We own and manufacture the sensing technology used in the majority of our products which enables us to innovate, bring new products to the market, and remain in a leadership position.
TDLAS: Tuneable diode laser spectroscopy
Tuneable Diode Laser Absorption Spectroscopy (TDLAS) products use the interaction between light and the molecules in a gas stream to determine the concentration of a given substance within that gas stream. In the case of Michell’s OptiPEAK TDL600, this is specifically water concentrations within a natural gas stream. The wavelengths used are specific to water molecules and therefore laser energy causes the water molecules to vibrate and absorb energy. This effect is used to calculate the concentration of water in a background gas.
Fast-Responding Capacitive Polymer Sensor for Relative Humidity
Capacitive polymer sensors provide high-accuracy, excellent long-term stability and negligible hysteresis. They are insensitive to contamination by particulate matter, are not permanently damaged by liquids and are resistant to most chemicals. A capacitive humidity sensor works like a plate capacitor. The lower electrode is deposited on a carrier substrate, often a ceramic material. A thin polymer hygroscopic layer acts as the dielectric, and on top of this is the upper plate, which acts as the second electrode, but which also allows water vapour to pass through it, into the polymer. The water vapour molecules enter or leave the hygroscopic polymer until the water vapour content is in equilibrium with the ambient air or gas. The dielectric strength of the polymer is proportional to the water vapour content. In turn the dielectric strength affects the capacitance, which is measured and processed to give a relative humidity measurement. By also measuring temperature a dew point or absolute humidity value can also be obtained.
Advanced ceramic dew-point sensors
The ceramic sensor is constructed using state-of-the-art thin and thick film techniques. Its operation depends on the adsorption of water vapor onto a porous non-conducting "sandwich" between two conductive layers built on top of a base ceramic substrate. The active sensor layer is very thin - less than one micron and the porous top conductor that allows transmission of water vapor into the sensor is even thinner. Therefore, the sensor responds very rapidly to changes in applied moisture, both when being dried (on process start-up) and when called into action if there is moisture ingress into a process.
Quartz crystal microbalance
The Quartz Crystal Microbalance (QCM) technology for moisture measurement is based on monitoring the frequency modulation of a hygroscopic-coated quartz crystal with specific sensitivity to water vapor. Bulk adsorption of water vapour 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.
Michell's chilled mirror dew-point hygrometers are precision instruments for critical measurement and control applications. A miniature polished stainless-steel mirror is cooled by a solid plate Peltier thermoelectric heat pump until it reaches the dew point of the gas under test. When this temperature has been reached, condensation forms on the mirror surface. An electro-optical loop detects that condensation is forming by a reduction in the intensity of light reflected from the mirror surface and through the control electronics of the cooled mirror instrument. This modulates the cooling power applied to the Peltier.
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 fundamental nature of this method means that chilled mirror instruments can be used as either extremely reliable and stable field instruments or as laboratory reference standards for the calibration of other devices.
Electrochemical galvanic sensors
Galvanic sensors generally consist of four elements: a membrane, electrolyte, a lead anode and a cathode. As oxygen comes into contact with the sensor it pushes through the membrane and reacts with the electrolyte, generating a current. Electrochemical sensors are cost-effective, small with low power requirements and they are also simple to use.
They can measure trace oxygen in the presence of hydrocarbons or in flammable gases such as hydrogen
The thermo-paramagnetic sensor uses a combination of paramagnetic and thermal conductivity techniques to accurately measure the oxygen content within a process gas. Oxygen is a paramagnetic gas, which means that it is attracted to a magnetic field. It is this property that can be exploited to help determine the level of oxygen in many background gases. The magnetic susceptibility of oxygen decreases inversely with its temperature. The thermo-paramagnetic analyzer uses a temperature-controlled measuring chamber to create a flow of the process gas (known as a ‘magnetic wind’) between a pair of thermistors. This ‘magnetic wind’ alters the equilibrium temperature between the thermistors. The resulting change in the electrical resistance produces a signal that is proportional to the oxygen concentration in the sample gas.
