HSS VF-500 Visibility Sensor

(with analogue output)

The HSS VF-500 Visibility Sensor is a top of the range sensor for measuring visibility and fog density. It can be used in extreme conditions as it is able to withstand the rigours of many years in marine environments.

With the optional fog warning relay the HSS VF-500 Visibility Sensor is used to automatically switch external devices such as warning lights, alarms and fog horns on lighthouses and offshore platforms when the visibility reaches a user defined limit.

Features:

• highly resistant to sea-water corrosion
• very reliable and built to last
• low level of maintenance
• proven accuracy and repeatability
• optional fog warning system for switching alarms and lights
• suitable for portable or fixed installation
• low power requirements (mains, battery, solar)
• EEx zone I and II configuration available

---

Measurement Principle

The  HSS VF-500 Visibility 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 Visibility Sensor is lightweight and can easily be installed by one person. The visibility sensor 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 (20 m) apart for safe and convenient access.

---

Maintenance and calibration

The  HSS VF-500 Visibility 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  HSS VF-500 Visibility Sensor operates in temperatures ranging from -58º F to + 140º F (-50º C to + 60º C). For operation below -27º F (-32º C) the heated version is recommended (please see information on the heating option below).


NB The temperatures quoted apply when using the sensor in a non-condensing environment. If you are unsure whether or not you require heating for your own application please contact us for advice.

---

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.

Measuring / Switching ranges

 

At the time of manufacture your sensor is scaled to provide the greatest possible resolution for your specific application i.e. the best useable data.

We have 3 standard measuring and switching 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).



Figure 1 diagrammatic representation of the measuring and switching ranges




Key to which range to select

• If you will be using the sensor with the Fog Warning System to switch equipment and do not wish to send the output to a data logger then please select using the Fog Warning Switching Range
• If you will be using the sensor to send data to a logger please select using the Total Measurement Range
  

• If you will be using the sensor for both then please select the scale with the most suitable combination of both ranges.

0.1V - 0 V range note
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 (100 m). These ranges are indicated by the Low Signal Range (l l l l l l).


Figure 2 - the same information depicted in tabular format

	Fog Warning Switching Range	Total Measurement Range	Low Signal
Range X	28 ft - 289 ft (8.5 m - 88 m)	9 ft - 18.6 miles (2.7 m - 29.9 km)	984 ft - 18.6 miles (300 m - 29.9 km)
Range Y	289 ft - 0.8 miles (88 m - 1.2 km)	98 ft - 18.6 miles (29.8 m - 29.9 km)	1.86 - 18.6 miles (2.99 km - 29.9 km)
Range Z	0.6 mile - 8 miles 0.96 km - 12.8 km)	984 ft - 186 miles (300 m - 299 km)	18.6 - 186.4 miles (29.9 km - 299.98 km)

---

The HSS VF-500 Visibility Sensor System

The  HSS VF-500 Visibility Sensor 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:

• 0-10 V analogue output
• window de-misters
• power line surge arrestors
• signal line surge arrestors
• electro magnetic interference protection
• 19 ft (5.7 m) interconnect cable
• calibration reference certificate
• manual

It is also supplied with a stainless steel mounting kit.

Stainless steel mounting kit

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 inches (46 - 74 mm).

---

Options / Variants

In addition the following variations are available:

• fog warning system
• heating
• output 0-20 mA or 4-20 mA as well as the standard 0-10 V

 

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 fog warning 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.

Heating

The VF-500 visibility sensor comes with window de-misters as standard allowing operation of the sensor in temperatures down to - 27º F (- 32º C). 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  (-50º C).

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.

---

Accessories

The following accessories are available:

• calibration reference kit
• transit case

Calibration reference kit

The calibration reference kit is 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.

Transit case

The HSS VF-500 Visibility Sensor is delivered in an environmentally friendly, triple ply, heavy duty carton with foam inserts. Whilst this is suitable for normal shipping, you may wish to consider ordering the scientific transit case if you intend to move the sensor frequently or the sensor will have to endure extreme handling. This transit case is even more rugged than the heavy duty carton with 3 inch (76 mm) foam to hold the sensor securely in place.

---

Delivery

This unit is usually dispatched within 2-4 weeks ARO (After Receipt of Order)

Warranty

The HSS VF-500 Visibility Sensor comes with 2 years warranty as standard.

---

Contact Biral for more information

To find out more about this instrument or to discuss your application requirements please do not hesitate to contact Biral.

• wwwmet@biral.com (or use the Make Request button below the product photograph)
• telephone to 01275 847787 (from the UK) or +44 1275 847787 (International)

---

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:

• wwwmetsupport@biral.com
• telephone to 01275 847787 (from the UK) or +44 1275 847787 (International).

---

This range is in continuous development therefore specifications may change without prior notice. E&OE.

Product Information

• VF500 Product Information.pdf
• HSS Visibility Sensor Brochure.pdf
• comparison_of_hss_and_sws_visibility_and_present_weather_sensors.pdf

Application Related Information

• HSS VF500 Visibility Sensors on the Severn Bridges.pdf
• Marine - HSS visibility sensors for coastal use.pdf
• Marine - HSS visibility sensors for offshore use.pdf

Scientific Papers and Articles

• how to measure fog.pdf