1. A process variable transmitter, comprising: A sensor sensing a process variable and providing a sensor value indicative of the sensed process variable; a memory storing a filtered sensor value that is calculated based on a prior received sensor value, and a filtered rate of change value that is calculated based on a prior rate of change value; and a controller receiving the sensor value, from the sensor that senses the process variable, and comparing the sensor value to the filtered sensor value to obtain a rate of change value, the controller further comparing the rate of change value to the filtered rate of change value to obtain a deviation value, and generating an output indication based on the deviation value.