glaverty
Member
I have an application where I need to control the temperature of a product in a vessel. The basic setup of the system is a container for the product a blower to move air through the product and a heater. There are two RTD's in the system, one placed to measure the temperature of the air leaving the heater and another to measure the temperature of the product. The heater output is controlled using a 4-20mA signal. The blower remains at a constant speed.
Different products will be run in this machine that need different temperatures and times so profiles will need to be developed based on the product.
There are multiple heating steps in the process going from one temperature to the next and remaining at a set temperature for a set time during certain steps until a final temperature is reached. Each successive temperature is greater than the previous.
The customer wants to be able to go from Temp A to temp B and tell the controller to do it in certain amount of time. This is the part I am having trouble with. Your basic PID loop is just going to try and get to the Setpoint as fast as it can and then remain at that temp.
The program is going to have to calculate the rate that the temperature needs to change based on the difference between the starting temp and ending temp and the time it should take to make the change. Then adjust the heater output accordingly to get that rate of change. Once it reaches the temperature setpoint it will then need to remain there for some amount of time.
Can this be done using a built in PID Loop? I’ve read through the posts on SMC and looked at the code Peter Nachtwey wrote but that seems more built for ON/OFF heater control and doesn’t really take into account trying to maintain a certain slope in the temperature.
The PLC being used is a GE Versamax.
Any suggestions or insights are appreciated.
Different products will be run in this machine that need different temperatures and times so profiles will need to be developed based on the product.
There are multiple heating steps in the process going from one temperature to the next and remaining at a set temperature for a set time during certain steps until a final temperature is reached. Each successive temperature is greater than the previous.
The customer wants to be able to go from Temp A to temp B and tell the controller to do it in certain amount of time. This is the part I am having trouble with. Your basic PID loop is just going to try and get to the Setpoint as fast as it can and then remain at that temp.
The program is going to have to calculate the rate that the temperature needs to change based on the difference between the starting temp and ending temp and the time it should take to make the change. Then adjust the heater output accordingly to get that rate of change. Once it reaches the temperature setpoint it will then need to remain there for some amount of time.
Can this be done using a built in PID Loop? I’ve read through the posts on SMC and looked at the code Peter Nachtwey wrote but that seems more built for ON/OFF heater control and doesn’t really take into account trying to maintain a certain slope in the temperature.
The PLC being used is a GE Versamax.
Any suggestions or insights are appreciated.