NETWORKED FACILITIES MANAGEMENT SYSTEM WITH BALANCED DIFFERENTIAL ANALOG CONTROL OUTPUTS

A networked system having a wide variety of applications and particularly applicable to facilities management systems has multiple levels of software in processing nodes. The levels include a "features" processing level which communicates requests for data to a software object level containing databases of processes and attributes and database managers. The database managers in the software object level operate to provide data to the high level features in the same format. The software object level communicates with a hardware object level which also contains databases and database managers to mask differences between operational hardware units. By categorizing operational units by type, additional units of a known type can be added with only low level hardware object database changes. Adding units of a new type is facilitated by software changes confined to the lower level hardware and software objects, avoiding software changes at high level features. Individual software objects are tailored for typical types of inputs and output devices encountered by facilities management systems. Universal drive circuitry also provides applicability to a broad range of devices. The sum of an analog input signal and a feedback signal is provided to a buffer circuit. A current sensing network connected to the output of the buffer forms a first control signal. An equal amplitude, oppositely polarized signal forms a second control signal. An external signal switches the feedback network to produce a voltage derived from a current output of the first control signal and a voltage output of the first control signal.