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Sentry User Tips

Sentry is the most comprehensive gas detection system available and provides the user with a wide range of capabilities and features.

Front Panel: Select Scanning Mode (Continuous, Condition Safe, etc.)

Most users are very comfortable with the default "Continuous" scanning mode for Sentry controllers. In Continous mode each sensor number and concentration is displayed in sequence by sensor type. But there are two other scanning modes which are useful. From normal operation, Press Mode, Mode, Enter and check the following alternatives:

Another great feature is the ability for the operator to lock the display onto one sensor address. While in Continuous mode just press Enter to stop the scanning. Press the arrows to move to the required address. - A great feature for troubleshooting a system or a plant process. Note that the lower display shows [square brackets] around the display to warn that the display is locked.

Finally, users can be assured that the scanning mode is simply the display function, and the Sentry Controller is always performing its monitoring functions for all sensors connected to the controller.

Front Panel: Gas Tags and Module Tags

Sentry makes it very easy to display sensor module tag data and the gas type on the controller. Of course, the easiest way to do this is to have the factory burn the information into the EPROM prior to shipment. This service is included in the Enhancement Package. The burned EPROM method makes the tag data non volatile. But in some applications it is not possible to provide all the tag information prior to installation. In other applications the system configuration is changed in the field. In these cases, while it will require many key presses, the user can update the tag information in the field.

Module Tags: In Change/Calib Mode, fine the menu item j"Change Module Tag". Select the sensor module address to be changed and then type the new Module Tag. The up and down arrows on the key-panel are used to increment alphas, numbers, space and signs. The editing is real-time so as soon as the input is complete the new Module Tag will display on the second line of the display whenever the resprective sensor module concentration is displayed.

Gas Tags: There is a library of standard gas tags which can be assigned to any module in Change Module. Gas Tags have "rule" which avoid the same tag being assigned to two different sensor module types. If a user needs a Gas Tag which is not in the library, then use "Change Gas Tag" to rewrite one of the unused library entries. An important feature of gas tags is that the Global Gas Tag" to rewrite one of the unused library entries. An important feature of gas tags is that the Global Calibration routine groups modules by gas tag. A good trick is to use slightly differing gas tags to create special calibration groups.

Front Panel: Use of Passwords

Sentry gas monitoring system alarm and configuration parameters plus calibration variables are established via the front panel key panel and display. The configuration must be protected from unauthorized changes. Also data stored in the controller memory must be protected against accidental erasure. User code passwords are used for this requirement. The "Change User Code" function allows a supervisor to establish up to eight "users" each with their unique user number and four digit numeric password. Users 1 through 4 have system management rights while users 5 through 8 have calibration rights only. When user codes have been established all protected menu activities require the user code to be entered for access.

Interconnect Tip: Expand the Relays

Sentry systems are often installed in a manner where alarm relay output requirements are satisfied by the integral double pole/double throw relays in the controller. But, there are powerful additional options available. Adding the Individual Relay panel (Model 5392) provides 16 additional single pole/double through relay outputs. The panel plugs into that blue connector on the back of the Sentry controller.

Individual Relays: In the standard configuration eight relays are assigned as low alarm, per sensor address, and eight relays are assigned as high alarm per sensor address. – A great feature for driving individual warnings per sensor.

Zone Relays: A factory installed option is to change the sixteen relays into zone alarms. Users can assign any relay to a Zone function where groups of sensor alarms are the members of the zone. An added feature is that the zone alarm can be based on voting. For example five sensors might be in a zone but at least any three sensors must alarm before the zone relay activates. – A great feature for redundancy requirements.

Another great feature of optional Sentry outputs is the Model 4314-01 relay panel which provides all of the above features but also supplies individual 4-20 ma outputs for each sensor address.

Interconnect: Spare Channels

All Sentry controllers are supplied with eight channels of wiring terminals. Users who install multiplexed channels do not use all eight physical channels. The spare channels offer important benefits:

Interconnect: Double pole relays and their use

Gas monitoring specifications generally call for alarm functions at two levels. The first level is a warning and the second level is an emergency. Typical systems use a set of relay contacts which will turn on a warning light and a second set of contacts to activate an emergency horn or siren. These required alarm contacts are integral to the Sentry controller. By supplying Double Pole, Double Throw (DPDT) dry contact alarm relays, Sentry allows for the standard device to consume one pole while the second set of contacts is available for other functions. A possible use for the second set of contacts is to connect them as inputs to a plant SCADA system or a process shut-down control system.

