Key advantages

A Hilase instrument offers wide measurement concentration range, fast response time, excellent selectivity, ruggedness and long term fully automatic operation with minimal operational costs. The expected operational lifetime of a Hilase instrument exceeds ten years! Operational costs are minimal.

Hilase instruments

A typical Hilase instrument contains one or two telecommunication type diode laser (with the exception of the MuWaPas instrument, which is based on a Nd:YAG laser and on its wavelength converted harmonics), a high sensitivity detection cell or cells and a fully programmable DSP based electronics for complete system control, concentration calculation, data storage and transfer by using various communication possibilities such as 4-20 mA, RS232, RS485/422. Various communication protocols can be used such as Modbus RTU etc.

The photoacoustic principle

The photoacoustic effect is based on the absorption of modulated laser light in a photoacoustic cell, which creates an acoustic wave at the modulation frequency when the laser is tuned to an absorption line of at least one of the gas components. This photoacoustic signal generation happens through a periodic non-radiative relaxation of the molecular excitation resulting in a periodic heating of the irradiated gas volume, followed by a periodic thermally induced expansion and contraction of the gas volume, i.e. sound generation. The amplitude of the acoustic wave, which is sampled with a sensitive microphone, is proportional to the concentration of the absorbing component(s).

Diode laser based photoacoustic gas detection offers a combination of advantages with its simple construction and automatic operation, minimum detectable concentration in the low-ppm or even sub-ppm range (depending on the measured analyte), linear response over more than four orders of magnitude, high selectivity (i.e. insensitivity to the presence of other components), response time below one minute and accuracy in the few percentage range. Besides, our photoacoustic systems have high reliability in critical applications and they have to be calibrated only on a yearly (or even less frequent) time basis, due to the inherent stability of the system's components as well as the operation of the numerous in-built self testing and correction procedures.