,
Abstract
PMI’s Boomerang family of products (as shown in Figure 1) is available in multiple form factors and channel configurations. All Boomerangs are capable of communication over either a cellular data network or a wired network. They are designed to be a monitoring type of device (versus a recording device) and capable of remotely reporting monitored data to a central server. The central server can be either PMI’s Canvass Cloud-based Data Analysis Software or a customer’s third party SCADA (Supervisory Control and Data Acquisition) system or both simultaneously. This whitepaper reviews the role of a Boomerang as an endpoint within a SCADA network and the configuration of Boomerang parameters.
Figure 1. Image of Boomerangs
SCADA Systems
A SCADA system is comprised of one or more masters (server) and one or more outstations (clients). A SCADA master is capable of communicating with outstations via serial connections and network connections. The SCADA network itself can be setup in a variety of ways with differing levels of security. These topics have been the subject of previous whitepapers so will not be covered here. Please see WP118 (Overview of DNP3 and the Boomerang Point Map) and WP110 (Boomerang Networking Options for SCADA and Canvass) for more details.
One of the more typical SCADA network configurations is shown in Figure 2. It is comprised of a single SCADA master that monitors data from multiple Boomerang outstations using the cellular data network. Boomerangs are designed to monitor voltage (all models) and/or current (most models). Voltage is by far the most commonly monitored data point but in addition to voltage and current there are many other data points available. These include average versus instantaneous values, real power, binary counters for measurement thresholds, binary values for alarm states, device run time, data transmission counters and various others. See WP167 (Boomerang DNP3 Point Map 2.0) for the complete list.
Figure 2. Image of SCADA network
The SCADA master is programmed to collect and possibly act on specific information from each Boomerang in its network. A typical setup will have the SCADA master requesting data from each device on a timed basis. A short time interval between requests yields a more “real-time” look at the data but at the expense of data transmission. Since most Boomerangs are using the cellular data network it is important to balance the frequency of data collection against the amount of data being transmitted to avoid exceeding the Boomerang’s monthly data limit.
It is also possible to set up each Boomerang to report data without a specific request from the master but instead based on custom thresholds in the data being monitored. This is referred to as unsolicited data because the outstation (Boomerang) sends the information based on preprogrammed parameters instead of simply responding to a query from the master. A combination of slower timed requests for data along with the Boomerang’s capability to deliver unsolicited data based on significant changes in monitored data makes for an especially efficient data acquisition setup.
Configuration
The Boomerang adheres to an industry standard protocol, DNP3 (Distributed Network Protocol) and is therefore able to communicate with third party SCADA systems. Since Boomerangs utilize an IP data network (cellular or wired), each must be configured correctly in order to communicate with the SCADA master. PMI supplies its Network Management Software for configuring Boomerangs. The basics of getting started with this software are described in WP47 (Introduction to PMI Network Management Software). The configuration parameters below are all located in the “Send DNP3 Settings” option under the “DNP3” tab.
Master DNP3 Address: This parameter is entered as a numeric value that signifies a particular SCADA master. It is not strictly necessary but it is potentially useful for debugging reasons to set the same value in all Boomerangs in the system to identify their common SCADA master. The DNP3 usage is in a multiple master SCADA system utilizing a common communications bus. Since Boomerangs are using an IP network they will respond to the master IP connection or address extracted from received messages.
Slave DNP3 Address: This parameter is also entered as a numeric value. Each Boomerang in the system should be given a unique slave address. As with the master address, the slave DNP3 address is not strictly necessary but potentially useful for debugging. The original DNP3 usage for this parameter was to address a particular slave device when on a shared communication bus. This is not the case with an IP network.
UDP or TCP: This is an either/or selection that determines the underlying communication method of the IP network. The details of the differences are explained in WP82 (DNP3 – UDP vs TCP Configuration). Also, a case study of how the two types can impact Boomerang communications is shown in WP138 (UDP vs TCP on a Cellular Network).
TCP Port: This parameter is a numeric value. When TCP is selected this is the port number used by the Boomerang to listen for TCP connection requests. It must match the value used by the SCADA master. This parameter is ignored if UDP is active.