Integration: Commander

Sentry controllers are packed full of features and are extremely flexible on a stand alone basis. But some applications require that data be shared between Sentry Controllers or require more programmable functions. Sentry Commander, Model 5800 answers this challenge. Multiple Sentry controllers can be connected to a Commander via the Modbus serial option. Sentry Commander acts as a Modbus master and polls data from the controllers to create a real time database.

A simple configuration system, using either the Commander front panel or an Excel spreadsheet, is used to create process blocks to create logical conditions, drive physical relay outputs, and send reports to a printer. The process blocks allow up to 48 sensor values to be used as arguments. Processes include voting, time delays, inversion, or, nor, nand logic, and other functions. Results drive relays and can be displayed on the Commander front panel.

A great feature is the ability to display data on an exception basis such as only when the result of a process is true. Also, there are nine LED’s on the face panel which can be assigned any function required for the application.

Sentry Commander can control up to 32 relays by installation of two Model 5392 Relay panels.

Integration: FieldServer

The gas monitoring system is installed and up and running and now the plant requires data from the system in a control room. Maybe they require a web server capability? Maybe the data must be supplied in a particular protocol such as Modbus TCP or EtherNet/IP. Sierra Monitor's FieldServer Technologies division meets this challenge with the off-the-shelf FieldServer solution. A FieldServer can be connected as a client to the Sentry Modbus serial prot and will then serve the data to the plant system or web browser as applicable.

Integration: LANServer

An earlier tip discussed the use of a FieldServer to provide connectivity using foreign protocols. But FieldServer can also be used as a LANServer. Sentry's unique LANServer package allows immediate connection to both Ethernet local area or wide area networks and the Internet. Standard LANServer functions include a graphical overview screen, a tabulation of sensors by type and by number, an active alarm screen and an event log. In addition, tools are provided to allow users to add unique floor-plan or photo files and to move sensor ActiveX objects into position to provide a custom view of the gas monitoring system. Sierra Monitor offers engineering service to implement the custom screens and to consolidate multiple controllers onto a single LANServer application.

Expansion: Add more gases

Many gas detection applications require monitoring of more than one gas type. For example, wastewater treatment plants require detection of combustible gases, Hydrogen Sulfide and Oxygen. Semiconductor plants require Hydrogen detection, many toxic gases and Oxygen. Refineries, chemical plants, food process plants and storage facilities are all candidates for multi gas requirements. Sentry makes it easy to add gases. The following are three simple options to expanding Sentry to multiple gas types:

Add Sentry gas sensor modules: Most primary industrial toxic gases can be monitored using one of the standard Sentry gas modules. Taking advantage of multiplexing, users with extra controller capacity can simply add the modules to existing wiring.

Add analog modules; When a specialty gas is not on the standard Sentry list, users can purchase analog (4-20 ma) modules form other sources and tie them in to Sentry using one of the Sentry A/D options. Multi-channel inputs or single channel inputs are available.

Change gas tags and scaling factors: Users who require monitoring of more than one combustible gas will find it useful to change the Sentry gas tag library so that each combustible module is assigned a different gas tag. By this method, calibration, scaling and data display can be grouped and managed by gas type.

Expansion: Using Existing Wire by Multiplexing

Plants change, they grow, they change processes and the gas detection system must keep pace. Installation of additional wires is a key expense in the expansion. Sentry multiplexing can mitigate some of the added wiring costs. Following uses an example of an installation with eight sensor modules, each with a home run wiring to a controller. The gas detection system can be expanded by rerouting field connections so that the sensors are multiplexed. In the example, it may be possible to free two, three or four home runs of wiring to be used on an expansion gas detection system. Let Sierra Monitor technical services review the layout and advise on the appropriate use of multiplexing.

Expansion: Commander to provide Printer reports from multiple controllers

All Sentry controllers are available with either Modbus data interface, or serial printer output. But, because these functions are mutually exclusive, users who require both Modbus and printer interface need a solution. Additionally, users who install multiple Sentry controllers need to avoid installation of multiple printers. The solution to these challenges is Sentry Commander. Described in an earlier tip as an alarm handling system, Commander also has the ability to consolidate and print hard copy reports of data generated by multiple Sentry controllers. Parameters which are added to the Commander configuration file provide the ability to consolidate sensors into groups. Each group is then reported on hard copy output in the same way it would be reported from a single controller.