Gas Utility Monitoring using TBox - Case Study
TBox ultra low and low-power products have been applied to natural gas utility installations throughout the world. Typical applications include line pressure monitoring, regulator monitoring and telemetry for metering installations.
The TBox ultra low power and low power families include the TBox WM “Wireless Monitor,” TBox LP RTU and the TBox LT Ethernet RTU. Selection among these products depends on the I/O count, whether power is available, and whether Ethernet networking is a requirement.
TBox WM best accommodates low I/O counts (up to 2 AI, 4 DI, 4 DO) while minimising current draw and making operation on batteries feasible. For larger processes (up to 4 AI, 8 DI and 8 DO), TBox LP features very low current draw and can run on batteries or solar power. TBox LT accommodates up to 32 I/O points and provides an Ethernet interface. Current draw is appropriate to solar power systems or other dc power sources.
The simplest application is monitoring of a single line pressure. TBox WM is very cost-effective in this case, as it integrates monitoring, telemetry and battery power in a ready-to-install, IP67 housing. TBox WM interfaces readily with low-power, voltage pressure sensors and pressure transmitters, which operate on a 4–20 mA loop.
By managing the power source for the pressure sensor or transmitter, TBox WM simplifies the installation. Regulator monitoring usually requires two, pressure inputs as well as ancillary status inputs. In most cases, TBox WM provides a perfect I/O compliment. Discrete inputs are often used to connect with float switches for those installations in which water can accumulate in the regulator vault. Unlike the Nema 4 enclosures commonly used with RTU and pressure recorder products, the TBox WM IP67 enclosure can be temporarily submerged and provides a great deal of installation flexibility for regulator vaults.
When a third or fourth, analogue input is needed for additional pressure or temperature measurements, TBox LP is used instead of the Wireless Monitor. The LP provides similar, ultra low power operations with integral batteries but with twice the I/O count of the Wireless Monitor. Alternatively, the LP can be ordered with a dc input for use with small, solar power systems.
In metering applications, TBox RTU products have interfaced to gas meters using analogue inputs, pulse counter inputs and serial, RS-485 connections using the Modbus protocol. For meters, which do not include integral corrections for pressure and temperature, TBox devices additionally interface with pressure and temperature sensors or transmitters.
Basic requirements for all sites include monitoring the gas flow, pressure and, depending on requirements of individual sites, ancillary inputs such as weather conditions or water levels; periodically reporting this information to operations management; and reporting on exception when appropriate, for example, when an alarm indicates low pressure or high pressure. Availability of this information not only ensures end-customer satisfaction but also allows the utility to schedule and route field personnel in the most efficient manner possible.
Via one or two, analogue inputs, TBox WM interfaces with transducers or transmitters for level, pressure, differential pressure or temperature.
To simplify the installation, TBox WM provides power to operate the transducer or transmitter. Optimally, low-power transducers are used in order to minimise battery drain. Such a transducer provides an output range of 1-5 V dc and operates using nominal 6 V dc or 12 V dc power. Current draw is typically 3 mA or less.
Many operators prefer an analogue transmitter, which provides a 4–20 mA signal and operates using nominal 12 V dc or 24 V dc power. Although the current draw is much higher, T-BOX WM is still able to provide power to these transmitters and uses intelligent management to permit operation on a lithium battery.
A key factor is that, in most cases, the measurements need not be continuous. On a user-selected interval, TBox WM will power-up the transmitter, wait for another, user-configured time to allow the transmitter output to stabilise, take a reading, then power-down the transmitter. Typically, readings take place, once-per-hour or once-per day. NOTE: If readings are required significantly more often, up to “live” once-per-second, TBox LP or LT can be employed, instead, with solar power or commercial dc power.
Power savings using this type of operation are substantial. Consider an analog transmitter that draws 60 mA at 12 V dc. If it is powered on for one minute every hour, the duty cycle is 1/60 and the equivalent, continuous current draw is only 1 mA. In fact, most transmitters draw less current than the one in the example and many operations require readings on a daily rather than hourly basis.
In contrast to some monitoring products on the market, TBox WM allows both, analogue inputs to operate, simultaneously. There is no multiplexing in terms of time or hardware.Local Display Operation
Even though it consumes very little power, the LCD is normally turned off because local operations are infrequent. A technician will simply press the “Activate” key, on the front panel, to power-up the LCD. The LCD will remain active for a user-configured time, typically five minutes. This allows, as an example, the technician to see the live measurements over varying conditions.
The display will also indicate whether there are any alarms such as low flow, low line pressure, low battery, or transducer/transmitter failure.
In a manner similar to that for external transducers or transmitters, the internal communications device operates intermittently. Depending on the technology employed, the entire module may or may not be completely powered-down in order to minimize the start-up delay time.
TBox WM will initiate communications as specified by the user. “Push” communications via e-mail, SMS text or FTP will take place on a periodic basis or when an alarm occurs.
