SmartSMS User Manual Soft dB inc.
User Manual p. 72
7.2 Wiring for the active system
All the wiring for the active system should be done using standard coaxial cable (RG-58, RG-59 or
RG-174 type) with BNC connectors. The maximum coaxial wire length should be approximately
100 m (328 ft). Please contact Soft dB if you have specific requirements.
SmartSMS units with integrated active preamplifiers:
SmartSMS units manufactured after september 2008 will have an integrated active preamplifier that
is be able to supply power to a maximum of 4 sensors. To ensure that your SmartSMS unit has that
integrated preamplifier, check the serial number of the unit. The 7
th
number indicates whether the
SmartSMS unit has an integrated preamplifier (if this number is 1) or not (if this number is 0). For
example, 0808121262 is a SmartSMS unit with integrated active preamplifier.
The integrated preamplifier can supply power to up to 4 sensors. All the sensors can be connected
in parallel on the Active Input. Simply use BNC female "T" connectors to connect the sensors on a
single active input. Soft dB can provide those "T" connectors on demand.
The maximum distance for the coaxial run between the SmartSMS unit and the last sensor should
be 500 feet (150 meters). If you need a longer run, use a SMS-PRE-4 unit near the sensors to
boost the signal.
Wiring Verification: Sensors have an internal impedance of approximately 1000 Ohms ±30%. So
you can measure the impedance at the end of the line to make sure the connection is good. If you
have many sensors, divide 1000 by the number of sensors and add the coaxial wire resistance.
Figure 66: Connection of the sensors with an integrated preamplifier
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