The Aprilaire 50 is the correct replacement for the following humidifiers:
The Aprilaire 50 Humidifier Current Sensing Ray will detect a current when the furnace blower fan is running. If you have a multi-stage furnace, this current sensing ray will simplify your installation without needing accessory terminals. Also known as part number 50, this Aprilaire Current Sensing Ray has a voltage range of 21-24 VAC.
Aprilaire Current Sensing Ray 50 specifications:
When you run the fan wire through the top loop of the relay when the fan turns on, the relay will close and allow the 24 volt power on the relay side to flow through in order to turn the humidifier on. The Aprilaire brand is also known by the following spelling variations: Aprilair, April Aire and April Air.