Inline UV sensors: continuous irradiance measurement for UV systems

The calibration uncertainty stated above is the expanded uncertainty of the calibration (k = 2, confidence level approx. 95 %) and applies to the calibration source and the calibration conditions. In use the measurement uncertainty is larger: spectral mismatch at the source actually used, the sensor temperature, ageing since calibration as well as distance and alignment to the source are added to it. How these combine into an uncertainty budget is explained under Measurement uncertainty in UV measurement.

The inline sensors FLT are designed for installation in machines with low clearance (68 × 25 × 15 mm) and measure irradiance permanently at a fixed position, for example next to the workpiece in a UV dryer or below a packaging line. The measuring ranges extend to 20 W/cm² depending on configuration; the spectral ranges UVC, UVB, UVA, UVA+, UVBB, VISB and VIS can be chosen. The operating temperature is 0 to 60 °C.

The FLT delivers a sensor signal that an instrument or display evaluates: the RMD or RM-12 for check measurements and the panel-mount RM-32 for permanent monitoring with threshold and alarm relays (0–10 V version). For direct connection to a PLC without a display unit, the PLC sensors with 4–20 mA or 0–10 V or the PLC.D with RS-485 are the right choice.

The permanently installed sensor always sees the lamp from the same position; a slow decrease of irradiance over weeks indicates ageing, a sudden drop after a production break indicates deposits on the window or sensor. Opsytec recommends documenting the initial value after a lamp change as 100 % and setting a warning threshold, for example at 80 %, in the evaluation. The sensor itself typically ages by less than 3 % per year and is recalibrated every 12 months.

With a permanently installed sensor that measures continuously at a fixed position, instead of spot checks by hand. The measurement is taken in the process plane, not in the free beam; the FLT inline sensors cover 0 to 20 W/cm² in spectral ranges from UVC at 200 to 280 nm through to LUX. The value applies to this one position only, and the mounting position has to be reproducible after every service.

The continuous measurement of UV irradiance during operation at a permanently installed measuring point and in a defined spectral band, for example UVC at 200 to 280 nm. An evaluation unit or the controller reads the values continuously. The difference from a test measurement lies in the purpose: the test measurement qualifies the system, inline monitoring keeps the condition between tests traceable. Contamination, ageing and lamp failure become visible before they show up in the product. A traceable calibration certificate is required for the absolute value.

First the measuring position is fixed: as close to the process as possible, without disturbing it. Distance is no minor detail here – between 13 and 38 mm there are measurable losses. Cooling, window transmission, a procedure against contamination and a reproducible mounting position after service also have to be settled. The flat inline sensors are designed for confined space in existing systems; the output signal follows the controller already in place.

The calibration certificate states the expanded calibration uncertainty with k = 2; for the inline sensors FLT it is typically 4.5–6.0 %. In use the measurement uncertainty is larger, because spectral mismatch at the source actually used, sensor temperature, ageing and measuring geometry are added to it. How these combine into an uncertainty budget is explained under Measurement uncertainty in UV measurement.

This design is operated directly on the radiometer RMD.

This design delivers an analogue signal directly to the machine control.

Scope of delivery: the FLT sensor and the factory calibration certificate. Please state the design, the spectral range and the measuring range with your order.

The FLT inline sensor for PLC operation is supplied with a cable without a connector, so there is no pin assignment. Sensors from 2025 onwards use wire colours V2, earlier ones wire colours V1.