Abstract: A remote measurement unit for testing and conditioning one or more telephone lines includes multiple electronically erasable flash memory banks, which contain respective versions of the operating system employed by the test unit's micro-controller. An operating system modification routine employed by the host processor of a remote site allows the functionality of the remote test unit to be selectively modified by electronically installing an upgraded or downgraded version of the operating system, or by electronically selectively activating or deactivating one or more operational features of the currently active operating system. A reset routine ensures that the operating system modification mechanism will only boot up the `correct` one of the two quasi-redundant systems available to the RMU's microcontroller after a system modification has been performed.

Abstract: A door phone controller has a door ajar feature for alerting a user that a door was left open. The door phone controller accommodates the door ajar feature in several different ways depending upon how it is configured to interface with the central office line. If the door phone controller is configured to interface with the central office line as an individual station, then when a door is left open, the controller alerts the user via auxiliary alert contacts specifically provided for activating a customer chime. When the door phone controller is configured as a ring-down station, the door phone controller alerts the user that the door was left ajar by dialing a pre-programmed telephone number and sending a door ajar tone. If the door phone controller is configured as an interface with a trunk port, then when the door is left open, the controller alerts the user by ringing the trunk line and also energizing the auxiliary alert contacts.

Abstract: A remotely controlled line conditioning apparatus is installed in the terminal where access to the telephone loop to be tested is readily available. Although a metallic bypass pair from the central office to the (remote) terminal may also be available, its presence and/or condition does not affect the ability of the apparatus to condition the line under test. The line conditioning apparatus includes a telephone line termination unit and an intelligent control unit. The telephone line termination unit has a telephone line access port to which a telephone line pair is selectively coupled, and is operative to controllably impart a selected one of a plurality of electrical signalling conditions to the telephone line pair under test. The control unit has a communication modem through which communication signals containing telephone line conditioning messages are coupled to and from the central office/remote terminal communication link.

Abstract: Disclosed is a ventilator including a heat exchanger having a fresh air channel and a stale air channel. The respective channels are pneumatically isolated, but, are arranged in contiguous and interwoven fashion such that incoming fresh air may pass in countercurrent heat exchange relation to the outgoing stale air twice. The fresh air channel has an inlet in communication with air external to the ventilated space and an outlet in communication with the ventilated space. The stale air channel has an inlet in communication with the ventilated space and an outlet in communication with the external space. The heat exchanger features heat transfer means in communication with the fresh and stale air channels which is formed by a septum having a first surface in heat exchange relation with the fresh air channel and a second surface in heat exchange relation with the stale air channel. The septum is wrapped in successive spaced turns to form alternating sections of the fresh air and stale air channels.