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Communications Setup and Operation T400 Ozone Analyzer Operator’s Manual
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Example Connection Setup window:
Example MODBUS Poll window:
6.7.2. HESSEN
The Hessen protocol is a multidrop protocol, in which several remote instruments are
connected via a common communications channel to a host computer. The remote
instruments are regarded as slaves of the host computer. The remote instruments are
unaware that they are connected to a multidrop bus and never initiate Hessen protocol
messages. They only respond to commands from the host computer and only when they
receive a command containing their own unique ID number.
The Hessen protocol is designed to accomplish two things: to obtain the status of remote
instruments, including the concentrations of all the gases measured; and to place remote
instruments into zero or span calibration or measure mode. API’s implementation
supports both of these principal features.
The Hessen protocol is not well defined, therefore while API’s application is completely
compatible with the protocol itself, it may be different from implementations by other
companies.
The following subs describe the basics for setting up your instrument to operate over a
Hessen Protocol network. For more detailed information as well as a list of host
computer commands and examples of command and response message syntax,
download the Manual Addendum for Hessen Protocol from the Teledyne API web site:
http://www.teledyne-api.com/manuals/index.asp .
06870C DCN6332