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.

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.

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: