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Instrument I/O Interface
The J405 I/O port is a DB-25F connector on the back of the instrument that provides numerous
specialized functions for specific industrial applications and for factory use. System integration
utilizing the 4-20mA output feature is the most common use of the I/O port.
4-20mA Output
The 4-20 mA output can be used to indicate the Hg reading level on a proportional scale from
4-20 milliamps for connection to certain industrial systems, such as SCADA. A 4 mA current
level always corresponds to a Hg reading of 0.5 µg/m
3
or less, while a 20 mA current level
corresponds to a Hg reading of 500 µg/m
3
or higher. Current levels between 4 and 20 mA
correspond to Hg readings between 0.5 and 500 µg/m
3
on a proportional scale, as determined by
this equation:
When the J405 is powered off, either manually or automatically, the output current will drop to
3.5mA to indicate this condition. However, if the J405 is operating with the internal battery
disconnected and loses AC power, the J405’s 4-20mA circuit will continue to output the last
current value as long as power to the external current loop is maintained.
The relationship between the Hg concentration detected and the current level present can be
represented graphically as follows:
NOTE: This is NOT a printer connection.
It is a specialized interface. Connecting any non-AZI authorized
device to this connector may damage both the device and the J405
and may void the warranty on the J405.