GPS over RS232

[einnh]

I have a two part question regarding reading serial information.

I am looking to implement a GPS antenna into my control system using something similar to this:

http://www.tigergps.com/garmingps19xhvs.html

This antenna uses NMEA0183 over RS232. I have never used serial data in a project and am curious how to read it. Is it just a stream of ANSI characters? How would I read the data into my PLC? Is there a special function block or bit of code to sort the data stream?

I have the stream format from this:

http://www.gpsinformation.org/dale/nmea.htm

I will be using CLX.

Thank you,

 

[einnh]

Nothing?

 

[Ken Roach]

I did an implementation of that a few years ago with a Magellan GPS that just outputted NMEA sentences in ASCII format.

It wasn't difficult, once I had the data coming in, to parse it out into strings. But I don't have access to that code anymore.

Are you using an older ControlLogix with an RS-232 port, or are you going to use a modern L7x family controller with a network or chassis serial module ?

Each sentence begins with a '$' and ends with a carriage return/line feed sequence and can be no longer than 80 characters of visible text (plus the line terminators).

This happens to fit very nicely with SLC/PLC and ControlLogix default String datatypes. I had logic to read the serial port using the ASCII Read Line (ARL) instruction repeatedly. If the first character wasn't "$", I used the ASCII Clear Buffers instruction and did another ARL.

If you're using an external module or network gateway, the techniques will be a little different.

 

[harryting]

If you don't have a serial port (L7x) you might as well buy the 1756HP-TIME module.

 

[the_msp]

Harryting, I don't have experience with either units, but if the OP just requires GPS, would the -GPS module not work? (It is a lot cheaper...)

1756HP-TIME ControlLogix GPS Position and Time Services Includes GPS receiver.. $ 3,500.00 1769HP-GPS This module is able to provide precision timing information across the 1769 backplane. Other GPS information is also available including Position, Velocity and GPS receiver status. $ 1,950.00

 

[Ken Roach]

We don't know if einnh is using a full-size ControlLogix or one of the CompactLogix, or the reason for his GPS inputs.

I've seen the Hiprom GPS modules used for mobile machinery as well as for very precise time synchronization across large power distribution systems.

There are a bunch of ways to get this data into a ControlLogix system from an RS-232 GPS receiver. You could use the serial port, or a 1734 POINT serial module, or a 1769 or 1756 serial module, or a network gateway like the HMS Communicator, or a Red Lion DataStation Plus, or even the serial port on a PanelView Plus.

Hopefully einnh will revisit the topic with some info about his control platform and the application. I'm curious about it and eager to help.