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ZED Sensors for UV, VUV and temperature measurement - overview back

ZED offers several types of sensors for measurment/monitoring especially in UVC systems
for water/air purification and disinfection:

ZED sensors are used together with customers PLC or with ZED devices for measuring/monitoring UV lamps to ensure the required efficiency of disinfection.
• Decreasing UV values indicate a lowered UV lamp output (e.g. at the end of lamp lifetime) or a lowered transmission in water/air caused by pollution.
• Alternating UV values might be an indication of a lamp operated outside specification (e.g. lamp temperature too high), might be caused by bubbles or solids in the medium or might be effects of electrical interferences on long cables with analog sensors.

A wide range of displaying systems for measurement visualization is available:

ZED sensors differ concerning housing form, mounting type (slide-in sensors, 1/4inch or 3/4inch threads), material (stainless steel or teflon) and signal. Silicon carbide (SiC) diodes, if needed with additional UV-C filter, are used in all ZED UVC probes. These daylight insensitive semiconductor material is said to be the best available material for UVC sensors.

All sensors are designed, developed, produced and adjusted at ZED. Our product range in this field is accompanied by appropriate UV-monitors, special accessories like the measurement window MF001 according DVGW and OENorm and radiation meters for checking the UV-sensor calibration. Obviously we offer a recalibration service for the appropriate UV-sensor types.

Contact ZED for special UV-sensor design or additional features to customize your UV-sensor.

Types and Features - Overview

Digital UV-sensor types with RS485 interface
  • UV-values in "W/m²", "mW/cm²" or "%"
    (D-SLS types: "%" only)
  • one sensor for all applications,
    wide intensity range due to automated measuring range selection, internal digital signal processing
  • UV sensors connect to PLC using ModBus via RS485
  • multi sensor operation by connecting sensors in parallel
  • fail safe signal transmission up to 30m cable length
  • DVGW and ÖNORM compliant UV-sensor types available
  • "side-looking" UV-sensor types available
Digital UV-sensor types with 4-20mA, 0-2V or 0-10V signal
  • UV-values in "W/m²", "mW/cm²" or "%"
  • one sensor for all applications,
    wide intensity range due to
    internal digital signal processing
  • adjusted for the complete measurement range
  • reference value for analog output can be set by customer via ZED SmartMeter or Sensor Configurator software
  • UV sensors connect to PLC using standard analog industrial interfaces
  • DVGW and ÖNORM compliant UV-sensor types available
UVC Reference Sensors
UV-Sensor types with photodiode signal output
  • UV-values in "%"
  • cost efficient
  • daylight insensitive SiC photodiodes
  • sensitivity adjustment with ZED UV monitors
  • max. cable length 3m
  • UV sensors connect to PLC using special amplification interfaces
VUV 185nm Sensors
Temperature sensors - digital and analog types
  • for temperature measurement in liquids or gases
  • for temperature measurement on surfaces
  • types with RS485 interface and classical analog interfaces available
  • digital sensors connect to PLC using ModBus via RS485

Measurement Generals

Application of UV radiation becomes more and more important in the last couple of years. Along with classical application fields like disinfection of liquids, UV radiation is more and more applied in air cleaning, paint curing and other chemical, catalytic or analytic processes.

According to the specific process a minimum energy flux or an accurate level of irradiation is required. In both cases the radiated power or intensity respectively has to be measured. This helps to avoid over- or underdosing and saves energy resources.

There are 2 different methods of measurement:

  • qualitative and quantitative evaluation of the overall process of using UV irradiation:
    This includes bacteriological and chemoanalytic methods, that can give precise results. It is used to characterize the performance in the design and certification process of systems. Due to high cost of time consuming bacteriologic analysis this method cannot be used for instant measurement.
  • Alternatively selected operation condition like irradiance Ee and radiant flux can be measured by keeping other operating parameters constant. The measurement of UV intensity is the field of application of ZED UV sensors

UV Measurement

Measurement of radiometric quantities like irradiance Ee, radiant density Le, radiant intensity Ie and radiant flux Φe are very expensive if conducted in the spectral band of UV radiation. A large number of boundary conditions have to be observed, resulting in a very complex physical-mathematical process of measurement value calculation. This makes it very difficult to conduct measurements outside of a well equipped laboratory.
Serial measurements can only be conducted if a minimum set of specified boundary conditions are maintained. This set of boundary conditions includes a defined geometry, sensor configuration and calibration data and allows a quantitative estimation.

