FieldServer Guide: Extracting Live Data with XPath Expressions for Modbus TCP and BACnet/IP

Step 2 - Generate an API call (using your API key) to get current weather data in Vancouver, BC

1. First, please visit this web page: OpenWeatherMap.org/current

   Our next task is to use the information from this page to create an API Call. Note: This section – located near the top of the page (or see below) - will show you how to write an API call.

   

   
   

   Note: You may also add these parameters to the API call: q, appid, mode, units, lang:

   

   Here is the example API call from their documentation

   api.openweathermap.org/data/2.5/weather?q={city name}&appid={API key}




2. Since we want the current weather in Vancouver - replace {cityname} with Vancouver and {API key} with your generated API Key (see "YOURAPIKEYHERE"). Note: It takes time for the generated API key to become active. If your key isn't active yet, please retry again later. This is how it should look…

   http://api.openweathermap.org/data/2.5/weather?q=Vancouver&appid=YOURAPIKEYHERE




3. Before we paste this API call into our browser, let's add a couple additional parameters. Since we want the data presented to us in XML format, we will add &mode=xml at the end of the URL. Since we want this data to be in metric units, we will also need to add &units=metric. If we've done it properly, the finalized API call should look like this:

   http://api.openweathermap.org/data/2.5/weather?q=Vancouver&appid=YOURAPIKEYHERE&mode=xml&units=metric

4. Copy and Paste the above API call into your browser. Remember to replace YOURAPIKEYHERE with your generated API key or it will not work properly. If you've done this correctly, you will see an XML file that appears formatted like this this (Your values will be different since the weather changes):
   

Place the API Call and XPath Expressions into the FieldServer

1. Bring up the GUI of your Fieldserver. Please use the following URL and be sure to include the IP address of your FieldServer.

   http://{YourFieldServerIPAddress}/chipkin/ui/#

   
   

2. Once you're in, look on the left side and locate the Menu. Click the 'Drivers' tab and you'll see a drop-down menu. Then click on 'XPATH' (see image below):

   



3. Locate the "Create Connection" button under Connections – then click it:

   

4. Create the connection

   • Name: create any name for this connection.
   • Type: connection type – either Ethernet or Serial.
   • Parameters/Port: physical ethernet port to use.
   • Click "Create"





5. On that same page, please locate the Create Node button and then click it:



6. Now it's time to use your API call and place it directly into a Node on the FieldServer. To do that, we will use the following information to create a node.

   • Name: use any name you'd like.
   • Connection: should default to your connection
   • URL: Insert your API call's URL. This is the API call that we created earlier.

   http://api.openweathermap.org/data/2.5/weather?q=Vancouver&appid=YOURAPIKEYHERE&mode=xml&units=metric

   • Scan Interval: Insert how many seconds you would like in between scans.

   

   
   

7. Next, click "Create Task" as seen in the screenshot:

   

8. One task will be created for EACH XPath Expression. First, let's use the XPath expression for current temperature in Vancouver.

   • Name: use any name you'd like. "Temperature" is suggested.
   • Node: It may default, but please choose the correct node you would like this task to run on.
   • Data Broker: Select "Protocol Engine" since we will be using a PE-type config file.
   • Name: The name of the Data_Array that will store the value from our Task. In the example config.csv (Section 5) we will define our Data_Array as DA_01. To store and serve the data, remember the name you choose here so you can include it in your config.csv file.
   • Start: Starting offset value goes here. In the data array we just defined (DA_01), we will need to choose which starting offset to store the data in.
   • Pattern: The XPath expression will go here.

     /current/temperature/@value

   • Pattern: It may default, but please choose the correct node you would like this task to run on.
   • Type: Select "XML"
   • Click "Save"

     

9. Create a new task to store the current Humidity value in Vancouver

   • Note: Watch the offsets. Since we used offset "0" for the temperature, we will use offset "1" for the humidity. You cannot use the same offset to store more than one data point.

     

   • If you've followed the steps properly, your screen should look like this:

     

Upload the configuration file to the FieldServer

1. Go back to the FieldServer GUI

2. Locate "Diagnostics" on the left-side menu & click it.

• It will bring up a screen that looks like this:

• Once the download is complete, a message bar will appear confirming that the configuration was updated successfully.

XPath Tutorial Conclusion:

As you can see, on Data Array 'DA_AI' there is incoming data on offsets "0" and "1". On offset "0" we can read that the current Temperature in Vancouver is 6.27°C. Also, the Humidity in Vancouver is 87%. These values are constantly updating every 30 seconds (scan-interval) with the current weather values.

What can you do with these values? Quite a bit! Outdoor weather of high winds, rain levels, freezing temperatures, snow, high humidity etc. can cause damage to essential business functions. Imagine an airport during a heavy freeze/snow. If required to land on an iced surface, it may be difficult for a pilot to ensure the safety of their passengers. With these values, reactionary measures can take place. If there is below freezing temperatures, an automated response might be to heat up the asphalt to reduce the ice. This would obviously require more than one system to do, and this is just an example. The possibilities are endless.