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8.10 WATLOW Series 988 User’s Manual
General Software Features, Chapter 8
General Software
Heater Current
Requirements
Choose the heater current option (98_ _-_4_ _-_ _ _ _) for input 2 and an
appropriate current transformer. A current transformer must be ordered
separately.
Output 1 cannot be used as a process output. The heater current feature
monitors only output 1.
Overview
The heater current feature measures and responds to heater current in a
system. This is an ideal method for detecting heater loss in applications
with multiple heaters. The current is measured when output 1 is on. For
instance, if a system has five, 10-amp heaters, the heater current input
measures 50 amps regardless of the percent output.
To view the heater current press the DISPLAY key and advance to the
Process 2 prompt [Pr`2]. The upper display indicates the last valid cur-
rent reading.
The Input 2 prompt [`In2] under the Input Menu [InPt] can be set to
current [Curr] or loop error detect [LooP]. Current [Curr] allows you to
monitor heater current and set alarm set points based on high and low
heater current values. Alarms can only be configured as process alarms
(see Alarms, in Chapter 7). Setting to loop error detect [LooP] enables
monitoring and alarm functions, and also triggers an error and shuts off
all outputs if current is present with output 1 off or when no current is
present and output 1 power is more than zero.
There are limits associated with this feature:
• To obtain a reading, the output on-time must be a minimum of 0.3
seconds. To calculate this, multiply the percent output by the cycle time
setting. Example: With 30-percent output and a 2.0 second cycle time, the
on-time would be: 0.30 x 2.0 = 0.6 seconds. This would yield a valid
reading. If a valid reading is not possible, the 988 will display the last valid
reading.
• The heater current feature will not function with the cycle time on
output 1 set to [brSt]. (This does not apply to output 2, output 3, or
output 4). This does not necessarily apply to the loop error detect feature.
If enabled, any current detected with no output triggers an error.
• This feature will not function when the Series 988 has a process output
for output 1 (98_ _-F _ _ _-_ _ _ _). A known cycle time is required to detect
the current. There is no cycle time associated with process outputs.
The maximum signal the input can accept from the current transformer
secondary is 50mA. So, you must calculate the output range of the cur-
rent transformer before wiring the system.
˜
NOTE:
To obtain a reading,
the output ON-time
must be a minimum
of 0.3 seconds.
˜
NOTE:
The heater current
feature will not
function with burst-
fire outputs.
˜
NOTE:
The heater current
feature will not
function when the
Series 988 has a
process output for
output 1.
NOTE:
Current transformer
(up to 50A), Part
#16-0246)
C8.wc 5/14/1999 8:55 AM Page 8.10