Vaisala WS425 - Manual (Page 66)

USER'S GUIDE____________________________________________________________________
66 __________________________________________________________________ M210361EN-E
The response is the following:
a+x<CR><LF>
where
a = The sensor address.
x = Currently active wind speed unit. The options
are:
0 = mph
1 = kt
2 = km/h
3 = m/s
<CR><LF> = Terminates the response.
SDI-12 TIMING
The Figure 12 on page 67 shows a timing diagram for an SDI-12
command and its response. The tolerance for all SDI-12 timing is ±0.40
milliseconds. The only exception to this is the time between the stop bit
of one character and the start bit of the next character. The maximum
time for this is 1.66 milliseconds, with no tolerance.
- A data recorder transmits a break by setting the data line to spacing
for at least 12 milliseconds.
- The sensor will not recognize a break condition for a continuous
spacing time of less than 6.5 milliseconds. The sensor will always
recognize a break when the line is continuously spacing for more than
12 milliseconds.
- When receiving a break, a sensor must detect 8.33 milliseconds of
marking on the data line before it looks for an address.
- A sensor must wake up from a low-power standby mode and be
capable of detecting a start bit from a valid command within 100
milliseconds after detecting a break.
- After a data recorder transmits the last character of a command, it
must relinquish control of the data line within 7.5 milliseconds
following the end of the stop bit. (Tolerance: +0.40 milliseconds.)