two protections is triggered first. Whether drive trips on I2t or due to thermal sensor, the different fault messages will be shown on HMI and different error codes in the communication register
Protection I2t trips when the motor thermal state reaches 118%. Reset is possible when a motor thermal state falls below 100%, see the page attached from the programming manual
Parameter ttd [Motor thermal Thd] is a configurable parameter but is related to warning only. A warning means that HMI will display an exclamation mark (possible to assign relay output to warn), but no fault is shown and the motor will continue running. As soon motor's thermal state exceeds 118% drive will go to a fault. Value 118% is a fixed value for trip level and cannot be changed.

If thermal protection by I2t is not required, it can be disabled by setting tHt=No or by setting Ith to max value. See details in the attached file.

Analog reading of PTC is not possible from its principle. PTC has strongly non-linear dependance on temperature, therefore it is not possible to convert resistance of PTC into temperature. For more information search for general information on web regarding PTC sensor characteristics.

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