PRTG Manual: Channel Settings

A sensor has one or more channels in which it handles the actual monitoring data. In the channel settings, you can define how to display the data from the sensor's different channels displayed in graphs, gauges, and tables. Additionally, the channel data can determine the sensor status. Use the limit settings to define desired sensor states for values.

On the sensor's Overview tab, click b_channel_settings below a gauge to change the channel's settings. Click b_channel_primary below a gauge to make this channel the primary channel of the selected sensor.

You can also open the settings of a channel by clicking b_channel_settings_2 in the channels data table.

i_round_blueFor lookup channels, we recommend that you stay below 120 lookup values to get expressive gauges. For non-primary lookup channels, the upper limit is around 40 lookup values.

The Gear Icon of an SNMP Traffic Total Channel to Open Channel Settings

The Gear Icon of an SNMP Traffic Total Channel to Open Channel Settings

The available options are nearly the same for all sensors. An exception applies to the Downtime channel, which PRTG automatically calculates and which does not offer all settings. Channels with absolute values additionally have an option to define the Value Mode. Custom channels have a Lookups and Limits setting to distinguish between alerting by lookups or numeric limits.

You can choose a different channel via the dropdown list at the top of the channel settings list.

Channel Settings for a Disk Sensor

Channel Settings for a Disk Sensor

Edit Channel

Setting

Description

Name

Enter a meaningful name to identify the channel. The name appears in graphs and tables.

i_round_blueYou can automatically add the sensor's ID to the name by using the placeholder [#id].

i_round_blueYou cannot edit the name for script sensors after sensor creation.

i_round_blueIf 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?

Unit

This setting is only visible for custom sensors.

Enter the unit for the values that this sensor returns. Enter a string. PRTG uses the unit string for display purposes and shows it in graphs, data tables, and gauges.

i_round_blueIf you want to change the unit after sensor creation, you can change it in the sensor's channel settings.

Scaling Multiplication

This setting is only visible for channels with a custom unit. If you want to multiply the received raw data by a certain value, enter the multiplier here. Otherwise, use the default value 1 to not change the received value. Enter an integer value.

For example, the following sensors provide the scaling factor for received values with custom units in their settings.

i_round_blueIf the channel uses lookups, the scaling factor does not modify the values that are defined in the lookups. Any applied lookup always uses the raw value as it is retrieved from the target device. If you use a scaling factor for such a channel, you notice the scaling in data graphs, but the channel value appears unmodified in data tables.

Scaling Division

This setting is only visible for channels with a custom unit. If you want to divide the received raw data by a certain value, enter the divisor here. Otherwise, use the default value 1 to not change the received value. Enter an integer value.

For example, the following sensors provide the scaling factor for received values with custom units in their settings.

  • Sensor Factory sensor (you can use multiplication and division in the channel definition)
  • SNMP APC Hardware sensor
  • SNMP Custom sensor
  • SNMP Dell Hardware sensor
  • WMI Custom sensor

i_round_blueIf the channel uses lookups, the scaling factor does not modify the values that are defined in the lookups. Any applied lookup always uses the raw value as it is retrieved from the target device. If you use a scaling factor for such a channel, you notice the scaling in data graphs, but the channel value appears unmodified in data tables.

ID

Shows the ID of the channel. You cannot change the ID. PRTG uses it for unique identification. For example, you need the ID for Sensor Factory sensors.

There are a few special, fixed channel IDs.

  • -1 is for sum channels of traffic sensors (for example, of the SNMP Traffic sensor).
  • -4 is for the Downtime channel (you can use it, for example, for an uptime percentage calculation in a Sensor Factory sensor).
  • -2 (coverage) and -3 (error) are internally used.

Limits

i_round_blueThis setting is not available for custom channels.

Define if you want to set limits for this channel. The channel can affect the status of the sensor that it is a part of. By setting limits, you can define when the sensor shows the Warning status or the Down status, depending on the channel data. For example, you can use this function to set a traffic sensor (that is usually never in the Down status) to show the Down status when the monitored values reach critical limits.

Choose between:

  • Disable limits: Do not use the channel data to define the sensor status.
  • Enable alerting based on limits: Define limits for the numeric values that are returned by the device. The sensor of which this channel is a part of shows the Warning status or the Down status when limits fall below the defined value or when limits are exceeded.

i_round_blueThe Limits option is not available for the Downtime channel.

i_round_blueYou can show limits in graphs (highlighted in yellow or red) if you select exactly one channel with a limit in a graph.

Lookups and Limits

i_round_blueThis setting is only available for custom channels.

Define when the sensor shows the Down status and alerts you, either based on the lookup definition or based on limits for returned values. Only the option that you select applies. For example, if you select limits as the alerting method, an error status that is defined in the lookups does not show up.

