Ametek Drexelbrook Impulse GW Series, Installation And Operating Instructions Manual

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Impulse™ Series
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4.6 Modbus
The Impulse acts as a Modbus slave, responding to data requests from a
Modbus master in RTU or ASCII format
The the serial communication parameters, and Modbus device number
are selected by using the built-in keypad and display.
Individual data items (product, level system, status.) are obtained by
issuing a Modbus request with a specific register number, as per the
Modbus protocol specification. Multiple values can be obtained by
specifying a starting register and the number of registers desired.
The data returned from a Modbus request can be in many formats: 16 bit
integer, 32 bit integer (long), or floating point. The Impulse has a unique
feature which allows the user to specify the data format desired by the
selecting the correct register. For example, the value for the product
reading can be obtained as an integer (16 bits), a long word (32 bits), or
a floating point value (32 bits) by simply choosing different registers.
In addition to the length of the data, the order of the bytes in the returned
data must be known by the Modbus master in order to assemble the
data correctly. The Impulse allows for all byte ordering combinations by
specification of the correct register number.
In traditional Modbus, 1 register represented 16 bits of data. To obtain
a 32 bit value, the master requests 2 registers to get the 32 bits. A
variant of Modbus called Enron Modbus allows for 32 bits of data to be
returned with 1 register request. The Impulse will work with either type
of Modbus master. Again, the format type is controlled by the register
number requested.
All of the Modbus formats available are shown in the following Section.