Circuit function and advantage The current in the circuit monitoring system shown in Figure 1 can operate at a positive high common-mode DC voltage of up to +500 V with an error of less than 0.2%. The load current is passed through a shunt resistor external to the circuit. The shunt resistor value should be chosen so that the shunt voltage is approximately 500 mV at maximum load current. Figure 1: High Common Mode Voltage and Current Monitor (all connections and decoupling not shown) When used with an external PNP transistor, the AD8212 can accurately amplify small differential input voltages with a positive high common-mode voltage greater than 500 V. Galvanic isolation is provided by the four-channel isolator ADuM5402. This is not only to provide protection, but also to isolate downstream circuits from high common-mode voltages. In addition to isolating the output data, the digital isolator ADuM5402 provides +3.3 V isolated power to the circuit. The measurement results of the AD7171 are provided in digital form via a simple two-wire SPI-compatible serial interface. This device combination enables an accurate positive high voltage rail current sensing solution with low component count, low cost, and low power consumption. Circuit description This circuit is designed for a full-scale shunt voltage of 500 mV at maximum load current IMAX. Therefore, the shunt resistance value is RSHUNT = (500 mV) / (IMAX). The AD8212 process has a breakdown voltage limit of 65 V. Therefore, the common mode voltage must be kept below 65 V. By using an external PNP BJT transistor, the common-mode voltage range can be extended to more than 500 V, depending on the breakdown voltage of the transistor. Figure 2: AD8212 uses a high-voltage mode of operation with an external PNP transistor The AD8212 does not have a dedicated power supply. Instead, the device actually “floats†itself out of the 500 V common-mode voltage using an internal 5 V series regulator, creating a 5 V supply, as shown in Figure 2. This regulator ensures that the largest negative terminal COM (pin 2) in all terminals is always 5 V below the supply voltage (V+). In this mode of operation, the supply current (IBIAS) of the AD8212 circuit is based entirely on the supply voltage range and the selected RBIAS resistance value. For example, for V+ = 500 V and RBIAS = 500 kΩ, IBIAS = (500 V −5 V)/RBIAS = 990 μA. In this high voltage mode, IBIAS should be between 200 μA and 1 mA. This ensures that the bias circuit is active, allowing the device to function properly. Note that the 500 kΩ bias resistor (5 &TImes; R2) consists of five separate 100 kΩ resistors. This is to provide protection against resistance voltage breakdown. Additional breakdown protection can be added by eliminating the ground plane directly below the resistor string. The load current flowing through the external shunt resistor generates a voltage at the input of the AD8212. Internal amplifier A1 responds by causing transistor Q1 to conduct the necessary current through resistor R1 to equalize the potential at the inverting and non-inverting inputs of amplifier A1. The current flowing through the emitter of transistor Q1 (IOUT) is proportional to the input voltage (VSENSE) and therefore proportional to the load current (RSHUNT) flowing through the shunt resistor (ILOAD). The output current (IOUT) is converted to a voltage by an external resistor, and the external resistor value depends on the input-to-output gain required in the application. The transfer function of AD8212 is: IOUT = gm &TImes; VSENSE VSENSE = ILOAD &TImes; RSHUNT VOUT = IOUT &TImes; ROUT VOUT = (VSENSE × ROUT) / 1000 gm = 1000 μA/V The input sense voltage has a fixed range of 0 V to 500 mV. The output voltage range can be adjusted based on the ROUT value. When VSENSE changes by 1 mV, a 1 mA change can be made on IOUT, and when the latter flows through a 5 kΩ resistor, a 1 mV change is produced at VOUT. In the circuit shown in Figure 1, the load resistance is 24.9 kΩ, so a full-scale input voltage with a gain of 5.500 mV produces a 2.5 V output, which corresponds to the full-scale input range of the AD7171 ADC. The AD8212 output is designed to drive high impedance nodes. Therefore, if interfacing to the converter, it is recommended to buffer the output voltage across ROUT to ensure that the gain of the AD8212 is not affected. Note that the supply voltage for the ADR381 and AD7171 is provided by the isolated power supply output (+3.3 VISO) of the four-channel isolator ADuM5402. The reference voltage for the AD7171 is provided by the precision bandgap reference ADR381. The ADR381 has an initial accuracy of ±0.24% and a typical temperature coefficient of 5 ppm/°C. Although the AD7171 VDD and REFIN(+) can both operate from a 3.3 V supply, using a separate reference provides higher accuracy. A 2.5 V reference can be selected to provide sufficient headroom. The input voltage to the AD7171 ADC is converted to an offset binary at the output of the ADC. The ADuM5402 provides isolation for the DOUT data output, SCLK input, and PDRST input. Although the isolator is an optional device, it is recommended to protect the downstream digital circuitry from high common-mode voltages under fault conditions. The code is processed in the PC using the SDP hardware board and LabVIEW software. The graph in Figure 3 shows how the circuit under test achieves less than 0.2% error over the entire input voltage range (0 mV to 500 mV). In addition, the ADC output code recorded by LabVIEW and the ideal code calculated based on the ideal system are compared. Figure 3: Output and error vs. shunt voltage Fire cable type Fire Survival Cables,Fire Fighting Cables,Fiber Optic Cable,Fire Alarm Cable Jiangsu QiSheng Cable Co., Ltd. , https://www.shuaihe-cable.com
UL flame retardant standards mainly have the following grades: CMP, CMR, CM, CMG, CMX.
1) Boost stage CMP stage (air combustion test / boost combustion test / Steiner tunnel test)
This is the highest rated Plenum Cable in the UL fire protection standard. The applicable safety standard is UL910. The test stipulated that several samples should be laid on the horizontal air duct of the equipment and burned with 87.9 kW gas burner Bunsen burner (300,000 BTU/Hr). 20 minutes. Pass criteria is that the flame must not exceed 5 feet in front of the Bunsen burner flame. The peak value of the optical density is 0.5 at the maximum, and the maximum value of the average density is 0.15.
