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EnerVista PMCS 6.15 Quick Start Guide
and creates a Modbus request(s) for the required registers. If all the registers required can fit into one
Modbus return message (124 registers in sequential order) than only one request for one block of data
is made. With only one request needed the GE device update time will be roughly 250ms.
However if the amount of registers are too many for one return message or the registers needed are
more than 125 registers apart than the server breaks the request into two or more Modbus requests
requiring two or more blocks of data. Devices with small register maps, such as an MVT trip unit ,
generally need only one Modbus request with a device response time of about 500 Milliseconds (the
MVT has a longer device response time than most devices thus it takes 500ms to process and return a
request). . But larger devices (MLPQM, UR, ML750, etc.) may require 4, 5, 6 or more Modbus requests
with a device response time that could be as much as three seconds. To poll the entire register map of
a UR can take over 6 seconds requiring over 24 modbus requests. The device update cycle time is, to
a high degree, independent of the physical network. A single device on a 19.2K baud serial line will
have roughly the same update time as a single device on Ethernet.
The Enervista Modbus Master supports each network independent of other networks. So what
happens on network A does not affect what happens on network B. A network is defined as a specific
serial line or IP (and its IPport) address. If network A has only 1 device on it and only one register block
is needed than data updates will be 250ms. But if network B has 4 devices on it requiring a single
block from each than the ‘round robin’ time will be 1000ms.
Enervista PMCS, Integrator and PMCS also support polling of the devices Alarm/Event Registers and the
Oscillography registers. These registers are constantly polled along with any other device registers. If
a new device alarm/event or waveform is detected in the device (this condition is monitored via
dedicated registers) the Enervista software then initiates an auto download of the required data.
These data is interleaved with the real time data request so the impact on performance is minimized.
New alarm/events can be downloaded very quickly but waveforms can take up to 10 minutes to
download (it depends on the device and waveform settings).
Test Case:
Generic data retrieval:
Configuration:
Network Device 1 Device 2 Device 3
Multinet 1.1.1.1 MLPQM MLPQM ML750
UR 1.1.1.2 F60
Multinet 1.1.1.3 ML750
*ML750 1.1.1.4 ML750
*ML750 with built in Modbus TCP/IP
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