Initial commit

README.md

@@ -0,0 +1,42 @@
+# node-red-contrib-msg-speed
+A Node Red node for measuring flow message speed.
+
+## Install
+Run the following npm command in your Node-RED user directory (typically ~/.node-red):
+```
+npm install node-red-contrib-msg-speed
+```
+
+## Usage
+This node will count all messages that arrive at the input port, and calculate the message speed *every second*. 
+
+For example when the frequency is 'minute', it will count all the messages received in the *last minute*: 
+
+![Timeline 1](https://raw.githubusercontent.com/bartbutenaers/node-red-contrib-msg-speed/master/images/speed1.png)
+
+A second later, the calculation is repeated: again the messages received in the last minute will be counted.
+
+![Timeline 2](https://raw.githubusercontent.com/bartbutenaers/node-red-contrib-msg-speed/master/images/speed2.png)
+
+The measurement interval is like a **moving window**, that is being moved every second.
+
+The process continues this way, while the moving window is forgetting old messages and taking into account new messages:
+
+![Timeline 3](https://raw.githubusercontent.com/bartbutenaers/node-red-contrib-msg-speed/master/images/speed3.png)
+
+Remark: The message count will be displayed on the screen:
+
+![Timeline 4](https://raw.githubusercontent.com/bartbutenaers/node-red-contrib-msg-speed/master/images/speed4.png)
+
+Moreover the message count will be send to the output port as message payload. An extra 'frequency' message field is also added (containing 'sec', 'min', 'hour', 'day').
+
+Some use cases: 
+* Trigger an alarm e.g. when the message rate drops to 0 messages per minute.
+* Performance measurement, e.g. track the number of images per second (received from a camera).
+
+## Node configuration
+
+### Frequency
+The frequency ('second', 'minute', 'hour', 'day') defines the interval length of the moving window.
+
+Remark: when the interval becomes longer, more calculations need to be stored into memory...