COOLING

[ppa.ghana 0]

Hi everyone, I just joined this forum. I am using AB SLC 505 to control a cooling sequence. How do I go about this? The control is as follows: I have a PID loop with a changing setpoint. The setpoint should change based on time which I will set in a recipe. For example, I want the set point to change linearly from 45deg c to 35 deg c in 65 minutes. Thanks

[Ken Moore 23]

Should be pretty easy to do with a 390 second timer, just decrease the setpoint every time the done bit goes true. If timer.dn is true, and setpoint > 35, then setpoint = setpoint-1 Or use a 65 minute (3900 seconds) timer and ten compares. If timer.acc > 0 and <= 390 then setpoint = 45 If timer.acc > 390 and <= 780 then setpoint = 44 If timer.acc > 780 and <= 1170 then setpoint = 43 etc....

[TConnolly 13]

The SLC5/05 has a RMP instruction. That is the simplest way. To calculate a ramp the formula is: Start_setpt + (End_Setpoint - Start_Setpt)/Total_Ramp_Time * Ramp_Timer.ACC I encountered an application once where a long ramp had to be calculated but a one second time base resulted in a stepped output that was not acceptable to the customer, but using a .01 second time base would not provide the required time. I built a long duration floating point high resolution timer using two timers. I have never encountered another application where this was required, so its of dubious use, but I attahced a code snip of what I did. You can see the ramp equation I posted above in the last rung of the code snip. The same method could be used with some adjustment to create a timer that would count for thousands of years. long_hi_res_timing.RSS

[gravitar 3]

Just make sure the customer doesn't expect to see the timer reach "Done" before they'll pay you :)

[ppa.ghana 0]

Hello Thanks to everyone for your contribution. The ramp equation did work. Thanks alot Alaric