The trend in manufacturing is toward automation: recording data, recognizing correlations in real time, controlling plant operation. To achieve this, more and more process data must be captured inline. However, implementation is easier for some measurands than for others.
But how can even complex measurands be reliably captured inline?
When Measurement Is More Than Temperature and Pressure
Standard measurands characterize the state of the apparatus: temperature, pressure, level, and volume and mass flows. These measurands can be captured very accurately and reliably with little effort.
It's a different story with optical measurands. Capturing these inline poses greater challenges for measurement technology manufacturers and users alike. Optical measurands characterize the state of the fluid in the apparatus: composition, turbidity, color, viscosity, and the velocity and size of particles.
Optical measuring devices all work on the same principle: a beam of light (source: lamp, LED, or laser) is sent into the fluid and is altered there (intensity, direction, wavelength …). A detector records the change. The result is a signal or an image.
So What Are the Challenges in Implementation?
- Sight glasses: The optical access to the apparatus must remain clear for the passing light at all times. Fouling or adhering bubbles significantly distort the measurement.
- Sensitive electronics: The light source, detector, and lenses must be shielded against high temperature and humidity. The solution here is often temperature control and inerting with purge media.
- Optical axis: The alignment between light source and detector must be exact and remain stable even when the apparatus vibrates.
- Data interpretation: Signals must be modeled and calibrated, image data must be evaluated, and the relevant image information must be passed on.
- Invasiveness: The measurement technology should have no influence on the flow in the apparatus — invasiveness must be ruled out.
- Lighting: Choosing the right lighting source is particularly delicate for image generation. The lighting should be strong enough and homogeneous. At the same time, exposure times must be short to avoid motion blur with moving fluids.
- Cost: Optical components are expensive, which means optical measurement technology cannot be used across the board.
Conclusion
Imaging optical inline measurement devices are full of innovation and technology. Deployment is especially worthwhile for processes with high savings potential, sensitive process steps, products with strict specifications, and safety-relevant plant components.
Want to find out what technical solutions we've found for these challenges in our sensors?