Ed,
As you allude to, the exhaust may play a factor here. I would spend some
time making sure that all the "higher temp" zones are clean. If, for the
sake of argument, the exhaust flow was reduced on either Zone 4 or 5, you
might see some of the air, and thus the "energy" flow from zone 4 out
through the zone 3 exhaust, thus raising the temperature.
Good luck,
Hal
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ed Popielarski
Sent: Wednesday, August 06, 2003 10:28 AM
To: [log in to unmask]
Subject: [TN] Temp stability in Zone 3
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
WWW.QTA.NET
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