PST’s Advanced Ceramic Metal-Oxide Moisture Sensor technology allows for measurements of dew-point, moisture content and trace moisture in both gases and liquids. From extremely dry parts-per-billion measurements (-120 °Cfp) to high-humidity conditions with dew-points up to +20 °C, our sensors are designed to reliably measure moisture in a wide range of applications. The versatile sensor is a cost-effective solution for industrial dewpoint applications.
The ceramic substrate and inert protective layer provide excellent chemical resistance to a broad range of substances found in industrial and process applications. The robust design of the sensor allows operation at pressures up to 450bar with immunity to pressure shocks, and is temperature compensated across a wide operating range.
The sensor is produced using advanced thin film and thick film deposition techniques. Its operation depends on the dielectric property of water molecules adsorbing onto a hygroscopic monolayer, sandwiched between two layers of conductive metal, therefore changing the capacitance between the two metal layers.
PST’s latest development in Quartz Crystal Microbalance technology is designed for fast and highly accurate measurement of trace level moisture content across a range of 0.1 to 2000ppmV. Combined with an internal moisture generator with a traceable calibration, the system will self-verify and adjust to ensure consistently accurate measurements of trace moisture in both laboratory and industrial applications.
Moisture measurement is achieved by monitoring the frequency modulation of a hygroscopic-coated quartz crystal with specific sensitivity to water vapor. Bulk adsorption of water vapor onto the coated crystal causes an increase in effective mass, which reduces the resonant frequency of the crystal, in direct proportion to the water vapor pressure. This sorption process is fully reversible with no long-term drift effect, giving a highly reliable and repeatable measurement.
Self-Calibrating Trace Moisture Analyzer - Michell QMA401
The latest Process Sensing Technologies thick-film polymer moisture sensor allows fast, stable and repeatable measurements all the way from dew point applications at -60 °Cdp, to relative humidity at temperatures up to 200 °C.
The novel thick film design functions as a parallel plate capacitor with a polymer hygroscopic layer that acts as the dielectric sandwiched between two conductive plates. The porous plates allow water molecules to move freely into the polymer layer from the surrounding environment.
This construction allows the sensor to reach equilibrium with a sample gas extremely quickly and with excellent repeatability.
PST’s TDLAS technology employs the latest techniques in laser absorption spectroscopy and signal processing to offer moisture measurements in natural gas with a lower detection limit (LDL) 1 ppmV or better. The wavelengths used by the analyser are specific to water molecules. The water molecules absorb the near infrared energy, therefore attenuating the level of reflected light measured by the photodetector. By application of the Beer-Lambert law this absorption is used to precisely determine the moisture content.
The maintenance-free, simple dual pass cell offers reliable measurement results throughout its range. It combines sensitivity and robustness without the upper range limit which could make the analyzer likely to saturate quickly at higher moisture levels.
By utilising the innovative ‘D-MET’ dynamic background gas compensation system, the moisture measurement is independent of changes in the methane level. No further manual correction factors are required. Measurement response times are very fast and the non-contact measurement is resistant to contamination.
The continuous laser optimization system ensures that the laser remains locked to the correct water absorption peak for the highest measurement integrity at all times. This avoids any to reduction in sensitivity and drift in measured readings normally associated with the possible drift inherent to tuneable diode lasers.
Portable Dew-Point Tester – Michell CDP301
PST’s chilled mirror hygrometers are precision instruments for critical measurement and control applications. Chilled mirror sensors measure a primary characteristic of moisture - the temperature at which condensation forms on a surface. This is considered a fundamental measurement and is therefore the standard technique for high level references in metrological institutes worldwide.
Our chilled mirror expertise is rooted in history. We developed the first “transfer standard” chilled mirror hygrometer used in the UK national standards laboratory, the National Physical Laboratory in London. We rely on our time-tested chilled mirror references instruments in our own UKAS-accredited calibration laboratory, which was the first laboratory in the UK to receive accreditation for dew-point and humidity calibrations.
The PST chilled mirror sensor functions by focussing a beam of light from an LED on the mirror surface with a fixed intensity. As the mirror is cooled and condensation forms, less light is reflected due to the scattering effect of the condensate. The levels of reflected and scattered light are measured by two photo-detectors and compared against a third reference detector measuring the intensity of light from the LED.
The signals from this optical system are used to precisely control the drive to a solid-state thermoelectric cooler (TEC), which heats or cools the mirror surface. The mirror surface is then controlled in an equilibrium state whereby evaporation and condensation are occurring at the same rate. In this condition the temperature of the mirror, measured by a platinum resistance thermometer, is equal to the dew-point temperature of the gas.
The latest innovations in this technology have been made by PST to develop the fastest responding chilled mirrors in the market, capable of highly accurate and stable measurement of dewpoint across a wide range from -100 °Cfp to +120 °Cdp.