Watlow CLS - Manual (Page 38)

30 CLS User’s Guide
Installation
PID Control and Alarm Output Connections
Typical digital control outputs use external optically isolated solid-state
relays (SSRs). The SSRs use a 3 to 32 Vdc input for control, and you
can size them to switch up to 100 amps at 480 Vac. For larger currents,
you can use these optically isolated relays to drive contactors. You can
also use Silicon Control Rectifiers (SCRs) and an SDAC for phase-
angle fired control.
NOTE
Control outputs are SINK outputs. They are Low when the
output is On. Connect them to the negative side of Solid
State Relays.
The figure below shows sample heat/cool and alarm output connections.
Watchdog Timer
The CLS watchdog timer constantly monitors the CLS microprocessor.
It is a sink output located on TB-18 terminal #3, or on TB-50 terminal
#6. (Do not exceed the 10 mAdc rating for the watchdog timer.) Its
output is Low (on) when the microprocessor is operating; when it stops
operating, the output goes High (off), which de-energizes the SSR.
This figure shows the recommended circuit for the watchdog timer
output.