Luminescent Pressure Sensor prodused by OPTROD Ltd. is a luminescent multi-component paint sensitive to air pressure. It is applied both to the model surface to be tested and to a sample plate for calibration means and consists of three layers:

• Screen Layer to create an optical uniformity of the model surface and to increaselight reflection;
• Adhesive Layers to ensure an adherence of the Active Layer to the Screen Layer;
• Active Layer that is sensitive to air pressure.

LPS being applied to the model surface are to be illuminated by excitation light (300?345nm). The intensity of light emitted by LPS is inversely proportional to the partial pressure of oxygen, i.e. to the air pressure, and is directly proportional to excitation light intensity and to the Active Layer thickness. To exclude the influence of excitation light intensity and coating thickness to the measurement accuracy the ratio of reference image at known (wind-off) condition and operating image at unknown (wind-on) condition must be taken.

Active Layer of Luminescent Pressure Sensor is the main element of LPS and basically consist of polymer binder containing luminophore molecules. LPS L4 and LPS F2 contain only active — pressure sensitive — luminophore, while Binary Luminescent Pressure Sensor LPS B1 contains active and reference luminophores mixed together. Active and reference luminophores are excited by the same excitation light and emit luminescence of essentially different spectral range that makes it possible to separate them easily with optical glass filters. Binary Luminescent Pressure Sensor allows to correct excitation light intensity variation in each point of the model surface.

Unicomponent LPS-paint kits contain Luminescent Reference Paint (LRP). LRP is a paint containing luminophore molecules, whose luminescence is independent on pressure and temperature and is directly proportional to excitation light intensity. LRP is applied to the model surface in any selected spot and is used to correct a difference of excitation light intensity at wind-off and wind-on conditions (fluctuations of excitation light intensity, model displacement, dust covering, fog in the flow, etc.).

LPS is available in two modifications — LPS-paint and LPS-tape. LPS-paint is applied to a model by a sprayer like an ordinary paint, while LPS-tape is attached to the model surface like an ordinary adhesive tape. Application of LPS-paint to the model surface needs two days, while application of LPS-tape needs few minutes. However LPS-paint allows to cover models of complicated shape, while LPS-tape may be applied only to a flat surface. The total thickness of LPS-paint is 40?80 micrometers and the total thickness of LPS-tape is 80-100 micrometers.

Different types of LPS are the most suitable for the next applications:

• LPS B1 — Binary pressure sensitive paint for pressure measurement in transonic and supersonic wind tunnels and flight tests, steady flow.
• LPS B1T — Binary pressure sensitive tape for pressure measurement in transonic and supersonic wind tunnels, steady flow.
• LPS L4 — Pressure sensitive paint for pressure measurement in transonic and supersonic wind tunnels, flight tests and on propellers, steady flow.
• LPS L4T — Pressure sensitive tape for pressure measurement in transonic and supersonic wind tunnels, steady flow.
• LPS F2 — Pressure sensitive paint for pressure measurement in shock wind tunnels,helicopter rotor blades, aeroballistic ranges and unsteady transonic and supersonic flows.
• LPS F2T — Pressure sensitive tape for pressure measurement in shock wind tunnels and unsteady transonic and supersonic flows.

Technical data

Type	Pmax [bar]	Sensit.a) [%/bar]	Temp. range [oC]	Temp.b) coeff. [%/oC]	Resp.c) time [sec]	Efficiencyd) [%]	Emission range [nm]
LPS B1/B1T	5	70	-20-60	0.35	0.5	10	425-550 reference: 610-640
LPS L4/L4T	5	70	-20-60	0.35	0.5	10	425-550
LPS F2/F2T	10	55	0-100	0.2	0.005	6	425-550

• Luminescence intensity of LPS and PSP I is approximately inversely proportional to the pressure p. Sensitivity=-[(dI/dp)/I]*100%, p=1 bar, T=20&degC.
• Temperature coefficient = [(dI/dT)/I]*100%, p=1 bar, T=20&degC.
• Response time corresponds to 99% relaxation of luminescence intensity after pressure change.
• Efficiency = Luminescence intensity / Excitation intensity*100%, p=1bar, T=20&degC.

Typical calibration characteristics of Luminescent Pressure Sensors at T=20&degC.

Typical temperature dependencies of Luminescent Pressure Sensors at p=1bar.

Emission spectra of Luminescent Pressure Sensors.

Excitation spectra of Luminescent Pressure Sensors.