Before the list is executed it is advised to define criteria for which the program decides whether the sample temperature is already stable. Two text boxes at the bottom of this form set the temperature error and the observation time. For example, if the error of 0.2K and time 30s are set, this means that before the subsequent script is started the program waits as long as the average difference between the current and set temperature during 30s is less than 0.2K. The additional condition which has to be here fulfilled is that the current difference between the sample temperature and the set point cannot be larger than 150% of the average value. This additional condition is set to avoid short temperature overshoots which do not influence the average temperature error. This 150% condition cannot be changed. When the above conditions are fulfilled the script is started. The temperature history is always taken from the temperature diagram on the Temperature tab of the main form. If this diagram is visible the temperature history and stability can be viewed.
If the subsequent scripts do not invoke any change of temperature set point then the stabilisation criteria can be set to very weak ones and they will not cause any delay between the scripts.
- Two-temperature-sensors cryostats
In some cryostats two temperature sensors are used. One for the temperature control and stabilisation the other one as the sample temperature. The set point refers to the control temperature, while the sample temperature is read by the system. As a result, sometimes there is a constant difference between the set point and the sample temperature. In this case setting up the temperature error is not a good criterion for the temperature stability unless the cooling/heating process in the cryostat is reproducible. For example, if it is known that it always takes 300s for the temperature to stabilise when the sample temperature is different by a few Kelvin from the stable one then it is enough to set the error larger than the difference between the control and sample temperatures (by around 0.5K) and the stability time set to 300s.
An alternative way to avoid problems relating to the control and sample temperature difference is to set a constant temperature offset up to ±10K by the vertical scroll bar on the right-hand side of the temperature diagram. However, usually the real value of this difference changes depending on the heating/cooling conditions in the particular cryostat, thus this option has to be used on the try-and-error basis.
In same cases a use of the error criterion is not sufficient to assure proper temperature stabilisation before the script is executed. Then one can additionally allow and set the differential criterion. If the criterion of the temperature derivative of 1K/min during 60s is set then this means that besides the error criterion the largest temperature change during last 60s cannot be larger than 1K/min. Any set point change makes this derivative very large thus the program would wait at least 60s until the next script is started.
As a temporal utility, when the program waits for meeting the temperature stabilisation criteria on the Temperature stabilisation panel one can see values of the current and average temperature error and the highest value of the temperature derivative.
When the Save log file check box is checked then the TemperatureLog.txt file is being saved in the current directory. In this file one can view the sample temperature history when subsequent scripts are executed.