Monitoring Remote Chemical Tanks

Transcription

1 Monitoring Remote Chemical Tanks Introduction Economically meeting requirements for monitoring of mobile assets and remote processes always presents project engineers a considerable challenge. While the initial requirements are reasonable, complexity invariably emerges when the needs of all interested parties are assessed. This is particularly the case when the asset or process consists of a small number of monitoring points. Monitoring of vendor managed inventory, such as a chemical level in a tank, is an economically driven example of this challenge. Only a single measurement, tank level or pressure, is required. Basic requirements include monitoring the chemical level in the on site storage tank, periodically reporting it to operations management, and reporting on exception when appropriate, for example, when an alarm indicates low level or pressure in the tank. Economic goals include customer satisfaction and operation of the delivery/service fleet in the most efficient manner. Basic Monitoring Requirements for Asset Management As the project begins with reasonably simple goals, basic requirements for a remote monitoring device are established: Monitoring of discrete inputs such as float switches, on/off status, contacts on doors, entryways Monitoring of a primary process measurement such as flow, liquid level, pressure, or temperature Reporting of alarms and other live conditions Wide area communications, e.g. cellular or land line telephone Rugged packaging for outdoor installation Compatibility with a corporate computer system or support by HMI/SCADA software The team evaluates the possibility of packaging data communication equipment (DCE), such as a modem or cellular radio, or procuring a commercial off the shelf (COTS) dialer or notification product. Even with the packaging requirement, DCE devices represent the least expensive approach. A DCE will reside on a wide area network, typically using cellular technology, and can be programmed to communicate with computer systems. While a DCE device can readily be adapted to discrete process measurements, cyclical measurement of such analog inputs as flow, level, or pressure present problems. At a higher but still reasonable price, dialers and similar notification products are able to process the analog measurements and communicate this information to a variety of computer systems.

2 Inputs/Outputs For a remote chemical tank application, monitoring functionality may require as few as one or two I/O points with a number of others optional: Level measurement for single or dual tanks via analog inputs Optional, contact input indicating whether the instrument enclosure door is opened Another optional contact input indicating whether an entry door or gate is opened Optional, contact input indicating the open/closed status of the feed line valve(s) Optional, discrete outputs to drive an audible alarm or status light Optional, discrete outputs to open/close the feed line valve(s) Communications Communication functionality requires a modem, which accesses the hard wire or cellular telephone network in the area. A problem with many, monitoring devices available today, is that they have integrated only one cellular communications technology. In many areas of the world, North America most notably, multiple technologies are required to guarantee coverage. GSM is available in North America through major carriers such as AT&T but asset operators covering broad areas find that it serves less than 50% of their customer locations. In North America, CDMA is the other most popular technology. For example, Verizon Wireless provides CDMA for data services throughout its network. Still, a combination of GSM and CDMA leaves too many areas uncovered. While this often leads to suppliers reverting to older, hard wired technology such as a PSTN modem, costs of running telephone lines out to assets such as tanks continues to be very expensive. In order to ensure communications coverage, the monitoring device must integrate at least one additional, non cellular technology, such as spread spectrum radio. This license free technology provides a means for the operator to implement its own private network. Although spread spectrum radio range is limited to about 20 miles, this is normally sufficient to reach a relay node that resides on a cellular network. Instead of operating an extensive spread spectrum network, short paths are used to access the nearest cell. Power Management Even at factory locations, running power to the monitor and level transmitter has become expensive. This necessitates use of an alternative source such as a battery or solar power system. Since they are located inconspicuously inside the instrument enclosure, lithium batteries are preferred to solar panels as the latter are subject to theft and vandalism. Power management in the monitor minimizes power draw in order to keep power systems costs down. Advanced Functionality Very often, additional requirements emerge to meet the needs of IT, accounting or operations:

