Meriam 4150X ATEX I.S. Certified HART Communicator - Manual (Page 15)

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Auto polling directs the 4150 / 4150X to always poll for HART device address 0 (zero) first. When
found, communications begin automatically. If address 0 is not found, the unit automatically asks
for direction; select Multi soft key to start a multi-drop poll from address 1 – 15 or select Retry
soft key to try to find address 0 again (for more details see the HART Communications section)
Digital polling directs the 4150 / 4150X to always poll for HART device addresses 0 – 15. This
polling method is best for 4 – 20 mA loops where one device with address 0 is present and another
device with a non-zero address is on the same loop.