Industries Information

Dissolved CO₂ instruments are analytical devices that measure the amount of carbon dioxide (CO₂) dissolved in a liquid sample such as water. They typically include a submerged probe that is covered by a thin organic membrane. When the probe is submerged in the liquid sample, carbon dioxide diffuses through the membrane at a rate proportional to the partial pressure. Increasing the partial pressure increases the diffusion amount. The liquid sample is considered to be saturated when the molecular activity of the carbon dioxide equals that of the liquid. Air contains only 0.035 % carbon dioxide by volume; however, CO₂ is nearly 30 times as soluble in water as oxygen. Carbon dioxide moves across the air-water interface according to the same physical process that affect the dissolving of oxygen. Both temperature and pressure affect the diffusion rate measured by dissolved CO₂ instruments. Accuracy and diffusion range are typically measured in parts per thousand or parts per million.

Dissolved CO₂ instruments vary in terms of user interface, features, and output options. Some devices provide analog or digital displays. Others include devices such as cathode-ray tubes (CRTs), liquid crystal displays (LCDs), or flat panel displays. User controls may consist of knobs or potentiometers mounted on a simple front panel. Digital front panels are programmable and work with a keypad. Some devices are battery-powered, self-calibrating, or equipped with self-test diagnostics. Others are triggered by events or include signal processing or filtering. Output options include analog voltage, analog current, analog frequency, and switch or alarm relays. Analog voltage outputs are a simple (usually linear) function of the measurement. Analog currents use feedback to provide an appropriate current regardless of variables such as noise and impedance. Analog frequencies use continuous physical variables such as voltage amplitude or frequency variations to transmit information.

Important specifications for dissolved CO₂ instruments include the maximum number of input channels, the maximum bandwidth, the resolution in bits, and the sampling frequency. Environmental considerations include the operating temperature, minimum shock rating, and maximum vibration rating. Dissolved CO₂ instruments that feature a computer interface are commonly available and may include non-volatile memory or removable hard drives. Communication protocols and bus types for dissolved CO₂ instruments include ARCNET, AS-I, Beckhoff I/O, CANbus, DeviceNet, Ethernet, Foundation Fieldbus, general-purpose interface bus (GPIB) or IEEE 488, InterBus, PROFIBUS, and SDS.

Density and specific gravity instruments are meters used to determine the density and specific gravity of a mixture that may be solid, gas, or liquid.  The density range (mass per volume), accuracy, and response time characterize most of these instruments.  Simultaneous measurements and user interfaces are also important in choosing the proper density and specific gravity instruments.

Density digital meters that use the principle of either oscillating tubes or radioactive adsorption to determine density and specific gravity are the most common types of density and specific gravity instruments.  An oscillating tube is a hollow glass tube that vibrates at a certain frequency.  The vibration frequency changes when the tube is filled with a sample.  The higher the mass of the sample, the lower the vibration frequency.  This frequency is measured and converted into density. A built-in thermostat controls the temperature (no water bath required).  A thermostat is often necessary since the density of the sample could be changed by temperature variations.

Radioactive adsorption, the use of gamma rays or x-rays to determine density, is helpful in applications such as piping or mining where intrusion into the system may be costly.  Energy is emitted by a source that passes through the pipe walls and the process material.  The process material adsorbs the energy.  The amount of energy reaching the detector varies with each material.  Electronics convert this energy reading to a density measurement.  This method is particularly effective in process applications that involve extremely high flow rates, high pressure, and high / low temperatures.

Another noninvasive method used by density and specific gravity instruments includes microwave phase difference measurement. Microwave phase difference exploits the way a fluid’s density affects the propagation of microwaves when they pass through it.  This allows a reliable measurement of the fluid’s density by monitoring the difference in microwave phase between the original wave and the one that passed through the measured fluid.  Measuring fluid density by observing a wave’s phase difference is unaffected by flow velocity and/or is not affected by the contamination and/or bubbles.  This technology is effective in various applications where determining the consistency of suspended solids, slurries, and sludge is necessary such, as in the pulp and paper and wastewater industries.

Suspension methods include measuring the density gradient and the Schlieren method.  Density gradient is measured when two liquids of different densities are layered in a glass tube so that over time, diffusion results in a vertical density gradient.  The Schlieren method involves immersing a liquid-filled tube in another liquid,  the liquid will only flow horizontally from the tube if the densities of the two liquids are equal.

Density and specific gravity instruments provide various readouts are available based upon the user’s needs.  Analog and digital displays are available on portable instruments.  Display parameters may include Brix, Plato, % alcohol, API gravity, percent solids, percent mass, and percent volume may be available.  Other options may include computer interfaces and software for programming customized concentration or specific gravity tables, data analysis, and/or control.

