When using a temperature compensated ultra-sonic sensor as part of a flow measurement system it is crucial that the sensor is not exposed to direct sunlight. This is because the speed of sound varies with temperature and if the sensor is not properly shrouded then changes in temperature will result in inaccurate level readings.
With a shroud in place, the sensor compensates against the true ambient air temperature, yielding a more accurate result.
SIRIS have developed a cost effective robust sun shade which covers the entire sensor body thus preventing errors caused by solar gain. SIRIS Sun Shades fit the majority of commercially available sensors such as Siemens, Pulsar, Mobrey etc.
"Solar radiation directly onto an exposed sensor has a measurable impact - errors equivalent to almost 20% of flow over a V-notch weir"
WRc on behalf of UK Environment Agency
"Temperature compensated air ranging ultra-sonic sensors should be shrouded from direct sunlight when used on flow measurement applications”
Environment Agency MCERTS Site Inspectorate