Common Problem Solving for Optical Terminal Installation and Construction
As the fiber optic market continues to mature, the application fields of optical terminals have become increasingly extensive, and their cost is basically on par with that of using cables, or even lower in some cases, making fiber optic transmission increasingly advantageous.
Analog Optical Terminal Series
The following situations take 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: An optical power meter can directly measure the continuity and attenuation of the fiber optic link. A measured optical power within -7dB to -26dB is considered normal.
(2) Both optical terminals 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 optic link attenuation has reached the critical value.
Test method: Use an optical power meter to check. If the attenuation is above 20dB, or the optical power meter reading is approximately -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 selection.
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 has come loose, and measure the loaded voltage with a multimeter.
- Video image shows rolling, black stripe interference, or screen distortion. Possible causes:
(1) The fiber optic link attenuation is too high; it can be measured 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 fields or magnetic fields.
Test method: Confirm whether such interference sources exist around the site, and relocate the equipment for debugging.
(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 debugging, and install a voltage stabilizer. In the master control room, if conditions permit, 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, control cable distance too long, or wiring not following the bus topology.
Test method: Since the 485 protocol has strict requirements for impedance matching, impedance matching may vary at many project sites due to different wiring practices. Please use bus topology to connect decoders as much as possible. If star topology is used, it is recommended to install a TC-3001 485 isolator.
Digital Optical Terminal Series The following situations take 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 wiring is correct. 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: An optical power meter can directly measure the continuity and attenuation of the fiber optic link. A measured optical power within -4dB to -21dB is considered normal. Without an optical power meter, the link status can be identified by observing the indicator status of 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, it indicates that the fiber optic link is disconnected or the attenuation is too high. Under normal conditions, if the first channel of the transmitter has video input (indicator lit) and the fiber optic link is properly connected, the video indicator of the first channel on the receiver will also light up while the other indicators remain off, which also indicates that the optical terminal itself is working properly.
(3) Both optical terminals 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 optic link attenuation has reached the critical value.
Test method: Use an optical power meter to check. If the attenuation is above 20dB, or the optical power meter reading is approximately -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 selection.
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 optic link attenuation is too high; it can be measured 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 fields or magnetic fields.
Test method: Confirm whether such interference sources exist around the site, and relocate the equipment for debugging.
(3) The optical terminal power supply is faulty.
Test method: Replace the power supply for debugging, and install a voltage stabilizer. In the master control room, if conditions permit, 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, control cable distance too long (exceeding 150 meters), or wiring not following the bus topology.
Test method: Since the 485 protocol has strict requirements for impedance matching, impedance matching may vary at many project sites due to different wiring practices. Please use bus topology to connect decoders as much as possible. If star topology is selected, it is recommended to install a TC-3001 485 isolator.
- One or several channels of video image are missing, 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 connected.
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, control cable distance too long (exceeding 150 meters), or wiring not following the 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 working properly, and whether the input voltage and output voltage meet the requirements.
Symptom 2: The video image is displayed on the monitor, but with a lot of noise.
Handling: The effective transmission distance of the fiber optic link may have reached its limit, or the fiber optic connector may be of poor performance or damaged.
First, use an optical power meter to measure whether the output optical power of the transmitter meets the requirements. After the optical signal is transmitted over distance, first wipe the fiber optic connector with alcohol, then use an optical power meter to measure the received optical power to check whether it meets the sensitivity requirements of the optical receiver.
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 turned on, the video monitor is turned on, and the fiber optic system is operating (power LED is lit), but no image is visible on the monitor screen.
Handling: The cause may be that the coaxial cable is connected, but the channel position connected does not match the channel of the optical terminal transmitter or receiver.
(1) At the monitor end, replace the potentially faulty card with a known good card. If that does not work, install the potentially faulty card in another slot that is known to be working properly. If the receiver fails to work properly, the card needs repair. If it works properly, reinstall it in its original position.
(2) At the transmitter end, replace the potentially faulty card with a known good card. If that still does not work, install the potentially faulty card in another slot that is known to be working properly. If the receiver fails to work properly, the card needs repair. If it works properly, 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 work, the problem may lie in the card slot connection. If the transmitter works, it indicates that both the transmitter and the card slot are problem-free. Install the original receiver in another card slot of the desktop rack/rack-mount chassis and check whether there is a problem with the backplane connection. If the receiver works, the problem lies in the backplane connection. If the receiver fails to work, replace the power supply and recheck. If replacing the power supply still has no effect, install the chassis on a known good link for testing and replace the power supply. If it still does not operate, try moving the card to another slot. If the card fails to work in only 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. Check whether the transmitted data format matches the optical terminal model.