Instrumentation Telemechanics of gas metering unit

1 Basis of Design

The project was carried out on the basis of the technical assignment for the design of the "Inter-settlement gas pipeline"..........., tasks of adjacent departments and in accordance with the requirements of the current norms and rules .

2 Design solutions

The design provides a gas flow metering unit based on the TFGS series TurboFlow flowmeter with telemetry data transmission (STEL telemetry system) installed in the thermowell with a special heated one.

The TurboFlow TFG-S flowmeter consists of a flow converter and a flow cabinet. The flow converter is an analog digital converter that measures and calculates flow parameters, converts the measured flow parameters to standard conditions, and transmits information to the RN via the RS485 interface. PP is made in explosion-proof design, has explosion protection marking ExibllAT1.

The scope of automation provides for remote monitoring of process parameters:

gas flow rate - thermoanemometric flow rate meter;

gas temperature at the point of average gas flow rate - thin-film platinum resistance thermometer;

gas pressure in the gas pipeline by a pressure sensor of type 415DiEx;

temperature inside the heated cabinet.

All parameters are monitored by the computer in the flow cabinet.

RSh provides indication of the following parameters:

current gas flow rate reduced to standard conditions;

temperature of the measured medium;

pressure;

total gas volume for the current day, reduced to standard conditions;

total gas volume for the previous day reduced to standard conditions.

PP with pressure sensor is installed on gas pipeline in protective casing. The RSH and the controller of the StelTurbo KS-234 object are installed in the thermowell with a special heated one. To ensure the intrinsic safety of circuits from instruments located in an explosive zone, an intrinsically safe isolation unit for PCB is used, located on a connecting board made in a metal housing and located in the WD. The flow cabinet is supplied from the designed power supply network with voltage ̴ 220 V.

The StelTurbo KS-234 object controller is designed to transfer data from the TurboFlow TFG-S flowmeter to the control room. The "StelTurbo234" object controller transmits data from the flow computer to the central controller of the "Stel" upper level telemechanics system, at the control room. The central controller of the control room receives data from the object controller via the GSM channel through the built-in GSMmodem.

3 Power supply

Electrical receivers of commercial gas metering units belong to the first category of reliability and have power supply from two independent sources :

input from 220 V network (for the main source, see POS section);

built-in storage battery (BCS) (backup source).

The battery capacity of the battery ensures its continuous operation for at least 24 hours. Switching of power modes is performed automatically.

4 Earthing

To protect against electric shock, the design provides a TNS grounding system.

All metal non-current-carrying parts of instrumentation and telemechanics equipment are connected to the grounding system by P750 wire. The armor of cables is connected to the grounding circuit by P-1 conductor. All metal non-conductive parts of the equipment are connected to the grounding system through specially laid PE conductors of control cables.

The grounding device is provided with five vertical grounding terminals made of round steel with a diameter of 18 mm and a length of 3 m, connected by strip steel 40x5 mm.

Resistance of the grounding device of telemechanics equipment is not more than 4 ohms.

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