5. How to Calibrate your vacuum oven.
NOTE: Before calibrating your oven, make sure you are familiar with basic oven heating operation.
Every oven has been calibrated and tested before leaving our factory, usually self calibration is not necessary.
However, if the temperature requirements are very strict, or if target temperature is set around upper or lower
limits of the oven temperature range, the measured temperature might not be accurate against the actual
temperature in the oven.
5-1. Calibration by Auto-Tune (AT)
Use auto-tune to set a more accurate temperature control and faster heating rate.
a. Set temperature to your maximum target temperature, press “Set” to confirm.
b. Under running mode, press and hold “Shift/AT” button for 5 seconds until the indicating light “Run/AT”
starts to blink. The oven is now in PID auto-tune mode.
c. After two cycles of fluctuation, auto-tune is done and the AT light goes off. This could take a few hours. The
“Set” button is disabled during this period.
d. New PID parameters are automatically saved for future use.
e. Now set the target temperature. You will be ready to use the oven.
5-2. Calibration by formula
First, calculate the offset value using the formulation below. Then press and hold “Set” button for 3 seconds;
controller will display “Lc”. Enter 3 and press “Set”. Go to “PK” and set it to your calculated offset value.
Press and hold “SET” for 3 seconds to confirm.
Offset value = (temperature measured by exterior thermocouple(s) – temperature displayed by
controller) x 1000 / temperature displayed by controller
5-3. Calibration by adjusting PID manually (requires experience and practice)
After an auto-turn, if you still feel that temperature is unstable, you can manually adjust PID. PID adjustment
is a very useful for you to control the oven temperature in an acceptable range but requires some practice and
patience.
After an auto-tune, if you still feel that temperature is unstable, you can manually adjust PID. PID adjustment
is a very useful tool for controlling the oven temperature within an acceptable range, but requires some
practice and patience.
a. First, adjust P whenever you start a PID adjustment. P represents proportion adjustment; increasing P
reduces temperature overshooting, while decreasing P to allow for a faster heating rate. (You may need to try
this step a few times before you get the best result).
b. “I” represents integral time. Increase I to lower temperature fluctuation. It can be used to eliminate the
steady-state error after the system enters a steady state by correctly setting P. In other words, I is often used
after P. Give I a big value before decreasing P a little, in order to get to a steady state, and then decrease I to
eliminate errors under the steady state. Check if the PV is in your desired range. Continue to try to change
P and I to get the best result.
c. “D” represents differential time, which can overcome the unstable and oscillating state. Adjust D to reduce
temperature overshooting. It is usually set after I adjustment. Firstly, set D to 0, then gradually increase it to
check if you have an acceptable result (In this process, P and I may also be changed).
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