Trial burns are very complicated procedures from both technological and personnel points of view, and “stuff happens.” For example, power may be lost unexpectedly for any one of a number of reasons. With mass flow meters all data is automatically saved to disk every fifteen seconds, so the spiking data can be reproduced accurately at any subsequent time. With scales, the exact moment of loss of power may be unknown, so the amount of material spiked may be subject to significant error.
As noted earlier, most trial burns are conducted outside, so inclement weather (rain, hail, high winds) may make the scales difficult to read accurately. Mass flow meters are unaffected by weather.
Incinerator problems occur during almost every trial burn, and mass flow meters are vastly superior to scales both in alerting the operator to potential problems and in maintaining flow rates. When the back pressure from the incinerator either increases or decreases, the mass flow meters compensate quickly and automatically, while the scale metering pumps do not. Thus if the pressure in the waste feed line drops (as during a waste feed cutoff), the mass flow meters maintain flow rates, and the operator always knows how much spiking material went into the incinerator. On the other hand, using scales, when the back pressure drops, the spiking rate increases, and the operator does not know this until he takes another weight reading, or until he is informed by the kiln operator that he is off-line. And then, for accuracy, he needs to try to recreate his spiking rates without data, since his data points are wide apart.