Zirconium-oxide sensors are based on the principle of a solid-state electrochemical cell. A layer of yttria-stabilized zirconium oxide is typically heated to between +600°C and +700°C, allowing oxygen ions to pass through it from a higher concentration to a lower concentration. The movement of ions produces an electromotive force which is used to determine the oxygen concentration. The greater the differential of oxygen on either side, the higher the voltage produced, allowing measurements from 100% to less than one part per million.
We offer three types of Zirconium-oxide based sensors: Metallic sealed reference sensor (MSRS), micro ion pump sensor (MIPS) and air-referenced zirconia.
Metallic Sealed Reference Sensor (MSRS)
The MSRS sensor contains a metallic sealed reference which eliminates the need for reference air, and ensures reliable measurements. The sensor technology was developed to measure oxygen levels in gas in extreme conditions, so is robust enough to withstand extreme heat and highly corrosive gases. These properties, combined with the design of the sample probe, make the MSRS very effective for high-temperature applications (up to +1300°C) such as flue-gas analysis.
Micro Ion Pump Sensor (MIPS)
The MIPS offers a compact, cost-effective percentage level oxygen sensor. The sensor can operate in temperatures up to +400°C, or higher if combined with an extractive sample probe . It has a different approach to our MSRS in that it continuously ‘pumps’ oxygen ions from the sample around the sensor into a sealed chamber and back out again depending on the direction of the DC current applied. The pumping is controlled so that the pressure inside the chamber is always less than the ambient oxygen pressure outside the chamber.
Air Referenced Zirconia
The majority of Zirconia sensors use ambient or compressed air as a reference, but function in a similar way to our MSRS and MIPS cells. Air-referenced sensors are ideal for laboratory and clean industrial applications.
The phase shift of fluorescence light due to oxygen present in the sample gives an indication of the oxygen concentration. The sensor measures the partial pressure of oxygen (ppO2) which, along with the internal sensor temperature is communicated serially to the host microcontroller. Non-depleting, maintenance-free optical sensor offer significant reduction in maintenance complexity and frequency.
Does not consume the analyte which is particularly important for low ranges. The patented technology allows PST to produce a sensor that provides low power operation with longer lifetime.
Thermal conductivity for binary gas analysis
All gases conduct heat to differing degrees, and the amount of heat transferred by a gas is determined by its 'Thermal Conductivity' (TC) value. This property can be exploited in sensing because each gas has a different TC value. Michell’s Thermal Conductivity Sensor uses this property to accurately measure one of the two gases present in a sample of a binary or pseudo-binary mix.
The sensor uses matched thermistors forming one half of a Wheatstone bridge. One thermistor is in the sample cell, the other is housed in a reference chamber (sealed and flowing reference versions are available). The whole assembly is heated to +50°C to ensure an iso-thermal environment, where the condition of the sample is consistent, providing an accurate and stable platform for measuring the target gas concentration.
When gas is flowing through the sample chamber, heat is drawn from the thermistor and this changes one element of the bridge. A current is required to keep the bridge balanced and from this, the TC value of the gas can be determined.
Plasma emission detector (PED)
LDetek’s Plasma Emission Detector (PED) ionizes the sample gas which releases energy in the form of light. Each impurity emits a characteristic light at a specific wavelength, which is collected though a filter to discriminate the undesired wavelengths. The intensity of the light is proportional to the amount of each impurity present which is proportionally converted into an electrical signal via a photodiode. The signal is subsequently amplified, contributing to this technique being extremely sensitive for trace level impurities measurements.
Infrared gas sensor
Dynament infrared sensors operate by using nondispersive infrared (NDIR) technology to monitor the presence of a target gas. The sensor contains a long-life tungsten filament infrared light source, an optical cavity into which gas diffuses, a dual temperature compensated pyroelectric infrared detector, an integral semiconductor temperature sensor and electronics to process the signals from the pyroelectric detector.
These NDIR sensors offer fast-response and high-resolution for the detection of hydrocarbons (including methane and propane), carbon dioxide, and nitrous oxide.
The Dynament sensor portfolio also includes a revolutionary Dual-Gas High Resolution Methane / Carbon Dioxide Sensor providing the capability to simultaneously monitor methane and carbon dioxide in a single sensor package while only consuming the power of a single infrared sensor.