VP Supplementary Sensors, Stations and Accessories
There is a wide choice of extra sensors and accessories that can be added to Vantage Pro 2 stations to allow the design of sophisticated environmental monitoring systems. These include:
- Solar radiation and UV sensors;
- Supplementary stations to measure additional parameters including soil moisture and leaf wetness;
- Additional data display units;
- Installation accessories, including:
- Ancillary wireless units;
- Fan-assisted radiation shields;
- Mounting accessories;
Each of these types of accessories is introduced below. Please contact us for advice on how best to include these items in a system configuration.
Solar radiation and UV sensors
All
Vantage Pro 2 stations - cabled and wireless - will accept either
or both of these two sensors, which are mounted on a small shelf
assembly that sits alongside the rain gauge and that needs to be
bought as a separate accessory item. Both sensors, together with
the mounting shelf, are included pre-assembled in the VP2 Plus
models.
The UV sensor in particular is a relatively expensive item to make and this accounts for the significantly higher cost of the Plus models. Users interested only in the solar radiation sensor - pictured left, though the UV sensor looks similar - can buy this as an accessory (plus mounting shelf) for the standard VP stations at lower cost than buying a VP Plus model. (But for users looking to add both solar and UV sensors soon after buying their initial station, remember that the Plus package price offers a substantial cost saving compared to adding both solar and UV sensors separately).
The solar sensor's function is to monitor the strength or power of sunshine (mostly in the visible part of the spectrum), obviously an important weather parameter in its own right, but especially relevant also to stations for agricultural applications, for example to allow the calculation of evapotranspiration (ET), which the VP console can display directly. The UV sensor's main application is in monitoring of UV intensity, which is of particular health-related interest, for example to assess sunburn risk.
Note that the solar sensor measures global solar irradiance levels. This is the sun's strength in units of watts/square metre and the best objective measure of the sunshine's power. The VP console has no direct ‘hours of sunshine’ readout, although this can be calculated, to a first approximation, by the Weatherlink software from logged solar radiation data. More sophisticated algorithms for conversion of logged solar data to sunshine hours are also available in add-on software.
Measuring additional temperature/humidity values, soil moisture and leaf wetness
The extra sensors necessary to measure additional temperatures, humidity, soil moisture and leaf wetness are termed 'supplementary stations' by Davis - a term we find a little confusing though we use it here for consistency with the Davis catalogue. These so called stations are a set of wireless-only units consisting of a wireless transmitter in a weatherproof shelter plus various attached sensor elements. But these are not standalone units - a console is also still required to display the data. Typically, each supplementary station is mounted completely independently of the main ISS and relays data directly back to the standard VP2 wireless console via its own separate wireless data channel (and not via the ISS).
When considering supplementary stations, please bear in mind :
- Supplementary temperature sensors read to a resolution of ±1°F rather than the 0.1°C of the ISS temperature sensor. (This is a result of how the supplementary data streams are handled rather than of poorer intrinsic temperature accuracy);
- Only certain combinations of supplementary stations can be used to report data back to a single VP2 console. Data from all permitted combinations can be viewed on the VP2 console - read how;
- Data from supplementary stations can be logged and handled by the standard Weatherlink logger and software, but there are different constraints on the permitted combinations of numbers and types of sensor as compared to the VP2 console display;
Wireless temperature and temperature/humidity stations
The
6372 Temperature Station (left) and 6382 Temperature/Humidity
station (right) have related but distinct applications. The 6382
Temp/Hum station is similar to an ISS unit in monitoring both air
temperature and humidity and is supplied complete with radiation
shield. The 6372 Temperature station measures temperature only and has a sealed stainless steel sensor on a 12' (3.6m) cable
that can be used to measure air, soil or water temperatures. (NB
Accurate measurements of unshaded air temperature would require
purchase of a separate radiation shield.)
A maximum total of eight stations can report back to a single VP2 console. (Remember though that eight would use all available wireless channels and therefore no other station, not even an ISS, could be used in this configuration.) Each 6372 or 6382 station accepts only a single temperature sensor and therefore one station is required for each additional temperature reading that is to be measured. These units run on a single lithium battery only, that is without solar panel assistance. Each battery should last a minimum of 6-9 months.
