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計測機器 CARLO GAVAZZI EM 21のPDF 通信プロトコル・マニュアルをオンラインで閲覧またはダウンロードできます。CARLO GAVAZZI EM 21 10 ページ。 3-phase energy meter
CARLO GAVAZZI EM 21 にも：マニュアル (4 ページ)

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Energy management

1.3

Application notes

1.3.1

RS485 general considerations

1. To avoid errors due to the signal reflections or line coupling, it is necessary to terminate the bus at

the beginning and at the end (inserting a 120 ohm 1/2W 5% resistor between line B and A in the last

instrument and in the Host interface).

2. The network termination is necessary even in case of point-to-point connection and/or of short

distances.

3. For connections longer than 1000m or if in the network there are more than 160 instruments (with

1/5 unit load as used in EM21 interface), a signal repeater is necessary.

4. For bus connection it is suggested to use an AWG24 balanced pair cable and to add a third wire for

GND connection. Connect GND to the shield if a shielded cable is used.

5. The GND is to be connected to ground only at the host side.

6. If an instrument does not answer within the "max answering time", it is necessary to repeat the

query. If the instrument does not answer after 2 or 3 consecutive queries, it is to be considered as

not connected, faulty or reached with a wrong address. The same consideration is valid in case of

CRC errors or incomplete response frames.

1.3.2

MODBUS timing

Fig. 1 : 2-wire timing diagram

Timing characteristics of reading function:

T response: Max answering time

T response: Typical answering time

T delay: Minimum time before a new query

T null: Max interruption time during the request frame

EM24-DIN Communication Protocol

msec

500ms

40ms

3,5char

2,5char