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Demo: KTA-291 GPS Modbus Gateway

The KTA-291 GPS Modbus Gateway provides a Modbus interface for the high performance Venus638 GPS receiver. Acting as a Modbus RTU slave, any Modbus master (PC, PLC, SCADA system, etc) can poll the unit over RS-485 and retrieve extremely accurate time and positioning data.

Data Available:

  • UTC Date and Time (accurate to 60 nanoseconds). Useful to give accurate timestamps when logging data.
  • Latitude, Longitude, and Altitude accurate to 2.5 metres CEP. Useful for location tagging and surveying.
  • Speed and direction (accurate to 0.1m/s). Useful for navigation.

In this demo, we will use the cloud service Xively to display our current position on Google Maps, along with temperature and humidity readings.

Things You'll Need:

The KTA-323 miniPLC forms the heart of the system. It is perfect for this kind of application, as it has onboard Ethernet to push data up to Xively, RS-485 to poll the KTA-291 for its values, and some analog inputs to read the 4 to 20mA temperature and humidity readings from the RHT-003. It is also Arduino compatible, so can be easily reprogrammed to suit a custom application.

Looking Xively

Once everything is plugged in and powered on, this custom Arduino sketch is uploaded to the KTA-323 to push the data to Xively. The code does the following:

  • Polls the KTA-291 over RS-485 for its data, using the common and popular Modbus protocol.
  • Reads the temperature and humidity from the RHT-003 using its analog inputs.
  • Pushes data up to Xively over Ethernet (one data point every ten seconds).

The real time data can be viewed on our Xively page: https://xively.com/feeds/1943194817.

Surveying the Landscape

This demo shows data from a fixed location (our office in Seaford), though it is often more useful to use this kind of equipment to plot environmental variables at changeable locations, to survey a landscape. For example, it may be useful to a meteorologist to plot barometric pressure and temperature against elevation to get accurate lapse rates for a region. Or a marine biologist to plot water PH against location at the mouth of an estuary. Or (as a customer required recently) plotting the hardness of tarmac at different locations on a racetrack.

If you have a custom project you want assistance with, please contact us with your specification. We offer obligation free quotes on any custom electronics work.

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