Field Report: FM Services TLM-1


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It was inevitable, with the changes in technology over the past years, that items started shifting to a microprocessor-based design. From studio automation systems to remote control units and transmitters, those pesky, rectangular ICs with all the leads cropped up everywhere. I could hardly believe my eyes when I saw an ad for the FM Services TLM-1, a microprocessor-controlled tower light monitor. What really caught my attention was the claim that multiple beacons and sidelights could be monitored by sensing one wire. Over the years I have used other types that required each beacon level and each sidelight level to be monitored by a separate wire going up the tower to that level; a condition that didn't always exist either by design or tower wiring changes over the years. I have built several of my own basic design tower light monitors using a toroid core to sense the current and then rectify and smooth the flash transitions for a remote control to sense. However, the idea of being able to monitor the whole tower with a single current sense was intriguing.

Performance at a glance
Senses current on power supply lines
Multiple alarm outputs
Opto-isolater alarm and status outputs
Remote alarm reset
Single-phase or three-phase monitoring

With the TLM-1, installation is very easy and straightforward if your system uses single-phase power and either 120V or 240V supply. With a 120V feed system, the hot wire from the breaker panel is fed through the current-sense transformer so the total current — beacon and sidelights — is sampled by the TLM-1. In the case of a 240V feed, where two hot wires are used to feed the tower light system, both are fed through the current sense transformer, but one lead is inserted in a reverse direction so the currents, which are 180 degrees out of phase, will be additive through the current transformer. Sampling of a tower light system fed by three-phase power will require three of the TLM-1 units. Single-phase power was used in both locations where this unit was tested.

FM Services
P
W
E
336-667-7091
www.towermonitor.com
info@towermonitor.com

Once the electrical feed to the tower light system is fed through the current sense transformer, with the lights all operational in a normal mode, the unit is calibrated by pressing a button. This tells it what normal current flow is for beacons, sidelights, and even if you have a steady burning bulb in the tower light circuit. This is a handy feature if you leave a light on constantly for humidity control. It is now ready to provide status alarms for changes it senses as abnormal operation.

System status

The TLM-1's status outputs indicate problems:

  • Photocell circuit failure
    If the status of the lights does not change in 20 hours, it is assumed there may be a problem with the photocell circuit. Instances where the tower lights are on 24 hours each day, this function can be disabled by a dip switch.
  • Flasher failure
    If beacon current is constantly on or off, or if the flash rate and duration are not according to FAA specs, then this status will alarm. Note: the beacon on vs. off time is monitored for FAA specifications.
  • Beacon failure
    Activated if a beacon bulb fails or flasher is in constant off state.
  • Marker failure
    Activates with a failure of any sidelight bulb.
  • Summary Alarm
    Any of the four above alarm conditions causes a summary alarm. This alarm may be reset locally or remotely and the unit is ready to monitor for an additional lamp or condition to fail.



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