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Extensible monitor-and-control module uses cellphone link

Posted: 10 Jan 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Alex Mendelsohn? Compulogic LinkTx? Saelig? Ethernet? GPRS?

Compulogic LinkTx system

Operable from 6V to 24Vdc, the $699 Compulogic LinkTx system, as offered by Saelig, can be used as-is, or it can be equipped with an optional combined Ethernet and GPRS (General Packet Radio Service) Web server module. The optional module lets you monitor the LinkTx's inputs and outputs, and change them using a Web connection and your PC's browser. There are other modules that can be used to extend this system, too.

The LinkTx module itself gives you four digital inputs. These can be enabled via relay contacts, switch contacts, or voltage levels. You also get a pair of analog inputs that can each accommodate 0 to 40V levels.

Temperature probe inputs
There are also two temperature probe inputs, and means to monitor ambient temperature. The box's internal temperature sensor can deliver data from -50C to 80C. The two external temperature sensing inputs can be used to measure temperatures from -100C to 300C using an external PT100 temperature probe. Temperature alarms are programmable from -99.9C to 99.9C.

As mentioned in the press release, text message status reports can be readily requested from the LinkTx module. An Alarm Summary Report shows status of all monitored conditions.

A more detailed report shows current values of monitored conditions, such as voltage or temperature. A Settings Report shows current settings for triggering alerts, such as when monitoring battery voltage, temperature, or perhaps contact position.

Text message commands
As referred to in Saelig's notes, text message commands can also be sent to the LinkTx unit. These commands can perform functions such as setting mobile numbers to receive alert messages, setting alert threshold values for voltage or temperature, and setting optional password and incoming number filtering. Finally, the system's template-driven text message command system eliminates the need to remember commands.

Output modules
In addition to its monitoring functions, the LinkTx module includes three output control signals. The output control signals can also interface to accessory switching modules. These can be set up to switch loads as high as 16A at 240Vac or 12Vdc. There are also three programmable relay drive outputs. These deliver 5V at up to 25mA each.

You can also outfit a LinkTx with an NMEA (National Marine Electronics Association) input option. It supports remote monitoring of various parameters if instruments with NMEA outputs are available, such as a GPS (Global Positioning System) satellite receiver. With an NMEA GPS, you could use a LinkTx to monitor things such as geographic position, speed over-the-ground, course, water depth, altitude, and wind speed and direction.

The relay drive output can control power to the NMEA instruments. This lets NMEA instruments be powered only when a status message is requested, or they can be powered periodically to test for alarm conditions.

- Alex Mendelsohn

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