precise and adds to the cost and mechanical complexity of the system. The labor for frequent replacement of desiccant dryers, permeation components, and sensor heads greatly increases the operational costs. Additionally, slugs of water render the system non-functional for the long periods of time as the sensor head has to “dry-down.” Aluminum oxide and silicon oxide The oxide sensor is made up of an inert substrate material and two dielectric layers, one of which is sensitive to humidity. The moisture molecules pass through the pores on the surface and cause a change to the physical property of the layer beneath it. An aluminum oxide sensor has two metal layers that form the electrodes of a capacitor. The number of water molecules adsorbed will cause a change in the dielectric constant of the sensor. The sensor impedance correlates to the water concentration. A silicon oxide sensor can be an optical device that changes its refractive index as water is absorbed into the sensitive layer or a different impedance type in which silicon replaces the aluminum. In the first type (optical) when light is reflected through the substrate, a wavelength shift can be detected on the output, which can be precisely correlated to the moisture concentration. A Fiber optic connector can be used to separate the sensor head and the electronics. This type of sensor is not extremely expensive and can be installed at pipeline pressure (in-situ). Water molecules do take time to enter and exit the pores, so some wet-up and dry down delays will be observed, especially after a slug. Contaminants and corrosives may damage and clog the pores, causing a “drift” in the calibration, but the sensor heads can be refurbished or replaced and will perform better in very clean gas streams. As with the piezoelectric and electrolytic sensors, the sensor is susceptible to interference from glycol and methanol, the calibration will drift as the sensor’s surface becomes inactive due to damage or blockage, so the calibration is reliable only at the beginning of the sensor’s life. In the second type (silicon oxide sensor), the device is often temperature controlled for improved stability and is considered being chemically more stable than aluminium oxide types and far faster responding due to the fact they hold less water in equilibrium at an elevated operating temperature. Whilst most absorption type devices can be installed at pipe line pressures (up to 130 Barg)