Ramp temperature change with speed change during ramp


Thread Starter

Pat Russell

I have an process that needs to ramp a furnace temperature so that it is at a new setpoint by a specified point in the process. The problem I am having is that the speed of the process line also changes, possible in the middle of the temperature ramp. For example: The furnace needs to ramp up 50F at 80F/min heat rate, line speed is 100fpm. This calculation is easy as long as line speed does not change, but there are situations where line speed will change (up or down) and I still need the furnace to be at the new temp at the same time. My math instruction is failing me at the moment and I cannot remember
any specifics on how to do this. Any help is GREATLY appreciated.

Pat Russell
J&L Specialty Steel, Inc.

david mertens

Gradient = deltaT/time. If time becomes shorter then your gradient has to increase according to the change in time. If like you say the time depends on the speed, (v = distance/time) then time can be calculated out of the distance of your product to the controlled zone.

The gradient (ramping setpoint) will then have to be (deltaT * v / distance) in order to reach the setpoint temperature by the time your product reaches the position where the temperature is controlled.
One way you may consider doing this is to use a lookup table (x,y pairs) that allow different ramp rates to be selected based on line speed, allow a non linear curve to be easily implemented. If you use a modicon with concept
software this is fairly easy to implement. With other software, you will need to see if this function is available.

Allen Nelson

This doesn't seem difficult. You want to ramp the temperature at 80 ºF/min when the line is moving at 100 ft/min. If the line were moving at 50 ft/min (half as fast), would your temerature ramp rate be 40 ºF/min (half as fast)?

If so, you want to ramp at 0.80 ºF/ft, and stop the ramp at +50ºF, or 50/0.8 = 62.5 ft.

Instead of ramping based on time, continuously totalize the footage that's gone into the furnace. Divide that total by 62.5, to get X%. The temperature setpoint at any given moment will be Starting_Temp + (50ºF * X%).

As the line moves faster (or slower), you'll totalize faster (or slower). When 62.5 ft have moved in, you'll be at +50ºF.