The weight average bed temperature (WABT) is typically used to compare the relative activity of the catalyst. The actual WABT should be calculated base on the actual catalyst bed weights and the actual bed temp.
The rate of increase in WABT is referred to as the deactivation rate expressed as °C per m3 of feed per kilogram of catalyst, or more simply as °C per day.
It is usually monitored through thermocouples installed in bed at different locations e.g located across the reactor diameter, at the top of the catalyst bed, and at periodic levels down the bed.
It is measured by the sum of the average reactor temperatures and multiplied by the fraction of catalyst in reactor.