PRTG Manual: MQTT Subscribe Custom Sensor

Channel #1 Name

Enter a name for the channel.

You can change this value later in the channel settings of this sensor.

Channel #1 Unit

Enter the unit for the numeric value that this sensor monitors.

You can change this value later in the channel settings of this sensor.

Sensor Name

Enter a name to identify the sensor. By default, PRTG shows this name in the device tree, as well as in alarms, logs, notifications, reports, maps, libraries, and tickets.

If the name contains angle brackets (<>), PRTG replaces them with braces ({}) for security reasons. For more information, see the Knowledge Base: What security features does PRTG include?

Parent Tags

The tags that the sensor inherits from its parent device, parent group, and parent probe.

This setting is for your information only. You cannot change it.

Tags

Enter one or more tags. Confirm each tag with the Spacebar key, a comma, or the Enter key. You can use tags to group objects and use tag-filtered views later on. Tags are not case-sensitive. Tags are automatically inherited.

It is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with parentheses (()) or angle brackets (<>).

For performance reasons, it can take some minutes until you can filter for new tags that you added.

The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor:

• mqtt
• mqttsubscribecustom

Priority

Select a priority for the sensor. This setting determines the position of the sensor in lists. The highest priority is at the top of a list. Choose from the lowest priority () to the highest priority ().

Topic

Enter the topic that you want to monitor.

The sensor supports single-level (+) and multi-level (#) wildcards.

Time Since Last Message

Select if you want to add a channel that shows the time since the last message was received:

• Disable (default): Do not create this channel.
• Enable: Create this channel. The sensor remains in the Up status even if it received no messages during the last scan interval.

You can define a threshold notification trigger to receive notifications if no data is received for a certain amount of time.

Last Message Handling

Define what PRTG does with the last message received if there are no new messages in the following scanning interval:

• Dismiss (default): The sensor dismisses the last message received after a new scan.
• Retain: The sensor saves the last message received until a new message is received.

Sensor Message JSONPath

Optionally enter the path to the value in the JSON data. The sensor shows the received value as the sensor message.

The data must be in valid JSON format. For details about the format, see Channel #x JSONPath below.

The sensor only shows the received value if the sensor is in the Up status. If the sensor changes to the Down status, the sensor message shows the error message instead.

Channel #x JSONPath

Enter the path to the numeric value in the received JSON structure that you want to monitor.

The data must be in valid JSON format, for example like this:

{
"Sensor1": {"Temp":25,"Unit":"°C"},
"Sensor2": {"Humidity":36,"Unit":"%"}
}

To query temperature, enter the following JSONPath:

$.Sensor1.Temp

To query humidity, enter the following JSONPath:

$.Sensor2.Humidity

Channel #x Value Type

Select the value type that the channel displays:

• Absolute (integer): Integer64 values with or without an operational sign, such as 10 or 120 or -12 or 120.
• Absolute (float): Double values, such as -5.80 or 8.23.
  If you select Absolute (float), the sensor automatically shows all decimal places of the received value in the channel. You can define how many decimal places of the channel's data that you want to display in graphs and tables in the channel settings.
• Delta (counter): Counter values. The sensor calculates the difference between the last and the current value. Enter an integer. The sensor additionally divides the delta value by a time period to indicate a speed value.
  This mode only works if the difference between the last and the current value is positive and increases with each scanning interval. This mode does not support negative values and decreasing values.
• Status (string): The sensor shows a status depending on how you map the returned strings and shows the returned strings as sensor message.
• Lookup: The sensors shows a status depending on how you define values in a custom lookup file.

Absolute (integer) and Absolute (float) support the extraction of numerical values from a received string. The sensor parses the numerical value from the beginning of the string until it encounters the first element that is not part of a numerical value, for example a letter. The sensor ignores whitespace characters.

You cannot change this value after sensor creation.

Channel #2 - #10

You can define up to 10 channels. You must define at least one channel, so you see all available settings for Channel #1. Specify how to handle all other possible channels:

• Disable (default): Do not create this channel.
• Enable: Create this channel.

If you select Disable (default), you can still see the channels, but they do not receive data anymore.

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, the last value of the primary channel is always displayed below the sensor's name. The available options depend on what channels are available for this sensor.

You can set a different primary channel later by clicking below a channel gauge on the sensor's Overview tab.

Graph Type

Define how different channels are shown for this sensor:

• Show channels independently (default): Show a graph for each channel.
• Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This generates a graph that visualizes the different components of your total traffic.
  You cannot use this option in combination with manual Vertical Axis Scaling (available in the channel settings).

Stack Unit

This setting is only visible if you select Stack channels on top of each other above.

Select a unit from the list. All channels with this unit are stacked on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Result Handling

Define what PRTG does with the sensor result:

• Discard result: Do not store the sensor result.
• Store result: Store the last sensor result in the \Logs\sensors subfolder of the PRTG data directory on the probe system. The file name is Result of Sensor [ID].log. This setting is for debugging purposes. PRTG overwrites this file with each scanning interval.

This option is not available when the sensor runs on the hosted probe of a PRTG Hosted Monitor instance.

In a cluster, PRTG stores the result in the PRTG data directory of the master node.

Downtime

In the channel table on the Overview tab, this channel never shows any values. PRTG uses this channel in graphs and reports to show the amount of time in which the sensor was in the Down status

[Value]

The returned numeric values in up to ten channels