Endress+Hauser EngyVolt RV12, Руководство по эксплуатации

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EngyVolt RV12 Appendix
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will detect the order used to send this value and set that order for all Modbus Protocol
transactions involving floating point numbers.
It is perfectly feasible to change EngyVolt devices set-up using a general purpose Modbus
Protocol master, but often easier to use the device display, especially for gaining password
protected access.
Password
Some of the parameters described above are password protected and thus require the
password to be entered at the Password register before they can be changed. The default
password is 0000. When the password has been entered it will timeout in one minute
unless the Password or Password Lock register is read to reset the timeout timer. Once the
required changes have been made to the protected parameters the password lock should
be reapplied by
• allowing the password to timeout, or
• writing any value to the Password Lock register, or
• power cycling the instrument.
11.3 RS485 general information
Some of the information in this section relates to other product families, and is included to
assist where a mixed network is implemented.
RS485 or EIA (Electronic Industries Association) RS485 is a balanced line, half-duplex
transmission system allowing transmission distances of up to 1 200 m (3 900 ft). The
following table summarises the RS-485 Standard:
PARAMETER Value
Mode of Operation Differential
Number of Drivers and Receivers 32 Drivers, 32 Receivers
Maximum Cable Length 1 200 m (3 900 ft)
Maximum Data Rate 10 Mbaud
Maximum Common Mode Voltage 12 to –7 V
Minimum Driver Output Levels (Loaded) ±1.5 V
Minimum Driver Output Levels (Unloaded) ±6 V
Drive Load Minimum 60 Ω
Driver Output Short Circuit Current Limit 150 mA to GND
250 mA to 12 V
250 mA to –7 V
Minimum Receiver Input Resistance 12 kΩ
Receiver Sensitivity ±200 mV
Further information relating to RS485 may be obtained from either the EIA or the various
RS485 device manufacturers.
11.3.1 Half duplex
Half duplex is a system in which one or more transmitters (talkers) can communicate with
one or more receivers (listeners) with only one transmitter being active at any one time.
For example, a “conversation” is started by asking a question, the person who has asked
the question will then listen until he gets an answer or until he decides that the individual
who was asked the question is not going to reply. In a 485 network the “master” will start
the “conversation” with a “query” addressed to a specific “slave”, the “master” will then
listen for the “slave’s” response. If the “slave” does not respond within a pre-defined