What are the common issues in optical terminal installation and construction?
As the fiber optic market continues to mature, the application fields of optical terminals have become increasingly extensive. Moreover, their cost is basically on par with that of cable, and in some
As the fiber optic market continues to mature, the application fields of optical terminals have become increasingly extensive. Moreover, their cost is basically on par with that of cable, and in some cases even lower, making fiber optic transmission increasingly advantageous.
Analog Optical Terminal Series
The following scenarios use a one-channel video and one-channel reverse data optical terminal as an example; other models operate on the same principle.
- No video image and unable to control the PTZ. Possible causes:
(1) The fiber optic link is disconnected or the attenuation is too high.
Test method: Use an optical power meter to directly measure the continuity and attenuation of the fiber link. A measured optical power within -7dB to -26dB is considered normal.
(2) The optical terminals at both ends are not properly powered.
Test method: Check the power supply condition. If power is properly supplied, use a multimeter to measure the loaded voltage at the optical terminal power interface. The normal values are approximately +9V and -9V.
(3) The transmitter and receiver are reversed.
Test method: The transmitter is TS with video input at VID IN; the receiver is RS with video output at VID OUT.
- Video image is present, but the PTZ cannot be controlled. Possible causes:
(1) The fiber link attenuation has reached the critical value.
Test method: Use an optical power meter to check. If the attenuation is above 20dB, or the measured optical power is around -30dB.
(2) Whether the DIP switch address of the decoder matches the address selected by the master control device.
Test method: Refer to the manual and verify that the decoder DIP switch settings match the channel selected on the master control device.
(3) Whether the protocol selected on the master control device matches the decoder.
Test method: Refer to the manual and check whether the protocols are consistent.
(4) Whether the data interface type of the optical terminal matches the decoder model.
Test method: Tiandy TC-615 series decoders (including dome PTZ) and decoders from other manufacturers using 485 communication should be paired with optical terminals with 485 interfaces; Tiandy TC-618 series decoders (including decoders) should be paired with optical terminals with TTL interfaces. Please check the interface type.
(5) Check whether the data wiring is correct.
Test method: Refer to the data port definitions in the manual and check whether the control wires are reversed.
(6) The distance of the front-end data cable exceeds 150 meters.
Test method: Check whether the distance between the optical terminal at the front-end monitoring point and the decoder exceeds 150 meters. If the data cable is too long, it may result in insufficient drive capability.
(7) Too many decoders are connected to one pair of optical terminals.
Test method: The number of decoders connected to one pair of optical terminals should not exceed the number of video channels of the optical terminal.
(8) The power supply provides +9V and -9V, but the -9V supply is not connected.
Test method: Check whether the optical terminal power supply is normal, whether the -9V wiring is loose, and measure the loaded voltage with a multimeter.
- Video image shows rolling, black stripe interference, or screen distortion. Possible causes:
(1) The fiber link attenuation is too high; measure with an optical power meter.
Test method: Use an optical power meter to check; < -25dB is considered normal.
(2) The optical terminal is subject to interference from strong signal sources, such as strong electric or magnetic fields.
Test method: Confirm whether such interference sources exist at the site and relocate the equipment for testing.
(3) The optical terminal power supply is faulty or the voltage is unstable, causing crosstalk between video channels.
Test method: Replace the power supply for testing, install a voltage stabilizer, and, where conditions permit in the master control room, install a UPS power supply.
- Data control is intermittent, or the PTZ rotates automatically (485 data interface). Possible causes:
(1) Poor 485 impedance matching, excessive load, excessive control cable distance, or failure to wire in a bus topology.
Test method: Since the 485 protocol has strict requirements for impedance matching, impedance matching may vary at different project sites due to different wiring practices. Please use bus topology to connect decoders wherever possible. If star topology is used, it is recommended to install a TC-3001 485 isolator.
Digital Optical Terminal Series
The following scenarios use a four-channel video and one-channel reverse data optical terminal as an example; other models operate on the same principle.
- No video image and unable to control the PTZ. Possible causes:
(1) No video input, or the data cable is not connected.
Test method: When a video signal is connected to the transmitting optical terminal, the corresponding video channel indicator will light up. If it does not light up, the video input is not normal. Check whether the data cable is wired correctly. For 485 data (paired with Tiandy 615 series decoders), connect to terminal 1 (485A) and terminal 2 (485B); for TTL data (paired with Tiandy 618 series decoders), connect to terminal 1 (MS) and terminal 8 (GND).
(2) The fiber optic link is disconnected or the attenuation is too high.
Test method: Use an optical power meter to directly measure the continuity and attenuation of the fiber link. A measured optical power within -4dB to -21dB is considered normal. If an optical power meter is not available, the link status can be identified by observing the indicator lights on the optical terminal. When no video signal is connected to the transmitting optical terminal, if all status indicators on the receiving optical terminal are lit, the fiber link is disconnected or the attenuation is too high. Under normal conditions, if the first channel of the transmitter has a video input (indicator lit) and the fiber link is properly connected, the first channel video indicator on the receiver will also light up while the other indicators remain off, which also confirms that the optical terminals themselves are working properly.
(3) The optical terminals at both ends are not properly powered.
Test method: Check the power supply condition.
(4) The transmitter and receiver are reversed.
Test method: The transmitter is TS with video input at VID IN; the receiver is RS with video output at VID OUT.
- Video image is present, but the PTZ cannot be controlled. Possible causes:
(1) The fiber link attenuation has reached the critical value.