Listener Port (UDP): This parameter is a numeric value. When UDP is selected this is the port number used by the Boomerang to listen for UDP based messages. Again, it must match the value used by the SCADA master. This parameter is ignored if TCP is active.
Respond on Same Port used by Master (UDP): This is a checkbox field and only valid when UDP is active. When selected the Boomerang will respond to the SCADA master on the same port where the message was received. If this field is not selected then the UDP port to be used is specified in the “Dest Port” field.
Destination Port (UDP): This is the “Dest Port” field referenced above. It is entered as a numeric value to specify the UDP port number where the SCADA master is expecting UDP responses from the Boomerang.
Unsolicited Port (UDP): This field is a numeric value that is only valid when UDP has been selected. The unsolicited port is the UDP port number on the SCADA master where the Boomerang will send unsolicited events. These events are generated as a result of monitored voltage exceeding preprogrammed limits (described below under threshold programming). If this field is zero then unsolicited data will be sent the same as other UDP messages.
IP Address (unsolicited UDP): This field is specified as an IP address and is used as the destination for unsolicited UDP events along with the destination port described above.
ACK Timeout: This timeout parameter is specified in milliseconds and represents the time the Boomerang will wait for an acknowledgement from the SCADA master for solicited data. The solicited data will be retransmitted if the timeout is exceeded without an ACK from the master.
Threshold Programming
The Boomerang will generate DNP3 events based on monitored values crossing the boundaries of preprogrammed thresholds. These events are either collected during a timed polling interval of the SCADA master or received as an unsolicited event. There are four thresholds that may be specified per measurement type. The four threshold values essentially define 5 ranges where events will be generated. The typical or nominal value for the measurement will be the middle range with two ranges above and two ranges below. A threshold value of zero will be ignored and its range will merge with the adjacent range.
Low-Low Threshold: This is the lowest value expected to be seen and defines a range from zero to this threshold value.
Low Threshold: This level would typically be the midpoint between the lowest expected value and the nominal value. It defines a range from the low-low threshold to this threshold value.
High Threshold: This level would typically be the midpoint between the highest expected value and the nominal value. It defines a range from this threshold up to the high-high threshold.
High-High Threshold: This is the highest value expected to be seen and defines a range from this threshold up to the maximum value measurable by the Boomerang.
Hysteresis: This is a modifier value used to filter minor variations when a measurement is near one of the threshold boundaries. It specifies the amount that the measurement must exceed the threshold before triggering an event. The hysteresis is used to define a small expected variation in the measured value around the threshold points. This will avoid excessive events being generated when a measured value is hovering near a threshold boundary.
Trigger Delay: This is another modifier value for threshold processing. It defines the number of seconds that a measured value must be in a new range before an event is generated. If the measured value transitions into and out of a range before the trigger delay time has expired then no event will be generated.
Recommendations
The key decision in setting up a Boomerang for a SCADA network is whether to use TCP/IP or UDP/IP. Often this is a decision made by the customer’s IT department or based on the SCADA vendor’s suggestion. PMI recommends the use of UDP whenever possible due to the interaction between TCP and DNP3. Both TCP and DNP3 have mechanisms that attempt to validate the delivery of data and these mechanisms can interfere with data delivery causing excessive data transmission to result.
Due to the nature of the cellular data network it is expected that data transmission times are much slower than wired or Wi-Fi networks. Regardless of the communication method chosen (TCP or UDP) the SCADA master time delay for device response should be set to a minimum of 45 seconds. In some cases of poor cellular signal coverage this delay can exceed 1 minute.
If UDP is being used as the communication method then responding on the same port as used by the master is the preferred selection. This is easier to set up and doesn’t limit functionality in any way.
Conclusion
Configuration of a Boomerang to work on a SCADA network is a straightforward process. The terminology used and the pertinent data fields are often the stumbling blocks. The TCP versus UDP question is a key decision that will affect configuration details. As shown in this whitepaper, Boomerangs can be added as endpoints in a SCADA network with only a few parameter changes along with SCADA master settings. PMI’s sales and technical support departments will work with customers to select the optimum configuration for their needs and to assist with successful integration of Boomerangs into their SCADA network.
Wayne LaFleur
Senior Engineer
wlafleur@powermonitors.com
https://www.powermonitors.com
(800) 296-4120
