Hi everyone,

I ran into an issue that has me scratching my head (no, it's not fleas!) My customer is having temp stability problems in Zone 3 of a BTU VIP70 reflow oven no gas. Below are the setpoints of each zone in deg C:

Z1T: 140
Z1B: 140
Z2T: 140
Z2B: 140
Z3T: 140
Z3B: 140
Z4T: 180
Z4B: 180
Z5T: 230
Z5B: 230

All zones are holding +/- 1 deg C EXCEPT Z3T which after setpoint is reached, climbs very slowly (about 5 deg C/hour) and Z3B at half that rate. Once this 5 deg deviation is reached, the system alarms (as it should).  I have confirmed the solid state relays are not "leaking" (swapped them with good zone), the computer is setting the duty cycle of these at 0% (once setpoint has been reached) , this has been confirmed electrically, and there are no ground faults in the heaters, convection fans are running. BTU has offered the customer little, if any advice.

My theory is that "stray energy" from Z4 and possibly Z5 are heating Z3 which, possibly due to inadequate ventilation, cannot cool. I was hoping someone in the forum might have experienced a similar issue and would share that experience. I haven't measured the exhaust flow rate yet, as I didn't want to chase a "ghost", but it IS running.

It's not often I get stumped (Steve G. can attest to that!) but this one really has me baffled.
 
Regards,

Ed Popielarski
QTA Machine
27291 Jardines
Mission Viejo, Ca. 92692

Phone:949-581-6601
Fax: 949-581-2448
Cel: 949-337-2578


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