Technical Articles
What is the TNV circuit?
TNV circuit is the abbreviation of telecommunication network voltage circuit, that is, remote communication network voltage, which is a circuit that carries remote communication signals under normal operating conditions.
It is a circuit in equipment with limited access to the contact area, which is properly designed and protected so that its voltage does not exceed the specified limit value under normal operating conditions and under single fault conditions.
A circuit that carries a communication signal under normal operating conditions.
TNV circuit classification:
TNV circuits will be further divided into TNV-1 circuits, TNV-2 circuits, and TNV-3 circuits in the future, depending on their normal operating voltage and the overvoltage they may be subjected to.
TNV-1 circuit
Under normal operating conditions, its normal operating voltage does not exceed the limits of the SELV circuit; And to its circuit may be accompanied by an overvoltage from the communication network TNV circuit.
TNV-2 circuit
Under normal operating conditions, its normal operating voltage exceeds the limits of the SELV circuit; And does not accompany the overvoltage from the communication network TNV circuit.
TNV-3 circuit
Under normal operating conditions, its normal operating voltage exceeds the limits of the SELV circuit; And on its circuit may be accompanied by an overvoltage from the TNV circuit.
TNV circuit test
1. Applicable conditions:
When equipment is interconnected with communication equipment, it is necessary to prevent users and maintenance personnel of the communication network from being harmed by equipment and cause insecurity, and also to prevent equipment users and maintenance personnel from suffering harm from the communication network and causing unease. Ensure that the TNV circuit of the equipment meets the requirements of the TNV circuit electric shock protection, protect the maintenance personnel and other users of the communication network from hazards from the equipment, and protect the users of the equipment from the hazards from the communication network.
2. Measuring principle:
Standard resistors are used to sample between test points, storage oscilloscopes are used to measure voltage drops across standard resistors, and storage oscilloscopes are used to measure continuous or periodic voltages and derive voltage periods. The current is calculated from the measured voltmeter, and the type of TNV circuit is determined by using the period of the measured continuous voltage or periodic voltage, and then what kind of insulation is required and what further tests are required.
3. Steps:
To determine the type of TNV circuit, the steps are as follows:
In a TNV circuit or several interconnected TNV circuits, the measured voltage between conductors of any two TNV circuits or between circuits or between any such conductor and ground.
a. TNV-1 circuit measurement determines that the equipment works under normal working conditions, and the measured voltage (peak voltage and DC voltage) cannot exceed the voltage limit of the SELV circuit; When the device is operating under a single fault condition, the measured voltage (peak voltage and DC voltage) across the 5000Ω±2% resistor between the measured points cannot exceed the specified limits. And its circuits may withstand overvoltages from communication networks.
b. TNV-2 circuit and TNV-3 circuit measurement judgment, under normal working conditions, when the measured circuit voltage (peak voltage and DC voltage) exceeds the peak 42.4V or DC 60V, disconnect other loads, measure the current (peak current and DC current) on the 5000Ω ±2% resistor connected to the voltage source. The telephone ring signal should not exceed the limit required by the specified ring signal. For circuits without telephone ringing signals, under normal operating conditions, the combination of AC and DC voltage should meet the following requirements:
Uac / 70.7+Udc / 120 ≤1
Under a single fault condition, the voltage measured across a 5000Ω±2% resistor cannot exceed the specified value.
TNV-2 circuit: A TNV circuit that meets the above condition b and does not withstand an overvoltage from the communication network is a TNV-2 circuit.
TNV-3 circuit: A TNV circuit that meets the above condition b but whose circuit may withstand an overvoltage from a communication network is a TNV-3 circuit.
4. Verdict:
The isolation between the SELV circuit, TNV-1 circuit, accessible conductive parts and TNV-2 and TNV-3 circuits shall be such that the voltages of the SELV circuit, TNV-1 circuit, and accessible conductive parts shall not exceed the limits of normal operating conditions specified for TNV-2 and TNV-3 circuits in the event of a single fault.
If basic insulation is provided as required in the table below, the above isolation requirements are considered to be met.
Nina She