Errors of Ash Content Analyzers in Monitoring and Control Applications

The main features of on-line ash monitors as measuring gauges have been discussed in the paper: accuracy of the indirect measuring method used, response time and general reliability as monitoring and control instrumentation. Errors of these measurement methods depend on the applied method itself, but mainly on measurement conditions such as: type of coal, size distribution of coal, chemical composition of ash, homogenisation of coal in a cross section of a coal stream, moisture content. It has been shown that errors of on-line radiometric ash measurements due to sample representativeness are negligible in comparison to such errors in conventional laboratory methods. The response time of a monitor depends on the average intensity of electric pulses at the output of the radiation detector, which usually is a scintillation counter. The longer the time of measurement, the lower the statistical error of determination of pulses mean intensity. At the same time, if the input signal varies, the dynamic error of the measurement is higher. This suggests that for a given input signal and a structure of the monitor circuit, one can find an optimal averaging time of input pulses, which gives the minimum dynamic error according to the accepted criteria