The temperature overshoot is can be caused by and in many cases is caused by the change of the phase of the solder between the heaters and the thermal sensor...As solder cools shrinkage occurs depending on the local thermal gradients and alloy...The shrinkage and local solidification generates separation between the sensing elements and the heaters...These then can cause a decoupling between the sensor and the heaters as the heaters try to liquefy the slurry/solid solder mix causing solder phase separation and voiding in the solder pot...This then forces the heaters to higher power level until the sensor is in full thermal conduction with the heaters... Then the heaters and their attached thermal mass will have to "cool down" to the controller's set point... Paul Paul Edwards Surface Art Engineering -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane Sent: Thursday, September 02, 2010 8:37 AM To: [log in to unmask] Subject: Re: [TN] Wave Temperature Overshoot We have the same wave and I have never seen any temperature shoot overshoot. The temperature reading increases to 520F and stays constant at that valve from a cold start. Takes about 3 hours from room temp to reach 520F. Amol S. Kane Process Engineer Catalyst Manufacturing Services 941 Route 38 Owego NY 13827 Office : 607-687-7669 X349 Fax : 607-687-9733 E-mail: [log in to unmask] ??Please consider the environment before printing this e-mail -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard D. Krug Sent: Thursday, September 02, 2010 8:34 AM To: [log in to unmask] Subject: Re: [TN] Wave Temperature Overshoot I'd suggest talking with Electrovert for recommendations on changing PID controller settings. You've got me thinking about additional cost savings here. We use the timer functions to turn off the solder pot heaters at night and then turn then back on in the morning. We turn on the heaters at 2:00 AM M-F, even when pot may have been off all weekend. Pot always is ready for production at 7:00 AM. I'm going to record pot temperature for a week to see what actual temperatures are. I may have a temperature overshoot but have never seen it based on our warm up timer settings. A record of actual overshoot could provide insight into PID controller setting changes. Dick Krug, CSMTPE SMT Process Engineer Sparton Corporation 30167 Power Line Road Brooksville, FL 34602-8299 p (352) 540-4012 (Internal Ext. 2012) [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood Sent: Thursday, September 02, 2010 7:41 AM To: [log in to unmask] Subject: [TN] Wave Temperature Overshoot The following problem is on an Electovert Vectra with SN100C alloy. Due to a decision to allow the bath to cool over night, to save energy, we are experiencing over temperature shoot for several hours after reaching temperature. Once the overshoot has gone the bath then seems to control OK. The PID controller for the bath has the same terms in it as it had for SnPb. If I make an assumption that SN100C is 100% Sn in terms of its Specific Heat then I have 0.244 J/gm/K vs. 0.180 J/gm/K for 60/40 Sn/Pb. (1.36:1) This is a big difference in specific heat. Intuitively I feel that the SN100C should be less likely to overshoot. Does anyone have experience of having to have the PID terms adjusted in their wave having changed the alloy in order to maintain temperature? Has anyone done the arithmetic to show that allowing the alloy to go through a phase change in cooling down is more economic than just keeping it above the phase change point? Again my intuition says it is better to let it cool but I've been asked justify my assumption! :-) Regards Rex Rex Waygood Technical Manager Hansatech EMS provides value manufacturing through engineering and quality Hansatech EMS Limited Benson Road Nuffield Industrial Estate Poole Dorset BH17 0RY +44 (0)1202 338200 ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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