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Network/Modbus Communications
79
N2 Communications
Description of Variables
NPT - Network Point Type
Variables are defined as analog inputs, binary inputs, and analog outputs. Analog inputs are current control
parameters and items that the controller is measuring. Binary inputs represent controller states. Analog outputs are
the programmable set points for the isolation room pressure controller and monitor. These set points can be changed
through the keypad or by overriding the current set point.
NPA - Network Point Address
Address of the desired point.
Change of Status (COS) - Room Pressure Analog Input
The 8682 has the ability to change control set points locally. The alarm set points need to be based on the
controller’s control set point (AO #1). For example the set point could go from -0.002 in. H
2
O to +0.001 in. H
2
O. If
the COS alarm set points are not changed to accommodate, you could get low alarm or low warning messages when
the unit is working correctly. If these alarm points are set outside of the negative and positive set point values,
incorrect alarm messages can be prevented.
Override Analog Input Command
Analog Input values can be set using the override command. These values will be reset to the correct items when the
Override is released. There is not a time-out on the override command.
Override Binary Input Command
Overriding a 1 to Emergency binary inputs enables that mode. To release the controller from emergency state,
override a 0 to the Emergency input or press either the emergency or reset key. Releasing the override will return
the controller to the Normal state.
The alarm and data error variables can be overridden, but this will not affect the controller. Overriding the low
alarm variable will result in a change of status, but will not put the controller into low alarm mode. The local alarm
modes can only be controlled locally. Only override these variables for diagnostic purposes and release them for
normal operation.
Binary Input Data Error
Data Error binary inputs are used to indicate if something has gone wrong with the controller. Data Error indicates
when some of the data stored on the device has been corrupted. The calibration and set point values should be
checked on the controller.
Override Analog Output Command
The analog output variables can be overridden to change their values. The overridden value will be checked for
validity. If invalid, the override command will be ignored and the value will not change. The override flag will not
be set when the value is ignored. The override command will be cleared when the variable is reset in the menus. The
variable will not reset with the release command.