| + UK Met Index | HSS VF-500 fog / visibility sensorSensors with unrivalled accuracy and long-term reliability |
Links to previous pages Fog / Visibility
Section
_______________ Tel UK: 01275 847787 Fax UK: 01275 847303
by Biral to rigorous IS0 9001:2000 quality standards. _______________ |
Originally designed for the US military, the HSS
VF-500 sensor is configured for accurate measurement of visibility in the densest of fogs
to very clear air conditions and is the refinement of 2 decades of experience and
technology resulting in a compact, robust instrument with excellent performance. The HSS VF-500 can be used for automatic switching of warning lights and alarms, such as lighthouse fog signals and roadside traffic warning systems,as well as for datalogging purposes. The data is output as an analogue signal of either 0-10 V or 4-20 mA and can be used with or without the optional fog warning system (with in-built relay contacts for automatic switching of additional equipment).
The VF-500 sensor uses forward scatter meter technology to measure visibility in all weather conditions. The sensor measures the amount of light scattered by small suspended particulates (i.e. fog, haze and smoke aerosols) or larger particles (i.e. rain, snow, ice pellets, drizzle and mist) passing through the sample volume. The sensor calculates the atmosphere EXtinction COefficient (EXCO) from which the Meteorological Optical Range (MOR) is calculated. Using an infra-red light source and intelligent sensing technology the measurements are unaffected by other light-sources. Construction The HSS VF-500 is lightweight and can easily be installed by one person and consists of a sensor head which makes the measurements and a control box housing the electronics. The sensor head is constructed of dip brazed high grade aluminium. All components that are exposed to weather are hard-coat anodised for protection against corrosion. The sensor head and control box can be sited up to 66 ft apart for safe and convenient access. Maintenance and calibration The sensor is fully calibrated at the time of manufacture. Routine maintenance, including a check on calibrations, can be performed easily by one person in a matter of a few minutes and a re-calibration (although this should never be required) takes only slightly longer. Operation in temperature extremes The sensor operates in temperatures ranging from - 58º F to + 140º F. For operation below - 27º F the heated version is recommended (please refer to the heated option below). The VF-500 System The system consists of two parts, a sensor head and a power and communications unit (mounting pole is not included) The sensor head is constructed of high quality aluminium which is hard anodised to give a superior finish that lasts for years and does not require painting.As standard the sensor has:
In addition the following variations are available:
Available Variants / Options Fog warning system - the fog warning system allows an external device such as a fog horn, road warning sign or ventilation fan to be switched automatically at a given visibility range, and the monitoring and adjustment of the intensity of warning lights. The system features user adjustable activation and de-activation delays ensuring smooth and effective switching. For example, the delays could be set for 5 minutes so that a device would only be activated after 5 minutes of continuous reduced visibility. This allows for local transient events such as fumes from passing vehicles or vessels thus avoiding false alarms. Additionally power is used more effectively as the device is only turned on when necessary. Heated version - the sensor comes with window de-misters as standard allowing operation of the sensor in temperatures down to 27º F. However, where the temperature drops below 27º F for more than a couple of hours a day the heated version is recommended. This version will provide error free operation in conditions down to - 58º. Additional Analogue Outputs - in addition to the standard 0-10 V output the sensor can be ordered with either 0-20 mA or 4-20 mA output. For accessories see below Examples of data output The EXCO values (which are related to visibility) are output in the form of an analogue 0-10 V DC logarithmic signal in the range according to your application needs. Optionally available is a 4-20 mA logarithmic output. For more information on the ranges please see measuring ranges below.