This type of CMP cable is usually installed in a return air pressurizing system used in ventilation ducts or air handling equipment and has been approved by Canada and the United States. FEP / PLENUM materials that meet the UL910 standard have better flame retardancy than lower-smoke halogen-free materials that meet IEC 60332-1 and IEC 60332-3 standards, and have lower smoke concentrations.
2) Relay Level - CMR Level (Riser Fire Test)
This is a commercial-grade cable in the UL standard. The applicable safety standard is UL1666. The test stipulated that a plurality of samples be laid on a vertical axis of simulation, using the specified 154.5 kilowatt gas burner (527,500 BTU/Hr) for 30 minutes. Passing the standard is that the flame cannot spread to the upper part of a 12-foot-high room. The trunk cable does not have a smoke concentration specification and is typically used for floor vertical and horizontal cabling.
3) Commercial grade CM grade (vertical tray flame test)
This is a universal cable in the UL standard. The applicable safety standard is UL 1581. The test stipulated that a number of specimens should be placed on an 8-foot-high vertical stand and burned (70,000 BTU/Hr) for 20 minutes using the prescribed 20 KW band torch. By the standard, the flame should not spread to the upper end of the cable and extinguish itself. UL1581 is similar to IEC60332-3C except that the number of installed cables is different. Commercial grade cables do not have smoke density specifications and are generally only suitable for horizontal cabling on the same floor. They should not be used for vertical wiring on the floor.
4) Universal CMG (vertical tray flame test)
This is a universal cable in the UL standard. The applicable safety standard is UL 1581. Business class and common test conditions are similar, and they are also approved for use in Canada and the United States. Universal cable does not have smoke concentration specifications. They are usually applied only to horizontal cabling on the same floor and not to vertical cabling on the floor.
5) Home level - CMX level (vertical line flame test)
This is a UL standard residential cable (restricted cable). The applicable safety standards are UL1581 and VW-1. The experiment stipulated that the sample remained vertical and burned (30,000 TU/Hr) for 15 seconds with a test torch, then stopped for 15 seconds and repeated 5 times. The pass-through criteria for the remaining flame should not exceed 60 seconds and the sample should not burn more than 25%. The bottom of the surgical cotton should not be ignited by falling objects. UL1581-VW-1 is similar to IEC60332-1 except for the burning time. This grade also has no smoke or toxicity specifications and is intended for use in home or small office systems where a single cable is placed. This type of cable should not be bundled together and must have a sleeve. [1]
Low-smoke halogen-free cable (LSOH).
Low-smoke and halogen-free cables, as their name suggests, are smoke-free and halogen-free cables. The principle of low-smoke and non-halogen is that when the cable is burned in the flame, it will not produce a lot of toxic gas and smoke, so that people will not cause great casualties in the combustion, which greatly improves the people's survival rate in the fire.
The test requirements for low-smoke halogen-free cables meet three requirements:
Flame retardant requirements: Low smoke, halogen-free cables must be flame retardant. There are two flame retardant grades that are required to comply with IEC 60332.1 (vertical burning test for single cable) and IEC 60332.3C (vertical burning propagation test for bunched cable). Among them, the flame retardant requirements of IEC 60332.1 require the use of ordinary cable flame retardant requirements, while IEC 60332.3C requires relatively high flame retardant requirements at the trunk level.
Smoke Density Requirements: Smoke density tests are performed on low-smoke, halogen-free cables. It uses a fire to ignite a cable in a confined space. After the flame is extinguished, the final indoor smoke density is tested. It is required that in the presence of smoke, the light transmission capability can reach 60%. This ensures that people can see in the smoke. the way.
Toxicity requirements: There are several current toxicity testing methods, such as mouse experiments and so on. Halogen acid gas emission test (for low-halogen test) and gas acidity test (for halogen-free test) are used in the low-smoke halogen-free cable. The test principle is to determine the halogen content of the gas produced by the low-smoke halogen-free material at high temperatures (800°C and 935°C, respectively).
Some information describes the CM class requirements of IEC 60332.1 that are equivalent to UL (IEC 60332.2 is a test method for small diameter cables, that is, an alternative test method that cannot be used when testing 60332.1), and IEC 60332.3C is equivalent to UL CMR class requirements. In fact, the test methods of the four standards are not the same and cannot be directly compared.
In summary, there are two series of cables, one is the American CMX highly flame-retardant cable (the US standard clearly requires the CMX cable to contain halogen, in order to increase the temperature of the cable decomposition); the other is European FR/LSOH flame retardant/Low Smoke Zero Halogen Cable.
Folding this paragraph Fire Resistant Cable
In order to ensure the security of data, people hope that after a fire, they will have enough time to return all data before the entire network and transfer them to a safe place to minimize the possibility of data loss. Therefore, in the cable standards, there is also a type of fire protection standard called the "Line Integrity" standard. Its goal is that the cable can still keep the line open in the fire, so that the power and information can still be transmitted normally. Therefore, cables that meet the requirements for series integrity are also called fireproof cables.
At present, there are two types of common fireproof cable levels:
Chinese Standard: At 750°C, it can still work for 90 minutes (E90).
German standard: At 800-850°C, it can still work for 180 minutes (FE180).
Although the newly released China Data Center standard requires all cables to use CMP-grade integrated cable, that is, they can still be destroyed without damage at the temperature of 500°C, and the data can be transmitted normally, leaving a certain amount of time for emergency information backup. However, it does not meet the requirements of national standards for fireproof cables. It cannot be called fireproof cable.