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Model 9110TH NOx Analyzer Communications Setup and Operation
Teledyne Analytical Instruments 151
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. TAI’s implementation supports both of these principal features.
The Hessen protocol is not well defined; therefore, while Teledyne-API’s application is completely
compatible with the protocol itself, it may be different from implementations by other companies.
6.7.2.1. HESSEN COMM PORT CONFIGURATION
Hessen protocol requires the communication parameters of the 9110T’s COMM ports to be set
differently than the standard configuration as shown in the table below.
Table 6-4: RS-232 Communication Parameters for Hessen Protocol
PARAMETER STANDARD HESSEN
Baud Rate 300 – 19200 1200
Data Bits 8 7
Stop Bits 1 2
Parity
None Even
Duplex Full Half
To change the baud rate of the 9110T’s COMM ports, See Section 6.2.2.
To change the remaining COMM port parameters listed in the table above, see Section 6.2.1, Table 6-1.
Note Ensure that the communication parameters of the host computer are also
properly set.
Also, the instrument software has a 200 ms latency period before it
responds to commands issued by the host computer. This latency should