Guarantee Low Assignment

 

An opcode with a GL prefix stands for guarantee low.  During a recipe, a guarantee low will allow the recipe timer to run only while the PV is at or above the lower limit.  The lower limit is the value of the set point minus the wait limit. 

 

 

If the PV moves below the lower limit, the recipe will pause and a new timer will begin.  This timer is called the Default Hold Time and can be found and adjusted in the Menu under Furnace Setup.  This timer will keep track of the amount of time the PV has been below the lower limit.  If the PV fails to move above the lower limit within the Default Hold Time, the programmer alarm will be activated.  Once the PV moves above the lower limit, the recipe timer will resume.   

 

For example, if the PV is temperature with a 1500° set point and the wait limit is 15°, the recipe timer will continue to run as long as the PV is at or above 1485°.  If the PV moves below 1485°, the recipe timer will pause and the Default Hold Time countdown will begin.  The recipe timer will resume once the PV moves back to 1485° or above.