Campbell Scientific SR50-L CSC Ultrasonic Distance Sensor - Manual (Page 10)

SR50 Sonic Ranging Sensor
4
DISTANCE = READING
T KELVIN
273.15
SR50
°
FORMULA 1. Temperature Compensation
The SR50 calculates a distance reading using the speed of sound at 0 °C (331.4
m/s). If the temperature compensation formula is not applied, the distance
values will not be accurate for temperatures other than 0
°C. A temperature
compensated distance is obtained by multiplying the SR50 reading by the
square root of the air temperature in degrees Kelvin divided by 273.15. An
example program that includes this correction is shown in Section 3.2.
On rare occasions, measurements made by the SR50 can
be adversely influenced by strong electromagnetic fields.
Electromagnetic fields can be generated by the operation
of heavy electrical machinery and the presence of radio
frequencies with field strengths greater than 3V/m.
Symptoms of this problem are erroneous measurements
randomly dispersed among accurate measurements.
This problem can be fixed by tying the probe body to earth
ground. This is done by scraping away a small patch of
the clear anodize coating and attaching a bare section of
stranded wire over the scraped area with a band clamp.
Copper wire and a stainless steel band clamp work best. It
is recommended to confirm with an ohmmeter that the
copper wire is making contact to the probe body.
3.1 SDI-12 Operation
SDI-12 is a Serial Digital Interface standard that is used for communication
between data recorders and sensors. Campbell Scientific’s CR10(X), CR500,
CR510, CR23X, BDR320, and CR200 series dataloggers have the capability to
read SDI-12 sensors (CR10’s with the correct PROM can do SDI-12).
The SR50 can be set to one of ten addresses (0 to 9) which allows up to ten
sensors to be connected to a single digital I/O channel (control port) of an
SDI-12 datalogger.
The SR50 is shipped from the factory with the address set to 0. The SR50
needs to be opened in order to change the SDI-12 address. Refer to Section 7.0
for details on opening the SR50 and Figure 8 for the Address/Option jumper
settings.
When it is necessary to measure more than one SR50, it is easiest to use a
different control port for each SR50 instead of changing the address in each
SR50.
SPECIAL CAUTION
But only for SR50’s
with a detachable cable
and connector directly
on the sensor housing.