Manufacturing and Quality Control Processes with a Miniaturized Molecular Spectrometer

Production and quality assurance (QA) processes are monitored in industry, using a number of remote sensing techniques, in order to better understand a specific processes. This approach helps companies improve profits and satisfy the key societal challenges of reducing environmental impact through improved efficiency, reduced emissions and a reduction of waste by the better use of raw materials.

In addition to being used for academic purposes, spectral measurements are now increasingly used in industry. The use of light for monitoring a process can aid the production process and help monitor a wide variety of products, from measuring the concentration levels in materials by means of method such as Raman analysis through to determining the temperature of an environment by applying the data obtained from its black body curve (Figure 1). This curve’s shape and peak are a function of a specific object emissivity and temperature.

Black body curves from 100 – 1300 nm for 7000 and 5770 K

Figure 1. Black body curves from 100 – 1300 nm for 7000 and 5770 K

Optical equipment deployed in a steel continuous casting plant to acquire data about an ongoing process and to investigate product quality is depicted in Figure 2. Atomic spectroscopy and molecular spectroscopy are the two categories of optical spectral measurements. The former analyzes individual elements and the latter includes methods such as Raman observations, NIR techniques, color measurement, IR spectroscopy, and UV-VIS spectroscopy.

As cast steel, (colour can determine its temperature)

Figure 2. As cast steel, (colour can determine its temperature)

The advent of charge coupled devices (CCD) and more recently CMOS detectors has considerably reduced the cost of spectrometers, or spectral measurement systems, with systems now offered by many major manufacturers for below £10,000. This is the driving factor behind the widespread adoption of spectrometers in industries, including heavy manufacturing. However, spectrometers are still considered as a costly affair in most small and medium size companies (SMEs) despite these price reductions. As a result, most companies are not in a position to recognize the measurement options available in spectrometers and their potential use as a key QA tool.

According to Markets to Markets, the molecular spectroscopy market was estimated to be $4.3 billion in 2013 with an expected compound annual growth of 6.7% for at least the next five years. So the demand for more flexible, compact, cost-effective, and easily operable spectrometers is also expected to increase. The need for portable/handheld, user-friendly systems is the driving factor for future growth.

New Advances

If this trend of widespread adoption of molecular spectrometry in industries continues, systems have to address end-user requirements and their involvement is crucial in developing a circular economic model that will aid in creating a value-added solution. An example is cost-effective devices that can be networked to allow for data acquisition in real time from different locations and can be subsequently examined to obtain a clearer picture of a specific process. This could be performed while maintaining an economical, compact package.

Spectrometers with this capability support the circular economy and gain from new plug-and-play instruments for spectral analysis that facilitate the upgrading process and eliminate the difficulties of performing the measurements. Such advancements can go along with pervasive computing, by embedding micro-processors in the devices, providing users web-access, improved functionality providing greater control, remote access, improved diagnostics minimizing the need for potentially predictive fault management and expert support.

However, every instrument has its own limitations as each situation has trade-offs, which have an impact on its resolution and precision. The market has many different instruments for performing spectral measurements or varying different configurations to facilitate different sensitivities. Specialized high precision, high sensitivity equipment is needed in some cases, for instance, transmission Raman analysis for the pharmaceutical sector. For this purpose, equipment such as IS-Instrument’s HES range of instruments is needed.

Cost, user-friendliness and reliability are the key drivers in other sectors requiring colour measurements, especially if instruments are to be used by SMEs. To address this requirement ISI has devised a new plug and play compact miniature spectrometer that can be used for a range of applications (Figure 3). It is possible to use the device as a stand-alone system or as a suite of networked sensors for applications, ranging from simple colour measurements for high precision agriculture to the production of daily product such as furniture to health care in the community.

Miniature Spectrometer from ISI

Figure 3. ISI new miniature spectrometer

Monitoring on-line process measurements such as combustion processes, chemical composition, temperature, monitoring pigments in paints, and the release of gaseous compounds like carbon dioxide and the motion of objects is another key application. These potential markets, along with more conventional users in education and academic research, provide considerable potential market growth that could be exploited by the low cost hand-held portable instruments.

It is possible to integrate ISI’s spectrometer easily with other instruments to further expand the monitoring potential of the system. An example is integrating an economical spectrometer with an inexpensive integrated sphere (Figure 4), also devised by ISI, to develop a spectroradiometer, ideal for analyzing LED colour and luminance, reflectance, retro-reflected colour, light sources, and transmittance with a myriad of industrial applications, ranging from horticultural to lighting in transport networks to photovoltaic device performance.

Integrating Sphere for Miniature Spectrometer

Figure 4. ISI integrating sphere

A New WI-FI Miniature Spectrometer

Using the advanced production methods, ISI can provide its new range of miniature spectrometers in a compact package of less than 500 g at a cost of less than £800. These Wi-Fi enabled systems can be remotely controlled. Systems are engineered to operate with roughly 1-2 nm scale resolution and wavelength range of 350–850 nm. The fibre-coupled devices do not require any complex alignment.

The user-friendly operational software (Figure 5) is the key driver that can be run by even novice users and adapted for a specific process of observation. The systems are built on a simple Czerny Turner configuration (Figure 6) and can be supplied as OEM and stand-alone systems.

Mercury calibration lamp spectra acquired with the miniature spectrometer

Figure 5. Mercury calibration lamp spectra acquired with the miniature spectrometer

A Czerny turner spectrometer

Figure 6. A Czerny turner spectrometer

Table 1. The technical specifications of the ISI new range of miniature spectrometers

Specification Value
Optical
Wavelength range From <390 nm to >850nm.
Resolution (FWHM) <2nm across whole range
Exposure time 1 ms — 10 seconds
Fibre input SMA 905
Thermal stability  
Read noise 50 counts (Max. Standard deviation)
Stray Light  
Linearity > 98 % (corrected)
Electronics
Connectivity Ethernet
WiFi (optional)\
Supply voltage 4.75 — 5.25 V
Mechanical
Dimensions 59×108×131 mm
Weight Approx 500 g
Storage and working environment  
Temperature 0 — 40 °C
Humidity noncondensing

The Integrating Sphere

The light entering the spectrometer is homogenous and lacks structure in most observations to ensure reliable and accurate spectral measurements. An integrating sphere is a well-established device for use in the observational process. Such a sphere has a highly reflective internal surface (> 95%). This means the incident light is reflected off the internal surface of the sphere before exiting (Figure 7).

Illustration of an integrating sphere

Figure 7. Illustration of an integrating sphere

This process “mixes” the light eliminating factors like spatial distribution factors. Power measurement observation and colorimetry are the common applications of these devices. Most of the currently available spheres have a reflectivity of more than 98% and can be highly expensive. IS-Instruments has created a new integrating sphere with a cost of < £500 using the same process of designing the mini spectrometer with sophisticated manufacturing method.

Integrating sphere reflectance as function of wavelength

Figure 8. Integrating sphere reflectance as function of wavelength

Figure 8 shows the reflectance of the integrating sphere as a function of wavelength. The integration of the sphere into the spectrometer allows obtaining “clean” spectral data, which could, in principle, enable accurate observations of spectral properties such as color for a total cost of less than £1500. This could result in the expansion of the spectral measurements to routine use, improving efficiency in the manufacture of different systems and even minimizing CO2.

This information has been sourced, reviewed and adapted from materials provided by IS-Instruments Ltd.

For more information on this source, please visit IS-Instruments Ltd.

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