Campbell SDS-122, User Manual

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User Guide
5
3. Installation
You should install the SDS-122 in a dry, non-condensing environment. The
ENC12/14 datalogger enclosure, available from Campbell Scientific, provides an
ideal environment for, typically, a CR10/10X datalogger and the SDS-122, plus a
power supply or other equipment.
Use one SC12 cable to connect the SDS-122’s ‘datalogger’ port to a datalogger
port, and a second to connect port ‘B’ to a compatible modem. A computer/short
haul modem can be connected to port ‘A’ using a standard RS232 cable.
Normally, for most applications, there will be no need for a connection to be made
between the 3-way terminal block on the SDS-122 and the datalogger, unless
direct measurements of the switch status, or manual control is required. It is
recommended that a ground wire is connected between the ‘G’ terminal of the
SDS-122 and the system protective ground, to ensure optimum internal transient
protection of the device.
Although the SDS-122 has built-in transient protection, it is not
protected against secondary lightning damage.
Devices that are connected to port A or port B which are likely
to be subject to large transients should have external
protection fitted. For long cable runs on port A, RAD-SRM
Short Haul modems fitted with RAD-SP lightning arrestors
should be used.
4. Configuration
The configuration of the SDS-122 is defined by internal jumpers. To access these
jumpers it is necessary to open the case by removing the four case screws and
pulling the two halves of the case apart.
Before touching any components or jumpers, take precautions
against electrostatic damage when handling the exposed
circuit board – either by using an ESD protection earth strap
connected to the sensor case, or, at the very least, by making
sure that you discharge any static by touching the case or
metal shell of the 'D' type connectors on the circuit board.
The jumpers control:
•
The way in which the SDS-122 switches from one port to another
•
The RS232 port configuration (DCE or DTE)
•
The degree of isolation between the datalogger and the RS232 device.
It is important to understand the different methods of isolation, as this can affect
the accuracy of measurements made by the datalogger. In permanent installations
it is good practise to ensure that the datalogger ground and computer ground are
isolated, otherwise ground loops and digital noise could result in errors on low-
level analogue measurements. The SDS-122 can be set to provide opto-isolation
to prevent such ground loops, but this mode of operation is not suitable for all
RS232 devices, either because the device needs to source power from the
CAUTION
CAUTION