Watlow CAS - Manual (Page 29)

Installation
CAS User’s Guide 19
Outputs
NOTE
All digital outputs are sink outputs referenced to the 5Vdc supply.
These outputs are low (pulled to common) when they are ON.
All digital inputs are Transistor-Transistor Logic (TTL) level inputs
referenced to control common.
The alarm outputs are located on the 50-pin header which connects to
the 50-pin flat ribbon cable. This section explains how to wire and
configure alarm outputs.
Wiring Outputs
The digital outputs sink current from a load connected to the CAS'
internal power supply, or from an external power supply referenced to
CAS ground.
• If you use an external power supply, do not exceed +12 volts.
• If you tie the external load to ground, or if you cannot connect it as
shown below, then use a solid state relay.
• If you connect an external supply to earth or equipment ground, use
solid state relays to avoid ground currents. (Ground currents may
degrade analog measurements in the CAS).
The outputs conduct current when they are "True". The maximum
current sink capability is 20 mA (for all outputs, refer to spec. for
details). They cannot "source" current to a ground load.