Specifications
ST900 Family General Handbook
667/HB/32900/000 Issue 12 Page 26 of 265
The two RJ-45 connectors on the PHS card marked “IO” are used to connect to the
Intelligent Detector Backplanes and IO cards. It is not important which connector is
used for the IO and which is used for the Intelligent Detector Backplanes.
2.8 Serial I/O Card
The I/O card provides a rugged interface for up to 24 digital inputs and 16
changeover outputs for the connection of pushbuttons and above ground detectors,
or to provide a free-standing UTC Interface or for linking between controllers.
A sub-equipped variant of this card is also available, fitted with only 4 changeover
outputs. If the IC4 Configuration requires the 24 in / 4 out variant but one is not
available, then a 24 in / 16 out card can be fitted in its place.
The I/O card connects to the PHS or previous I/O card via a high-speed serial cable
through which the card also obtains its logic power supply.
2.8.1 IO Card Outputs
The IO card outputs are volt-free fully isolated outputs that are compliant with
TR2523:2005 as follows:
Maximum ON resistance of 50 Ohms
When ON, an output is rated at 50mA maximum
When passing 50mA, the output shall drop no more than 2.5V
When OFF and output will withstand 75V DC continuous
When OFF and output will present a resistance of greater than 100k Ohms
The COMMON, NORMALL OPEN and NORMALLY CLOSED contacts of each
output are isolated from any other output by 3750 volts minimum
2.8.2 IO Card Inputs
The IO card inputs are compliant to TR2523:2005 as follows:
Closed-Circuit is indicated when a resistance of 250 Ohms or less is present across
the input terminals
Open-Circuit is indicated when a resistance of 100k Ohms or greater is present
across the input terminals
The open-circuit voltage across the input terminals is less than 50V DC (typically
less than 20V DC)
The short-circuit current is less than 50mA (typically less than 2.5mA)
In practice, any resistance across the input terminals that results in a voltage of
greater than 7.5V across the input terminals will be read as Open-Circuit
Any resistance across the input terminals that results in a voltage of less than 2.5V
across the input terminals will be read as Closed-Circuit