User manual

Page 18 915U-2 Wireless I/O
Page 18 User Manual
2.2.2 Expansion I/O Supply
To allow increased I/O Capacity, a second 4-way terminal labelled “Expansion I/O”
provides a +12 Volt supply (up to 1A) and RS485 communications for any 115S serial
expansion I/O modules.
B
A
-
+
915U-2
B
A
-
+
115S- XX
B
A
-
+
115S- XX
Figure 4 – Expansion I/O power & RS485
As a guide when using the I/O power connection from the 915U-2, the number of I/O
modules is limited to three x 115S-11(using inputs), one x 115S-12, or one x 115S-13.
If more I/O Modules are required, you will need to calculate the overall current
consumption using the following criteria and power the modules from an external
supply.
115S Module Static Current drain = 120mA
115S Digital Inputs require 13mA per active input
115S Digital Outputs require 25mA per active output
115S Analog Inputs and Outputs require 50mA per I/O when operating at 20mA
E.g. a single 115S-11 using inputs only has a current consumption of approximately
320mA so you could connect up to three 115S-11 modules to the Expansion port
without overloading the on board I/O power supply.
A single 115S-12 using all analog inputs and digital outputs has a current consumption
of approximately 720mA so you could only connect one.
Keep in mind that when calculating the current consumption for the expansion I/O, the
maximum available current from the onboard power supply is 1 Amp. If the overall
Expansion I/O current consumption is over the 1 Amp maximum an external power
source will be required.
2.2.3 Internal I/O
The internal supply voltages can be monitored by reading the register locations below.
See Section 5.1 “IO Diagnostics” for details on how this can be done.
The values can also be mapped to a register or an analog output on another module
within the radio network.