Campbell Scientific SR50A Distance Sensor - Manual (Page 17)

SR50A Sonic Ranging Sensor
3.6.3.2 Auto Measure Auto Output Mode
In this mode the SR50A will automatically exit its low power mode, initiate a
measurement and output the data. The frequency by which the SR50A will
perform this is set by adjusting the Measurement Interval Units and the
Measurement Interval Value parameters.
• No command is required from an external device to obtain a measurement.
• The data recorder or equipment simply needs to read the incoming serial
data from the SR50A.
3.6.3.3 Auto Measure Polled Output Mode
In this mode the SR50A will automatically exit its low power mode, initiating a
measurement. The output data string will not be sent until a poll command is
received. When a poll command is received by the SR50A the output data will
typically commence 100ms after the poll command is sent.
The frequency by which the SR50A will perform the measurement is set by
adjusting the Measurement Interval Units and the Measurement Interval
Value parameters.
• The main advantage of this operating mode is that the receiving device
will only have to wait 100ms for the data as opposed to 1 second.
• This configuration is also more conducive to a multidrop RS-485 system
where individual sensors do not transmit until they are addressed.
3.6.4 Distance to Target or Depth
The SR50A can output either distance to target values or calculate snow depth
values. To obtain a valid snow depth value the parameter distance to ground
must be entered.
The SR50AT will compensate the readings for temperature; the SR50AT is
available on special order only.
Do not use this option on the SR50A sensor unless the
SR50A is sent valid temperature readings via the
Temperature Input command (see Section 3.6.10). CAUTION
3.6.5 Distance to Ground
A valid distance to ground must be entered when the SR50A is configured to
output snow depth values. The value must be in Meters regardless of the
output units that are selected.
If the exact value cannot be obtained it is better to slightly overestimate the
value rather than underestimating it. If a Distance to Ground value is too
small, the SR50A will output an error value as the snow surface should not be
below the ground surface.
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