October 18, 2015
There are many situations where connecting devices to control rooms by hard wiring is not feasible. In some cases, the devices are in the field where no wiring is available. In other instances, older plants may not be in a position to cost-effectively use new wiring. In these instances, creating a wireless network is the preferred solution.
Moore Industries provides an efficient and cost-effective solution with our WNM Wireless Network Module. It is a bi-directional, spread spectrum radio modem that delivers the flexibility and cost-saving advantages of wireless data transmission. It is ideal for use with Moore Industries’ NET Concentrator System (NCS), as well as other SCADA and distributed I/O systems.
One example of its use is at a custom chemical manufacturer that is creating small, granular crystals for a client. It is important that the size of crystals stay within a reasonable amount of variation. Having crystals of varying sizes can adversely impact the quality of the application.
The way that the crystals are cooled can have an impact on their size. Plant cooling tower water is used to cool the product. However, the temperature of the water can vary with the season, with colder water in the winter and warmer water in the summer. Since the rate of cooling impacts the size of the crystal it was important for the chemical manufacturer to monitor and control the temperature of the cooling water for any extreme variances.
The application uses an agitated jacketed Pfaulder kettle to crystalize the product. Two Moore Industries 535 PID controllers are tied to an automated cooling water valve which regulates the rate of cooling and placed at a point beyond where the water exits the jacket. The 535 is programmed at a gradient based on temperature over time (such as 1°C/10 minutes). The controller opens the automated valve for a period of time based on the temperature over time programmed. Once the gradient endpoint is reached, it closes the outlet valve to restrict any more cooling water from entering. This process is repeated throughout the cooling cycle.
The two 535 controllers and an NCS remote I/O system is located in a plant production area about 100 meters away from the front office. The plant did not have the infrastructure needed to interface the production area to the front office. This was critical to allow engineers and QA experts to monitor the process and to allow recording of the process to prove that it was done within acceptable temperature variance levels. Hard-wiring the NCS to the control area would have been cost-prohibitive, so a wireless solution was needed.
The solution involved a set of WNM radios and a peer-to-peer NCS system. The field-mounted NCS TIM Temperature Input Modules were mapped to the control room NCS’ AOM Analog Output Module channels. This allowed 4-20mA signals, which represented remote temperature data, to be monitored by an existing host monitoring system. The WNMs and NCS systems were pre-programmed at the factory, essentially making it a “plug and play” operation for site engineers.
Another example of the use of wireless technology to improve the efficiency of a process was at a pulp and paper company in the Pacific Northwest, which needed to monitor effluent water flow draining into a remote pond at its facility.
New government regulations had meant that personnel had to make a lengthy drive to the remote site three times a day to log the height of the pond.
The company wanted to create a more efficient process by monitoring changing water levels in a V-neck weir entering the pond to calculate flow rate.
In addition, they needed to have the data displayed on an Ethernet-based Human Machine Interface (HMI) in their boiler room and recorded in a historical collection and archiving system to comply with state regulations.
A HART radar level transmitter with precise measurement capabilities was installed at the site. This was connected to a Moore Industries HCS HART Concentrator System, a HART to MODBUS RTU convertor that serves as a HART master. It polls the HART radar level transmitter to obtain its Primary Variable (PV) data – in this case water flow levels. It can also receive and convert the level transmitter’s Secondary Variable (SV), Tertiary Variable (TV) and Fourth Variable (FV) along with any diagnostic data.
The ability to collect additional process variable data and diagnostic data about the transmitter’s health and performance was one reason the HCS was selected for this application. Another was its ability to convert this HART data directly to an industry-standard MODBUS RTU format, a serial communications standard supported by almost all industrial radios.
The flow level data needed to go to an Ethernet-based host HMI panel and a historical collection system. With no Ethernet networks, fiber lines or twisted pair wires available from the pond site to the control room, installing a local wireless network utilizing the WNM was the best method.
An initial wireless site inspection showed potential problems in establishing a direct line of communications from the pond to the control room due to expected tree growth or snow accumulation that could block a direct line of sight. To combat this, a decision was made to use 900MHz Frequency Hopping Spread Spectrum (FHSS) versions of the WNM rather than a 2.4GHz model. This provided a longer signal wave length to better penetrate foliage.
The WNM is available with an Ethernet interface, meeting the customer’s preference for Ethernet communications throughout operations. 900MHz Yagi antennas were installed at both the pond and boiler control room with narrow RF beams pointed at each other. The boiler control room’s antenna was later changed to an omnidirectional antenna to enable the expansion of the control room to communicate via wireless Ethernet to all locations within the facility.
The final piece of the solution was using an NCS to deliver the level transmitter’s signals to their host systems. Since the NCS can be a MODBUS master and slave simultaneously, it was able to poll the pond side NCS and then make that data available as a MODBUS RTU slave to the control room HMI display. Additionally, the NCS system was able to reproduce the level transmitter’s data as 4-20mA signals that could be fed into the analog based DCS/historian.
Moore Industries International