SNMP get / Virtual Sensors
Every LAN-based remote control system from the manufacturer Didactum® offers the user virtual sensors. The virtual sensors are provided via the SNMP Get function, enabling the continuous acquisition and monitoring of important data from external equipment via a TCP/IP network.
SNMP Get (analog or discrete)
The virtual "SNMP Get" sensor of the networked Didactum® remote control system is used to read data from external devices via SNMP PDU GET (v2c). The "SNMP Get" sensor can be either analog or discrete. The analog sensor interprets the value read from SNMP as a decimal number, discarding any special characters or foreign characters (if present in the data set). The discrete sensor compares the read value with a predefined value (called the "normal value"). If this value is present in the data set, the element assumes the "normal" state. If the value is not present in the data set, it assumes the "alarm" state.
Setting up SNMP Get (Analog) in the remote control system
To create a virtual sensor in the SNMP-compatible Didactum® system, please click on the "+" symbol (top left) under "System Tree" in the web interface (screenshot shows firmware 2.8.3 b333). The menu item "Add a new element" will then open.
After clicking on “SNMP Get (analog)”, the corresponding configuration menu will open:
| # | Label | Description |
| 1 | Name | Name of the created SNMP Get (analog) element. |
| 2 | Custom type | Defines the symbol displayed in the “System tree” of the remote monitoring system. |
| 3 | Units | The unit in which the value is displayed in the “System tree” (e.g. Volt). |
| 4 | Minimum value | Defines the minimum measurement range; if the value falls outside this range, the virtual sensor switches to the state “Not connected”. |
| 5 | Maximum value | Defines the maximum measurement range; if the value falls outside this range, the virtual sensor switches to the state “Not connected”. |
| 6 | Alarm and warning levels | Here you can set alarm and warning thresholds individually. |
| 7 | Hysteresis | Here you have the option to enable the Didactum hysteresis function. |
| 8 | Expression (mathematical) | Formula f(x). The default value for the sensor equals the measured value: “x”, i.e., this corresponds to the expression “x”. To calculate an indirect sensor value, you can use any valid arbitrary expression such as:
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Setting up SNMP Get (Discrete) in the remote control system
To create a virtual sensor for SNMP Get (discrete) in the Ethernet-based Didactum® remote control system, please click the "+" icon (top left) under "System Tree" in the web interface. The menu item "Add a new element" will open. Select the entry "SNMP Get (discrete)."
The following configuration options can be set in the SNMP‑compatible remote monitoring system:
| 1 | Name | Name of the created SNMP GET (discrete) element. |
| 2 | Custom type | Defines the symbol displayed in the “System tree” of the cabinet monitoring system. |
| 3 | Current status | Computed state of the element. |
| 4 | Current value | Current measurement value of the element. |
| 5 | Value string | The data record read via SNMP GET (discrete). |
| 6 | Mode | Normally open / normally closed of the discrete sensor. |
| 7 | Normal value | Substring; if this substring is present in the data record, the element enters the “normal” state, otherwise it enters the “Alarm” state (depending on the behavior). |
Additional settings in the menu “SNMP Get (discrete)”
Under “Additional” you can configure advanced settings for the discrete SNMP GET command:
| 1 | State | Display of the connection setting. |
| 2 | SNMP server | IP address of the SNMP agent. |
| 3 | SNMP port | Port of the SNMP agent (typically port 161). |
| 4 | SNMP version | SNMP protocol used: SNMPv1 or SNMPv2c. |
| 5 | Group | SNMP read community of the SNMP agent. |
| 6 | Polling interval (sec.) | Polling period (in seconds). |
| 7 | OID identifier | Object Identifier (OID) in textual form. |