Abstract: There is provided a frequency analysis system, comprising: an analog to digital converter having a sampling frequency fs; a first band pass filter and a second band pass filter, the first band pass filter and the second band pass filter being arranged in parallel with one another; and a feedback loop from an output to an input of the system, wherein the system has an initial center frequency equal to a nominal frequency f0, and a revised center frequency dependent upon the output of the system that is fed back into the input of the system, wherein the transfer functions of the first and second band pass filters have the same poles, and wherein the system is configured such that, when the center frequency fc equals the frequency of the signal fi, the output of the first band pass filter is in phase with the input, the output of the second band pass filter lags the output of the first band pass filter at a constant phase of ? 2 , and the two band pass titers have equal gain amplitude.

Abstract: An apparatus for measuring a condensable component of a gas sample, such as a hydrocarbon gas sample, includes a slightly roughened measurement surface for exposure to the gas sample. An electronic cooling device cools the measurement surface to cause at least some of the gas sample to condense on the measurement surface. A light source is arranged to transmit light to the measurement surface and the presence of condensate when formed thereon is detected by a change in light intensity detected by a light detector. The apparatus initiates a sequence of cooling cycles for generating an optimal cooling profile such that the rate of cooling of the measurement surface decreases near the dew point temperature of the gas sample for accurate dew point measurement.