The benefits of HSS sensors As with all the sensors in the HSS visibility sensor range there are a number of benefits which have been proven over many years of operation: Long-Term ReliabilityThe Biral HSS sensors are designed to withstand years of abuse problem free and are the best choice for long life expectancy. For two decades customers such as the Dutch Motorway Authorities have been using HSS sensors and they are still enjoying the reliability and durability of the sensors (most have run the entire time without a single problem!). The US Military also continues to uses Biral HSS sensors in land and maritime roles. Extensive Trial History As Biral HSS sensors were the first sensors on the market, we have an extensive library of independent test results comparing the HSS brand against the competition. Not only do the reports show excellent performance but also Biral can show the consistency of the sensors’ performance since their conception in 1984. The sensors have been used by nearly every national weather service, several defence organisations, aviation authorities, offshore oil platforms, numerous lighthouse authorities and institutes carrying out meteorological research. Indeed, in the past, we have even sold to our competitors! References and test reports are available on request. Lightweight and Low-Powered Biral HSS sensors are some of the lightest around and can easily be installed by a single person. They are also designed for very low power consumption, allowing additional flexibility for a wider range of applications. HSS Sensors were developed two decades ago and were the first Forward Scatter Meters (FSM) to use an infra-red light-source, they have remained ahead of the competition ever since. There are three models available, all offering: Corrosion-Free Corrosion is not an issue with HSS sensors due to the fact that we only use hard anodised aluminium combined with a salt-dip brazing process. The dip brazing ensures that the sensor enclosures are strong and leak-free while the military standard anodising provides unrivalled corrosion resistance. The extra expense of this process has proven worthwhile for strength, accuracy and long-term durability. Performance and quality are paramount and only the best results are accepted. Unbeatable Accuracy The combination of design, light-source type, wavelength and undisturbed sample volume gives Biral HSS sensors unbeatable accuracy. Design Using a unique patented design, the HSS range is considered to provide the best correlation of extinction coefficient (EXCO) to observed visibility. In reduced visibility conditions, whereas other sensors using different scattering angles report only precipitation, Biral HSS sensors continue to provide accurate visibility AND precipitation data. Light-Source The light-source is an infra-red diode which has been proven to provide higher accuracy, longer life and much more consistent readings than sensors using visible light-sources. The patented design of the HSS sensors means that no other sensor can match their performance. Wavelength Biral’s choice of light-source and wavelength (880 nm) is considered to be the best for accuracy where it counts most - around the 1 mile range. The choice of the wavelength is critical when deciding how the sensor performs in terms of accuracy and shifts in light spectra. The wavelength used is perfect for the shift in light from white (visibility below 1 mile) to blue (visibility from 1 mile to several miles). Almost all sensors using FSM technology can detect the white spectrum well, but HSS Sensors also detect the shift from white to blue spectrum and therefore maintain accuracy values to much higher visibility ranges. Undisturbed Sample Volume Accurate visibility and precipitation measurements require the sample volume to see only what is actually present. Other designs often suffer from precipitation splashing off the instrument enclosure, turbulence effects and unwanted reflections. The unique design of Biral HSS sensors ensures that the sample volume remains undisturbed regardless of wind direction and precipitation conditions. Optical Geometry Reflections from snow and surface water may cause measurement errors if they are allowed to enter the receiver, a common problem in some sensor designs. The sensor heads of all Biral HSS sensors are positioned in the horizontal plane to ensure that the measurements are not influenced by surface reflections. Biral HSS sensors also provide "no-dew window heaters" and optional hood heaters to ensure that the heads remain free from mist and obstruction even in the most challenging blowing snow conditions.
Specifications for HSS VF-500 Visibility / Fog Sensor
*FSM = Forward Scatter Meter
This range is in continuous development
therefore The following accessories are available:
Calibration reference kit - recommended for end-user confidence checks and recalibration. The kit contains a carrying case, zero plugs and a calibration plaque to a specific EXCO value. One kit can be used on any number of sensors of the same range. Stainless steel mounting kit - includes U-bolts, fasteners and adapters to secure the sensor and power control unit to any pole with a diameter between 1.8 - 2.9 inch. Transit case - scientific case lined with 3 inch foam to hold the sensor securely in place in extreme handling conditions.
Specifying Measurement / Switching Range when ordering At the time of manufacture each sensor is scaled to provide the greatest possible resolution for your specific application i.e. the best useable data. We have 3 standard ranges and these are shown below in Figures 1 and 2 (the information is the same in both but one is a diagrammatic representation and the other tabular). If you would like us to help you decide on the best range for your application or would like an alternative range please email us: wwwmet@biral.com Guide to selecting the correct scale when ordering:
NB In the measurement range 0.1 V - 0 V the signal resolution will be quite low and we would not recommend using the sensor within this range with a data logger or where the cable lengths are in excess of 328 ft. These ranges are indicated by the Low Signal Range (l l l l l l).
Figure 2 tabular
E&OE This unit is usually dispatched within 2-4 weeks ARO (After Receipt of Order) Warranty The VF-500 Visibility Sensor comes with 2 years warranty as standard. After Sales Support Biral offers free advice and technical support for the lifetime of the instruments we sell. Once you have purchased the unit you can contact us for help on wwwmetsuppport@biral.com |
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| Links to previous pages Fog / Visibility
Section |
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| Links to previous pages Fog / Visibility
Section |
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| Links to previous pages Fog / Visibility
Section |
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Links to previous pages Fog / Visibility
Section
Tel UK: 01275 847787 Fax UK: 01275 847303 Email: wwwmet@biral.com |
Not sure if this is the right sensor for you and would like help selecting a sensor? email us: wwwmet@biral.com
This range is in continuous development therefore specifications may change without prior notice. E&OE
Thank you for visiting www.biral.com/met/fog/vf500.htm |
