С этой библиотекой заработало как должно:
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2020-06-16 09:04:01 Initialize communication line 3 "USB>RS485"
2020-06-16 09:04:02 Start communication line 3 "USB>RS485"
2020-06-16 09:04:02 Open serial port /dev/ttyUSB0
2020-06-16 09:04:02 Communication session with the Device 4 "IVTM-3", type: KpIvtm7M, address: 4
Запрос текущих данных
Send: $0004RR000008B4
Receive: !0004RR2B8ED741DF2B2C4233
OK!
2020-06-16 09:04:07 Communication session with the Device 4 "IVTM-3", type: KpIvtm7M, address: 4
Запрос текущих данных
Send: $0004RR000008B4
Receive: !0004RR9D8ED741493E2C4223
OK!
2020-06-16 09:04:12 Communication session with the Device 4 "IVTM-3", type: KpIvtm7M, address: 4
Запрос текущих данных
Send: $0004RR000008B4
Receive: !0004RRF491D741EE582C421F
OK!
2020-06-16 09:04:17 Communication session with the Device 4 "IVTM-3", type: KpIvtm7M, address: 4
Запрос текущих данных
Send: $0004RR000008B4
Receive: !0004RR0295D74167492C42EE
OK!
2020-06-16 09:04:22 Close serial port /dev/ttyUSB0
2020-06-16 09:04:22 Stop communication line 3 "USB>RS485"
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Терминал:
!0004RR2B8ED741DF2B2C4233
$0004RR000008B4
!0004RR9D8ED741493E2C4223
$0004RR000008B4
!0004RRF491D741EE582C421F
$0004RR000008B4
!0004RR0295D74167492C42EE
Благодарю за помощь!
В чём была проблема и как вы ёё решили?