12
which avoid false and joint welding and oxidation. The high voltage current should be avoided especially.
2.7.4 Audio signal output
Commonly the output parameter of DVR audio signal is greater than 200mv 1KΩ (BNC) which can connect
the low impedance earphone and active sound box or other audio output equipments through power amplifier.
If the sound box and the tone arm can not be isolated, howling phenomena is often existed. There are some
methods to deal with the following phenomena.
1
、
Adopt better directional tone arm.
2
、
Adjust the sound box volume to be under the threshold that produces the howling phenomena.
3
、
Use fitment materials that absorb the sound to reduce reflection of the sound.
4
、
Adjust the layout of the sound box and the tone arm.
2.8 Alarm input and output connections
Before connecting the support equipment, notice the following situations:
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 grounding of the PTZ decoder and DVR must be shared otherwise the common-mode voltage will
lead to the PTZ control failure. The shielded twisted pair is recommended.
B. Avoid the entrance of high voltage. Make the layout reasonably. Take precaution from the thunder.
C. In the outlying end connect 120Ω resistance paralleled to reduce the inflection and insure the signal
quality.
D. The 485 AB lines of DVR can not connect with other 485 output equipments paralleled.
E. The voltage between the AB lines of the decoder must be less than 5V.
