1. Optical Transceiver Optical Path Issues:
In security monitoring and control projects, most optical cables are installed by users themselves, typically using G652 single-mode fiber. Since the system coverage is generally not large, the optical link loss for standard equipment (up to 20KM) is usually minimal. Therefore, the optical transceiver does not require excessive optical path loss. However, users often encounter problems such as no image, image jitter, or poor image quality. Most of these issues occur at the fiber pigtails, jumpers, or adapters at the ends of the optical path, rather than in the main trunk line. Common causes include: 1. Incorrect insertion of fiber optic connectors; 2. Contamination of the fiber optic connector core (ceramic sleeve). The solutions are: 1. Reinsert the connector or replace the fiber jumper; 2. Clean the plug with 99.9% anhydrous ethanol and reinsert it; 3. Use a multimeter to check the camera's video cable and determine if there is a video signal.
2. Optical Data Interface:
To meet the needs of security monitoring systems, equipment like matrix switches, hard disk recorders, and decoders provide RS-485 data interfaces. This type of interface offers long transmission distance, strong load capacity, and can form a four-wire full-duplex communication bus, allowing any two devices on the line to communicate bidirectionally. In contrast, a four-wire RS-422 bus only allows communication between the master and slave, not between slaves. However, the downside is that it uses a three-state enable, which can lead to instability or even "dead" communication. If there is no communication (i.e., the system is unresponsive), check the following: 1. Confirm whether there is a control signal. Use a multimeter to check the RS-485 port output from the controller (matrix, hard recorder, etc.) to see if a control signal is being sent. 2. Check if the RS-485 interface of the optical transceiver is functioning properly. If the UA-B voltage is zero, it indicates a fault. If the pan/tilt cannot be controlled, this may be due to: a) Reverse wiring of the A+ and B- ports; b) Serious impedance mismatch.
3. Optical Switch:
The switch signal is a TTL-level pulse train used to control warning lights, alarms, relays, and more. The load capacity of the switch interface depends on the current it can handle. For example, the EW series optical transceiver has a maximum switch load capacity of ≤1.5A.
1. The EW series optical switch interface supports normally open switches. When connected as shown in the diagram, both normally open and normally closed modes are supported.
2. The digital interface should not be used in parallel directly. If needed, it must be accessed through a distribution circuit.
3. Some customers use the RS-485 bus to transmit switch signals. Based on our experience, this approach is not recommended. Problems often arise after a few days of operation, and the issue might be related to the RS-485 converter.
4. Hazards of Transient Interference on Optical Transceivers and Countermeasures:
1. Sources of Transient Interference: Transient interference is typically caused by large inductive loads, such as the switching of motors, transformers, and relays. During lightning events, it can also enter the optical transceiver via electrostatic induction.
2. Hazards of Transient Interference: Due to its high frequency, short duration, and high amplitude (hundreds of kilovolts), transient interference can damage key components of the optical transceiver, including the RS-485 interface chip and the main chip. This is especially problematic during summer thunderstorms, causing significant trouble for users, businesses, and manufacturers.
3. Countermeasures: Although manufacturers use various protection methods—such as bypassing (self-healing diodes), absorption (bidirectional suppression diodes), and isolation (optocouplers)—it is still difficult to completely eliminate damage caused by transient interference. As a result, the RS-485 interface is frequently damaged, creating pressure for both users and manufacturers.
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