HSS VPF-730 Visibility and Present Weather Sensor

INTRODUCTION

Originally designed for the US military, the HSS VPF-730 Present Weather Sensor is one of a kind, being the only infra-red based forward scatter meter to measure visibility AND present weather including precipitation type and rate.

It is the best combined visibility and present weather sensor on the market today. Using proven technology, this sensor is designed for a wide variety of applications such as Runway Visual Range (RVR), RADAR or other instrument calibrations (research into atmospheric phenomena) and / or roadside stations for now-casting ice or other dangerous conditions. The only sensor to provide true criteria for visibility and state of the ground according to World Meteorological Organizations (WMO) table 4680.

Using optional input cards, other weather parameters can be measured, providing a complete weather station which is compact and requires little power.

It is a robust and accurate instrument with excellent performance proven over 20 years of operation often in extreme conditions.

The VPF-730 is used for a variety of applications including:

• airport visibility
• RVR (Runway Visual Range)
• atmospheric research
• now casting
• RADAR calibration
• to calibrate other manufacturers’ visibility sensors

Features

• measures visibility AND present weather
• proven accuracy, reliability and repeatability
• self-test and monitoring system
• very low power requirements
• the only sensor with adjustable matrix for varying wind conditions
• long and trouble-free operational life
• minimal maintenance requirements and running costs

Measurement Principle

The VPF-730 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 atmospheric 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.

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Data Output

The sensor is configured with RS-232C signal output as standard with RS-422 communications available as an option. The data is output in various ASCII data strings, such as a small compressed data string, expanded data string and monitoring data string amongst others. The unit can be set in either automatic or polled mode and data sent to a printer or to a PC for tagging, processing and archiving.

Example of data output (pdf - opens in new window)

Construction

Corrosion is not an issue with HSS sensors as they are constructed from hard anodised (dip brazed), high grade aluminium which provides a long lasting superior finish. This durable metalwork does not require painting or maintenance.

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.

The sensor condition and performance can be monitored remotely using the self-test and monitoring system detailed below.

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).

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The VPF-730 System

The HSS VF-730 is a single lightweight unit which can be easily installed by one person.

The sensor has:

• RS-232C digital output
• window de-misters
• power line surge arrestors
• signal line surge arrestors
• self-test and monitoring system (see below for description)
• 19 ft power and signal cable
• waterproof mini-connectors
• calibration reference certificate
• manual

The sensor software (self-test and monitoring software)

The sensor condition and performance can be monitored remotely using the self-test diagnostic software which comes as standard (see also advanced self-test software under variants below).

The standard self-test diagnostic software monitors:

• Optical Source Power
• Transmitter Window Contamination
• Non-Volatile Memory Check Sum Test
• EPROM Check-Sum Test
• Restart Occurrence
• Sensor Sample Interrupt Verification
• RAM Read/Write Verification
• Register Read/Write Verification
• A/D Control Signal Test
• A/D Conversion Accuracy Check
• Forward-Scatter Background Illumination Level
  

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Available Options / Variants

Variations to the standard system are available at the time of order as follows:

• heating
• advanced self-test and monitoring system
• alternative RS-422 output
• ambient light sensor
• weather station module

..... see below for a wider description of each option

Optional heating

All HSS models are fitted with window de-misters allowing operation in temperatures down to 27º F. However, where the temperature drops below 27º F for more than a couple of hours a day the optional heating is recommended. This heating will provide error free operation in conditions down to - 58º F giving an operational range from - 58º F to + 140º F.

IMPORTANT - Please note that optional heating is available for all mains powered units (any voltage between 100-250 VAC) and 24 VDC battery powered units, but there is a restriction on heating for 12 VDC units.

A low power heater can be provided for 12 VDC units but it will operate at half of the standard rating (standard heater output = 15 W per hood and reduced heater output = 7 W per hood).

These reduced heating units can be controlled by three methods:

1. ON all of the time...power hungry but effective.

2. OFF all of the time...conserve power but may ice up if snow accumulates.

3. switched on and off situation depending on temperature settings monitored internally by the sensor (best use of power and error free measurements).

Optional advanced self-test and monitoring software

Even greater self-test and monitoring is available with the optional advanced self-test and monitoring system provides increased levels of diagnostic testing which in addition to the functions of the standard self-test and monitoring will also allow you to monitor:

• Forward-Scatter Receiver Sensitivity
• Back-Scatter Receiver Sensitivity
• Forward-Scatter Receiver Window Contamination
• Back-Scatter Receiver Window Contamination
• Power Supply Voltages
• Input Voltage Check (Battery Check- DC Powered Sensors Only)
• Back-Scatter Background Illumination Level

Optional RS-422 communications

Where there is 39 ft or more between the sensor and control computer RS-422 configuration is required.

Optional ambient light sensor

Sometimes referred to as a background luminance sensor the ambient light sensor connects directly to the VPF-730 allowing ambient light conditions to be measured according to ICAO (International Civil Aviation Organization) rules ie 4 level and with specific angle of view.

The ambient light sensor is designed for use with RVR (Runway Visual Range) systems on airfields and for use with Allard’s Law if night time visibility conditions are to be determined according to this instead of using the standard Meteorological Optical Range values (MOR).

Optional weather station module

this module provides 3 analogue inputs (0-10 V) allowing the VPF-730 to be used as a weather station. Output is a single time correlated data string.

For available accessories see below.

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Accessories

The following accessories are available:

• calibration kit
• stainless steel mounting kit
• transit case

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 a U-bolt and fasteners to secure the sensor to any pole with a diameter between 1.5 - 2.5 inch.

Transit case - scientific case lined with 3 inch foam to hold the sensor securely in place in extreme handling conditions.

VPF-730 Specifications  

*FSM = Forward Scatter Meter     

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