RS422 Turbine Test Stand to PC Interface
This application note details how serially generated RS422 data
from a jet turbine test stand can be translated into RS232 level for reading into a PC via the serial comport.
- Antona adapters will work anywhere an off-the-shelf personal computer can operate.
- Temperature range of adapter operation is 0 C (32 F) to +70 C (+158 F).
- Using a PC comport simplifies serial data input and output.
- Cabling is stranded sheilded CAT-5 terminated on both ends.
- Other examples are CNC machine tool control and shipboard GPS position monitoring.
When a customer calls or emails a question involving an unusual interfacing application the first question often is: "Can I use your adapter
in a harsh working environment?". The short answer is you can use our adapter products anywhere you can
use a store bought PC. The electronic components used in all Antona adapters are the same commerical grade as used in a personal computer.
That includes any model desktop, laptop or notebook type PC. The main limit to operation of our adapters is heat. The temperature range
for adapter operation is 0 C (32 F) to +70 C (+158 F). One of the unusual applications for our adapters came from an aircraft maintenance
depot for monitoring the operation of a running jet turbine engine undergoing upgrades or repair.
Supported ANC-6185 Interface Modes:
There still are many manufactures of equipment that rely on using serial interfacing through RS422 or RS485. Though ethernet
and USB are making inroads, the lower speed, higher voltage differential interface provided by RS422 or RS485 are still king when it comes to long
distance noise immunity of
digital data. Additionally, using a PC comport provides an easy hardware link to the outside world. While each introduction of a new
operating system may require updated driver software for ethernet and USB, that is not the case with the PC comport interface.
The diagram above illustrates using one of our ANC-6185R adapters to connect
a remotely located jet turbine test stand to a laptop computer.
Data is collected with the turbine running for operation pressures, fuel flow, temperatures, etc. and transmitted by the RS422 interface
to the PC. Software running on the laptop reduces, stores and displays the readings in near real time.
Cabling from the test stand is stranded sheilded CAT-5 cable terminated on both receive data lines (+Rc and -Rc) with a 120 ohm resistor.
The ANC-6185R provides an internal 120 ohm resistor which the user enables with a 2mm shunt (JP4). The designer should insure that the
remotely connected RS422 interface also has a 120 ohm resistor across its +Rc and -Rc lines. The terminating resistor adds
limits the level of induced signal across the transmit lines from other equipment
and reduces reflected transmissions from the RS422 driver. Wiring from the adapter +Tx and -Tx lines should use one twisted pair
of the CAT-5 cables 4 pairs of wire, and go to the equipment's +Rc and -Rc inputs respectively. The adapter +Rc and -Rc lines should use
another twisted pair to go to the equipment's +Tx and -Tx outputs. Ground should be through the cable's shield from the equipment
connector shell to the adapter ground pin. The suggested baud for such applications is 9600, 8 data, 1 stop and odd parity. The lower baud
rate is a compromise between the rate of received valid bytes and the required data transmission speed
needed to keep up with the generated data.
One additional note about powering the adapter - if the ANC-6185 is only receiving data from the attached RS422 (or RS485) equipment, the
adapter can be powered solely from the serial port. An example would be receiving the serial data stream from a remotely located GPS that
is sending a continuous stream of position data. Externally powering the ANC-6185 could well be required for extended cable runs of
high baud rate transmissions. The designer can control the transmit data lines, the highest source of adapter current use, so that only when the
adapter is transmitting will power be used.
The ANC-6185R uses an RJ-45 connector with the CAT-5 cable for a fast crimp connection. We also have an
ANC-6185T version which is
the same electronics, but provides a 6-pin terminal block for discrete wire connection to CAT-5 cable.
RS-422 mode - 4 wire (used in this application)
RS-485 mode - 2 wire, transmit controlled by RTS
RS-485 mode - 2 wire, AutoXmit - transmit controlled by data
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Updated 02/21/09 14:00
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