30
override the controller’s temperature control and force its output switch off or on. As a TEMPBUS™
temperature source, either controller can control its output switch using the
TEMPBUS™ temper-
ature rather than temperatures from
TS 1 or TS 2.
Setting: NOT USED, TEMPBUS (V3.11+), INHIBIT or FORCE ON (V3.11+)
Procedure: If the
EXTERNAL INPUT is not being used by either point, select NOT USED. If either
point requires a
TEMPBUS™ temperature signal, select TEMPBUS™ and set the point TS CONTROL
MODE
to a mode using the EXTERNAL INPUT (see section 3.5.12 on page 24). For TEMPBUS™
operation description see section 5.4 on page 53.
If a remote dry contact closure should force either point’s output switch off, select
INHIBIT. If a
remote dry contact closure should force either point’s output switch on, select FORCE ON.
If the
EXTERNAL INPUT is set to INHIBIT or FORCE ON, the point’s OVERRIDE SOURCE (for V3.11+)
must be set to
EXT. INPUT or its INHIBIT CONTROL (for V3.00) must be enabled.
Notes:
• When used with the
INHIBIT/FORCE ON feature, a contact closure sensed by the EXTERNAL
INPUT
will initiate the INHIBIT/FORCE ON mode. An open input will cause the controller to
revert to normal temperature control operation. One possible use of the
INHIBIT feature is to
use an external device (such as a flow meter) to provide a contact closure if there is flow in a
line. As long as the line has adequate flow, the heating will be off (
INHIBITed from operating).
See Appendix C on page 68 for typical connection diagrams when using this input.
•
EXTERNAL INPUT must be set to INHIBIT or FORCE ON before OVERRIDE SOURCE (for V3.11+)
can be set to
EXT. INPUT; or INHIBIT CONTROL (for V3.00) can be edited. For V3.11 and up, set-
ting
EXTERNAL INPUT to NOT USED or TEMPBUS™ will automatically set OVERRIDE SOURCE to
REMOTE.
3.6.4 EXTERNAL OUTPUT PORT
Purpose: The
EXTERNAL OUTPUT port can be programmed to allow Point A to function as a “mas-
ter” 920
HTC to control up to 25 “slave” 920 HTC units. A “master” can either force its “slaves” to
override their temperature control and force their output switch off (INHIBIT), or it can send its
control temperature to its “slaves” so they can do their own temperature control using this tem-
perature (
TEMPBUS™).
An INHIBIT “master” may be useful when a number of “slave” controllers use their own RTDs,
but are to be turned off based on the ambient temperature. This will allow disabling of the
“slave” controllers during the summer months, during a maintenance shutdown, etc.
A
TEMPBUS™ “master” may be useful when a number of “slave” controllers do not have their
own temperature sensors and are set to control the ambient temperature.
Setting:
NOT USED, TEMPBUS (V3.11+) or INHIBIT
Procedure: Select NOT USED if Point A is not a “master” controlling the EXTERNAL OUTPUT port.
Select
INHIBIT if Point A will be controlling the EXTERNAL OUTPUT port as an INHIBIT “master.”
Select
TEMPBUS™ if Point A will be sending its control temperature out the EXTERNAL OUTPUT
port. For
TEMPBUS™ operation description see section 5.4 on page 53.
Notes:
• The “master” and “slave” controllers must be installed in the same enclosure. The
EXTERNAL
OUTPUT PORT
signal is not intended to be connected over extended distances or between
enclosures.
•If
EXTERNAL OUTPUT is set to INHIBIT, then the DEADBAND parameter for Point A will be used
to define the operation of the
EXTERNAL OUTPUT port, even though the SWITCH CONTROL
MODE
for Point A may not be set for DEADBAND operation. See section 3.5.5 on page 22 for
additional details regarding the
DEADBAND mode.
• If the
EXTERNAL INPUT PORT input is not being used, Point B may be configured as a “slave”
for a controller with its Point A configured as a “master.”
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