Wireless leaf wetness and soil moisture/temperature station
This
is effectively a multi-sensor
station comprising a 6345 wireless transmitter unit (shown left - mounting pole not included) to which can be attached a variety of
sensor probes for measurements of soil moisture (potentially at
different soil depths), and/or of leaf wetness, plus temperature. Clearly, the 6345 station is of most interest to potential
agricultural and horticultural users. Data from all sensors connected to a 6345 transmitter passes back to the display console over a
single wireless channel, so making optimal use of the available data bandwidth. The 6345 stations are powered in exactly the same way
as the mains ISS, ie a small solar panel is used to
supplement the standard lithium battery.
There are three types of sensor which can be fitted to these stations ; soil moisture, leaf wetness (shown right) and temperature. These can be used in various combinations. The temperature sensor is of a similar air/soil/water type as the 6372 station above and can therefore be used to measure the temperature of any medium.
A 6345-based station is specified by adding whichever additional sensor probes may be required to the 6345 transmitter unit itself. Comments on the different types of sensor probes are as follows:
- The 6345 transmitter can be fitted with up to four temperature sensors and can therefore become a specialist temperature-only sensing station if required. Although only one 6345 can be linked to a single VP2 console, it can pass readings from all four sensors to the console across a single wireless channel.
- The 6345 unit can also accept up to four soil moisture sensors, each probe being supplied with 15' (4.6m) attached cable. For soil moisture measurements, the moisture reading varies with temperature at the probe depth. The Davis stations are therefore designed to temperature-correct each moisture reading individually, which is achieved most accurately if a moisture probe is paired with its own temperature sensor buried close by and at the same soil depth. So up to four pairs of moisture and temperature probes can be added, for example to assess moisture at different depths at the same location.
- Up to two leaf wetness sensors (see image above right) can also be fitted, both optionally with paired temperature sensors. Leaf wetness sensors are mainly used in agricultural applications to provide data used in predicting disease occurrence, such as potato blight. (But they have also found other imaginative uses, eg as early indicators of rainfall.)
Please remember that supplementary temperature values such as those measured by 6345 sensors are limited to a resolution of 1°F (0.5°C).
Secondary Displays
Sometimes you may need additional data displays so that for example weather readings can be seen in two different rooms. Of course, if the Weatherlink data logger is installed then the PC display, which doesn't necessarily need to be in the same place as the VP2 console, can effectively function as a repeater display. And a large monitor or screen can act as an impressive secondary display for public areas. (Read more about PC-based repeater displays.) But often a smaller, always-on display will be preferred, for which Davis provide two options: a second VP2 main console or a Vantage Vue console. Note that both of these are wireless-only options - it is not straightforward to add secondary displays (other than those linked to a PC) to cabled VP2 stations.
Additional main VP2 console
The standard 6312 VP2 wireless console can be bought as a separate item, so adding this to a standard wireless VP station will provide a second display. The secondary display can receive its data from one of two sources:
- It can listen to the same (eg ISS) transmitter as the primary display and thereby receive the same primary data stream;
- The primary console can be set to retransmit mode, where it will rebroadcast the data it receives but on a different wireless channel. The secondary display will be set to receive the data stream on the rebroadcast channel. (This provides a potential mechanism by which a secondary display can receive the VP2 data even if there is not good direct reception from the ISS at the secondary display location.);
In both cases, all the usual comments for ensuring good wireless reception will apply equally to the secondary console; in other words it will need to be in good wireless range of either the primary transmitter(s) or of rebroadcast signal from the primary console.
Additional Vantage Vue console
Because the Vue uses exactly the same wireless technology as the main VP2 stations, it is possible to use a Vue console as a secondary display for a VP2 system. The main advantage here is that the Vue console is only around half the cost of a second VP2 main console. However, there are two minor drawback to using a Vue console in this way:
- The display area on the Vue console is smaller, being only about 2/3 the size of the VP2 console display;
- The Vue console cannot display data from supplementary VP2 transmitters (with the 6332 Anemometer Transmitter as a single exception);
Installation Accessories
Wireless repeaters
Wireless repeaters extend the range possible between primary
transmitter (eg the ISS unit) and the main VP2 console, by
receiving the wireless data and retransmitting again at full
power and thereby acting as a staging post for the signal. Each
repeater can extend range by 150-200m in clear line-of-sight
conditions and repeaters may be daisy-chained to cover longer
distances. Repeaters can be useful not only for extending range, but for taking the signal around an object such as a building which
would otherwise be in the direct signal path between ISS and console and otherwise preventing good reception. One repeater is able to handle signals from multiple
transmitters on different channels.