An alarm can be a transition on a discrete input or a condition that is determined by programmable logic. An example of the latter is a low pressure in gas line. TBox WM will set an alarm when the analog input is below a user-configured limit. Multiple limits could be used. Some operations implement three low limits, including low, very low and out-of-service.
Most commonly, periodic communications occur less frequently than readings are taken via the analogue inputs. For example, TBox WM will initiate a call on a daily basis while readings are taken hourly. As determined by the user, the daily call can provide the latest reading, each of the readings since the last call and/or figures from the historical log (please refer to the section, below, for information on the logging capabilities). E-mail and FTP messaging can include files, for example, tabular logs or trend graphs.Alarm Management
TBox WM uses an alarm management system that not only detects and reports alarms but can be configured to require alarm acknowledgement and escalate unacknowledged alarms.
If configured to do so, an alarm transition will initiate communications. Messaging can be to multiple recipients while escalation can be to multiple groups, each including multiple recipients. Alarm acknowledgement is performed by uses via a PC, PDA or even a cellular phone. Using a phone, the user sends a text message to acknowledge the alarm. TBox WM will not only clear the alarm, internally, but can initiate programmable logic functions in response to a text message.
TBox WM also maintains an alarm history, which can be displayed as a web page and attached, as a file, to e-mail and FTP messages. Each message includes a time and date stamp, signal i.d. and text description.
On user-defined intervals, TBox WM will perform statistical calculations on measured inputs and update the historical log. Averages, totals, minima and maxima can be run over intervals such as hourly, daily, monthly, etc. Historical logs can be displayed as web pages on a PC and transmitted, as files, with e-mail and FTP messaging. Logs can be maintained in tabular as well as trend graph format. To simplify configuration, Semaphore offers a software tool, Report Studio, which provides powerful trending capabilities.
While the historical information is commonly used for pressure profiling and billing purposes in metering applications, long-term trends also contribute to continuous improvement programs.Web Server
The integral web server provides an HMI capability, which can offer significant cost savings versus expensive licensing for SCADA software. Web pages can be accessed by users, anywhere in the world, via the Internet or an intranet.
For natural gas utility applications, web pages also comprise an inexpensive HMI for local technicians. Not only is process information provided but system diagnostic information is available in the TBox WM data base.
Servelec Technologies' software tools greatly simplify configuration of web pages and eliminate software integration problems. No programming is required. Using WebForm Studio, dynamic objects, entry fields, tables, trends, and links to other pages are simply added with a few clicks.Programmable Logic
Although most applications are for monitoring and telemetry, TBox supports a programmable logic environment that includes advanced, automation functions. Using Servelec Technologies' TWinSoft, engineers have a choice of programming environments to suit their preferences:
- IEC 61131-3 LD (Ladder Diagram)
- Microsoft Automation
TWinSoft contains a complete set of tools, such as editor, debugger, code generator, documentation generator, library manager, archiver, and online control. TWinSoft makes it easy to download identical programs into multiple RTUs and also eases programming changes in order to allow for continuous improvement.
Typically, TBox WM applications will use this functionality for calculations related to alarming, units conversions, timing functions such as rate-of-change, and data logging. Nevertheless, programmable control operations can also be performed via the discrete outputs.
Natural gas utility applications take full advantage of the features offered by Servelec Technologies' TBox product line, in particular, the Wireless Monitor:
- Fully integrated — Complete monitoring, telemetry and automation functionality is provided in a ready-to install, IP67 housing that includes the battery-based power source. End users or service providers need not incur any additional costs or scheduling delays for systems integration.
- Power management — Very low power consumption allows users to configure scanning and communications strategies that best utilize the included, low cost, lithium battery power source in TBox WM. This integral power source further reduces costs related to integration and installation. TBox LP operates using battery or solar power while TBox LT operates using solar or dc power.
- Dual batteries — One or two lithium batteries can be installed inside the TBox WM or LP enclosure. Using two batteries provides double the lifetime vs. a single battery and allows the WM or LP to operate on one battery while the other is replaced.
- Integral Web server — This feature provides significant savings vs. SCADA/HMI software, which could require expensive licensing. Web pages are accessible to users, anywhere, anytime. PC-based Web pages also provide all, local HMI operations when maintenance personnel visit the sites, thus saving the cost of additional software.
- Alarm management — The TBox alarm system detects alarm conditions and reports them using Push Technology. Alarm management ensures that un-acknowledged alarms will be escalated. Even cellular phone users can acknowledge alarms and send text commands to a TBox.
- Data logging — TBox data logging capability retains historical information, such as line pressures, in both tabular and trend graph formats and allows users to adapt operations for the highest efficiency. Trends can also assist in maintenance management and continuous improvement.
- Push technology — End user operations personnel are immediately notified of alarms and important events without the need for polling the TBox. This takes best advantage of inexpensive data communications plans on public networks.
- Programmable automation — A choice of programming via IEC 61131-3 LD (Ladder Diagram), Basic, or Microsoft® Automation provides calculation functions and control outputs, e.g. to open and close a feed line valve. These capabilities are very uncommon in products intended for monitoring only