LIR provides in-line, real-time flow characterization to industries and laboratories looking to improve the overall efficiency and enable scale up of their manufacturing processes. Majority of pharmaceutical, food, biologically active and other processes involving complex fluids, suspensions or powders require inline control to get a high quality product. The Lenterra Inline Rheometer (LIR) is an in-line process analytical technology (PAT) that allows real-time measurements of critical process parameters (CPP) such as viscosity in food processing or granule densification and wet mass rheology (consistency) in pharmaceutical wet granulation. LIR consist of Drag Force Flow (DFF) probean LOI optical interrogator and a host computer with control, measurement and data processing software. The thin probe placed in a desired location within the processing equipment is connected to the interrogator via fiber-optical cable. The LIR technique is minimally invasive, works with any type of fluids or powders and has no moving parts. To install the probe into an apparatus, a probe adapter is required.

Drag Force Flow (DFF) Sensor

Optical-based sensors have a number of advantages over electrical sensors. Fiber optics are insensitive to and do not produce electromagnetic interference (EMI), and they suffer virtually no signal degradation even over very long (100′s of meters) cable lengths. They can be used at higher temperatures than many conventional electrical sensors, and are safe for use with combustible materials and in HERO (Hazards of Electromagnetic Radiation to Ordnance) applications.

The drag force flow (DFF) sensor is essentially a hollow cylindrical pin, whose deflection is sensitively and accurately measured by an assembly of two optical strain gages, which are made up of Fiber Bragg Gratings (FBGs). The FBGs are affixed on the opposite walls of the inner surface of the pin. Information is collected via optical fibers that connect the FBGs with an optical interrogator. The interrogator continuously records the FBG spectra. When the hollow pillar is deflected due to force acting on it, one of the FBGs becomes stretched and the other one compressed, leading to the FBG spectra shift along the wavelength axis in opposite direction. The interrogator (with associated software) determines relative spectra shift which is proportional to the force causing pillar deflection. The ambient temperature variations also lead to the FBG spectra shift. Since both FBGs are exposed to the same temperature change the spectra shift along the wavelength axis in the same direction. Therefore, in addition to the force measurements, the interrogator can also provide information about ambient temperature by measuring averaged spectra shift. The sensor is very sensitive (pin tip deflection as low as one micrometer can be detected). The length, diameter and material of the pin define the measurement range and sensitivity of the measurement. The DFF sensor provides minimal intrusion to the flow, and its measurement sensitivity depends weakly on the amount of flow material that may stick to the sensor surface. The probe does not have any moving parts and/or traps, which makes it non-paralyzable. Due to high measurement rates achievable (up to 500 measurements per second) the sensor can identify non-uniformities of the flow, such as cell conglomerates or granules.

Temperature compensation and temperature measurement

Two micro-resonators are housed inside the sensor so that temperature effect can be compensated for. Strain shifts FBG spectrum, but so does temperature. To get information about strain independently from temperature, and measure temperature independently from strain, two FBGs are attached to opposite sides of the cantilever.

The differential signal (shift of FBG 1 spectrum less shift of FBG 2 spectrum) is independent from temperature, while the average signal (shift of FBG 1 spectrum plus shift of FBG 2 spectrum) is independent from the strain: