Campbell Scientific SR50-L CSC Ultrasonic Distance Sensor - Manual (Page 33)

A-1
Appendix A. Making Concurrent
Measurements with the SR50
Concurrent Measurement ability allows the datalogging system to initiate
measurements in SDI-12 devices and continue processing its program without
waiting for a reading from the SDI-12 device. When the sensor has a valid
measurement it will send this to the datalogger the next time it is polled. This
allows for faster execution of the datalogger program. Concurrent
measurement ability is available with SR50’s with OS version 1.1 or higher.
The OS Prom in SR50’s can be upgraded. Please call a Campbell Scientific
representative for details.
Of the Campbell Scientific product line, only the CR510, CR10X, and CR23X
dataloggers have the ability to make concurrent measurements. These
dataloggers use Program Instruction P105 SDI-RECORDER to measure the
SR50. Parameter two of P105 is where the Concurrent Measurement option is
set (use option code “ # -- “ where # is a number 0-8; see Table 1).
To Determine SR50 OS Version:
To determine the version of software in the SR50, insert ‘10’ in parameter 2 of
the P105 SDI-RECORDER instruction (SDI-12 command “aI” where a =
address). See Table 1 for list of all SDI-12 Commands. The sensor will
respond with a numeric signature. If the signature is 63845, you have version
1.1.
When using Concurrent Measurement option with several
SR50’s, it is possible that the sonic pulse from one sensor
may interfere or be intercepted by another sensor. For this
reason, make sure the sensors are mounted > 30 feet
apart. If this is not feasible, it may be necessary to
measure them the standard way without Concurrent
Measurement or at different times.
Concurrent Measurement Operation:
When Campbell Scientific dataloggers are using concurrent measurement
ability with the SR50, they will output –99999 until a reading is received from
the sensor. This occurs when using concurrent measurement ability because
the sensor receives the command to initialize a reading but does not have a
reading to send to the datalogger until the next scan. If the logger does not
receive a reading, it shows –99999 in the storage Input location (Numeric
Mode *6). The –99999 readings need to be filtered out except when
something is wrong, in which case the –99999 will indicate a problem.
The following algorithm is an example of how to filter out –99999 readings.
When 3 consecutive readings are bad (-99999) then we want to keep that
reading:
CAUTION: