Teledyne API Model 200A NOX Analyzer Instruction Manual, 02246, Rev. G, DCN 5247
The M200A uses the RS-232 communications protocol to allow the instrument to be connected
to a variety of computer based equipment. RS-232 has been used for many years and is well
documented. Generally, every manufacturer observes the signal and timing requirements of the
protocol very carefully. Problems arise when trying to specify connectors, and wiring diagrams
that attach the analyzer to various devices.
9.3.2.1 RS-232 Connection
If the RS-232 port is not working, check the following:
Physical Wiring
First is to get the physical wiring hooked up correctly. Refer to Table 9-9-9 for the wiring
diagram of the DB-9 plug on the M200A rear panel. There are 2 features that make connecting
the wiring easier. First is the red/green LED’s on the rear panel. The M200A provides the power
to run the red LED, the external equipment will provide the power for the green LED. If the
wiring is hooked up correctly both LED’s will be illuminated. Secondly, there is a DTE-DCE
switch, this switch interchanges pin 2 & 3 on the DB-9 connector. Set the DTE-DCE switch so
that both LED’s are illuminated.
RS-232 Protocol (BAUD rate, Data bits, Parity)
Second is to get the communication protocol for each instrument to match. In Table 9-9-9 the
default RS-232 parameters are listed. The BAUD rate can be changed in the software menus
under SETUP-MORE-COMM-BAUD.
Data Communications Software for a PC
You will need to purchase a software package so your computer can transmit and receive on its
serial port. There are many such programs, we use PROCOMM at Teledyne API. Once you set
up the variables in PROCOMM and your wiring connections are correct, you will be able to
communicate with the analyzer.
If connecting to a modem, check the following:
Modems are especially difficult because they may have pins that need to be at certain levels
before the modem will transmit data. The most common requirement is the Ready to Send (RTS)
signal must be at logic high (+5V to +15V) before the modem will transmit. The Teledyne API
analyzer sets pin 8 (RTS) to 10 volts to enable modem transmission. Once the physical
connection has been correctly established, it is necessary to establish the correct software
settings in the modem. If the RS-232 bit field #64 in the VARS menu has been set, the M200A
will transmit a modem setup string when the instrument is powered up. The contents of the string
are set for a US Robotics Sportster modem. We strongly recommend using this model of modem
to avoid modem connection problems.
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