Density and specific gravity instrument systems range from laboratory applications where autosamplers and cleaning components are integraged to tank management systems for remote monitoring to flow transfer and control applications.

Calibration of density and specific gravity instruments is dependent upon the technology type used.  Nitrogen gas or water at specific temperatures and pressures may be required prior to using the instrument.  Some density meters may include a calibration certificate.

X-ray fluorescence spectrometers (XRFs) use a spectroscopic technique that is commonly used with solids, in which X-rays are used to excite a sample and generate secondary X-rays.  The X-rays broadcast into the sample by X-ray fluorescence spectrometers eject inner-shell electrons. Outer-shell electrons take the place of the ejected electrons and emit photons in the process. The wavelength of the photons depends on the energy difference between the outer-shell and inner-shell electron orbitals. The amount of X-ray fluorescence is very sample dependent and quantitative analysis requires calibration with standards that are similar to the sample matrix.

The solid samples used with X-ray fluorescence spectrometers are usually powdered and pressed into a wafer or fused in a borate glass. The sample is then placed in the sample chamber of the XRF spectrometer, and irradiated with a primary X-ray beam. The X-ray fluorescence is measured either in simultaneous or sequential modes, and is recorded with either an X-ray detector after wavelength dispersion or with an energy-dispersive detector.

X-ray fluorescence spectrometers measure the emitted X-ray fluorescence in either a simultaneous fashion, or sequential.  Simultaneous mode typically measures the entire wavelength range around the emission line of interest simultaneously, while sequential mode typically measures one wavelength at time.

Wavelength dispersive detectors use a nondestructive analysis technique for the identification and quantification of elements in a material. Wavelength dispersive spectroscopy is the measurement x-ray energies emitted from the bombardment of an energy source impinged upon the material, producing characteristic x-rays.  Energy dispersive X-ray fluorescence spectrometers also use nondestructive analysis techniques for the identification and quantification of elements in a material. Energy dispersive spectroscopy is the measurement x-ray energies emitted from the bombardment of an energy source impinged upon the material, producing characteristic x-rays.

XRF was originally used to analyze geological samples. The advancement of computers and other technologies allowed the technique to develop even further.  XRF found its place in many different types of analytical laboratories and some industrial inspection systems. X-ray fluorescence spectrometers provide a number of distinct advantages including easy sample preparation, nondestructive rapid multi-element analysis, and the ability to screen unknowns in a wide array of sample matrices such as liquids, solids, slurries, powders, pastes, thin films, air filters, and many others.  Because of these advantages the technique, it is widely used for research, in industrial settings, and by quality assurance analysts.

Spectrometers, UV and visible, measure the amount of ultraviolet and visible light transmitted or absorbed by a sample placed in the spectrometer. The wavelength at which a chemical absorbs light is a function of its electronic structure and the intensity of the light absorption is related to the amount of the chemical between the light source and the detector, so a UV / Visible spectrum can be used to identify some chemical species.

UV and visible spectrometers may come with one of three common photometric design systems.  Scanning single beam systems can be one of two types of instrument, either a single wavelength light source or a selector for a single wavelength. The light from the lamp is dispersed before reaching the sample cell.  A scanning double beam instrument measures both the transmittance of the sample and solvent at each wavelength simultaneously and computes the ratio. The light from the lamp is dispersed before reaching the sample cell.  All wavelengths pass through the sample and the dispersing element is between the sample and the array detector. This allows the detector to simultaneously record the transmitted light power at multiple wavelengths.  Commonly UV spectrometers and visible spectrometers will have a monochromator, which is used to separate the wavelengths of the light source before the light passes through the sample and enters the detector.

Common detector types found in UV spectrometers and visible spectrometers include photomultiplier tubes, diode arrays and charge-coupled devices (CCDs).  A photomultiplier tube, useful for light detection of very weak signals, is a photo emissive device in which the absorption of a photon results in the emission of an electron. These detectors work by amplifying the electrons generated by a photo cathode exposed to a photon flux.  A diode array detects which light is absorbed and which is reflected.  A CCD chip, is an array of light-sensitive elements. Which are, in fact, some small electronic capacitors. The electrons generated by the light charge these capacitors. In fact, each light element (commonly called photon), that reaches the CCD array’s atoms, displaces some electrons, which are providing a current source. These current sources, are localized in small, delimited areas (the capacitors), called pixels.

