Virtual sensors of the Didactum IT monitoring systems
Didactum's SNMP-compatible monitoring systems and PDUs support SNMP protocols v1, v2c, and v3 (encrypted). Seamless integration with SNMP-compatible monitoring tools (MRTG, RRDtool, Cacti, etc.), network management systems (NMS), and automation and building management software is supported by the monitoring hardware. The required SNMP MIB file and the SNMP OIDs of the sensors contained therein can be loaded directly from the German web interface of the monitoring hardware. Additionally, Didactum's standalone monitoring systems offer virtual sensors in the form of SNMP GET functions. An SNMP GET command retrieves a value or a data record of a specific OID (Object Identifier).
The virtual "SNMP Get" sensor is used to read data from external devices using SNMP PDU GET (v2c). The virtual "SNMP Get" sensor can be either "Analog" or "Discrete." The analog sensor interprets the value read via SNMP Get as a decimal number. A discrete sensor compares the read value with the predefined data set (also called the "normal value"). If this value is contained in the data set, the element assumes the "normal" state. If the value does not correspond to the predefined data set, the element switches to the "alarm" state. This is also displayed in the German-language web interface.
SNMP Get (Analog) query by the IT monitoring system
To create a virtual “SNMP Get (analog) Sensor”, click the “Add” button in the “System tree” menu and select the “SNMP Get (analog)” element.
In the “SNMP Get (analog)” menu of the Didactum Monitoring System, the following configuration options are available (as of 01/2020):
| # | Setting: | Description of the settings: |
|---|---|---|
| 1 | Name: | Name of the newly created virtual sensor / SNMP Get (analog) element in the Didactum monitoring device |
| 2 | User‑defined type: | Definition of the icon / symbol that is displayed in the “System tree” of the device |
| 3 | Unit: | Unit of measurement for how the value is displayed in the “System tree” of the monitoring system |
| 4 | Minimum value: | Determines the minimum measurement range. If the value is outside this range, the virtual sensor goes into the “Not connected” state. |
| 5 | Maximum value: | Determines the maximum measurement range. If the value is outside this range, the virtual sensor goes into the “Not connected” state. |
| 6 | Thresholds: | Set the alarm and warning thresholds here. |
| 7 | Hysteresis: | You can define a hysteresis state here. Further information on hysteresis is available in the technology portal. |
| 8 | Expression (f(x), e.g. 2*x+123) | Function of the form f(x). The default value corresponds to the measured value “x”, i.e. the expression “x”. For calculating the indirect value of the sensor, you may use any valid expression, including “(”, “)”, as well as: · Operators: “+”, “−”, “*”, “/”, “%”, “^”; · Functions: “abs”, “sqrt”, “exp”, “ln”, “log”, “sin”, “cos”, “tan”, “asin”, “acos”, “atan”; · Constants: “pi” (≈3.1415926…), “e” (≈2.7182818…). |
SNMP Get (Discrete) query by the IT monitoring system
Click the “+” symbol in the top‑right corner of the “System tree” in the monitoring hardware. The “Add new element” window opens in the German web GUI. Select the “SNMP Get (discrete)” element.
In the “SNMP Get (discrete)” menu of the Didactum Monitoring System, the following configuration options are available (as of 01/2020):
| # | Setting: | Description of the settings: |
|---|---|---|
| 1 | Name: | Name of the newly created virtual sensor / SNMP Get (discrete) element in the Didactum monitoring device |
| 2 | User‑defined type: | Definition of the icon / symbol displayed in the “System tree” of the device |
| 3 | Current state: | Current computed state of the element |
| 4 | Current value: | Current value of the element (independent of behavior) |
| 5 | Value string: | Data set read by the SNMP GET command |
| 6 | Mode: | Normal or inverted behavior |
| 7 | Normal value: | Example substring. If the substring is present in the dataset, the element assumes the “normal” state; otherwise it is shown as “alarm”. |
The “Additional” tab contains further SNMP settings:
| # | Setting: | Description of the settings: |
|---|---|---|
| 1 | State: | Status of the SNMP connection |
| 2 | SNMP server: | IP address of the SNMP agent |
| 3 | SNMP port: | Port of the SNMP agent (e.g. port 161) |
| 4 | SNMP version: | SNMP protocol version used |
| 5 | Community: | Read community of the SNMP agent |
| 6 | Polling interval: | Interval for sending SNMP GET requests |
| 7 | OID identifier: | The OID (object identifier) of the device to be monitored. Must be entered in numeric form only, e.g. “.1.3.6.1.4.1.39052.1.3.1.9.203001” (without quotation marks). |