A Power Plant in the U.S. Northeast needed to monitor three safety relief valves on gas lines into their power plant. An alarm is required on each valve in case any of these relief valves experience a release of natural gas. Because it would have been too costly to run wiring out to these new valves, they opted to implement a wireless solution.
A wireless valve position monitor and controller was installed on each valve. The signals to and from these monitors are sent via a wireless gateway using wireless HART, and a Moore Industries NCS NET Concentrator System was used to pull the signals from the gateway via RS 485 serial communications. The NCS consists of three modules:
- EMM Ethernet/MODBUS Interface Module provides the communication capability for the NCS and powers the other modules.
- AOM Analog Output Module serves as a place to write the positioner values and make them available to the ‐MAA Multipoint Analog Alarm option. Setpoints are set up using the NCS configuration software.
- ROM Relay Output Module outputs to an explosion-proof light to alert the plant operators and sends a signal to a PLC so the control room will be alerted.
The EMM is the Modbus Master and reads the values from the gateway. These values are written to the AOM. The current outputs can be sent to the PLC or to local displays. The valve positions are available to the NCS –MAA option where alarms are configured. Relay outputs are wired to alert the operators of the relief valve state.
The alarm function on the NCS system would normally be programmed using ISaGRAF control software which is very powerful and versatile. However, they opted to add the –MAA Multipoint Analog Alarm option to the NCS EMM module which allowed them to easily set and implement the alarms using easy to navigate prebuilt web pages on the EMM's webserver with a standard browser, saving a day of engineering time.