Important parameters in specifying spectrometers, UV and visible are wavelength range, resolution and accuracy.  Wavelength range is the dispersion of the grating across the linear array; also expressed as the "size" of the spectra on the array.  The spectral resolution is the width of an analytical peak at half its height expressed in nanometers. A measure of the instruments ability to separate two overlapping peaks. At the point of resolution, two peaks of equal height are said to be resolved if you can see a dip between the tops of the two peaks separate two overlapping peaks. At the point of resolution, two peaks of equal height are said to be resolved if you can see a dip between the tops of the two peaks.  The wavelength accuracy is the agreement between a mean measured value and a true or accepted value as quantified by error. Related to determinate errors and quantified by bias.  Detector sample volume and sample flow rate range are also important specifications pertaining to UV and visible spectrometers.

Many UV spectrometers and visible spectrometers will give measurement values for transmittance, absorbance and reflectance.  Transmittance is the ratio of the radiant power transmitted by a sample to the radiant power transmitted by a blank in an equivalent cell or by some other means of compensation for solvent absorption, reflection losses, etc.  Absorbance is a measure of concentration of material present: negative log (base 10) of Transmittance [- log 1/ T] of product of extinction coefficient, path length, and concentration, written as A = e bc.  Reflectance is the ratio of the radiant energy reflected by a body to the energy incident on it. Spectral reflectance is the reflectance measured within a specific wavelength interval.

Spectrometers are analytical instruments which disperse an emission (such as particles or radiation) according to some property of the emission (such as mass or energy) in order to measure the amount of the dispersion. This product area includes visible, infrared (IR), ultraviolet (UV), atomic absorption (AA), optical emission (OE), Raman, X-ray fluorescence (XRF) and mass spectrometers. Specific search forms are also available. Performance specifications for spectrometers include: spectral range, spectral resolution, mass range, mass resolution, and mass accuracy. Spectral range is the dispersion of the grating across the linear array, or the “size” of the spectra on the array. Spectral resolution is the width of an analytical peak at half its height as measured in nanometers (nm). This value indicates the spectrometer’s ability to separate two overlapping peaks. Spectral accuracy is the agreement between a mean measured value and a true or accepted value as quantified by error. Mass range is a measurement of atomic mass that is expressed in atomic mass units (amu) or Daltons (Da). Mass resolution is the ratio of the mass divided by the change in mass over the area of two peaks.  

There are many different types of spectrometers. UV and visible spectrometers measure the amount of ultraviolet (UV) and visible light transmitted or absorbed by a sample placed in the spectrometer. Infrared (IR) spectrometers measure the wavelength and intensity of the absorption of infrared light by a sample. Atomic absorption (AA) spectrometers use the absorption of light to measure the concentration of gas-phase atoms. Atomic emission (AA) and optical emission (OE) spectrometers determine analyte concentration via a quantitative measurement of the optical emission from excited atoms. Raman spectrometers are used to measure the wavelength and intensity of inelastically scattered light from molecules. X-ray fluorescence spectrometers (XRF) use a spectroscopic technique that is commonly used with solids, in which X-rays are used to excite a sample and generate secondary X-rays.  Mass spectrometers separate ions by their mass-to-charge (m/z) ratios. They are used to identify compounds by the mass of one or more elements in the compound. They are also used to determine the isotopic composition of one or more elements in a compound.

Specialty spectrometers and accessories are specialty or proprietary products and accessories related to spectrometers, analytical instruments that are used measure the amount of dispersion of a property such as mass or energy. Like other types of spectrometers, specialty spectrometers are used to determine chemical composition and to perform electromagnetic radiation analysis by measuring light intensity across the visible, ultraviolet (UV), and infrared (IR) spectrums. A specialty spectrometer can be built using optical detectors such as charged coupled devices (CCD) or photo diode arrays, or fiber optics.

Specialty spectrometers and accessories are often application-specific and differ in terms of performance specifications such as wavelength range, optical resolution, sensitivity or absorption, and data capture speed. Products used in thin film analysis are different from those used in biomedical applications, or for monitoring inline process control. Some specialty spectrometers are used in medical imaging applications. For example, nuclear magnetic resonance (NMR) spectroscopy is used to determine physical and chemical information about a specific molecule, typically organic compounds. Resonance spectroscopy is based on the magnetic property of an atom’s nucleus and its response to an electromagnetic field. This is the technique used in magnetic resonance imaging (MRI).

Many other types of specialty spectrometers are available. Secondary ion mass spectrometry (SIMS) is a technique for analyzing the surface of a thin film test sample. An ion mass spectrometer is used to analyze the particles emitted by an object after it is bombarded with a stream of ions or charged particles. Electron auger spectroscopy is also used to analyze surface composition of materials. Auger electron spectroscopy (AES) measures the energies of Auger electrons, which are created by bombarding the sample with an electron beam. Auger electron energies are tabulated based on the Auger effect or process.

Suppliers of specialty spectrometers are located across the United States and around the world. They conform to various quality standards and regulatory requirements.