CS225 Temperature String
7
To use more than one string per datalogger, you can either connect the different
strings to different SDI-12 compatible ports on the datalogger or change the
SDI-12 addresses of the strings and let them share the same connection. Using
the SDI-12 addressing method minimizes the use of ports on the datalogger
(see below for limits on the total cable length).
There are two ways to set the SDI-12 address of the CS225:
By sending the required commands to the sensors via an SDI-12
recorder/datalogger that allows talk through to the sensor.
By loading a program into the datalogger that sends the required
commands
(see Section 7.5,
Changing the SDI-12 Address Using
LoggerNet, and a Datalogger
).
7.1.1 Long Cables
As the measurement data is transferred between the Temperature String and
datalogger digitally, there are no offset errors incurred with increasing cable
length as seen with analog sensors. However, with increasing cable length
there is still a point when the digital communications will break down,
resulting in either no response from the sensor or corrupted readings. The
original SDI-12 standard specifies the maximum total cable length for the cable
as being 61 meters (200 ft), but we are able to exceed this limit by:
Using low capacitance, low resistance, screened cable.
Ensuring that the power ground cable has low resistance and is connected
to the same ground reference as the datalogger control ports.
7.1.2 Power Conservation
The CS225 draws less than 1 mA of current per sensor between polling
sessions from its 12 V supply. In many applications this is minimal compared
to overall system power use, so the sensor can be permanently powered to
avoid the warm up period.
In very low power applications battery power can be conserved by turning the
12 V supply to the CS225 on a minimum of 10 seconds before the CS225 is
polled for a measurement (allowing for the warm-up period) and then turning it
off afterwards.
This switching can be achieved in different ways depending on the type and
model of your datalogger. If available, the switched 12 V output of the
datalogger can be used.
Summary of Contents for CS225
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