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2.6.4 Audio signal output
Commonly the output parameter of a DVR audio signal is greater than 200mv
1KΩ(BNC) which can connect a low impedance earphone and active sound box
or other audio output equipments through a power ampliier. If the sound box and
the tone arm can not be isolated, a howling phenomena is often experienced.
Here are some methods to deal with this phenomena.
1).
Adopt a better directional tone arm.
2).
Adjust the sound box volume to below the threshold that produces the
howling phenomena.
3).
Use itment materials that absorb the sound to reduce the relection of the
sound.
4).
Adjust the layout of the sound box and the tone arm.
2.7 Alarm input and output connections
1. Alarm input
A. Alarm input is grounding alarm input.
B. Alarm input demand is the grounding voltage signal.
C. When the alarm is connected with two DVRs or connected with DVR
and other equipments, it should be isolated by relay.
2. Alarm output
Alarm output can not be connected with high-power load(no more than 1A).
When forming the output loop it must prevent the big current from relay damage.
Use the contact isolator when there is a high-power load
3. PTZ decoder connections
A. The earth for the PTZ decoder and DVR must be shared otherwise
the common-mode voltage will lead to the PTZ control failure. Shielded
twisted pair is recommended.
B. Avoid high voltage. Take precaution against the thunder and lightning.
C. At the outlying end connect a parallel 120Ω resistance to ensure the
signal
quality.
D. The 485 AB lines of the DVR can not connected with other 485 output
equipment in parallel.
E. The voltage between the AB lines of the decoder must be less than 5V.
4. Front equipment earthing note
Bad earthing can lead to burnout of the chip.
5. Alarm input type unlimited
The DVR alarm output port is constant opening type.
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