Loop Break Alarm Option
An optional feature for any controller is the addition of a Loop Break Alarm. A loop break alarm (LBA)
guards against two mistakes than can result in devastating heating accidents. The first scenario is when a user sets
up a reaction, enters the desired setpoint, and then walks away leaving the thermocouple sitting on the lab bench
and not placing it in the heated solution. The second scenario is when a reaction is unmonitored and either the
thermocouple falls out of solution, or the flask breaks resulting in the thermocouple falling out of the flask. In all
of these cases, since the thermocouple is still measuring a legitimate temperature (i.e., room temperature) the
controllers never detects a heating error and continues to heat. Since the temperature of the thermocouple doesn’t
change as power is applied to the heater, the controller will eventually heat at full power resulting in a runaway
The loop break alarm feature detects when power is being applied to the heater but the temperature of the
thermocouple does not increase. After a certain period of time (5 minutes) if the thermocouple doesn’t increase in
temperature by 2.5 C, an error is declared and power is removed from the heater avoiding a heating accident.
Contact J-KEM for more information.
The loop break alarm is designed to protect against two specific scenarios:
1) A reaction is set up and power is applied to the heater but the thermocouple is not placed in solution.
2) A thermocouple falls out of solution, or the flask breaks resulting in the thermocouple falling out of solution.
Key features of the loop break alarm (LBA) are:
1) The LBA is active when the setpoint temperature is above 35 C, and not active when below 35 C.
2) The LBA is active when the process temperature is below 35 C and not active when above 35 C.
3) The LBA triggers when the solution temperature doesn’t rise by 2.5 C in a period of 5 minutes.
The examples that follow demonstrate the LBA function.
The Loop Break Alarm Circuit
When a controller powers up, if the controller has the optional LBA circuit the green digital meter displays
the message “LbA” in the display for about 2 seconds. This message confirms that the LBA circuit powered up
properly. The LBA becomes active (i.e., it begins to monitor the temperature of the thermocouple) as soon as a
setpoint is entered that is higher than 35 C.
There are times when the user may not want to use the LBA, and in those cases the LBA can be deactivated. An
example would be if you are performing a very slow temperature ramp from 25 to 50 C, at a rate of 0.1 C/min (a
rate that would trigger the LBA circuit).
To deactivate the LBA, turn off power to the temperature controller. Hold in the LBA reset button on the
back of the controller, then while holding in this button, turn power to the controller back on. As soon as a
temperature is displayed by the green digital meter you can release the reset button. When the reset button is held
in during power up, the controller doesn’t display the “LbA” message, this confirms that the LBA circuit is off.
When the LBA triggers, the setpoint in the controller is set to 0.0 C, which turns off power to the heater,
and the green meter display oscillates between showing the solution temperature and the message “LbA”. A LBA
alarm can be reset at any time by momentarily pressing the reset button on the back of the temperature controller.
When an active alarm is reset, this doesn’t disable the LBA, it simply resets the alarm condition and the 5 minute
clock used to determine when an alarm condition exists.