Air speed and/or Air Volume control
The basic function of a Fan Filter Unit (FFU) is to provide a continuous flow of filtered air over a clean zone in the front end of the tool or on the tool itself. How the air is controlled is one of the most important parts of the design. The air flow is typically controlled in one of 3 ways:
- Analog/Manual control, using a Rheostat speed control – The control can be physically located on the FFU, or in a remote box. The box might be cosmetic for a surface mount or with a face plate for a recessed mount on the tool.
- Dual Speed Control – Allows the FFU to deliver different amounts of air under two distinct tool conditions. With 2 ea. separate speed controls, the fans in the system are being controlled by either one or the other at any moment in time. When the tool is sealed up and operating, the first speed control sets the fan speed, then when the tool energizes an external low voltage relay on the FFU, the second speed control (set at a higher setting than the first) takes over and the fans ramp up to dump additional air into the space and reestablish the original differential pressure level under the new condition. Easy, cost effective, and functional.
- Automated Pressure Control (APC) – Increasingly the use of pressure controlled FFU operation is being written into specifications. In this case the rheostat speed control is replaced by a version of the Air-Care Variphase that, operating with information from a Setra 0.01″ range pressure sensor, can control the operation of the FFU to achieve and hold a “set pressure point” in the clean zone. This can be done with a single FFU or with a large “Primary/Secondary” installation. When the FFUs are first installed it is useful for the FFU(s) to be able to operate in a manual mode for the initial clean down of the tool. The pressure controlled option comes in two varieties:
- Full external control where every function (fans on/off, manual or pressure, PID, fan speed up or down, and etc.) is done via an Air-Care SP1 console, or directly from a computer hooked to the FFU via RSA 485.