La importancia de planificar el servicio de transporte urbano en las ciudades

This section provides an overview of the purpose and properties of the standard transmitter and actuator blocks as shown in Fig. 8-4.

Physical block

Transducer blocks

Block class Description

Administration

Physical Block The physical block contains the software and hardware characteristics of a field device that are associated with its resources, e.g. electronics, operating system, device status, etc.. Similar to the transducer block, the physical block isolates the application block from the hardware-specific properties of the device by the provision of a standardised parameter interface. The following functions are offered through read/write services:

• Nameplate information (read-only)

• Diagnosis information (read-only)

• Write protection management

• Warm and cold start of the device (write)

• Change of identity number (read/write)

Block class Description

Transducer Blocks (TB)

Temperature TB This block describes the characteristics of temperature measurement by resistance temperature devices, thermocouples and pyrometers. It contains the following functions:

• Characterization of sensor type with default examples

• Connection type setting (2, 3, or 4 leads)

• Reference temperature compensation

• Loadable linearisation table

• Various measured value combinations from two integrated sensors

• Provision of measured value in at least one of the following units:

K, °C, °F und Rk

• Monitoring of sensor, sensor lead connection and hardware

• Minimum and maximum measured value display

Pressure TB This block describes the characteristics of pressure and differential pressure measurement for pressure, flow and level measurement applications.

It contains the following functions:

• Characterization of sensor and measuring cell type

• Sensor calibration

• Loadable linearisation table

• Low flow cut-off

• Provision of measured value in the following units:

– Pressure: kPA, bar, psi and Hg

– Flow: m³/h, L/s, CFM cubic feet per minute and lb/s – Level: %, m und ft

• Provision of medium temperature

• Minimum and maximum temperature value display

Flow TB This block describes the characteristics of flow measurement by the Coriolis, magnetic, ultrasonic, vortex, variable area and themal mass principles. It contains the following functions:

• Characterization of sensor type and mounting

• Setting of specific parameters for the various measurement principles, e.g.

ultrasonic frequency, vortex frequency etc.

• Sensor calibration

• Low flow cut-off

• Readable sensor values

• Range limit values with signalling of violations

• Provision of measured value in at least one of the following units:

3

Function blocks

Level TB This block describes the characteristics of level measurement by the radar, ultrasonic, hydrostatic and capacitive principles. It contains the following functions:

• Characterization of sensor type and mounting

• Sensor calibration

• Consideration of tank characterisitics

• Loadable linearisation table

• Range limit values with signalling of violations

• Provision of measured value in at least one of the following units:

– Level: %, m and ft

• Provision of the temperature of the medium

• Readbale sensor values

• Minimum and maximum temperature value display

Actuation TB The actuation transducer block describes the characteristics of electro-pneumatic and electrical positioners and provides the following signals:

• Characterization of positioning principle

• Identification of the control valve and positioner (manufacturer, ...)

• Fail safe position

• Matching of control parameters

• Loadable linearisatioin table

• Suppression of small positioning changes

• Details of positioning time

• Details of torque

• Setting of braking performance

• Details of opening and closing times

• Storage of installation data and date of last maintenance

Discrete Input TB The discrete input transducer block provides the following signal processing functions:

• Sensor cabling check

• Identification of the sensor (manufacturer, ...)

Discrete Output TB The discrete output transducer block describes the characteristics of electro-pneumatic positioners and provides the following signal processing functions, dependent upon actuation priniciple:

• Identification of the control valve and positioner (manufacturer, ...)

• Fail safe position

• Details of positioning time

• Details on the number and limits of the positioning events

• Details on the time span of the start of movement after the change in set value as well as the time taken to open and close

Block class Description

Transducer Blocks (TB)

Block class Description

Application Function Blocks

Analog Input The analog input function block provides the following signal processing functions for the measured values arriving from a sensor transducer block:

• Scaling

• Filtering (PT1 element)

• Change of operating mode: hand/automatic

• Special arithmetic functions (e.g. square root for flow values from pressure measurements)

• Simulation of measured values without the use of a transducer block

• Provision of replacement values on device faults

• Warnings, alarms and limit values

Analog Output The analog output function block provides the following signal processing functions for setpoint values, which are then passed on to the actuator transducer block. It is particularly suitable for use woth controlled actuators:

• Scaling

• Change of operating mode: hand/automatic/local override

• Simulation of the actual value of the positioner

• Provision of replacement values (fail-safe) on positioner faults or loss of communication

Discrete Input The discrete input function block provides the following signal processing functions for the discrete value of a sensor transducer block:

• Change of operating mode: hand/automatic

• Inversion of discrete value

• Simulation of discrete value

• Provision of replacement values on fault recognition

Discrete Output The discrete output function block provides the following signal processing functions for set point values, which are then passed on to the actuator transducer block.It is particularly suitable for on/off actuators:

• Inversion of setpoint value

• Change of operating mode: hand/automatic/local override

• Simulation of the actual value of the positioner

• Provision of replacement values (fail-safe) on loss of setpoint value or loss of communication

Totalizer The tatalizaer function block provides the following signal processing functions for the setpoint values that are directly linked to a transducer block output:

• Change of operating mode: hand/automaticg

• Selection of counting mode (forwards, backwards, positive only, negative only, halt)

• Reset of totalizer

• Limit value monitoring

Block class Description

Application Function Blocks

In document El Transporte Urbano en Lima Metropolitana: Un desafío en defensa de la vida (página 57-63)