User manual

MetPak Doc No 1575-PS-0001 Issue 02 CN 4240 March 2006
9 ANALOGUE OUTPUTS AND OPTIONS
Note : Analogue outputs are only available from MetPak Option 4 and 6..
Voltage output
The WindSonic in MetPak is default Voltage (0 – 5 V) representing wind speeds between 0-60m/sec.
The HygroClip S3 humiduty and temperature sensor applied with MetPak option 3 only has a voltage output. If the
customer fit his own temperature and humidity probe with a current output the the mode of the Windsonic output can be
changed to suit.
Important :
1. When using the current outputs, the load resistance between the Analogue outputs (TB3-8 and 9) and Signal
Ground must be <= 250 ohms, including cable resistance.
This is to ensure that the voltage levels do not exceed 5V.
2. The current outputs must be returned to Signal Ground (TB3-3).
Polar and Tunnel modes
If the WindSonic is configured in Gill Polar mode then the analogue outputs will be in Polar mode.
Polar mode direction wraparound
The Wind Direction in Polar mode can be configured for either Standard (0 - 359°) or Wraparound (0 - 539°) options. If
the Standard mode is used with a chart recorder, large swings of the recorder pen will be experienced each time the wind
direction passes between 0 and 359°. Using the Wraparound mode, when the wind first changes from 0° to 359°, there
will be a step change on the output, but after this first time the output will change smoothly each time the wind passes
through 360°. (Similarly, the first time the wind veers from 539° to 180°, there will be a step change, after which the
output will change smoothly).
Voltage output (V) Current output (mA) Wind direction
(degrees)
Standard Wraparound Standard Wraparound
0 0 0 4.00 4.00
180 2.5 1.67 12.00 9.33
360 5.0 3.33 20.00 14.67
540 n/a 5.0 n/a 20.00
Low wind speeds in polar mode
Whilst the wind speed is below 0.05 metres/sec, the wind direction will not be calculated.
In CSV mode, the Channel 2 output will switch between 0 and 5V (or 4 and 20mA) at the output rate selected.
In fixed field mode, the last valid direction will be output until a new value can be calculated.
Wind Speed scaling
The Wind Speed output can be configured such that full-scale output represents 30, 50 or 60 metres/sec.
In all cases zero Wind Speed is represented by 0V or 4mA.
Tunnel mode
When configured in Tunnel mode, Channel 1 output represents the wind speed along the U axis (South – North) scaled
as described above.
Channel 2 gives the direction of the wind along the U axis, where a –U vector (= wind from the N direction) is
represented by 0V (or 4mA), and a +U vector is represented by 5V (or 20mA).
Configuring Analogue outputs
WindCom may be used to change the factory default settings to configure WindSonic, alternatively, the user may elect
to use another terminal emulator package.This section describes the commands used to change User and
Communications settings.
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