Campbell Scientific SR50A Distance Sensor - Manual (Page 16)

SR50A Sonic Ranging Sensor
Setting Description Options Default Value
Quality Output On
Off Off
Temperature Output On
Off Off
Output valid only for the
SR50AT (available on special
order only)
Diagnostics Output On
Off Off
3.6.1 BAUD Rate Setting
The factory Default BAUD Rate Setting of 9600 BAUD is suitable for most
applications. Lower BAUD rates (1200 or 4800) may improve communication
reliability or allow for longer cable lengths. Higher BAUD rates (19200 or
38400) may be used where faster communications are required.
The quiescent current draw for the SR50A in serial mode is normally 1.25mA
for BAUD rates of 9600 or less. The current draw increases to 1.5 and 2.25
mA for the BAUD rates of 19200 or 38400 respectively.
It is possible to download a firmware update to the SR50A via the RS-232 or
RS-485 communication interface. Higher BAUD rates may be desirable to
speed up this process.
It may take up to 30 minutes using a speed of 1200 BAUD, 7 minutes using
9600 BAUD, or 3 minutes using 38400 BAUD.
3.6.2 Address
The factory Default Address is 33. Normally for RS-232 applications there is
no need to change the default address. For RS-485 operation multiple sensors
can be polled individually if different addresses are assigned.
3.6.3 Operational Mode Setting
There are 3 different operational mode settings available on the SR50A.
Overall system design and desired performance determine which mode to
select. The SR50A operation for each of the 3 different modes will be
described as well as the advantages and disadvantages of each mode.
3.6.3.1 Measure in Poll Mode
In this mode the SR50A will remain idle until a measurement command is sent
(p33<CR>) where 33 is the default serial address. After the measurement
command is received, the SR50A will immediately begin a measurement and
transmit out the resulting data packet when complete. Typically the SR50A
will transmit the data packet within 1 second of receiving the command packet.
• The SR50A only performs a measurement when requested.
• The data output will lag the measurement command by 1 second.
• This configuration is conducive to a multidrop RS-485 system where
individual sensors do not transmit data until they are addressed.
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