FACTS Engineering Direct Logic 405, Manual

Page: 40 / 62

SUPPORTING LADDER LOGIC 3.2
ALARM WORD DECODING
The rung below copies the alarm bits for loop 1 (V5004) into Y0-Y4.
Y0 Temperature Low Alarm
Y1 Temperature High Alarm
Y2 Temperature Deviation Limit Alarm
Y3 Broken RTD or Thermocouple (Burn-out detected)
Y4 No Heater Current Alarm (open or disconnected)
ALARM WORD ENCODING
Some operator interface software packages do not permit examining discrete bits in user V-Memory.
The following example converts the bits in the Alarm Word into a corresponding BCD number.
If more than one alarm is on then the BCD number for the least significant bit in the Alarm Word will be
returned. Thus a "Low Temperature Alarm" will override a "Temperature Deviation Alarm". A "Broken
Transmitter Alarm" will always be recognized since in this case the Temperature Controller disables all
other alarms and loop processing.
Alarm Word
Encoded BCD Number Bit Number Description
1 0 Temperature Low Alarm
2 1 Temperature High Alarm
3 2 Temperature Deviation Limit Alarm
4 3 Broken RTD or Thermocouple (Burn-out detected)
5 4 No Heater Current Alarm (open or disconnected)
6 5 No Heater Current Control Alarm (output shorted)
Load Alarm Word for Loop 1 to accumlator
Shift bits 1 position to the left for ENCODE
Position of 1st bit is put in accumulator