Post by Professor Lake Shore on Jan 31, 2017 16:36:41 GMT -5
I am having trouble understanding how the setpoint on the temperature controller works because while it seemed to ramp fine the first time using it, it doesn’t seem to be doing it on second use. What exactly is happening?
For precision temperature control, particularly when measuring a sample that has to be warmed slowly, all Lake Shore controllers calculate the precise control output based on a temperature setpoint and feedback from the control sensor. The setpoint ramp feature specifically is used to ensure smooth, continuous changes in a temperature setpoint on a controller. It controls how fast the controller changes the setpoint value from where it is currently set to where you want it to go based on a ramp rate ranging from 0.1 K/min to 100 K/min. This feature provides for faster experiment cycles because data can be taken as the system is changing in temperature. It can also be used to make a more predictable approach to a setpoint temperature without the worry of overshoot or excessive settling times. When using a controller for the very first time, the default setpoint for the instrument is zero (0), and the user has to program in their setpoint before using the setpoint ramp function. Because ramping begins at zero, reaching the defined setpoint typically takes a bit of time. How long depends on the setpoint ramp rate entered. Usually, it is a gradual process because the instrument is having to constantly recalculate the control parameters, determining how much heater power to apply the closer it gets to a desired setpoint. But this isn’t necessarily the case with subsequent uses. If you don’t reset the setpoint to the current control sensor temperature before beginning a new setpoint ramp, reaching the setpoint can occur very quickly. This, however, can be avoided by always resetting the setpoint before beginning a new controlled ramp.
For more about how to fully benefit from the setpoint feature, you might want to read this app note written by Jeff Maynard, Lake Shore Service Manager.