Using SignalFire Wireless for Control Applications
In addition to monitoring various sensor data and transmitting that data to the Gateway, the SignalFire wireless system is capable of control applications that involve turning remote assets on/off. The decision to switch one or more remote devices on/off requires control logic. Instead of using a traditional SCADA or PLC, the logic is programmed and executed entirely within the SignalFire gateway saving the cost of hardware, software and programming.
While SCADA systems and local PLC’s often require complicated configuration or ladder-logic programming, the SignalFire gateway embeds the control logic that consists of a simple IF/THEN table using any variables from any node available at the gateway. As an example application, let’s consider a system consisting of two tanks with the level being monitored using Sentinel wireless units. The tank levels are being fed by a pump controlled using the discrete output switch from a SignalFire RSD stick based on the level measured a Sentinel equipped with a level transmitter. See diagram below.
The desired logic is IF either tank exceeds a high level of 10 feet or if the discharge pressure exceeds 100psi THEN the pump should be shut off. This control logic can be easily configured in the gateway using the SignalFire ToolKit software.
First when connected to the gateway, select the “Remote Shutdown Settings” from the Settings menu, this will open the RSD control logic table. Each row in the table is considered one logic rule consisting of the source value settings, the relay control logic setting and the destination relay settings.
- Source Value
To configure the source value section, first configure the Slave ID of the remote node that is providing the measurement. In this example row one is configured for Slave ID 100. Next select the node type and the register address from the drop-down selections. The correct register containing the data value to perform the logic must be selected.
- Relay Control Logic
The relay control logic consists of configuring both the run system threshold and the shutdown system threshold. In this example we have configured the pump to run when the tank levels are below 9.5 feet and the Pressure is below 90psi. The pump will shut down when if either tank or exceeds 10’ or if the pressure exceeds 100psi.
- Destination Relay
This section defines the relay to be controlled by the configured logic rule. The relay can be any relay within the SignalFire system, including relays on RSD-Sticks, WIOM modules, and the local digital outputs on DIN mounted Gateways. Simply set the Slave ID of the device containing the relay and then select the relay channel number to set which relay on the device to control.
Combining logic rules
On our example we have two tanks and one pressure that we want to control the same pump. To accomplish this, we will assign three rules as discussed all with the same Destination Relay. For a given Destination Relay, ALL rules must satisfy the “Run state” for the relay to be energized. If any rule triggers the shutdown threshold the relay will be de-energized, and the pump will be shut off.
Failsafe and Logging of shutdown events
All SignalFire devices used for shutdown applications also include configurable internal failsafe timers. This allows the user to configure the devices to automatically shut down should the wireless communications be lost for any reason. The SignalFire Gateway also logs shutdown events in its internal non-volatile event log which can be read using the SignalFire ToolKit. Also, the recent shutdown history can be read via a set of Modbus registers to be monitored by a SCADA system of local HMI.
The internal control logic is simple yet powerful and allows operators to implement wireless control systems in a fraction of the time compared with hardwiring sensors and complex PLC programming. Additional details on the SignalFire shutdown logic configuration can be found in the Gateway user manual.