Choose between:

  • Enable alerting based on lookups: Use the lookup definition of the channel to define the sensor status. Make sure that the channel uses a proper Lookup if you use this option. Select the lookup file either in the channel settings or in the sensor settings, depending on the sensor. If you do not want to use the channel data to define the sensor status, select None as Lookup.
  • Enable alerting based on limits: Define limits for numeric values returned by the device. The sensor of which this channel is a part of shows the Warning status or the Down status when limits fall below the defined value or when limits are exceeded.

i_round_blueIf you choose limit-based alerting, errors and warnings that you have defined in the lookup file do not apply.

Lookup

This setting is only visible for custom sensors and if you select lookups-based alerting. Select the lookup file that you want to use with this channel.

i_round_redDo not use this option for sensors that provide the unit Lookup in the sensor settings. The channel setting is overwritten with the next sensor scan. Define the lookup file that you want to use with this channel on the Settings tab of the sensor. Select the option Lookup for the setting Channel #x Unit (where x is the number of the channel) and define the desired lookup file under Channel #x Lookup. See section Define Lookups for affected sensors.

i_round_blueIf you choose None, alerting by lookups and limits is disabled and channels do not appear as lookups. If you want to keep the lookup representation without alerting, define the states accordingly in the lookup file.

Upper Error Limit ([unit])

This setting is only visible if you select Enable alerting based on limits above. Specify an upper limit for the Down status. If the channel values exceed this value, the sensor shows the Down status. Enter a valid number into at least one of the limit fields.

i_round_redThe value that you enter here must match the type of value that the device returns, either an integer or a float. See also Absolute Values and Delta Values for Limits.

i_round_blueWhile a sensor shows the Down status because of a limit, it still receives data in its channels.

Upper Warning Limit ([unit])

This setting is only visible if you select Enable alerting based on limits above. Specify an upper limit for the Warning status. If the channel values exceed this value, the sensor shows the Warning status. Enter a valid number into at least one of the limit fields.

i_round_redThe value that you enter here must match the type of value that the device returns, either an integer or a float. See also Absolute Values and Delta Values for Limits.

Lower Warning Limit ([unit])

This setting is only visible if you select Enable alerting based on limits above. Specify a lower limit for the Warning status. If the channel values fall below this value, the sensor shows the Warning status. Enter a valid number into at least one of the limit fields.

i_round_redThe value that you enter here must match the type of value that the device returns, either an integer or a float. See also Absolute Values and Delta Values for Limits.

Lower Error Limit ([unit])

This setting is only visible if you select Enable alerting based on limits above. Specify a lower limit for the Down status. If the channel values fall below this value, the sensor shows the Down status. Enter a valid number into at least one of the limit fields.

i_round_redThe value that you enter here must match the type of value that the device returns, either an integer or a float. See also Absolute Values and Delta Values for Limits.

i_round_blueWhile a sensor shows the Down status because of a limit, it still receives data in its channels.

Error Limit Message

This setting is only visible if you select Enable alerting based on limits above. Enter an additional message. PRTG adds it to the sensor message when the sensor shows the Down status. Enter a string or leave the field empty.

Warning Limit Message

This setting is only visible if you select Enable alerting based on limits above. Enter an additional message. PRTG adds it to the sensor message when the sensor shows the Warning status. Enter a string or leave the field empty.

Graph Rendering

Select if you want to show this channel in data graphs:

  • Show in graphs: Sensor graphs contain the data of this channel.
  • Hide from graphs: Sensor graphs do not contain data of this channel.

i_round_blueIf you choose to hide this channel in graphs, it also does not appear in the graphs of reports or maps.

Table Rendering

Select if you want to show this channel in data tables:

  • Show in tables: Sensor data tables contain the data of this channel.
  • Hide from tables: Sensor data tables do not contain the data of this channel. This option hides the gauge as well, but the channel is still available in the data table of the sensor's Overview tab.

i_round_blueIf you choose to hide this channel in data tables, PRTG also does not use it for the calculation of the Total channel of a sensor. It also does not appear in data tables of a report.

Line Color

Select the color of the channel display in graphs:

  • Automatic: PRTG automatically sets the color of this channel in graphs.
  • Manual: Individually define the color of this channel. You can enter the desired color code below.

Color (#rrggbb)

This setting is only visible if you select Manual above. Enter a color in hexadecimal notation as in .html and .css files, or choose a color from the visual color selector. The field with the hexadecimal color value automatically changes to the color you select.

Line Width

Enter the width of the channel line in graphs. Enter an integer value in pixels. The maximum line width is 25, but we recommend that you only use values between 1 and 7 to get optimal results.

Data

This setting is available for most channels. Define how to display data:

  • Display actual values in [unit]: Display the values in the shown unit.
  • Display in percent of maximum: Calculate and show percent values based on a maximum value. Enter a maximum below.
    i_round_blueIf you choose this option, you cannot display the data of traffic sensors as a positive and negative area graph.
     
    i_round_blueIf you choose this option, values in the Limits section are counted as percent values.

Maximum ([unit])

This setting is only visible if you select Display in percent of maximum above. Enter a value to use as the maximum. Consider the unit. PRTG calculates all percent values based on this value. Enter an integer value.

