Sine Systems ACM-2 AC Current Monitor allows monitoring of AC current by the RFC-1 remote control system. A common application is to verify the proper operation of obstruction lighting on communications towers. More generally, it may be used to meter the AC current consumption of any 115 or 230 volt device drawing from 1 to 70 amperes.

The ACM-2 consists of a current transformer and a PC board that converts the output of the current transformer to a DC voltage. The current transformer should be mounted at a location that is convenient to the AC wiring to be monitored. The "hot" AC lead should be passed through the insulation tubing in the current transformer.

The ACM-2 PC board can be mounted in any dry location. Applicable national and local electrical codes should be followed in the installation and wiring of the current transformer. Under normal conditions, the output of the current transformer is low voltage AC (less than 20 volts rms). However, during lightning strikes or other transient voltage conditions, the voltage may be very high and appropriate precautions should be taken.

As configured from the factory, the ACM-2 PC board is set up to monitor a tower lighting circuit. The DC conversion circuit will "smooth out" the voltage generated by the lighting current to a nearly constant value even if flashing beacons are used. Because of this, it is easy to monitor with a telemetry system like the RFC-1. Also, because the monitored voltage is an analog value, very small changes in lighting current can be observed. A current change of 1% is easily resolved. In most cases this is sufficient to detect the failure of a single bulb in the lighting system.

Telemetry alarm systems typically monitor for alert conditions 24 hours a day. This can become an issue for devices that are only active during a portion of day or night. One way to monitor the tower lights only during dark hours is to automatically disable the ACM-2 telemetry during daylight with a photosensor circuit. The ACM-2 comes with connections capable of allowing such a circuit to be added and the instruction book includes a sample circuit schematic diagram.