Electronic detecting apparatus for predicting the steady state value of a detector output

An electronic detecting apparatus is provided for detecting an output of an external device such as the light energy of a laser. The apparatus comprises a detector 1, such as a Peltier-Seebeck detector, operative to generate a detector output voltage 3 which rises substantially exponentially until a steady-state is reached. The detecting apparatus comprises electronic circuitry to predict the future steady state value of the detected variable such as the power of the light emitting device. A differentiator sub-circuit 21 generates a processed signal 33 proportional to the rate of change of the detected variable. An addition/subtraction sub-circuit 9 combines the detector output 3 (after amplification by pre-amplifier 5) and the processed signal 33 to provide the predicted signal. A signal compensation sub-circuit may be provided to generate a compensation signal to adjust the output signal to compensate for errors in the detector output. The apparatus speeds up the time taken for the steady state value of the variable to be determined.