Pakarab fertilizers limited multan
Configuring devices for multi-drop operation
Download 3.37 Mb. View original pdf
|
- Navigate this page:
- Difference between 275 and 375 HART Communicator
| Configuring devices for multi-drop operation Using the polling address structure of the HART protocol, up to 15 devices can be connected in a multidrop network. The analog current of a HART device can be fixed by setting its polling address to a number other than zero. With the HART protocol, each field instrument should be configured with different polling addresses or tag numbers before being connected to a multidrop network—otherwise, the master will not be able to establish communication with the slave devices. A HART field controller takes advantage of the HART protocol’s simultaneous analog and digital signaling by converting the transmitter’s traditional analog measurement output into a control output. The analog signal from the smart transmitter (controller) is used to manipulate the field device. The analog output signal also carries the HART digital signal, which is used for monitoring the process measurement, making setpoint changes, and tuning the controller. 113 Field Instrumentation GEN Rev) The communication rate of the HART protocol (2–3 updates per second) is generally perceived as too slow to support closed-loop control in the central host. With control in the field, the control function no longer depends on the HART protocol’s communication rate. Instead, the control signal is an analog output that is updated at a rate that is much faster than can typically be processed in a conventional control system. Processing rates vary from 2–20 updates per second, depending on the product. The HART digital communication rate remains sufficient for monitoring the control variable and changing setpoint values. 114 Field Instrumentation GEN Rev) Difference between 275 and 375 HART Communicator There is no significant difference between 275 and 375 HART Communicator except that 375 is anew model with touchscreen, It has more memory as compared to 275 and can store and configure more devices than 275 HART. 115 Field Instrumentation GEN Rev) |