__________________________________ ISO - 5167V MODEL 2470 SOLARFLOW PLUS
MAY 1998
1.5 GAS CHROMATOGRAPH INTERFACE
The SolarFlow Plus supports retrieval of gas composition and gas quality from the Model 2252
Danalyzer Gas Chromatograph Controller. SolarFlow Plus polls the chromatograph using the
auxiliary serial port on the LD computer. Before polling the GC, the SolarFlow raises RTS
(request to send) and waits to receive CTS (clear to send). If the CTS signal is not active, the
SolarFlow will abort the polling cycle and retry at a later time. The simplest means of providing
the CTS signal to the SolarFlow is to install a loopback jumper between RTS and CTS.
To enable the digital gas chromatograph interface, a jumper must be installed grounding digital
input Channel 18. In addition to this, only two pieces of information must be programmed into
the SolarFlow Plus. These are the MODBUS communication address of the chromatograph, and
the chromatograph stream number of the data required.
The SolarFlow Plus initiates a poll of the GC about once every four minutes. If the poll is not
successful, the poll will be retried every 20 seconds until the poll succeeds or attempts have been
unsuccessful for over six minutes. After that time a communications error is declared and
miscellaneous fault bit #4 is set. Each poll of the GC is made up of a series of MODBUS
queries for chromatograph data. If any query fails, the poll sequence is aborted.
The first poll to the GC is for the time of the current analysis. This time stamp is saved for
comparison later. Next, the current stream number is read. If this stream number does not match
the user programmed stream number in the SolarFlow Plus, the poll sequence is ended to be re-
tried in four minutes. Next a poll is issued for the HV content and specific gravity, followed by
a poll for the 11 component values supported by the Model 2252. The final poll retrieves some
chromatograph alarms and the analysis time stamp again. If the alarms denoted by MODBUS
registers 3046 and 3047 are non-zero, the analysis time does not match that of the first poll, or
certain values are out of range (SG>2.0, SG<0.4, N2>50, HV>75 or HV<10), the sequence is
aborted and the GC analysis is discarded. Otherwise, the data is processed and saved in the
SolarFlow Plus channels.
INTRODUCTION
1-8