There are two types of repeater: 7627 (pictured right) is the solar-powered variant and will operate in a completely isolated location. 7626 is an AC-powered version and lacks the solar panel; this is the cheaper version but is obviously only suitable for use when a mains supply is close at hand.
Long-range wireless repeaters
There are also two wireless repeater versions known as long-range (LR) repeaters. Instead of having a single whip antenna (as in the standard repeaters) the LR repeaters have two separate internal connectors - one for receive and one for retransmit - intended for linking to external antennas (which must be specified and purchased separately). Because these add-on antennas can have much higher gain than the standard whip they offer the possibility of much longer range in a single hop. With two high-gain antennas fitted, a range of up to 1km or potentially even more can be achieved, provided line-of-sight for each leg of the signal path is maintained.
As with the standard repeaters there are two LR repeater types available - 7653 (AC-powered) and 7654 (solar-powered).
Wireless anemometer transmitter
The 6332 wireless anemometer transmitter looks similar to the wireless repeater above and is specially designed to accept the input cable from a standard VP anemometer and to broadcast the wind speed and direction data on a separate wireless channel. With this transmitter, the anemometer can be completely separated from the main ISS sensor assembly and anemometer and ISS mounted in quite different locations. (Normally, the anemometer can be mounted separately from the main assembly, but the two must be connected by cable in order for the anemometer readings to be transmitted back to the console by the single ISS transmitter).
Fan-assisted radiation shield
The
standard versions of all VP2 stations are fitted with a passive
radiation shield to prevent sunlight falling directly on the
temperature sensor and hence giving erroneously high readings.
This passive shield works well for the great majority of days in
the year but, inevitably, on the hottest/brightest/calmest days
the air temperature inside the shield may be up to 1-2°C above
the outside air temperature. For users seeking ultimate
temperature accuracy, all VP2 stations can be specified with a
fan-assisted radiation shield (FARS) rather than the standard
passive type. A fan actively draws a steady flow of air over the
temperature sensor and hence reduces any disparity between
temperatures inside the shield and outside. In addition to providing more accurate readings of air temperature on calm/sunny days, the
FARS shields also improve the responsiveness of temperature readings under weather conditions where air temperature may be changing
rapidly.
There are two types of FARS shield available for the VP2 stations:
- The 24-hour FARS shield: As its name suggests the fan on this shield is intended to run continuously and this shield therefore has its own solar panel and rechargeable batteries. The 24-hour FARS is available only for the wireless VP2 models and is a factory-fit option only - for ordering you need to specify the 6153 (standard VP2 with FARS) or 6163 (VP2 Plus) stations. (In practice, we don't particularly promote the 24-hour FARS for use in the UK. In UK winters there can be a succession of short, gloomy days which provide insufficient sunlight to keep the FARS fan spinning. Under these conditions the temperature response may actually end up being worse than with a standard VP2 model.);
- The 7747 Daytime-only FARS (DFARS) shield: This is a simplified and therefore cheaper FARS version that runs off solar power only. It obviously runs only during the daytime, but this is of course the only time when shield heating effects are likely to be of major concern. This 7747 unit is a user-fitted kit that may be specified with a new station or bought at any time subsequently. The only slight drawback of the DFARS kit is that it must be installed by the user but this is a very straightforward job taking maybe 15 minutes.
A FARS shield inevitably adds somewhat to the cost of a VP station and many customers conclude that it is an unnecessary luxury for the few days a year in the UK when it might make a material difference to temperature readings. But for those users who are tempted by a FARS shield, the 7747 DFARS kit does offer a good compromise between cost and effectiveness.
Mounting accessories
Vantage
Pro stations are supplied complete with fixings to attach the
outside sensors either to any tubular mast of 32-44mm diameter
or to any screwable flat surface such as a wooden post. But
there may be circumstances where no suitable fixing point is
available. Davis offer two accessories to help out here.
One is a sturdy galvanised tripod (7716 - shown right ) carrying a central mast reaching up to 2.1m (7') in height, which forms an ideal mounting point for the ISS unit and/or for attaching a further extension pole, for example to carry the anemometer.
The second is a Mounting Pole Kit (7717), containing two pieces of galvanised tube which fit together to form a 3' extension pole.