Installation manual

Introduction
900M050U00  Athena Controls, Inc. 1-11
1.6 Setpoint
1.6.1 Introduction
The value of the PV and the setpoint currently being used (“active setpoint”) are always
displayed when a 16C, 18C, or 25C controller is operating in normal mode. The
setpoint used (and displayed) is not always entered by the operator as described in 2.4.2.
• The active setpoint can come from a recipe; see 1.6.2.
• The active setpoint can be written to the controller from a host computer; see 1.6.3.
• A second setpoint can be used when an external device triggers an optional switch in
the controller; see 1.6.4.
• The setpoint can come from an external device by means of an optional analog input;
see 1.6.5.
For the algorithm used by the controller to determine which setpoint is the “active”
setpoint, that is, the setpoint being used now, see 1.6.6.
1.6.2 Setpoint from a Recipe
The 1ZC, 16C, 18C, and 25C controllers can each be configured to execute a single
ramp to setpoint, or a multi-step ramp and soak recipe (eight steps maximum). As
execution of the ramp or recipe progresses, the setpoint is changed by the controller as
specified in the recipe. Starting, pausing, and terminating recipe execution is described
in 2.4.6. Instructions for configuring recipes are in Section 11. The setpoint range
applied to recipe soak levels is configured using the setpoint low and high limit
parameters described in 5.6.2 and 5.7.2.
Athena Multi-Comm software can be used to configure Multi-Comm recipes that have any
number of steps. (The recipes are stored on the Multi-Comm host computer, not in the
controllers.) If a controller is connected to a Multi-Comm host computer via an RS-232 or
RS-485 connection, the operator can execute a Multi-Comm recipe under the direction of
the host, which sends the controller setpoint values in accordance with the recipe.
Instructions for configuring Multi-Comm recipes are in the Multi-Comm User’s Guide.
1.6.3 Setpoint from a Host Computer
If a controller is connected to a Multi-Comm host computer via an RS-232 or RS-485
connection, or to a MODBUS master via an RS-485 network, the setpoint in the controller
may have been written to the controller by the host computer. The setpoint range applied
to setpoints that are configurable using a host computer is configured using the setpoint
low and high limit parameters described in 5.6.2 and 5.7.2.
Host computers can write a new setpoint to either RAM or the EEPROM (or to both). The
controller uses the setpoint stored in RAM. If the setpoint is also stored on the EEPROM,
the setpoint will be retained, even when power to the controller is turned off. The setpoint
stored on the EEPROM will be written to RAM when the controller is powered up.
However, a host computer can wear out the EEPROM by writing to it too many times. Do
not write the setpoint to the EEPROM when you are writing a temporary setpoint to the
controller, such as when you are ramping to a final setpoint under the direction of a
MODBUS master.