3 Historical data logging Programmable automation Maintaining long term or historical information has become a common feature in a number of COTS products. This feature is common in RTU products and is the key capability of a data logger product. The project team could spend extensive time distinguishing data loggers that include one or more DCE options from those not offering wide area communications. A problem with many data loggers is that they offer too few DCE options to work at all locations. Programmable automation capability also is a common requirement for operations. The ability to start or stop a motor driven device, open and close a valve, or regulate flow or level are basic requirements. Even if automation is not needed, some programming capability is necessary for customized calculations. While very few data loggers offer such capabilities, they are fundamental to most RTU products. Finally, the project team has determined that one product category, the RTU, meets all requirements. As a next step, the team determines that for small assets and processes the RTU solution is too expensive. The Solution: Wireless Remote Monitoring Wireless Remote Monitor technology, such Semaphore s T BOX WM, is a fully integrated solution that provides cost effective monitoring and telemetry for locations requiring only a few I/O points. Two analog inputs interface with low power transducers or 4 20 ma transmitters for level or pressure measurements. Four discrete inputs provide the status of contact inputs from devices such as security alarms and valve limit switches. Four discrete outputs are used to drive indicators or perform control functions such as opening and closing a valve. In order to provide communications coverage for practically any location, a variety of integral communications devices are offered including CDMA cellular modem, GSM cellular modem, PSTN modem and spread spectrum radio. This coverage is uncommon in devices that are designed for small assets or processes. The technology is also distinguished by a sophisticated IP/Web technology platform. It employs an integral web server, IP communications and push messaging via e mail, FTP and SMS text. T BOX WM can initiate communications whenever necessary, e.g. upon an alarm, event, or periodic update. There is no need for polling from a top end or host computer system. This communications strategy best exploits the benefits of inexpensive, public networks. Wireless remote monitoring allows users to access site information anytime, anywhere, using a cellular phone, PDA or laptop computer. This caters to operations management who are often traveling and making use of a mobile office. There is no need to operate the system from a central location.

4 The solution is housed in a ready to install IP666 weatherproof enclosure. Includedd in the enclosure are the main electronics, communications device, optional liquid crystal display (LCD) and one or two lithium batteries. The dual battery arrangement meets the requirements of operators who desire significantly reduced riskk of failure due to battery drain. A wireless remote monitoring solution such as T BOX WM,, will offer the following benefits: Level measuremen t: Via one or two analogg inputs, the solution will interface with transducers or transmitters for level, pressure or differential pressure. Local display operation: A delivery driver or techniciann can simply press the Activate key, on the front panel to power upp the LCD. The LCD will remain active for a user configured as specified by time, typically five minutes. Communications operation: The technology will initiate communications the user. Push communications via e mail, SMS text or FTP will take place on a periodic basis or when an alarm occurs. In the eventt of low level or low pressure in the tank, the solution will set an alarm when the analog input is below a user configured limit. Alarm managemen nt: The alarm management system will not only detect and report alarms, but be configured to require alarm acknowledgement and the escalation of unacknowledged alarms. Alarm acknowledgement is performed by users via a PC, PDA, orr even a cellular phone. Historical data logging and trending: On user defined intervals, the solution will perform statistical calculations on measured inputs and update the historical log. Logs can be displayed as web pages on a PC and transmitted as files with and FTP messaging. Web server: An integral Web server provides HMI capability offering significant cost savings over expensive SCADA software licensing. Web pages can be accessed by users viaa the Internet anywhere in the world. For tank monitoring applications, web pages also comprise an inexpensive HMI for local technicians. 8 (877)

5 Programmable logic: Although most applications are for monitoring and telemetry, the solution supports a programmable logic environment that includes advanced automation functions. Semaphore s TWinSoft software allows a choice of programming environments that include IEC LD (Ladder Diagram), Basic, and Microsoft. Conclusion Wireless remote monitoring technology is a highly attractive solution for chemical tank management applications. While a broad variety of commercial off the shelf dialers, data loggers, and notification products are on the market, new generation, to play for wireless monitoring applications. These products provide intelligent power management, extended battery life, input measurement, alarm management t, and data logging in an integrated weatherproof enclosure. In addition, an integral Web server, push messaging, multiple communications options, and ultra low power RTU products are bringing more advanced capabilities programmable automation comprise the advanced features that often make the difference for today s asset management and remote monitoring projects. Project teams investigating different chemical tank monitoring approachess should ensure they get full capabilities and functionality at the lowest possible cost. 8 (877)