Test method: Use an optical power meter to check. If the attenuation is above 20dB, or the measured optical power is around -20dB.
(2) Whether the DIP switch address of the decoder matches the address selected by the master control device.
Test method: Refer to the manual and verify that the decoder DIP switch settings match the channel selected on the host device.
(3) Whether the protocol selected on the master control device matches the decoder.
Test method: Refer to the manual and check whether the protocols are consistent.
(4) Whether the data interface type of the optical terminal matches the decoder model.
Test method: Tiandy TC-615 series decoders (including dome PTZ) and decoders from other manufacturers using 485 communication should be paired with optical terminals with 485 interfaces; Tiandy TC-618 series decoders (including decoders) should be paired with optical terminals with TTL interfaces. Please check the interface type.
(5) Check whether the data cable is reversed.
Test method: Check whether 485 A and B, as well as the MS and GND of the TD bus, are reversed. Refer to the data port definitions in the manual.
(6) The distance of the front-end data cable exceeds 150 meters.
Test method: Check whether the distance between the optical terminal at the front-end monitoring point and the decoder exceeds 150 meters. If the data cable is too long, it may result in insufficient drive capability.
(7) Too many decoders are connected to one pair of optical terminals.
Test method: The number of decoders connected to one pair of optical terminals should not exceed the number of video channels of the optical terminal.
- Video image shows rolling, black stripe interference, or screen distortion. Possible causes:
(1) The fiber link attenuation is too high; measure with an optical power meter.
Test method: Use an optical power meter to check; < -18dB is considered normal.
(2) The optical terminal is subject to interference from strong signal sources, such as strong electric or magnetic fields.
Test method: Confirm whether such interference sources exist at the site and relocate the equipment for testing.
(3) The optical terminal power supply is faulty.
Test method: Replace the power supply for testing, install a voltage stabilizer, and, where conditions permit in the master control room, install a UPS power supply.
- Data control is intermittent, or the PTZ rotates automatically (485 data interface). Possible causes:
(1) Poor 485 impedance matching, excessive load, excessive control cable distance (over 150 meters), or failure to wire in a bus topology.
Test method: Since the 485 protocol has strict requirements for impedance matching, impedance matching may vary at different project sites due to different wiring practices. Please use bus topology to connect decoders wherever possible. If star topology is selected, it is recommended to install a TC-3001 485 isolator.
- One or several video channels have no image, but the PTZ can be controlled. Possible causes:
(1) The input video signal is abnormal.
Test method: Check whether the corresponding video input channel indicator on the transmitting optical terminal is lit. If the video signal input is normal, the corresponding indicator will light up. If the indicator does not light up, there is a problem with the front-end signal source.
- When multiple decoders are connected, some can operate while others cannot. Possible causes:
(1) The control cable of the non-operating decoder is incorrectly wired.
Test method: Check the control cable.
(2) The DIP switch settings of the non-operating decoder are incorrect.
Test method: Refer to the manual for configuration.
(3) The control cable of the non-operating decoder is short-circuited.
Test method: Measure with a multimeter.
(4) Poor 485 impedance matching, excessive load, excessive control cable distance (over 150 meters), or failure to wire in a bus topology.
Test method: If star topology is used, it is recommended to install a TC-3001 485 isolator.
Symptom Handling
Symptom 1: The power indicator of the optical terminal is not lit.
Handling: Check whether the modular switching power supply is operating normally and whether the input voltage and output voltage meet the requirements.
Symptom 2: The video image is displayed on the monitor but with significant noise.
Handling: The effective transmission distance of the fiber may have reached its limit, or the fiber connector may be defective or damaged.
First, use an optical power meter to measure whether the transmitter output optical power meets the requirements. After the optical signal is transmitted over distance, wipe the fiber connector with alcohol, then use an optical power meter to measure the received optical power and verify whether it meets the receiver sensitivity requirements.
Second, check whether the cable from the signal source to the optical transmitter and from the optical receiver to the monitor is too long.
Symptom 3:
The camera is powered on, the video monitor is powered on, and the fiber optic system is operating (power LED lit), but no image appears on the monitor screen.
Handling: The cause may be that the coaxial cable is connected, but the channel position does not match the channel on the optical terminal transmitter or receiver.
(1) At the monitor end, replace the potentially faulty card with a known good card. If the problem persists, install the potentially faulty card in another slot that is known to work properly. If the receiver fails to operate, the card needs repair. If it operates normally, reinstall it in its original position.
(2) At the transmitter end, replace the potentially faulty card with a known good card. If the problem persists, install the potentially faulty card in another slot that is known to work properly. If the receiver fails to operate, the card needs repair. If it operates normally, reinstall it in its original position.
(3) If the backplane in the rack (the rack housing the transmitter) is normal, consider connecting the transmitter and receiver through a known good link. If the transmitter fails to operate, the problem may lie in the card slot connection. If the transmitter operates, it indicates that both the transmitter and the card slot are problem-free. Install the original receiver in another slot of the desktop rack/rack-mount chassis and check whether the backplane connection is problematic. If the receiver operates, the problem lies in the backplane connection. If the receiver fails to operate, replace the power supply and recheck. If replacing the power supply is still ineffective, install the chassis on a known good link for testing. If it still fails to operate, try moving the card to another slot. If the card fails to operate in one slot or in all slots, the backplane needs to be replaced.
Symptom 4: Data signal communication fails.
Handling: Refer to the DE15 pinout diagram and check whether the data input and output connections are correct. Verify whether the transmitted data format matches the optical terminal model.