UV Measurement via semiconductor sensors

UV measurements, using semiconductor sensors are widely used. While operated within the specifications, this sensors return a signal, that is proportional to the incoming radiant energy. Depending on the sensitive material, this sensors have a characteristic spectral sensitivity that can include a large range of wavelength (infrared, visible light, UV-A, UV-B and UV-C).
Often the range of sensitivity is adopted to the specific application by using appropriate filters or material doping. The resulting electrical output signal (normally current) must be conditioned and calibrated to get results with adequate accuracy.

Absolute Measurements

As already stated, the correct measurement of radiometric quantities is very difficult and requires special sensors and geometrical arrangements for specific measurement problems. Finally a photodiode receives irradiation, converts it into an electrical signal that is processed with calibrated data and the result represents the radiometric value.
This method is called absolute measurement because the result can be traced back to a physical quantity. It requires a sensor, that responds a predefined electrical signal from a fixed physical quantity. Typical specifications are 20mA is equivalent to 100W/m² or 10V is equivalent to 150W/m².

On common analog sensors this calibration is unchangeable for each sensor and cannot be adopted to different measurement problems. This means that only sensors with a matching calibration can be used. This can cause problems in stock holding, because a large number of different sensors have to be ready for use.

With the digital sensors ZED provides a solution for this problem. This sensors convert the incoming irradiation into a digital signal. By this method the process of converting an analog signal and its limits are avoided. For replacing sensors in analog environments ZED offers digital sensors with analog output. For these types the analog output value can be set by the customer using a ZED service device like ZED SmartMeter or Sensor Configurator software.

Relative Measurement

In most application it is just required to keep a certain level of irradiance. A relative value as a percentage will ensure that the irradiation is high enough to keep the process running properly. This is called relative measurement, because no reference to a radiometric quantity is required.

ZED offers a wide variety of sensor-monitor combinations. The simple solution is the use of UV-Diode sensors. The basic principle with these sensors is that an UV photodiode delivers a current signal that is linear to the irradiation over a range of multiple magnitudes. The current signal is processed with variable gain and converted into a voltage signal by the monitor device. This allows the monitoring of a wide range of UV intensities using the lower cost UV-diode sensors.
In combination with sensors with digital or analog interface ZED monitors allow the selection of the measurement type. Both relative and absolute measurement is possible.

Sensitivity adjustment on UV-Diode sensors

The simple ZED monitors (e.g. PRO3) use potentiometers for manual sensitivity adjustment. The more complex types use processor controlled sensitivity switches as well as mathematical models to provide optimal performance for different applications. The monitor models PRO11 and PRO16 allow an automatic sensitivity adjustment for UV diode sensors.
By a menu option a known actual measurement value can be assigned to a defined end value. This process is usually done after the monitored lamp is changed.
New lamps usually have an UV output of 110% and reach their nominal value of 100% after a run time of 100h. By doing the adjustment to a level of 110% right after changing the lamp an adequate adjustment for the whole lamp life is achieved.

Digital sensors

ZED's digital sensors have the following advantages if compared with analog sensors:

  • one sensor can be used for a wide intensity range
  • the measured values ​​are provided directly as a digital signal in W/m ²
  • digital data transfer via RS485 bus
  • high noise immunity for rough industrial environment
  • simple parallel operation of multiple sensors
  • low cabling effort

All signal processing is integrated in the sensor body. After analog/digital conversion, the digital signal is averaged and transmitted via RS485 interface. The monitoring system can retrieve and process the measurement data over the appropriate communication protocol.

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