Watlow 8LS Controller - Manual (Page 35)

Installation
8LS User’s Guide 27
Control Outputs
WARNING
Control outputs are connected to the 8LS logic
ground. Be careful when you connect external
devices that may have a low side at voltage other
than controller ground, since you may create
ground loops.
If you expect grounding problems, use isolated
solid state relays and isolate the control device
inputs.
PID Output Termination TB (Primary) or
Flat Ribbon (Secondary)
The 8LS PID control outputs are Dual Outputs for each loop. For
identification these are called primary and secondary control outputs.
Therefore, each loop has control of two outputs, a primary and a
secondary. These are set by factory default to be for Heat/Cool
applications whether or not they will be used for heat/cool operation.
Primary simply means that it is physically implemented on the terminal
block instead of the 50 pin ribbon cable. This is because many
applications use only one output, and a user will not have to buy a
remote terminal block to use the primary output. Also, the primary
outputs are the only ones which can be programmed to analog. Primary
outputs cannot be programmed for DZC outputs.
The default output assignment is for the heat output to be on the primary
terminal outputs and the cool output to be on the secondary 50 pin
ribbon outputs. This can be changed, however, on an individual channel
basis by assigning the heat output to the ribbon cable. The primary and
secondary outputs do not have to be used for heat/cool since:
1. Each output may be individually programmed as a different type:
ON/OFF, TP (both outputs), DZC (secondary only) and ANALOG
(primary only).
2. Each output can be individually programmed to be direct or reverse
acting [both outputs can be the same].
3. There may be a deadband programmed for heat/cool, and in that
deadband both outputs will be off.