NIR-Online Multipoint System Item ID: BUX-four

NIR-Online process analyzers rely on the following principle of operation. Light is constantly emitted from a tungsten halogen lamp on a sample. The diffusely reflected light from the sample is directed to a dispersive element (stationary grating) and the resulting spatially distributed monochromatic light is detected by means of a diode array usually consisting of 256 diodes. Each diode collects the intensity of a certain wavelength range depending on its spatial position.  These individual diode signals are commonly referred to as pixels. Division of measured intensity (I) by intensity of a white reference spectrum (I₀) as well as conversion of pixels to a wavelength scale results in a so-called spectrum, I/I₀ plotted against nm or cm^-1. Chemometric software predicts molecular properties of the sample from the measured spectra after according calibration.

Utilizing diode arrays gives rise to detecting a specified wavelength range without time delay in milliseconds. Averaging up to 200 spectra (see FAQ 1) per second yields excellent signal to noise ratio and allows detection of fast moving products in pipes or on conveyor belts. Therefore, measurement errors resulting from natural variance of the sample while averaging are excluded. Moreover, diode array based process analyzers do not contain any moving parts and are thus robust by design. They are perfectly suited for rough industrial conditions such as vibrations, extreme temperatures or humidity.

In a process environment diode array process analyzers are beneficial to scanning or interferometer based technologies. Rotating wavelength filter wheels or Fourier Transform (FT) spectrometers with moving parts results in long measuring / averaging times and quality of measured data relies on stable surrounding conditions.

AutoCal is a simple push or click button allowing to directly time stamp a sample. The sample is manually collected up- or downstream (with the optional by-pass sampler a time stamped sample is even automatically collected!) at a sampling point and subjected to internal or external reference analytics. Afterwards resulting values (e.g. protein, moisture and fat mass percentage) are directly entered into the software. In this example only three numbers for protein, moisture and fat content are typed in and they are automatically included in the calibration. It’s really that easy - no export of data and import to external chemometric software with exhausting calibration validation and re-import to analyzer software needed.

NIR-Online process analyzers yield direct and immediate information regarding a product or intermediate and displays these as real-time trend charts to a PLC. Fast intervention of process engineers may either optimize safety / tolerance margins for profit increase or simply reduce batches to waste or re-work. Moreover, entire incoming truck or shiploads or final products may be inspected. Errors resulting from sample taking for laboratory purposes are thus excluded. Therefore, proper storage and correct delivery are ensured.

Whenever the cost of optical fibers plus a Multipoint Head exceed the cost of a stand-alone NIR-Online process analyzer. As a rule of thumb the maximum distance between to Multipoint Heads should be less than 150 – 200 m simply owing to cost of investment for optical fiber.

The NIR-Online Multipoint Solution with its patent-pending daisy chain connection is ideal for measuring points at a close distance of up to 150 m e.g. found along a production line or at parallel production lines.

In the unlikely event of a Multipoint Head failure, it will be automatically bridged by an internal relay. All other Multipoint Heads in the daisy chain will continue measuring and the according values will be displayed to the PC / PLC.

The simple answer is: not in the near-infrared region.

In the low energy, near-infrared wavelength range used by NIR-Online process analyzers only mechanical aging of optical fibers owing to e.g. bending needs to be taken into account. Overall life time is in the order of decades in case of proper treatment. Additionally, any negative effects on the optical fiber are included in the white reference measurement as well as the sample measurement and therefore cancel when determining I/I₀ (see FAQ 1).

Tremendous aging of glass fiber bundles (signal damping within a fiber) is commonly observed for high frequency irradiation such as ultra-violet (UV) or X-ray leading to glass defects. These lower the degree of total reflection, the fundamental operating principle of an optical fiber. Above described irradiation induced glass defects do not occur in the near-infrared spectral range for mere reasons of physics.

Coupling of light into an optical fiber prior to a measurement always leads to intensity (signal) losses in comparison to a direct measurement. Only beams of light below a certain critical angle given by the numerical aperture may be transported (totally reflected) through the fiber. However, these effects are easily compensated by simply averaging spectra and therefore increasing signal to noise ratio. NIR-Online’s fast diode array technology allows to record up to 200 spectra / second (see FAQ 2). Sufficient SNR is obtained within a second!