Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 117)

Publication 900-UM007D-EN-E - January 2011
Configuration & Basic Operation 3-47
In the above diagram, heater power is considered to be ON (normal) if the heater current, measured by the
900-CTX current transformer, is greater than the heater burnout detection current during the T
on
interval. If the
heater is burned out, the measured current decreases and falls below the heater burnout detection value. The
configured controller output is then activated as the Heater Burnout Alarm.
In the above diagram, heater power is considered to be OFF (normal) if the leakage current, measured by the
900-CTX current transformer, is less than the HS alarm current during the T
off
interval. If the SSR output is
short-circuited, the measured current increases beyond the HS alarm value. The output is then activated as the
HS alarm.
In the above diagram, it is regarded as normal when the heater current is less than the heater overcurrent
detection current during the Ton period. Current is increased when excessive current flows to the heater,
causing the heater overcurrent detection value to be exceeded and an OC (heater overcurrent) alarm to be
output.
Figure 3.93
Note: Heater Burnout Alarms (HBA) are not detected if the control output
(heating) ON time (T
on ) - is 100 ms or less.
Note: Heater Short Alarms (HSA) are not detected if the control output
(heating) OFF time (T
off ) is 100 ms or less.
• For controller models with HBA, HSA, and HOA alarms, an OR output
is established between the ALM 1 function and the HBA, HSA, and
HOA alarm. If the ALM1 function is to be used for HBA, HSA, and
HOA alarms only, set 0 as the ALM1 type and do not use ALM1.
Table 3.P — Heater Burnout & Heater Overcurrent Detection
Heating Control Output Status
Power to Heater HBA Output HS Alarm Output
Heater Overcurrent
Alarm
Control Output
(Heating) Operation
Indicator
ON Lit Yes (Normal) OFF — —
No (Heater burnout) ON — —
OFF Not lit Yes (HS alarm) — ON —
No (Normal) — OFF —
ON Lit Normal — — OFF
Heater overcurrent status — — ON
T
ON
OFF
T
Control Output (heating)
on off