Value Mode

This setting is only available for channels that return absolute values. It is not available for sensors that show difference values, such as traffic channels. Depending on this setting, the channel can not only show averages, but also the minimum or the maximum values in the graphs for the respective time spans.

Choose from:

  • Average: The channel shows average values.
  • Minimum: The channel shows the minimum values.
  • Maximum: The channel shows the maximum values.

i_square_cyanFor more information about value modes, see the Knowledge Base: What is the Value Mode in channel settings?

Decimal Places

Define how many decimal places of the channel's data that you want to display in graphs and tables:

  • Automatic: PRTG automatically defines how many decimal places to use for optimal viewing results.
    i_round_bluePRTG rounds values between 10 and –10 to two decimal places. It rounds values that are very close to an integer to the integer, for example, it rounds 3.001 to 3.
  • All: Display all available decimal places.
  • Custom: Manually define the number of decimal places. If you choose this option, an additional field appears. Enter an integer value.

Spike Filter

You can use a spike filter to correct faulty monitoring data. Sometimes, sensors report values that are enormously high or far too low. This can be because of an error in data transmission, or because of incompatibilities of the physical device you are monitoring. This can make graphs unreadable. A spike filter can compensate for these flaws.

If you enable a spike filter, PRTG disregards values that are above and below a certain limit in the monitoring data for graphs and tables.

Choose between:

  • Disable filtering: Display all data as it is received. Do not filter out spikes.
  • Enable filtering: Enable a filter to remove spike values. Additional fields appear below.
    i_round_blueThis does not change monitoring data itself but only the presentation of the data. This setting is valid for all data of this channel, including historic data.

i_round_redUse the spike filter with care. For overflow values in SNMP sensors, check the SNMP Compatibility Options before.

i_round_blueThe spike filter option is not available for the channel Downtime.

Spike Filter Max. Value ([unit])

This setting is only visible if you select Enable filtering above. Enter the maximum value to show in the channel data. PRTG disregards all data above this value in graphs and tables. Enter an integer value or leave the field empty.

Spike Filter Min. Value ([unit])

This setting is only visible if you select Enable filtering above. Enter the minimum value to show in the channel data. PRTG disregards all data below this value in graphs and tables. Enter an integer value or leave the field empty.

Vertical Axis Scaling

Define how to display the vertical axis for the channel in graphs:

  • Automatic scaling: PRTG automatically uses the optimum scaling. Usually the scaling ranges from the minimum to the maximum value. PRTG uses one single scale for each unit label only.
  • Manual scaling: Manually define the scaling. Additional fields appear below. If you define manual axis scaling, it can make low values better visible in your graph, but it might result in a graph with multiple vertical axes for the same unit label.

i_round_bluePRTG ignores settings for this option if you select Stack channels on top of each other under Graph Type on the sensor's Settings tab.

Vertical Axis Maximum ([unit])

This setting is only visible if you select Manual scaling above. Enter the maximum value to use on the vertical axis for the channel. Enter an integer value.

Vertical Axis Minimum ([unit])

This setting is only visible if you select Manual scaling above. Enter the minimum value to use on the vertical axis for the channel. Enter an integer value.

i_round_blueClick OK to save your settings and to close the settings window. Click Apply to save the changed settings while the Edit Channel window remains open, for example if you want to change the settings of other channels of the current sensor as well. You can select a different channel via the dropdown list above the settings. You can close the settings window without saving by clicking Cancel.

i_round_blueIf you change any settings and either click Cancel or select a different channel via the dropdown list, PRTG asks you to confirm this step. Click Save to apply the changes or click Discard Changes to ignore the changes. PRTG closes the window or shows the settings of the selected channel respectively.

Absolute Values and Delta Values for Limits

The value type that you need to configure for limits depends on the type of data that the channel delivers:

Value Type

Description

Absolute values

For channels that measure absolute values, for example, for free disk space, you have to set limits with absolute values like 20.

Delta values

For channels that measure delta values, that is, measurements per second (x.xx/sec), you have to set delta values according to the formula number of errors/scanning interval in seconds.

For example, you have an SNMP Traffic sensor and want to receive an alert when the sensor reports errors:

  • Set the sensor to the Warning status when 1 error occurs.
  • Set the sensor to the Down status when 30 errors occur.

The following screenshot shows how to configure the limits for delta channels. You could set the following limits for the channel Errors in with a standard scanning interval of 60 seconds:

Setting Channel Limits with Delta Values

Setting Channel Limits with Delta Values

Because this channel uses per second (delta) measurements, the sensor reports a single error that occurs over a standard 60-second scanning interval as 0.016 # per second. So the warning limit for one single error within a scanning interval is 0.1 (errors/sec). To get an alert when there are 30 errors within a scanning interval, the limit needs to be 0.5 (errors/sec).

i_round_blueIf no new errors occur in the next scanning interval, the sensor shows the Up status again. To ensure that you do not miss any notifications for this sensor, set a notification trigger with 0 seconds.

More

i_square_blueKNOWLEDGE BASE

What security features does PRTG include?

What is the Value Mode in channel settings?

Device and Sensor Setup