Correlated Interference Polarization Spectroscopy (”CIPS”) is a patented optical method for detection of ultra-low concentration of various gases, such as methane, ethane, ammonia and many others. The CIPS technology is the core of DP-IR, manufactured and sold by Heath Consultants Incorporated (“Heath”). The DP-IR instrument is used by 75% of U.S. utilities to detect methane leaks in the natural gas transmission and delivery infrastructure. Currently over 4,000 DP-IR instruments are operating in the field.
Heath DP-IR natural gas leak detector, based on the CIPS technology.
CIPS technology utilizes periodical structure of absorption spectra of simple molecules, see next figure.
Left, IR absorption spectra of simple molecules, methane and ammonia. Right, Fourier transform of the spectra showing principal harmonics, including one used for methane detection in the DP-IR device.
The traditional correlation spectroscopy approach requires a reference cell filled with the substance of interest. This is only practical in a laboratory environment. The BAH technology realizes the correlation spectroscope in a compact tunable controlled interference polarization filter (cIPF).
Schematic diagram of CIPS filter showing effect of the Photo-elastic actuator of the transmission function of the detector. Blue and red lines correspond to maximum and minimum of the acoustic wave amplitude.
An external generator applies periodic voltage to the PEM inducing a standing acoustic wave. The acoustic wave propagates into silica causing the rotation of the incoming light polarization with 60 KHz frequency, see the next figure. Thus the transmission of the device changes from full rejection of the methane lines (red line) to full acceptance (blue line) within the oscillation period. Presence of methane is detected by oscillation of the absorption signal, which is detected by the IR imaging matrix and converted to the plume image. A tunable etalon crystal (E) changes the transmission function period thus allowing for a full Fourier analysis of the spectrum.