20
3.4 920 Functions
The sections that follow explain the various functions of the 920 controller and how they can be
accessed. The first line of each section identifies the function to be described. Each section goes
on to explain the Purpose of the function, the Range over which it may be set, the Procedure for
setting or enabling the feature, and finally any Notes or Cautions that pertain to the particular
function.
Setting and using the alarming functions of the 920 controller is a two step procedure:
1. The alarm must be enabled or disabled accordingly. When using the 920 Operator Console,
access to all alarming functions is available using the
CONFIGURE mode sub-menus. When
using the Model 780/GCC-9000 Group Communications Controller, the alarm masks may be
found in the
HTC SETUP Section. Please see the appropriate operating manual for instructions
on accessing these parameters.
2. The corresponding alarm point value may be modified appropriately for the application.
When using the 920 Operator Console, access to the alarm points is also available using the
CONFIGURE mode sub-menus. Modification of the alarm setpoint values is found in the HTC
SETPOINTS
Section of the Model 780/GCC-9000 Group Communications Controller. Please
see the appropriate operating manual for instructions on accessing this feature.
Note: The 920 Operator Console or the Model 780/GCC-9000 will not allow modification of an
alarm point value if the alarm has been disabled (
DIS) with the exception of the HIGH TS ALARM
temperature settings. These may still be modified if the corresponding
HIGH LIMIT CUTOUT has
been enabled (
ENA).
3.5 Control Point Setup
This Section describes the setup parameters that relate to a specific control point—either Point
A or Point B. These parameters must be configured for each of the two control points that are
used.
3.5.1 CONTROL SETPOINT TEMPERATURE
Purpose: The
CONTROL SETPOINT temperature is the value at which the heat trace controller
maintains the circuit temperature through either proportional, proportional ambient
SSR, propor-
tional ambient contactor, or deadband control, depending on the controllers’ configuration. The
CONTROL SETPOINT temperature is compared to the temperature measured by the control tem-
perature sensor (
TS). A decision is then made to turn on or turn off the output to control power
to the tracer.
Range: –76°F to 1058°F (–60°C to 570°C)
Procedure: Adjust the
CONTROL SETPOINT temperature value to the desired maintain tempera-
ture. The
HTC will switch the output ON and OFF in an attempt to maintain this temperature.
Notes:
• See section 5.2 on page 50 of this manual for an explanation of Proportional, Proportional
Ambient
SSR, Proportional Ambient Contactor and Deadband Control algorithms.
• When using an optional 920 Operator Console (for V3.11 and up) the
CONTROL SETPOINT
temperature range may be limited to the
CONSOLE SETPOINT MAXIMUM and MINIMUM values
(see sections 3.5.29 on page 29 and 3.5.30 on page 29). This is a safety feature to prevent
users in the field from modifying the
CONTROL SETPOINT temperature setting to a dangerous
level.
3.5.2 ALPHANUMERIC TAG ASSIGNMENT
Purpose: A 19-character alphanumeric
TAG may be assigned to a control point to allow it to be
easily associated with a pipe, vessel, process, circuit, drawing name or number.
Setting: Any combination of 19 characters from A-Z, 0-9, /, -, ., (,) or #.
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